Fresh-ct tri cy v rau qu l mt phn khc tng i mi v pht trin nhanh ca ngnh cng nghip sn phm ti. Fresh-ct sn phm c mi ct, ra sch, ng gi, v duy tr vi lnh. H ang trong mt trng thi nguyn v ngay c khi x l ti thiu, h vn trong trng thi ti, sn sng n hoc nu n. Cc Quc T tional ti ct Hip hi Sn xut (IFPA) nh ngha mi-sn phm nh tri cy ct hoc cc loi rau c ct v / hoc bc v v / hoc ct thnh cc sn phm c th s dng 100% l ng gi hoc ng gi sn cung cp cho ngi tiu dng cao, dinh dng, tin li , v hng v trong khi vn duy tr s ti mt ca n. Cng nghip c tnh M cho thy doanh s bn hng ti ct khong $ 11000000000 nm 2000 chim hn 10% tng s tri cy ti v rau th trng, vi dch v bn hng thc phm chim 60% tng s. Bn hng d kin tng 10-15% hng nm trong nm nm tip theo. Mc cht lng an ton i km vi cp trn l rt cn thit cho ngnh cng nghip duy tr tng trng v ct tiu th sn phm ti. Fresh-ct tri cy v rau sn phm khc nhau t tri cy truyn thng cn nguyn vn, v rau qu v ology ca h-physi, x l v cc yu cu lu tr. S ri lon trong m v ton vn t bo l kt qu ca gim ch bin ti ct gim sn xut thi hn s dng sn phm. Conse-quently, ti, ct gim cc sn phm i hi s quan tm rt c bit v tm quan trng ca yu t enzyme v h hp cng nh mi quan tm vi sinh vt c nh hng n an ton. Kin thc v tnh cht ca ti ct tri cy v rau qu c lin quan n trc v sau thu hoch x l, ch bin, ng gi v lu tr l rt cn thit cho ensur-ing lnh ca h v gi tr dinh dng, v pht trin cc th tc hiu qu nht v i mi cng ngh duy tr cht lng ca h p ng nhu cu tiu dng ngy cng tng. Ch n cc yu t th trng v kinh t cng s m bo kh nng ca ngnh cng nghip ny lun cung cp gi tr cho ngi tiu dng, pht trin v thc hin cc cng ngh mi v khen thng nhng ngi tham gia trong chui cung ng. Cun sch ny l mt ngun tham kho ton din lin ngnh cho cc mi ni ti ct tri cy v ngnh cng nghip thc vt. N tp trung vo cc sinh ha c o, Physiological, vi sinh, v cht lng thay i trong ti ct ch bin v bo qun v trn cc thit b ring bit v yu cu ng gi, kinh t sn xut v cn nhc tip th cho sn phm ti ct. Da trn nhng nghin cu su rng trong lnh vc ny trong 10 nm qua, ti liu tham kho ny l ngi u tin bao gm cc vi y cc cng ngh, khoa hc v cc vn tip th lin quan n lnh vc ny, bao gm sn xut, ch bin, sinh l hc, ha sinh, vi sinh, an ton, k thut , cm gic, cng ngh sinh hc, v kinh t. N s c c bit hu ch cho hc vin cao cp v sinh vin tt nghip, cc nh khoa hc thc phm, physiologists thc vt, vi sinh vt hc-, cc nh ha hc, sinh ha hc, k s ha hc, dinh dng, Econ omists nng nghip v sinh hc phn t. Ti bit n vi nhau ca cc tc gi cho kp thi, s tham gia ca h v hp tc cng nh nhiu ngi khc c t vn ca h, ng gp v khuyn khch s pht trin ca cun sch ny Chng 1 Fresh-ct Sn xut: Theo di v xu hng

Edith H. Garrett Chng 2 Cht lng tham s ca tri cy ti ct v sn phm thc vt Adel A. Kader Chng 3 Tng quan v vic ct gim Chu u-Fresh Sn xut Cng nghip Patrick Varoquaux v Mazollier Jrme Chng 4 Cc kha cnh an ton ca Fresh-ct Tri cy v Rau qu William C. Hurst Chng 5 Sinh l hc ca Fresh-ct Tri cy v Rau qu Peter M. A. Toivonen v Jennifer R. DeEll Chng 6 Enzyme Tc dng trn Hng v v texture ca ct-Fresh Tri cy v Rau qu Olusola Lamikanra Chng 7 Vi sinh vt trong sn xut ti ct Gillian M. Heard Chng 8 Enzym vi sinh kt hp vi ct-Fresh Sn xut Jianchi Chen Chng 9 iu tr bo qun ti ct Tri cy v Rau qu Elisabeth Garcia v Diane M. Barrett

Chng 10 ng dng bao b v kh quyn thay i ti, ct tri cy v rau Tareq Al-Ati v Joseph H. Hotchkiss Chng 11 cc-ti ct gim sn xut cng nghip Jennylynd James A. Cng ngh sinh hc v Chng 12 Hng v v hng thm ti ct ca Tri cy v Rau qu John C. Beaulieu v Elizabeth A. Baldwin Chng 13 nh gi cht lng gic ti ct Tri cy v Rau qu Karen L. Bett Chng 14 Tng lai kinh t v th cn nhc Greg Pompelli Chuong 1 GII THIU Fresh-ct sn xut c mt trong nhng mt hng nng nht trong cc ca hng tp ha trong 10 nm qua. Ngnh cng nghip tng ln trn 10 t USD ti M v bn l thc phm-dch v bn hng trong nm 1999, v khng c du hiu ca xu hng chm li (IFPA, 2000). Trong thc t, doanh s bn hng ct v ng gi tri cy ch va mi bt ln khi mt t, v mt hng mi nh c chua ct gim ang xut hin tr li mong mun ca ngi tiu dng thun tin hn trong cuc sng hng ngy ca h. iu g l s tng trng ny mi li xe ct? Trng hp lm cc ngnh cng nghip n t, v nhng g ang c trn th trng nh hng nh hng n s pht trin tip tc ca ngnh cng nghip? Trng hp khng x l c nhng tng cho sn phm mi, v theo di nhng g lm cc b vi x l thc hin xy dng thnh cng? Chng ny s bao gm lch s, xu hng hin nay v nhng vn nh hng n-ti ct gim sn xut cng nghip. SIZE CNG NGHIP

Theo Hip hi Sn xut Marketing (PMA), kch c ca ngnh cng nghip sn phm ti c $ 76000000000 trong bn hng cho nm 1999, bao gm c dch v thc phm v doanh s bn l (PMA, 2000; Kaufman v cng s, 2000.). Sn phm ti lun lun l ph bin vi ngi tiu dng v nhng hng v tuyt vi, cht lng dinh dng t nhin v ti mt. Trong thc t, Hoa K B Nng nghip (USDA) bo co rng sn xut tiu th M tng t 284 bnh qun u ngi nm 1990 ln 319 cho mi u ngi vo nm 1998 (al Kaufman v cng s, 2000.). Ti-CUT SN XUT Tt c nhng thuc tnh ny ging nhau, cng vi thun tin nht, tip tc li xe bn hng cho cc mt hng c o mi ct. Quc t ti ct Hip hi Sn xut (IFPA) nh ngha mi ct sn xut l "bt k tri cy hoc thc vt hoc s kt hp c th cht b thay i t hnh thc ban u ca n, nhng vn cn trong trng thi ti" (IFPA v PMA, 1999, p. 5). IFPA s c lng M ct ngt sn xut th trng vo khong $ 10-12000000000 doanh s bn hng trong nm 2000, vi doanh thu dch v thc phm chim khong 60% tng s (IFPA, 2000). ng gi x lch c tng sao trong cc ca hng tp ha trong thp k qua, v, vi tri cy v rau qu bao gm ct, loi ny c c tnh bng IFPA tip tc tng trng doanh s bn hng trong th trng bn l ca M 10-15% mt nm cho sau nm nm. Cc loi doanh thu dch v thc phm M ang kh khn o nhng theo c tnh ca IFPA tng 3-5% mt nm trong nm nm ti. SN XUT C Hu c c trng tri cy v rau qu cng l mt phn ca ngnh cng nghip sn xut mi c s tng trng mnh m trong nhng nm 1990. Th loi ny bao gm c hng ha ton v ti ct sn phm. Vic to ra mt c tnh khong 4 t USD doanh s bn hng nm 2000 (PMA, 2000), ngnh cng nghip sn xut hu c c d bo c mc tng 7% mi nm doanh s bn hng trong ba nm ti. Mt ln na, ngi tiu dng ang tm kim khe mnh, la chn thay th hng v cho ba n ca mnh, v hu c ti ct Duce-pro p ng cc tiu ch ny. Khi s sn c ca sn phm hu c tng, chi ph sn xut u gim, lm cho sn phm ny mt gi c phi chng phc v trong nh hng v bn trong cc ca hng tp ha thng thng. Fresh-ct x lch hu c hin nay c sn trn th trng. thc hin xy dng thnh cng? Chng ny s bao gm lch s, xu hng hin nay v nhng vn nh hng n-ti ct gim sn xut cng nghip. Theo Hip hi Sn xut Marketing (PMA), kch c ca ngnh cng nghip sn phm ti c $ 76000000000 trong bn hng cho nm 1999, bao gm c dch v thc phm v doanh s bn l (PMA, 2000; Kaufman v cng s, 2000.). Sn phm ti lun lun l ph bin vi ngi tiu dng v nhng hng v tuyt vi, cht lng dinh dng t nhin v ti mt. Trong thc t, Hoa K B Nng nghip (USDA) bo co rng sn

xut tiu th M tng t 284 bnh qun u ngi nm 1990 ln 319 cho mi u ngi vo nm 1998 (al Kaufman v cng s, 2000.). CI TIN TRONG HOT NG K t nhng nm 1940, sn xut cng ty ngh ra cch duy nht ct v ng gi sn phm bn. Ban u, mt s bn tm c s dng ra sn xut, trong khi nhng ngi khc s dng cc chu k quay kh vo my git cho bc sy. Ice c s dng trong bn tm nc lnh sn xut, v th s, ng gi c cung cp t hn tion-bo h khng b nhim bn trong qu trnh phn phi. Ngnh cng nghip xy dng nhiu trang thit b ca mnh nh sn xut gia tng trong nhng nm 1970 t s tng trng doanh s bn hng dch v thc phm, nhng thc s i mi trng hp vi s gia tng s lng cc nh hng trong nhng nm 1980. Ci thin T CHC CNG NGHIP Nhiu tin b cng ngh xy ra trong nhng nm 1980 v 1990 l ngnh cng nghip ny tr thnh t chc thng qua cc hip hi thng mi ca h, cc IFPA. Cc nh cung cp tham gia vo asso thng mi-ciation v tham gia vo mt chng trnh pht trin thng mi hng nm cc thit b bn cc thit b v mng li vi b x l. Din n ny trao i cng ngh mi gip thc y ngnh cng nghip pha trc v nng cao cht lng v an ton ca sn phm ti ct. Cng nghip nghin cu cho thy nhiu bc mi ci thin tui th v con-vinced ngnh cng nghip ny tp trung vo lm lnh nh l bc quan trng nht trong qu trnh sn xut. Cc cu thn ch tr thnh "u bc lnh, th tt hn sn phm hon tt." Trong cc din bin khc, i mi thit b chnh l ci thin cc tiu chun sn xut mi ct bao gm mng nc tm ng ca, nng cao ct cho mt lot cc kch c ct, my sy tin tin , my ng gi t ng, t ng thit b v sinh, thit b gim st in t. Mi tin b k thut tng tc sn xut nhng do mi bot-tlenecks. V vy, c phong tro tng i vi t ng ha cao hn v iu khin in t ca ngnh cng nghip. Ngy nay, vic thit k cc hot ng ct ngt trung tm v an ton thc phm v v sinh, lm lnh tuyt vi, tc sn xut cao hn thng qua vic t ng ha, nng cao cht lng v truy xut ngun gc sn phm. Cng nghip nghin cu cho thy nhiu bc mi cho k cuc i dch v thc phm NHU CU Trong gia nhng nm 1970, nh hng nhn thy mt c hi tuyt vi tit kim chi ph lao ng bng cch chuyn i-ing cho sn phm ti ct thun tin. p ng nhu cu ngy cng tng ca McDonald's v cc chui thc n nhanh khc, ngi trng v ch bin xy dng v kinh doanh rau dip thi nh hnh ty ct nh vo mt niche ng gm trong ngnh cng nghip sn phm ti sng (Lawn v Krummert, 1995). Vo gia nhng nm 1980, c s tng trng to ln trong cc nh hng Bc M. Salad thanh tr thnh cn st mi nht vi ngi tiu dng. Ngay sau , tri cy ti

v rau l ni sn xut ng hp trn thanh x lch trn khp nc M. mt ngnh cng nghip sng to Kin, McDonald ca Tng cng ty quyt nh h mun loi b salad thanh trong cc ca hng ca mnh gim thiu ri ro an ton thc phm cho ngi tiu dng. Cng ty yu cu nh cung cp ca n cho mt salad ti c thc hin v ng gi trong lb-5. ti m c th ng gi trong khay phc v n bn trong cc ca hng ca mnh. Pha trn vi nhau theo hng ha ng gi nim phong kn mt khng phi l mt thc t ph bin vo thi , nhng s thnh cng ca salad ca McDonald ng chui nh hng khc cung cp cc sn phm tng t. y cng l thi gian khi ph n bt u lm vic bn ngoi gia nh vi s lng ln, v gia nh c thu nhp hai cm thy thi gian khng hong bt u tm kim thun tin hn trong cuc sng ca h. Ct v ng gi sn phm ph hp vi nhng nhu cu hon ho, nhng ngnh cng nghip mi ct vo thi gian khng th cung cp cht lng ph hp v thi hn s dng y cho th trng bn l. Lm th no-bao gi ht, nhng tr ngi ny sm c khc phc. CI THIN CHT LNG C Mc d sn phm ti ct c bn l t nhng nm 1940, n khng hon ton thnh cng, bi v cht lng l khng th on trc v hn s dng hn ch. Ban u, b vi x l s dng din vin-off, mn sn phm, hng ha cht lng th hai cho vic ct gim sn xut. Ngoi ra, in lnh l ngi ngho trong c phn phi, v ng gi ph hp khng c pht trin. Do nhu cu cho sn phm tt hn vi thi hn s dng cn ln t cc khch hng dch v thc phm, nhng n lc ca ngnh cng nghip c tp trung vo ci tin cht lng. iu Mt b x l bit - thch thc hng u ca h l ngn chn cc sn phm t chuyn mu nu sau khi c ct. Sn phm xut hin l tp trung chnh cho o lng cht lng vo thi im , v b vi x l thy rng lm lnh mt mnh s khng iu khin s i mu v khuyt tt c th nhn thy khc. Thay vo , h phi bt u vi cc sn phm lnh mnh liu, th tc x l nh nhng trong khi ch bin v ng gi tt hn. Hm nay, b vi x l ang tp trung vo tm quan trng ca pht trin hng v tng cng cung cp tt hn sn sng n cc sn phm. Ngi trng bt u cung cp hng ha cht lng cho b vi x l u tin, v mi trang b-ment quy trnh c gii thiu nh l khng kh kh v tm nc nh nhng. Mt s th nghim vi b vi x l ra ha hc hoc cc b phim n c trnh mu nu, nhng t l thp trong ci thin khng bin minh cho nhng chi ph b sung. Ci tin bao b tr thnh bc tip theo trong cc nhim v gii quyt nhng thch thc ny cht lng. CNG NGH MI B Trong nhng nm 1940, trong nhng ngy u ca ti ct gim sn xut, ng gi, bao

gm cc giy gi giy bng knh trn khay tng cho cc sn phm nh xa lach trn hoc x lch (Hold-erfield, 1946). Giy bng knh, styrene v nha khc c s dng bc u sp l trong gia thp nin 1950 California sn xut cc lnh vc gim trng lng vn chuyn v ko di thi hn s dng. Trong nhng nm 1960, ngi trng rau bt u gi rau dip u. C hai sn phm vn cn ph bin ti cc th trng bn l hin nay (Anderson, 2000). Bc tip theo cho nhng ngi trng rau c ct v li bng tri Th trng trc khi ng gi chng trong ti nha vn chuyn n b bin pha ng. thc hnh ny vn thc hin ngy hm nay, v ngi trng thm ch cn lm sch v ng gi rau dip li trong thng ln cho l hng x l trn ton quc. Vo gia nhng nm 1980, ngnh cng nghip ti ct nh v phn tn M, v cc nh cung cp bao b khng tp trung n lc nghin cu v b phim ang pht trin specifiCally s dng vi ct gim sn xut. cng ty chu u, tuy nhin, c cng c v pht trin h thng thit b, bao b cng nghip ca h di chuyn v pha trc. Mi bao b cng khng phi l d dng tm thy ti M vo nhng nm 1980, bi v poly-ethylene phim l ch th phim trn th trng m bo qun c th sn xut v cha n cc iu kin x l th. Ban u, b vi x l s dng ti c thit k cho cc loi thc phm khc nh tht g ty v cc loi tht khc. S ra i ca my ng gi t ng trong cui nhng nm 1980 ht hi s pht trin ca bao b mi v sng to m gii quyt vn cht lng v gip khi ng ti ct thnh th chnh v cc knh phn phi. Vi s ra i ca my ng gi t ng ct-ti sn xut trong cui nhng nm 1980, ngnh cng nghip nha nhy vo hnh ng thit k vt liu cho sn phm ti ct. Phim cng ty tm kim cc polyme mi v quy trnh sn xut to ra b phim thong kh m c th chy trn cc my mc t ng. Cc cng ty nh Mobile, Exxon v Amoco polyme mi c cung cp t cc sn phm du kh v bc vo th trng hiu r hn nhu cu ca ngnh cng nghip. My t ng v nhng b phim ny mi kt hp cho php b vi x l khi ng nh hn, ti xch mang nhn hiu cho cc sn phm ti ct mi trong nhng nm 1990. Nm 1995, Hip hi ng gi linh hot (FPA) cho bit trong cuc kho st hng nm ca h v chuyn i bao b l ln u tin, sn xut vt qua bao b y t nh cc sn phm s mt cho cc c s sn xut ca h (FPA, 1995). c tnh $ 90.000.000 trong bn hng M (bao b cc chin lc, 1999), bao b cho sn xut s l sn phm s mt trong nm nm tip theo, tr li bo co trong cuc iu tra 2000 (FPA, 2000). Chuong 6 Hiu ng enzyme v hng v v texture ca Tri cy ti ct v Rau qu

Olusola Lamikanra

NI DUNG Gii thiu Lipoxygenase S ph bin v chc nng nh hng ca Lipoxygenase trn Aroma trung gian lo ha v Lipoxygenase C ch khng v Hng v Lipoxygenase hp cht v hp cht Phenolic Lipoxygenase trong Tri cy v Rau qu Mng ty Apple Bng ci xanh da chut c chua Kiwi Strawberry Melon Peroxidase Peroxidase-trung gian phn ng S ph bin v tnh n nh nh hng ca peroxidase trn chn v gi i nh hng ca peroxidase v phn ng Nh my Quc phng peroxidase, xc tc Browning Peroxidase trong Tri cy v Rau qu Mng ty c rt da chut Apple Bng ci xanh Peach Mango Orange Pear Melon Du Zucchini Squash Tri cy v rau khc Polyphenol oxidase Ph bin v phn phi Polyphenol oxidase-trung gian phn ng Browning nh hng ca oxidase Polyphenol v C ch c ch m thc vt Quc phng ca Polyphenol oxidase-trung gian phn ng Browning Polyphenol oxidase trong Tri cy v Rau qu Apple da chut Rau dip Mango48 Nm Melon Pear Prunus Qu da Enzym pectic Lm mm ca Tri cy v Rau qu Polygalacturonaza Lyases Pectinesterase

Pectic enzyme trong Tri cy v Rau qu Kiwi Apple Peach Mango Melon Pear c chua Kt lun Ti liu tham kho

GII THIU Enzyme v cht thng c t trong khoang khc nhau ca t bo, v chuyn giao ca h ang tch cc quy nh. Ct ca sn xut loi b vic bo v t nhin ca lp biu b v ph hy cc compartmentation ni b m gi h sepa sut. S thay i u tin quan st trc quan trn b mt ct ca m thc vt l kh ca lp u tin ca cc t bo b hng v mt cho mt thm vi lp subtending ca cc t bo (Kolattukudy, 1984). M gin on tng tnh thm v pha trn ca cc enzym v cc cht nn c nu khng c lp trong khng bo. S gia tng conse-quent trong hot ng enzim c th gy ra deterorations gic nh s i mu, ngoi hng v v mt cng. M ct tri cy ti v rau qu, do , d h hng hn v d b lo ha, so vi cc c quan cn nguyn vn t h thu c. V mng i cng gy nn nhng thay i trao i cht m bao gm cc qu trnh cha lnh vt thng (Picchioni v cng s, 1994;. Ramamurthy et al. Nm 1992; Bernards v cng s, 1999).. Chng ny l mt nh gi ca, s xut hin chc nng, phn phi v ti sn ca mt s enzyme c th nh hng ng k hng v v kt cu ca sn phm ti ct. Cc enzym chnh ph ang lipoxygenase,, oxidase peroxidase polyphenol v cc enzym pectic. Cc phn ng lin quan enzym v cc iu kin c tim nng nh hng n hot ng ca h trong tri cy ct v car-bn cng c tho lun.

Ph bin v chc LIPOXYGENASE

Lipoxygenase (linoleate: oxy oxireductase-EC 1.13.11.12) (LOX) hin din trong hu ht

cc m thc vt, v trong s hin din ca oxy, xc tc qu trnh oxy ha ca polyunsaturated axit bo (PUFA) c cha mt, cis-1 cis, 4 - pentadiene cu trc. Cc thut ng thng c chp nhn cho cc isozyme LOX ph bin nht l nh sau: LOX I, trng by cc vt kim pH cho hot ng ti a v im isoelectric ca khong 5,7; LOX II, vi cc hot ng pH ti u v im isoelectric khong 6,5 v 6,25, respec-tively; v LOX III, vi pH ti u hot ng rng trung vo pH 7 v isoelectric 6,15 im (Siedow, nm 1991; Boyes v cng s, 1992.). Trong khi c ba LOX loi c th c mt trong cc nh my nh: ht cy h u (Siedow, 1991), mt s loi LOX c nhiu u th trong nhng ngi khc, chng hn nh LOX II ti Kiwi (Boyes et al., 1992), mng ty (Gavanthorn v quyn hn, 1989), da leo (Feussner v Kindl nm 1994; Wardale v Lambert, 1980), c chua (Bonnet v Crouzet, 1977) v to (Kim v Grosch, 1979). LOX ti chuyn i acid linoleic u tin cho 13-hydroperoxide dn xut, LOX 2 mu 9hydroperoxide hp cht trong khi LOX III sn lng mt hn hp ca hydroperoxides. LOX loi II v III, vi s c mt ca axit bo v oxy ha tan, ng oxy ha carotenoids (Lebedev v cng s, 1978;. Canfield v Valenzuela, nm 1993; Ueno et al, 1982.) V cht dip lc (Cheour et al, 1992. ; Zhuang v cng s, 1994, 1997).. LOX II c kch hot bi canxi, trong khi LOX III l c ch canxi (Siedow, 1991). Trong a tht to, tri cy giu canxi v / hoc pht pho thp hn LOX ni dung (Marcelle, 1991). Kato et al. (1992) bo co s xut hin ca mi LOX (LOX IV, V, VI) trong l mm u tng ny mm. LOX V, VI u tin sn xut 13 (S)hydroperoxy-9-cis, 11-trans-octadecadienioc acid (13S-HPOD) nh l mt sn phm phn ng ca acid linoleic, trong khi LOX IV sn xut c hai 13S-HPOD v 9 (S)-hydroperoxy-10-trans, 12-cis-octadecadienoic acid. Tt c ba isozyme c pH Optima l 6,5, khng c hot ng pH 9.0 v a thch linolenic acid linoleic n nh l cht nn. Lin hp axt hydroperoxy (HPO) sn xut bi tri qua s trao i cht xc tc LOX bi lyase hydroperoxide (HPO lyase). HPO lyase xc tc tch ca HPO aldehyt, chng hn nh cis-3-noneal v hexanal t HPO acid linoleic v cis-3-, cis-6-nonadienal v cis-3-linolenic acid hexenal t HPO (et al Grun., Nm 1996; Wardale v Galliard, 1975). Bn cnh hydroperoxidation, hnh thnh cc oxoac-id v ketodienes c xc tc bi LOX (Vick v Zimmerman, 1980;. Sanz v cng s, 1993). Hydroperoxide isomerase cng c th xc tc cho isomerization ca oxit-hydroper nh l mt con ng phn ng trung gian (Vick v Zimmerman, 1976). HPO lyase l mt enzyme membrane-based/bound hin din trong mt lng nh trong m thc vt. Trn c s cc c trng b mt, lyase HPO c phn thnh ba loi: 9-HPO lyase, 13 HPO-lyase v lyase HPO khng c hiu (Perez v cng s, 1999a.).

Cc c trng c cht xc nh thnh phn hng thm ca cc sn phm thc vt nhiu, mc d cc hnh ng c th ca LOX. S hnh thnh ca cc aldehyd chui di bin ng ca C9 C6 v lan rng trong tri cy v rau qu (Kim v Grosch nm 1981, Gray v cng s,. Nm 1999; Perez v cng s, 1999a) v tin thu c nhanh chng khi t bo thc vt b gin on trong s hin din ca oxy.. Siedow (1991) m t hai con ng trao i cht cho HPO (Hnh 6.1). Mt lin quan n hot ng ca lyase HPO vo sn phm LOX, 13-thu-peroxylinolenic acid, dn n s hnh thnh cc acid hexanal v 12-oxo-cis-9dodecenoic. Sau l sau isomerized vo acid 12-oxo-trans-10-dodecenoic n nh hn, cn c gi l traumatin hoc nh Traumatin c bit l bt chc mt s tc dng sinh l kt hp vi lm b thng trong cc m thc vt, gy divi "vt thng ni tit t."- sion v hnh thnh m so sau ny. N cng c th c chuyn i thnh cc axit phi sinh ca mt qu trnh oxy ha nonenzymatic ca phn na aldehyde. Chn Thng acid cng xut hin

Hnh 6.1 "lipoxygenase ng" cho cc sinh tng hp acid jasmonic, traumatin v acid chn thng tm l t cc sn phm lipoxygenase, 13-hydroperoxylic acid (Siedow, 1991).

2002 bi LLC bo CRC

c tham gia vo phn ng nh my lm b thng. Con ng th hai c khi xng bi cc cyclase hydroperoxide enzyme (HPC) c xc tc s hnh thnh ca 8 - [2 (cis2'-pentenyl)-3-oxo-cis-4-cyclopentenyl] octanoic acid, thng c gi l 12 - oxophytodienoic acid. Hp cht ny phc v nh l tin thn cho s hnh thnh cc axit jasmonic cng c xut l mt promoter ca lo ha nh my v c dn truyn tn hiu lin quan n cy trng. HIU QU CA LIPOXYGENASE v c ch lo ha v khng Tng LOX hot ng l mt tnh nng ph bin trong m thc vt hoa gia. Cc xc tc

ca cis, cis-1 ,4-pentadiene cu trc c lin quan n vai tr quan trng ca LOX trong lo ha t bo thc vt. iu tr cho rng tr hon s khi u ca lo ha, chng hn nh vic b sung cc cht chng oxy ha cytokinin hoc gim mc ca LOX ni sinh lin quan n kim sot khng c iu tr (Siedow, 1991). S c ch s chm tr LOX chn v lm mm trong o (Wu v cng s, 1999.) V Kiwi (Chen et al., 1999). LOX hot ng cng c tng quan vi s pht trin t bo thc vt (McLeod v Poole, Nm 1994;. Tanteeratarm et al, 1989), cng nh tc nhn gy bnh (Avdiushko v cng s, 1993a;. Gardner, nm 1991; Ohta et al, 1990) v cn trng (Avdiushko v cng s, 1997;.. Duffey v Stout, 1996; thaler et al, 1996). c ch khng. C ch bo v lin quan l cc d ha hn na cc sn phm oxy ha thnh axit jasmonic v methyl jasmonate, l thnh vin ca mt chui dn truyn tn hiu trong t bo chuyn tn hiu n ht nhn v la chn biu hin gen kch hot (Gardner, Nm 1991; Feussner v Kindl nm 1994; Avdiushko v cng s, 1993a).. Tng LOX xy ra ng thi vi s gim st trong linolenic v linoleic acid v tng s cc axit bo trong cc nh my da chut tim virus Colletotrichum lagenarium hoc hoi t thuc l (Avdiushko v cng s, 1993b.). S tham gia ca LOX trong bnh tance-resis ca Kiwi c chng minh bng cc hot ng LOX tng trong Botrytis cinerea qu tim phng (McLeod v Poole, 1994). Linoleic acid v LOX sn phm ca acid linoleic cng c ch s ny mm v pht trin ca Botrytis cinerea lt c rt (Hoffman v Heale, 1989). Gorst v Spiteller (1988) pht hin mt lng ln cc hp cht khng bo ha LOX-oxy ha acid bo, 10-hydroxy-octadeca-8, 12 - dienoic acid v acid 10-hydroxyoctadeca-8enoic, trong homogenates dch nc ca du ty va hi. Cc hp cht ny hot ng c nm c v xut hin c tham gia vo c ch t v ca nh my. LIPOXYGENASE trung gian v cc hp cht hng v AROMA Aroma hp cht trong sch-ct tri cy v rau qu v s tham gia ca LOX trong biogenesis hng v c xem xt trong chng 12. Hng v sn xut bi LOX ng ni chung l hot ng g, tr khi c kch hot bi ngm hoc tn thng t bo (Gardner, 1989). Min ph cp tin trung gian trong cc phn ng mng thit hi sinh hc (Eskin et al., 1977), v mt h bi ca cc axit bo t do kt qu t thy phn lipid (Biale, 1975). Trong chic hoa sp l (Brassica oleracea L., nhm Botrytis), LOX trung gian tng t l pht-to-protein lipid xy ra thng qua trung gian gc t do (Voisine et al., 1991). Trong mng phong b t rau bina (Spinacia oleracea L.) chloro-plasts, LOX xc tc phn hy nhanh chng ca hydroperoxides acid bo (Blee v

Joyard, 1996). Axt bo l s lng cc tin cht d bay hi ln ca com-pound chu trch nhim v hng thm ca cc sn phm cy trng. hng v tiu biu c to ra bi LOX c chng minh bng cch x l LOX chit xut t to bin xanh (Enteromorpha intestinalis) vi acid linolenic (Kuo et al, 1996.). Ti nh to, xanh, da leo, xoi v hng liu to c tm thy trong bin ng tp trung. Vic b sung LOX nghin u xanh cng gy ra mi v v hng thm thay i m t nh l "chui cn xanh", "c", "rm" v "amoniac" (Williams v cng s, 1986.). LOX ng gp vo cc v chua trong nhuyn. Lactones c hng v quan trng ca o v m c sn xut thng qua hot ng LOX (Crouzet v cng s, 1990;. Sevenants v Jennings, 1966). LOX sn phm ng t rau dip (Letuca sativa L.) l ch yu cis-3-hexenal, cis-3hexenol v cis-3-hexenyl-acetate (Charon v cng s, 1996.). c homogenates tiu xanh v chung, vic b sung cc acid linoleic tng ln ng k mc hexanal va hexanol, trong khi mc cis-3-hexenal va-2 trans-hexenal c tng cng ng k bng cch cho thm acid linolenic (Luning et al., 1995). Trong nm (Agaricus bisporus), mt mi quan h r rng tn ti gia vic sn xut ca 1-octen-3-ol v cc hot ng LOX (Belinky et al, 1994.). LIPOXYGENASE v cc hp cht phenolic Cc hp cht phenolic c ch LOX hot ng v c tim nng ngn chn qu trnh oxy ha LOX qua trung gian ca carotenoid trong rau qu (Oszmianski v Lee, 1990). echin Ct-v epicatechin c tim nng c ch cao nht, v acid p-coumaric v ferulic trin lm hiu qu thp nht c ch. Nhn chung, flavans hin th hiu ng cao nht tip theo flavonols c ch v cc hp cht phenolic acid. Nh vy, s tp trung ca phenolics xut hin c mt tng quan cao vi cng tc phng chng ty trng carotene. Cc c ch c ch LOX c v l do gim trung gian gc t do c hnh thnh trong lipoxygenation (Takahama, 1985). LIPOXYGENASE trong rau qu Apple Khng bo ha chui thng cht d bay hi este xut hin pht sinh trong to ch bng con ng LOX (Rowan v cng s, 1999.). Mt cuc iu tra ca cc sinh tng hp ca R-octane v R-5-cis-1 ,3 octene-diol, hai khng sinh t nhin trong to v l sau khi p

dng cc cht nn v cht chuyn ha c nhn LOX LOX-c ngun gc cho thy rng hu nh tt c cc tin cht p dng c mt phn chuyn thnh R-octane1,3-diol (Beuerle v Schwab, 1999). Cc dn xut acid linolenic, vn cn cha 12,13-cis tri phiu tng gp i v octanol dn xut oxy-chc nng ha ti carbon 3 l tin cht hiu qu nht ca cc 1,3-diol. Mi quan h gia ni dung khong sn, sinh tng hp ethylene v cc hot ng LOX trong to "Jonagold 'l mt trong tri cy giu canxi v / hoc pht pho c thp hn LOX hot ng, 1-aminocyclo-propane-1carboxylic acid (ACC) ni dung v pht thi ethylene , trong khi tri cy giu kali v / hoc magi vi tng i cao K / Ca c mt hot ng LOX cao hn, mc pht thi ACC v ethylene. Cc ni dung khong sn tri cy l mt tc nhn tc ng ln LOX hot ng v h thng hnh thnh ethylene vi mt hiu qu v dung lng lu tr (Marcelle, 1991).

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Mng ty Mng ty LOX ch s dng axit linoleic monolinolein v l vt cht nhng hot ng thp, hoc di-tri-linolein cht. enzyme ny c mt hot ng pH ti u l 5,5-6,0 v n nh pH 4,5-8,0 khi bo qun 2 C (Ganthavorn v quyn hn, 1989). Ganthavorn et al. (1991), da theo tnh cht ng hc bc nht ca bt hot nhit, cho rng LOX isozyme trong mng ty khng c stabilities nhit khc nhau. Tuy nhin, Pizzocaro et al. (1988) quan st mt m hnh hai pha nhit tivation-inac v nhit tng i n nh trong mng ty LOX so vi LOX chit xut t u, c rt v zucchini. Bng cai xanh Nhit lm dng trong qu trnh lu tr v x l kt qu bng ci xanh trong gim poly-axit bo khng no (PUFAs) ni dung v hot ng LOX v lm tng phn ng acid thiobarbituric cht so vi nhng ngi bo qun 2 C (Zhuang v cng s, 1994, 1997.). iu tr ca bng ci xanh u nhng vo nc nng (45 C trong 14 pht), tuy nhin, kt qu trong lu gi tt hn v cht dip lc v ni dung protein ha tan trong khi bo qun 20 C. iu tr ny cng lm gim LOX v chlorophyllase hot ng (Kazami et al., 1991). PH ti u ca bng ci xanh Hoa con LOX xy ra 5,5-6,0 (Zhuang et al, 1994.).

c thay i khng kh lu tr ng gi (MAP) (7,5% kh CO2 v O2 11,2%) ca bng ci xanh dip lc t tng chic hoa (CHL) v gim LOX-suy thoi gy ra ca C-18 PUFA (Zhuang v cng s, 1994.). Thay i trong hot ng LOX nc ha tan trong MAP v mu nonpacked theo mt xu hng tng t nh PUFA. LOX hot ng, PUFA C18, C18 PUFA hydroperoxides, axit bo tng s, thiobarbituric acid phn ng cht (TBA-RS) v CHL cng tng n hoa hoa gia bng ci xanh trong thi gian bo qun sau thu hoch hoa n bng ci xanh ti 5 C. Thiu bao b nguyn nhn lm gim ng k m, PUFA, LOX hot ng, CHL v ha tan protein, v tng thiobar-bituric cht acid phn ng (TBA-RS) (Zhuang v cng s, 1995.). Da chut Min ph v polysomes kt ng gp cho LOX tng hp, v cc isozyme c t trong khoang khc nhau ca t bo thc vt. Qu da chut thng c s dng nh mt m hnh chit xut v nh v cc bo quan (Feussner v Kindl nm 1994; Wardale v Lambert, 1980). Trong vic xc nh v tr ni bo v cu trc lin kt organellar cc hnh thc LOX trong c th lipid, microsomes v cytostol, Feussner v Kindl (1994) qu-strated rng LOX isozyme xy ra trong cc khoang khc nhau ca t bo thc vt. Cc tnh cht xc tc ca c th-lipid v LOX microsomal trong da chut cng c tm thy s c khc nhau. PH ti u cho c th lipid-LOX l 8.5, trong khi ca LOX micosomal l 5,5. Wardale v Lambert (1980) quan st hot ng LOX cao nguyn sinh da chut cn nguyn vn t cc m c v v tht qu da chut. t khng bo nguyn vn v gim hot ng xy ra sau v LOX thm thu hn t cc m c tm t. Vic hu ht cc cht hot ng cho LOX da chut l linoleic acid (100%), acid linolenic (77%) v acid arachidonic (23%) c pH ti u v thng perature-l 5,5 v 40 C, tng ng. Canxi, EDTA, dithiothreitol, imidazol, cysteine v axit P-chloromercuribenzoic khng c ch hot ng LOX da chut.

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Kiwi LOX Kiwi cha t nht mt loi II LOX. Cc enzyme l tng i n nh nhit, tang vt

hot ng cao hn so vi cc loi qu khc (et al Boyes, 1992.). Cc axit bo ch yu trong qu Kiwi chn c palmitic (16:00), stearic (18:00), oleic (18:01), linoleic (18:02) v linolenic (18:03). hot ng LOX c th tng quan vi s gim cng ca hoa qu bo qun 20 C. 0 C, tuy nhin, LOX l c ch ng k n di 30% ca nhng ngi trong tri cy c lu tr 20 C, v chn chm (Chen et al., 1999). Cc h s pH ca LOX Kiwi l mt trong hai pH cc i (6,2 v 7,6-8,0) xy ra khi linoleic acid l cht nn. Linolenic acid gy ra mt s thay i trong hot ng cao im n 5,75 v 7,4-7,7. LOX ti a hot ng ca qu xy ra ti 36-46 C. Da gang Cantaloupe da (Cucumis Melo reticulatus) cho thy khng c hot ng LOX trong mesocarp trung (mesocarp) m ca tt c cc k hn khng ging nh trong cc mesocarp-hypodermal (di da) (Lester, 1990). Linolenic acid linoleic v trong m di da v ton vn mng huyt tng cng gim 30 ngy sau khi n. Trong cc m di da, xut hin LOX ng vai tr quan trng trong s lo da cantaloupe bi vic sn xut cc peroxit t acid bo t do, do , kt qu trong bation-pertur ca mng t bo. Enzym hot ng tng vi chn v lo ha. LOX hot ng trong qu trnh phn bo da cantaloupe v thi gian m rng pht trin cng cao hn so vi tri cy trng thnh. Trong ngt lai (Cucumis Melo inodorus Naud.), LOX hot ng xy ra trn c hai-hypodermal v trung bnh mesocarp m (Lester, 1998). Cc m hypodermal-mesocarp, tuy nhin, cho thy hot ng cao hn so vi cc m trung mesocarp trong tri cy trng thnh. s khc bit nh vy trong hot ng LOX c th c quy cho s khc bit trong s pht trin ca cc m v trong tnh trng thiu nc m. Homogenizing tht ca da cantaloupe LOX kch hot v hot ng lyase HPO v lm thay i thng tin hng thm ng (Wyllie v cng s, 1994.). LOX hp cht c ngun gc t nh cis-2-hexenol c sn xut ng thi vi mt s mt mt ng k cc este. Nhit v pH Optima cho LOX trong cantaloupe l 20 C v 7, tng ng (Lester, 1990). Hybrid ngt LOX ch c mt nh cao hot ng pH 6,8 v nhit ph thuc vi cc hot ng cao hn tem cao peratures. Tng LOX hot ng trng hp vi nhng thay i sinh l trong mng lipid huyt tng lai ngt cng xy ra vi mt s mt mt dn n tnh ton vn mng (Lester, 1998). Du LOX v HPO lyase trong du ty (Fragaria ananassa Duch X.) Tri cy c t ch yu

phn micosomal (Perez v cng s, 1999a.). Linolenic acid l mt cht nn thch cho LOX du ty, hnh thnh 13 - v 9-hydroperoxides trong t l 70:30. HPO lyase trong du ty s tch 13-hydroperoxides ca acid linoleic (13 hot ng% tng i) v acid linolenic (100 hot ng% tng i) to thnh hexanal v 3-cis-hexenal, tng ng. Mt nh hng bt li ca vic iu tr hng v du ty ozone trn xy ra vi mt lng kh thi gim cc este d bay hi trong tri cy ozonated (Perez v cng s, 1999b.).

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C chua LOX-do chuyn i v cc nhm acyl linolenoyl alpha-linolenoyl bo hexanal v hexenal (cis-3-hexenal v-2 trans-hexenal), tng ng, trong thi gian ngm cc loi tri cy c chua rt nhiu ng gp vo s kt hp ca cc hp cht d bay hi xc nh c chua hng v (Gray v cng s, 1999.). Hnh thnh cc C6 aldehyt t C18 polyunsaturated fatty acid (PUFAs) tin thu c bng cch tun t mt h thng enzyme lin quan n LOX (m u tin oxygenates v tr-9) tip theo l mt h thng phn ct hydroperoxide l, tuy nhin, c th cho cc 13-hydroperoxy v tr (Gallard v Matthew, 1977). LOX v activ HPO lyase-du khch v c xc nh trong phn microsomal, mt vin sau microsomal (PMP) v phn cytosolic ca c chua cho thy hnh thc microsomal ca LOX c s gia tng ln nht trong hot ng, vi s pht trin qu gia cc-trng thnh xanh v my ct giai on (Riley et al, 1996.). Hot ng t chi nh l tri cy chuyn sang mu , khng ging nh lyase HPO, trong cc hot ng phn microsomal thng tr trong tt c cc giai on pht trin. HPO lyase trong c chua l khng nhy cm vi pH trong khong 6-8 v khng th hin bt k thay i ng k trong hot ng vi s chn. Ha tan LOX hot ng cng chim u th trong cc phn s PMP ca tri cy cho tt c cc giai on pht trin. i vi cc phn phn on subcellular, LOX hot ng l cao hn pH 6 hn so vi pH 7 v pH 8 tt c cc giai on pht trin (Riley et al, 1996.). Peroxidase Peroxidases (POD; EC 1.11.1.7) l cht xc tc st-porphyrin hu c c phn phi rng ri trong cc nh my v dng nh l thnh phn bnh thng ca t bo thc vt nht. Hu ht cc thay i hng v tri cy nguyn v unblanched v rau qu c th

c tng quan vi hot ng POD, v c mt mi quan h thc nghim gia cc hot ng peroxidase cn d, ngoi hng v v off-mi trong thc n (Burnette, 1977;. Loaiza-Velarde et al, Nm 1997; Cano v cng s, 1998).. Thay i xy ra trong cc hot ng POD ngi b thng v ti ct tri cy v rau qu ng gp ng k cht lng sn phm ca h (Svalheim v Robertsen nm 1990; Loaiza-Velarde v cng s, 1997;. Lamikanra v Watson, 2001). PHN NG peroxidase trung gian Phn ng xc tc bi enzyme POD thng peroxidatic, oxidatic, catalatic v hydroxy (Vamos-Vigyazo, 1981). Phn ng peroxidatic l quan trng nht. Cc c ch ca phn ng c bn lin quan n mt hnh ng oxy ha bng cch mt hnh ban u ca mt trung gian phc tp vi mt ngi chp nhn hydro. Vic chuyn giao hydro t cc nh ti tr mt cht kt qu trong mt ln th hai phc tp lin ha gii trc khi ti to ca cc enzyme POD v s hnh thnh ca mt sn phm phn ng. Phn ng c th c tm tt nh sau: ROOH + AH2 H2O + ROH + A ROOH c th c HOOH hoc mt s peroxide hu c khc, AH2 l nh ti tr hydro trong cc hnh thc gim, v A l nh ti tr hydro dng oxy ha. Cc nh ti tr khu phc hp hydro v oxy ha univalent hai bc trung gian xy ra:

POD + H2O2 Complex ti Complex I + AH2 Complex II + AH Complex II + AH POD + A Peroxidative phn ng c th din ra theo cch ca mt s phn ng trung gian lin. Mc d hnh ng enzyme xut hin c kh nng tin hnh theo cch ca con ng heterolytic (Dixon v Webb, 1964), hot ng peroxidase c th c xc tc bi cc gc t do v chm pht trin do n xc thi gc (Adak v cng s, 1997.). Enzyme POD cng c th tng cng trit ti sn nht rc (Staehelin et al., Nm 1992; Wang, 1995). pH v nhit ti u cho hot ng peroxidase ph thuc vo ngun gc ca enzyme. PH ti u c th khong 1,8-8,5 (Lee v Tu,

Nm 1995; Rodrigo v cng s, 1996;. Otter v Polle, 1997). Nhit ti u dng nh l 25-60 C (Koshiba v Matsuyama, nm 1993; Campos v cng s, 1996.), Nhng c nhng trng hp c bo co trong hot ng peroxidase tng theo con ngditions (Scott, 1975; Cano et al. , 1998). Ph bin v N NH Peroxidases xy ra c dng ha tan v b rng buc trong tri cy v rau qu (Sanchez v cng s, 1993;. Brzyska v cng s, 1992; DaSilva v cng s, 1990;.. Ingham v cng s, 1998.). Cc POD isoelectric im m khc nhau 3,5-9,5 bng chng s tn ti ca c hai dng cation v anion ca POD thc vt (McLellan v Robinson, 1983). Bound POD thng km theo cc tng tc ion cc thnh t bo trong t bo nguyn vn (Giordani, 1977;. Thompson v cng s, 1998), v c th khc bo quan nh ty th v ribosome (Hideg v cng s, 1991;. RAA, 1973) . Ti sn ca POD rng buc khc vi ca POD c lp vi phn ha tan ca t bo (Penon et al, 1970.). POD enzym trong rau qu thng c tnh n nh cao vi nhit v, v iu ny, chng thng c s dng nh l cc ch s x l nhit hiu qu trong rau qu ch bin. Nhit n nh v ti to ti sn ca POD thng chu nh hng ca vic h ang trong trng thi ha tan hay b rng buc. Ionically POD rng buc hn nhit n nh trong xoi v cam (Khan v Robinson, nm 1993; McLellan v Robinson, 1984) trong tng phn vi nhng pht hin cho to POD (al khun mu v cng s, 1987.). Trong l, tuy nhin, c hai POD ha tan v ionically rng buc c nhit khng n nh vi ch khong 2% trong nhng hot ng enzim gc cn li sau 2 pht 80 C (khun mu v cng s, 1989.). Nhit ngng hot ng ca peroxidase l phi tuyn. S suy gim ln trong hot ng c quan st trong cc giai on ban u ca mt qu trnh nhit nht nh, nhng t l ngng hot ng sau thay i cho mt qu trnh chm hn nhiu (Clemente, nm 1998; Quyn hn v cng s, 1984.). Tnh cht hai pha ca bt hot nhit ca enzyme c lin quan n s hin din ca isozyme vi stabilities nhit khc nhau trong cc loi rau (Yamamoto v cng s, 1962.). Ti sinh ca POD sau ngng hot ng nhit ca cc enzym t Brussels v ci bp (McLellan v Robinson, 1981), to (khun mu et al., 1987), Kiwi (Prestamo, 1989) v xoi (Khan v Robinson, 1993) xy ra. POD hon ton bt hot sau khi x l nhit 20-10 pht ca sp l 80110 C (Bottcher, 1975; Vamos-Vigyazo, 1981), v n ch mt 15 pht lm gim hot ng POD ca mnh bng 98% 50 C (Lee et al, 1984.). A chu nhit isozyme trong sp l c trch nhim t hn 5% hot ng POD ca n, tuy nhin, phi mt hn 30 pht lm gim hot ng n 50% 50 C (Lee v Pennesi, 1984). Regen-eration sau ngng hot ng nhit ca Brussels khng c quan st cho phn lp POD

isoenzymes (McLellan v Robinson, 1987A). Arroyo et al. (1999) khng bt hot POD trong rau dip, c chua, mng ty, sp l, rau bina, hnh kt hp vi p lc cao v phng php tr liu nhit thp. Phng php iu tr sc nhit (rang-ing t 45 C trong 120 giy n 55 C trong 60 giy), tuy nhin, gy ra mt s gim xung trong khong 30% trong POD hot ng t letuce tng bng tri (Loaiza-Velarde et al, 1997.). Cc v tr v cc loi enzyme POD trong m thc vt c m t bi kVAR al-et atskhelia. (1997). Nh my v c phn thnh hai loi (Welinder, 1992). Ascorbate peroxidase (APX; lp ti), m l t thc vt v cystol lp lc, c phn bit vi POD cy c in (loi II) isozyme bi s khc bit ng k trong c cu chnh ca h. APX l mt POD H2O2-nht rc m s dng nh l mt nh ti tr ascorbate in t trong thc vt v to (Miyake v Asada, nm 1996; Asada, 1992). APX xy ra trong hai ng dng v ni a ha t bo ca n. Mt ng v ca APX c bn a ho trong lp lc v c tm thy c hai hnh thc (tAPX) thylakoid v to thnh mt ha tan trong stroma (sAPX). tAPX dn sch cc H2O2 l photoproduced trong thylakoids. Cc hnh thc khc ca APX c bn a ha trong t bo, v chc nng ca n dng nh l nht rc ca H2O2 sn xut trong bo tng (Miyake v Asada, 1996). Trong qu trnh pht trin cy trng, hot ng APX c quy nh bi ni dung ascorbate. B thng, nh trong ti ct ch bin, thng dn n s gia tng sinh tng hp ascorbate v ni dung (Diallinas v cng s, 1997;. OBA et al, 1994.). C in, tit thc vt POD c chung 50-95% trnh t tng ng trong siu h ca POD (loi II) c phn cng n lp III (Welinder, 1992). V guaiacol (2-methoxyphenol) thng c s dng nh mt cht nn gim, cc men ny cng c gi l POD guaiacol-loi. Hu ht cc tit POD cy trng l glycosylated (Johansson v cng s, 1992.). Khng ging nh POD guaiacol l c im c trng rng i vi cc nh ti tr in t v tham gia vo nhiu qu trnh sinh l, chng hn nh sinh tng hp ca lignin v ethylene, ascorbate vt POD nhy cao cho ascorbate l nh ti tr in t (Asada, Nm 1992;. Amako et al, 1994) v c c th trong vai tr sinh l ca n trong nht rc c kh nng gy hi H2O2 (Dalton v cng s, 1998) v cc gc t do (Wang, 1995).. Trong s hin din ca cht flavonoid, guaiacol POD c th tham gia nht rc H2O2 c in vivo v in vitro bng xc tc qu trnh oxy ha H2O2 ph thuc ca flavonoids. Trong phn ng POD flavonol-guaiacol, ascorbate c tim nng ti sinh flavonols bng cch gim cc sn phm oxy ha (Yamasaki v cng s, 1997.). Cc nhy cm ca POD ascorbate cht th thiol (Chen v Asada, 1992), p chloromercuriben--zoate (Amako v cng s., 1994) khc so POD guaiacol. Phc tp, ti c hnh thnh bi APX trong mt ng phn ng peroxidatic POD l cc k khng n nh v nhanh chng c chuyn n phc tp II m khng c s b sung ca mt

nn gim (Patterson et al., 1995), trong khi POD guaiacol c c trng bi n nh phc tp I. HIU QU CA peroxidase v s chn v lo ha Mt chc nng quan trng ca POD c lin quan n vai tr ca n trong hnh ng indole acetic acid oxy ha (IAA), do n tham gia trong cc quy nh tng trng (Acosta v cng s, 1986;. Grambow, 1986). Peroxidases c coi l ch s ca s chn v lo ha (Haard, 1973;

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Scott, 1975; Vamos-Vigyazo et al, 1981).. Cc cm ng ca isoenzymes POD trong lo ha etylen gy ra, l mt phn ng thng gp cy trng ca C. sativus, cc loi khc ca Cucumis v cc chi khc ca Cucurbitaceae (al Abeles v cng s, 1989.). Trong qu chn xung hang, POD v isozyme oxidase IAA c cng c vi s trng thnh ng h gressing, trong khi trong tri cy nonclimacteric, ni ethylene khng thay i ng ch trong qu trnh chn, ch c nng IAA oxidase isozyme tng, trong khi nng isoenzyme POD gim (Vamos-Vigyazo , 1981). Trong o pht trin, hai POD nh hot ng tng ng vi hai giai on ca tng cn (Flurkey v Jen, 1978). Vai tr ca POD trong suy thoi thnh t bo ca c chua c chng minh bi Araujo (1985). p dng cc POD cht bao gm IAA, NADH, KI v Na2SO3 dn n vic tng gim cn ca c chua chn m. 7-Hydroxy-2 ,2-dimethyl-2 ,3-dihydrobenzofuran c ch phn hy m. POD tng hot ng v ni dung IAA gim trong khi pht trin v senes cence-ca ci bp Trung Quc, bp ci v rau bina (Zhang v Zong, 1988). Trong con ngi i, POD hot ng gia tng cc m bt giy ln sn khu, xung hang ca s chn. Trong mt cch song song, s lng ca cc protein chit gim t preclimacteric qu chn hoc hoa gia. Thay i trong ba isozyme POD xut hin c lin quan n qu trnh chn (Marin v Cano, 1992). Cc hot ng ca POD v phyllase-chloro trong v ca qu xoi chn mu xanh l cy cng c khong mt na ca tri cy chn vng (Ketsa et al, 1999.). Thay i trong hot ng POD tng ng vi cc xung hang v bt u ca lo ha trong to "Golden Delicious" (Gorin v Heidema, 1976). Hot ng ti a POD c th cng xy ra ti "mu xanh l cy nh" v "mu xanh l cy ln" chn on ca du ty (Civello et al, 1995.). Kinetin, mt cytokinin lin quan n h hp v ethylene sn xut, tuy nhin, khng c tc dng xc tc vo POD da cantaloupe (Lamikanra v

Watson, 2000). Guaiacol POD hnh nh l lp POD chnh tham gia vo lignification ca thnh t bo, dation degra-ca IAA, sinh tng hp ca ethylene, cha lnh vt thng v chng li tc nhn gy bnh (Gazaryan v cng s, 1996; Kobayashi v cng s, 1996..).

HIU QU CA peroxidase v phn ng phng th NH MY POD c cho l quan trng trong mt lot cc phn ng bo v cy trng chng li tc nhn gy bnh. S tham gia trong c ch bo v thc vt POD c lin quan n vai tr ca n trong con ng trung gian shikimate trong tng hp ca cc axit amin thm, acid acetic indole (auxin), axit cinnamic (tin thn ca phytoalexin phenylpropanoid), coumarin v lignins (Biles v Martyn, 1993 ). enzym khc tham gia vo con ng shikimate, nh PAL, isomerase chalcone, polyphenol oxidase v dehydrogenase Shikimate, cng c kt hp vi c ch bo v thc vt hoc lo ha. POD hot ng tng nhanh hn trong kh nng chu hn so vi da chut hypoco d b-tyls sau khi tim phng vi cc tc nhn gy bnh Clasdoporium cucumerinum Ellis v Arth. (Svalheim v Robertsen, 1990) v Colletotrichum lagenarium (Pass.) Ell. v Hals. (Hammerschmidt v Kue, 1982). Cc m hnh ca isozyme c gy ra bi nhim nm hoc thn mm khng tng t nh m hnh ca isozyme gy ra bi b thng. enzyme POD t muskmelon, da hu, da chut cm ng vi C. langenarium c tm thy l khng nguyn v electrophoretically tng t (Smith v Hammerschmidt, 1988). Tuy nhin, da trn s bt lc ca ethylene to ra sc khng, v s bt lc ca thiosulfat bc tng tnh nhy cm, Biles

et al. (1990) kt lun rng POD khng xut hin chi mt vai tr trong vic hn ch pht trin bnh, da chut trong C. lagenarium h thng, mc d hnh ng ethylene vn xut hin l cn thit cho s pht trin tn thng v lo ha. Tc nhn gy bnh v vt thng do hot ng-POD c chng minh trong tri cy v rau qu (Biles v Martyn, nm 1993; Mohan v cc cng s, 1993;. Madi v Katan, nm 1998; Mayer v Harel, 1979; Miyazawa v cng s, 1998; Moran, nm 1998; Sutha et al, 1996)... Lu tr n nh xut hin c lin quan n POD hot ng trong cc loi rau ct. Baardseth v Slinde (1980) bo co mt s tng quan gia cuc sng thi hn s dng ca cc loi rau ct v POD v catalase (CAT) hot ng. Thy in (Brassica napus L.), trong c

lu tr lu di n nh trng thi ct, c hot tnh cao ca POD v CAT lin quan n ct c rt vi POD trung v hot ng ca CAT. Hot ng ca POD v CAT tng i thp Brussels. Ngoi cc hot ng tng i ca cc enzym trong cc-bng car, Thy in cng c s tin cao nht ca axit ascorbic mi mg protein. Ascorbic acid, hot ng nh mt cht kh v cht ni sinh cc chui h hp m cung cp cho ATP, cng c th ng gp ng k vo s n nh ca Thy in ct gim. Tng cng hot ng POD cng c tng quan vi lignification, protein lin quan n pathogenisis, glycoprotein hydroxyproline giu v suberization (Biles v Martyn, 1993). POD hot ng, c bit l APX hot ng, c th l du hiu ca stress oxy ha trong m thc vt (Gueta-Dahan v cng s, 1997;. Kampfenkel et al, 1995.). hot ng POD trong du ty , da v rau dip cng ngh c ch nh ca cc cp tng i ca qu trnh xy ho trong cc sn phm ti ct (Lamikanra v Watson, 2000). Peroxidase, xc tc BROWNING Kh nng ca POD ng gp cho nu enzyme c lin quan n mi quan h ca mnh chp nhn mt lot cc nh ti tr hydro, chng hn nh polyphenol (Richard-Hy qun i v Gauillard, 1997). H c th xi ha catechin (Lopez-Serrano v Ros-Bacelo, 1997), cc dn xut acid hydoxycinnamic v flavans (Robinson, nm 1991;. Nicholas et al, 1994) v flavonoid (Miller v Schreier, 1985, Richard v Nicolas, 1989, Richard-Hy qun i v Gauillard, 1997). Hai c ch c th c xut cho POD xc tc cc phn ng ha nu. Mt lin quan n cc th h ca H2O2 trong qu trnh oxy ha ca mt s hp cht phenolic c s dng nh trong mt hnh ng peroxidatic bnh thng tip tc xi ha cc phenol, trong khi th hai lin quan n vic s dng cc hnh thc hp cht Quinonic nh l cht nn ca POD. C hai c ch cho thy s hin din ca enzyme polyphenol oxidase (EC 1.14.18.1) s tng cng POD qua trung gian cc phn ng ha nu (Richard-Hy qun i v Gauillard, 1997). POD xi ha (+) catechin nng thp H2O2 thng qua s hnh thnh ca ti phc tp v phc tp II. Trong phn ng ny, (+) catechin cng l mt o diphenol-tuyt vi gim phc tp II (Lopez-Serrano v Ros-Barcelo, 1997). Peroxidase trong rau qu Apple POD hot ng tng ln vi chn ca to vi mt nh cao trong hot ng xung

quanh sn khu xung hang ca chn trong v v m bt giy (Prabha v Patwardhan, 1986; Kumar v Goswami, 1986). Hot ng cng tng ln trong thi gian lu tr atmocu kim sot (Gorin v Heidema, 1976) v dng nh trong thi gian lu tr lnh thng thng

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to, mc d cc bin th xy ra vi ging cy trng (Vamos-Vigyazo, 1981). Cc mu isozyme khc nhau gia cc ging cy trng v c th c s dng phn bit ging cy trng (Barnes, Nm 1993; Manganaris v Alston, 1993). Mng ty C bn isozyme im isoelectric (pI) ln hn chn chim u th trong POD mng ty. Cc phn phn on c tnh axit hn c tm thy trong cc tip gio (Quyn hn v cng s, 1984.). Ti u hot ng ca mng ty xanh POD xy ra pH 7. Cc regen enzyme-erated sau khi phi chu nhit gia 90 v 125 C trong thi gian ngn. Mng ty ti sinh t POD hot ng ti a ca n sau khi b lu tr su ngy 25 C (Rodrigo v cng s, 1996, 1997.). Cc phn c bn v c tnh axit cng tng t nh s n nh nhit, mc d cc phn nh c tnh axt l d dng hn ti sinh sau khi x l nhit 70 C (Quyn hn v cng s, 1984.). Bng cai xanh Toivonen v Sweeney (1998) chng minh tm quan trng ca bo v chng oxy ha c cung cp bi POD v superoxide dismutase (SOD) duy tr mu xanh trong bng ci xanh. POD v SOD hot ng c khong 30% cao hn trong "vnh ai xanh", mt ging cy trng c tnh nhy cm vng thp hn so vi ging cy trng d b 'Hong '. T l superoxide dismutase peroxidase hot ng cng thp hn 'Greenbelt.' POD v SOD cng tham gia vo cc peoroxy ha lipid tng cng trong mng t bo b cng thng xy ra hn hn. Vi thi gian v cng ca stress kh hn, hot ng ca SOD v POD gim trong hai ngy u, tng ln trong hai ngy qua su, sau gim xung trong nhng ngy su n tm ca stress hn hn (Yang v Yang,

1998). Khng c s khc bit trong POD, oxidase ascorbate v kt cu gia MAP bng ci xanh ng gi v nonpacked (Barth v cng s, 1993a.). Gim gi acid ascorbic, m, cht dip lc tng s v duy tr mu sc trong bng ci xanh c, tuy nhin, hn khi ng gi trong mt bu khng kh c cha CO2 8% v 10% O2. Barth et al. (1993b) quan st thp hn POD gio hot ng trong bng ci xanh ng gi bng cch s dng mt b phim na thm cao phn t v c lu tr 96 gi 20 C so vi bng ci xanh nonpackaged gio. Ascorbic acid cht dip lc, v duy tr m cng ln hn trong bng ci xanh ng gi. Mt bu khng kh O2 1,5% so vi khng kh bnh thng hot ng c ch rng buc ionically POD trong rau dip tng bng tri (Ke v Saltveit, 1989a). Bao b ca rau dip c lu tr di bu khng kh ny cng c ch ethylene v h hp, gy ra ethylene pht trin ti ch nu v PAL v indoleacetic acid (IAA) hot ng, v n lm gim hm lng phenolic tan trong rau. Tip xc vi m rau dip CO2 tng cao ionically rng buc POD khng ha tan v ionically rng buc hot ng oxidase IAA nhng gim hot ng ha tan oxidase IAA (Ke v Saltveit, 1989b). Vic s dng mt cm bin sinh hc ethanol di kim tra bao gm cc chromatogen mt v c nh enzym (POD v ru oxidase) pht hin nhng thay i cht lng khng kh trong bao b khng ng thit k chnh sa m kt qu mc O2 thp gy tn hi hoc li dng nhit c bo co Smyth et al. (1999). Cc cm bin sinh hc c hiu qu trong pht hin thng tch thp O2 MAP mu ca bng ci xanh ct, sp l, rau dip v cc gi ci bp bm nh.

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C rt S i mu trn b mt c rt ct xy ra ng thi vi mc tng ca phenolics ha tan, POD lignin, lyase amoniac phenylalanine (PAL) v syrin-galdazine oxidase (SOX) hot ng theo thi gian. Hi nc iu tr v stor tip theo tui ti 2 C lm chm s i mu b mt bng cch c ch s trao i cht phenylpropanoid. Ha tan phenolic v isocoumarin sn xut, hnh thnh lignin b c ch, v POD, PAL v SOX b bt hot trong c rt ct c iu tr (al Howard v cng s, 1994.). Trong mt nghin cu xc nh nhng tc ng ca mt ethylene hp th v lu tr 2 C vo s i mu b mt v nhng thay i phenolic trong MAP c rt, lignin hnh cng xy ra v tng ng vi s pht trin ca s i mu trng trong lu tr. Ct kch thch PAL v POD hot

ng, v c cc hot ng enzyme vn tng cao trong thi gian lu tr (Howard v Griffin, 1993). Da chut Ant POD isozyme t qu da chut thay i nhiu trong cht nn c trng ca h, nhng u tin phn ng vi cc amin thm (Miller et al, 1990.). Trong rau bina, s xung cp ca cht dip lc xut hin c iu chnh thng qua con ng peroxidase-hydro peroxide, m m vng porphyrin, do to nn mt hp cht khng mu (Yamauchi v Watada, 1991). An isozyme anion trong bp ci vi mt im isoelectric (pI) ca 3,7 v tng i n nh nhit, trong khi mt isozyme cation, pI 9,9, c d dng hn bt hot bi nhit (McLellan v Robinson, 1987b). Nhit thp lm gim hot ng lu tr nu v PAL nhng khng c hiu lc t ngy POD hot ng trong ci bp bm nh (Takahashi v cng s, 1996.). Mango Mt s isozyme POD c trch ra t xoi. Khan v Robinson (1994) bo co bn POD isozyme-anion hai v cc cation hai khc. Cc isozyme anion c trng lng phn t cao hn l 40 v kDa 44, tng ng, so vi isozyme cation vi trng lng phn t ca 22 v kDa 27 (Khan v Robinson, 1994). Marin v Cano (1992) tm thy ba isoenzymes ca POD trong chit xut t xoi 'Smith' m di chuyn v pha cc dng pH 8.3. Cc mu isoen-zyme ca POD ca cht chit xut t xoi 'Lippens' ng k khc nhau, hin th-ing bn bng tn di chuyn nhanh hn ngoi ba ban nhc c trng ca tri cy xoi 'Smith ". Pulp POD hot ng tng vi mc chn trong xoi (Marin Cano v nm 1992; Prabha v Patwardhan, 1986). Da gang Da hot ng da POD xut hin ph hp vi iu ca peroxidase ascorbate da trn cc cht c ch ascorbate khi guaiacol c s dng lm cht nn v c ch bi mercaptoethanol-, L-cysteine v p-chloromercuribenzoate (Lamikanra v Watson, 2000, 2001). Nhit hot ng ti u cho enzyme da cantaloupe l 50-55 C. Cc enzyme c n nh nhit di 40 C v 50 C cho n 10 pht. Trn 90% tng s hot ng b mt 80 C trong vng 5 pht. Cc Optima pH rng, 5,5-7,5 50 C v 6-7 30 C, l du hiu ca s hin din

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ca nhiu hn mt isozyme POD trong tri cy (Lamikanra v Watson, 2000). Hai bn in di POD bng vi trng lng phn t xp x 240 v 170 kDa, tng ng, bao gm su tiu n v c tnh axit (pI 5,1-6,1) c mt ti da (Lamikanra v Watson, 2001). POD hot ng trong cantaloupe ct gim l inhib-ited bi acid ascorbic. Hiu qu c ch xut hin c lin quan n mt phc tp ascorbatePOD trung gian. Cc ascorbate-POD trin lm c tnh chng oxy ha c lin quan n du vt ng yu t ion kim loi. iu ny tng cng chng oxy ha bo v ti sn carotene v ko di thi hn s dng sn phm. Honeydew da hu v POD trin lm cc hot ng ti u khong pH 7 v 6.5, tng ng. Trong khi trc y hot ng ti a ca n 50 C, POD trong da hu l tng i n nh nhit cao hn so vi da ngt, da v qu kiwi, v c nhit hot ng ti u trong khong 70 C (Lamikanra v Watson, cha xut bn). Da cam Da cam c cha mt POD tim n, m xc tc qu trnh oxy ha ca mt s tri cy ca ++ thnh phn cu to ca H2O2. Mn c yu cu cho cc hot ng ca POD nh oxidase mt vi O2 (Bruemmer v cng s, 1976.). Trong h thng H2O2 peroxidase, cc constit phn ng nht hp cht axit ascorbic uent c, caffeic v gentisic. Quercetin l tr trong kho nghim ny, khng ging nh POD t mt s loi tri cy v rau qu (Hemeda v Klein, ++ 1991). Trong O2 v Mn h thng, acid ascorbic v catechol v p-phenylene

diamine tr. Trong nc cam, tuy nhin, POD hot ng l rt thp, apparently v ni dung H2O2 thp ca qu (Bruemmer v cng s, 1976.). Cation v anion POD vi cc gi tr khc nhau, pI gia 4.5 v 9.0 v trng lng phn t 22-44 kDa cng c phn lp t cam (Clemente, 1998). ao POD hot ng thay i vi ba giai on pht trin trong o. Cc hot ng POD ha tan l cao nht trong mesocarp v exocarp giai on II, v thay i isoenzymatic trong nhng m ny tng ng vi qu trnh chuyn i t isoenzymes cation, ch yu giai on I, n isoenzymes anion giai on III. Cc hot ng peroxidase ionically rng buc trong nhng m ny l cao nht giai on I (Sanchez-Roldan et al., 1990). Cc v qu trong cc drupes tr thnh lignified, trong khi mesocarp vn mnh-enchymatous vi pht trin cy n qu. Axit POD t v qu trong lignifying cng tng t nh ca mesocarp nhiu tht. v qu trong c mt s lng ln hn v s POD c bn hn so vi mesocarp (Abeles v Biles, 1991). L S nh hng ca ngy thu hoch v s xut hin ca chng ri lon sinh l trong qu l c th lin quan n cc h thng nonenzymic v enzym chu trch nhim v d ha ca cc loi oxy hot ng. L (cv. 'Hi ngh') thu hoch by ngy sau khi thi gian l tng cho thu hoch thng mi duy tr mt hot ng POD i lin quan n nhng thu hoch v thi gian, nhng APX tng 2,5 ln. Concommitantly, hot ng ca SOD v CAT gim khong gp nm ln v gp i, tng ng, khi tri cy c

chn trng thnh hn, cho thy mt tim nng cao hn cho s tch t cc c t bo O2-v HO, tng ng (Lentheric et al, 1999.). POD hot ng khng u dis22 tributed trong tht ca ging qu l, v mc khng ng nht khc mi cy trng (Vamos-Vigyazo v Nadudvari-Markus, 1982). Ni a ha ca POD vo phn ht di ng c kt hp vi pht trin sclereid. Khong dinh dng trong qu su sc c th thay i s trao i cht lignin bi nh hng n ization, a phng v, do , vic kim sot trao i cht ca POD (Ranadive v Haard, 1972). POD mu isozyme trong qu l c trng c th, v iu ny c th c s dng quan n vic xc

varietal-identi (Santamour v Demuth, 1980; Hudina et al, 1996.). Pear POD ang tch cc tham gia vo phn ng enzym nu ca n (Richard-Hy qun i v Gauillard, 1997), mc d mc POD khng th c s dng nh mt ch bo ca mu nu tim nng (Vamos-Vigyazo v Nadudvari-Markus, 1982;. Zhang v cng s, 1994). Du Du qu hot ng gim ng k POD vi chn hoa qu, v enzyme c tm thy ch yu dng mng kt (Civello et al, 1995.). enzyme ny cho thy s n nh thp nhit, v hot ng ca enzym ti a xy ra 30 C v pH 6.0. Hai isozyme POD c bn ca khi lng phn t 58,1 v 65,5 kDa c pht hin ti cc k hn khc nhau ca cc loi qu bi Civello et al. (1995). Lopez-Serrano v Ros-Barcelo (1995, 1996, 1997), tuy nhin, tm thy mt isozyme POD c bn ca isoelectric im cao trong qu du ty chn qu trnh, l thnh phn duy nht ca tnh a hnh POD trong ton b tri cy. isozyme ny c kh nng oxy ha phenol ch c s hin din ca H2O2 v thiu cresolase, catecholase v cc hot ng lacaza. Zucchini Squash Thun ha nhit lnh trong qun th c tham gia vo cc hot ng ca POD, cng vi mt s enzyme nht rc gc t do. S pht trin ca cc triu chng tn thng lnh zucchini b (Cucurbita pepo L.) c lu gi ti 5 C b tr hon bi preconditioning cc tri cy nhit 15 C trong hai ngy (Wang, 1995). Nhit iu tr preconditioning n p gia tng hot ng peroxidase v gim s suy gim ca hot ng CAT trong b trong thi gian lu tr tip theo 5 C. SOD hot ng cng vn cn cao hn trong iu kin nhit b hn trong bng qun khng c iu tr trong lu tr. Cc hot ng ca reductase ascorbate gc t do, peroxidase ascorbate v reductase dehydroascorbate ban u sau khi lu tr tng t bn n tm ngy v gim xung sau kim sot v tri cy precondi-tioned, nhng hot ng enzyme tng ln n mt mc ln hn v vn cao hn trong tri cy preconditioned hn trong iu khin (Wang, 1996). Tri cy v rau khc isozyme POD trong c rt, c chua, qu kiwi, sp l, u xanh v ci nga c bao gm ba v su isozyme, tng ng trong c rt (36-70 kDa) v c chua (38-62 kDa), mt trong sp l (70 kDa), hai trong qu Kiwi (45-43 kDa) v mt lot cc isozyme (36-120

kDa) trong ci nga (Prestamo v Manzano, 1993). Ascorbic acid c ch hot ng POD trong chit xut. Polyphenol oxidase xut hin v pht Polyphenol oxidase (PPO) l bao gm mt nhm cc enzyme protein phc tp ng xc tc qu trnh oxy ha ca cc hp cht phenolic sn xut sc t mu nu ct hoc b h hng b mt ca tri cy v rau qu. thc vt, PPO ch yu l nm trong lp lc mng thylakoid (Sherman v cng s, 1991;. Hind et al. 1995) v c th tn ti trong trng thi hot ng hoc trng thi n (Mayer v Harel, 1979). Cc tin cht protein ca enzyme c cha cc trnh t nhm mc tiu cn thit nhp khu vo lp lc v a vo trong mng thylakoid (Sommer v cng s, 1994.). Lax v Cary (1995) bo co rng PPO c tng hp nh protein tin thn c mt chui qu cnh vn chuyn vo lc lp, nhng c v thiu t cho c th nhm mc tiu vo cc mng thylakoid. S phn b ca PPO trong cc phn khc nhau ca tri cy v rau qu cng nh t l ca cc enzym ht rng buc v ha tan vi k hn khc nhau ng k. Bo co v s phn b ca PPO trong to, v d, c v khng ph hp. Mc d hin din trong tt c cc phn ca qu, mt s bo co (Harel v cng s, 1964;.. Stelzig et al, 1972) ch ra mc ng k cao hn trong v hn l trong tht, trong khi nhng ngi khc (Klein, 1987;. Janovitz et al, 1989) c tm thy PPO cao hn trong v no hn so vi v. Murata et al. (1993) chng minh rng cc enzyme PPO trong nm ch yu l ging to a ho gn li v arily th hai gn da. Trong qu trnh chn, nng ca ht enzym gim vi s xut hin ng thi ca mt phn ha tan. Trong qu to chn, ni khng bo chim hu ht cc t bo, PPO c pht hin immunochemi-Cally gn thnh t bo c s dng cc khng th chng to PPO. Trong cc t bo ca tri cy cha trng thnh v nui cy m, PPO c pht hin trong cc bo quan khc vi cc khng bo, c l trong plastid (Murata v cng s, 1997.). Lm r cc loi nc p t qu l c thc tin, khng c cc hot ng tically PPO, v PPO hot ng vn gn nh hon ton vo bt giy (Vamos-Vigyazo, 1981). Trong l xanh, PPO l ch yu nm ccchlo roplasts (Golbeck v Cammarata, 1981; Chazarra et al, 1999.).

Polyphenol oxidase trung gian BROWNING PHN NG PPO hnh ng thng kt qu trong vic hnh thnh cc quinon d phn ng sau c th phn ng vi cc nhm amin v sulfhydryl ca protein v enzym cng nh vi cc cht nn khc, chng hn nh cc dn xut axit chlorogenic v flavonoid (catechin, anthocyanins, leucoanthocyanidins, flavonols v cc dn xut acid cinnamic ). Nhng phn ng ph c th mang li nhng thay i v c tnh vt l, ha hc v dinh dng

v cng c th nh hng n cc c tnh cm quan ca tri cy v rau qu. Quinon cng gp phn vo s hnh thnh sc t mu nu bng cch tham gia trong cc phn ng trng hp v ngng t vi cc protein (Shahidi v Naczk nm 1995; Mayer v Harel, 1979; Mathew v Parpia, 1971; Vamos-Vigyazo, 1981). enzyme PPO c phn loi da trn c trng b mt. Chng bao gm monophenol monooxygenase, cresolase hoc tyrosinase (EC 1.14.18.1), diphenol oxi-dase, catechol oxidase hay diphenol oxy oxireductase (EC 1.10.3.2) v lacaza hoc p-diphenol oxy oxireductase (EC 1.10.3.1). Hnh thnh cc o-quinon t monophenols, v d, tin thu c bng cch monophenolase (creolase) xc tc hydroxy o-diphenols tip theo diphenolase (catecholase) xc tc oxi-dation ca o-phenol oquinon (Hnh 6.2). BH2 l vit tt ca mt pound o-diphenolic-com. Cc hot ng u tin cho thy mt khong thi gian tr (Chazarra v cng s, 1999;. Perez-Gilabert v Garcia-Carmona, 2000) c gii thch bi c tnh n cc bc chem-ical ca tyrosinase hnh ng l cn thit sn xut-o diphenol (Cabanes et al., 1987), trong khi cc hot ng catecholase cho thy khng c hin tng chuyn i chm (PerezGilabert v Garcia-Carmona, 2000). Ty thuc vo cc phenol, o-quinon cng cho thy s khc bit rt ln trong s n nh, v cng mu khc nhau t mt trong nhng phenol n khc (Lee v Jaworski, nm 1988;. Rouet-Mayer v cng s, 1990). Hnh ng ca PPO trn cht nn c kt qu trong gim hot ng, mt s mt mt ca ng t cc trang web hot ng ca PPO, v sa i ca mt hoc nhiu d lng histidine rng ligand ng (Osuga v Whitaker, 1995). o, l, chui PPO khng c hot ng creolase (Osuga v Whitaker, 1995). -Quinones cng c th ng gp vo suy thoi PPO tng tc ca anthocyanins thnh cc sn phm khng mu. Cc c ch degra-dation lin quan n vic PPO v catechol trong mt qu trnh tun t (hnh 6.3). C tm anthocyanins, v d, ang nhanh chng xung cp do phenolases s c mt ca catechin v axit chlorogenic (Sakamura et al, 1966.). PPO chit xut t qu du ty v catechin-D vi nhau cng gy ra mt 50-60% trong cc sc t anthocyanin sau 24 gi nhit phng (Wesche-Ebeling v Montgomery, 1990).

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B thng v gy ra cc hot ng sn xut ethylene PAL r rng bi cc c ch ring bit (Abeles v cng s, 1992;. Lopez-Galvez v cng s, 1996;. Hyodo v Fujinami, Nm 1989; K v Saltveit, 1989a). PAL l enzyme xc tc cam kt u tin v bc hn

ch tc , s trao i cht phenylpropanoid trong sn xut cht xc tc phenolase oxidizable (Ke v Saltviet, 1989a; Martinez v Whitaker, 1995). PPO c kch hot nh l mt kt qu ca s ri lon ca t bo v ton vn khi ni dung ca cc plasid v khng bo c trn ln. Gy thng tch cho r rng u tin gy ra s gia tng hot ng PAL, v do , s gia tng cht oxidizable.

HIU QU CA polyphenol oxidase v thc vt v c ch M Active PPO xut hin c mt trong tt c cc sinh vt quang hp v thc hin mt s chc nng cn thit trong cc nh my, bao gm c ngn chn cc loi cn trng v nm gy bnh (Manibhushanrao v cng s, 1988;. Hoagland, nm 1990; Sherman v cng s, 1995.). Cc downregulation antisense kt qu biu hin thanh lp v gy ra PPO trong tibility-hypersuscep vi mm bnh trong c chua, cho thy vai tr quan trng cho qu trnh oxy ha phenol PPO trung gian trong vic bo v cy trng (Thipyapong v Steffens, 1997). Tng cng cc hot ng ca PPO, POD, LOX, chitinase v alphaglucosidase cng c pht hin trong l da chut trong vng ln cn ca cc tn thng gy ra bi cc mm bnh hoc ng dng pht pht (Avdiushko v cng s, 1993b.). Bng chng v s tham gia PPO trong rn e ca patho-Gens trong tri cy v rau qu khc bao gm to (Sharma v Kaul, 1996), nm phng (Jolivet v cng s, 1998.), Ht tiu v c tm (Ouf et al, 1998.).

S c ch trung gian polyphenol oxidase PHN NG BROWNING ng k cc nghin cu v cc iu kin theo PPO hnh ng ny l c ch hoc chm pht trin trong cc h thng thc phm v trn cc hp cht c tc dng inhibitive v hot ng PPO c thc hin. Cht c ch nu PPO xc tc c th hot ng bng cch kt hp cc ng phn ng. Mt s hp cht ngn nga melanosis bi hnh ng gim trc tip trn PPO (Kahn v Andrawis, 1986; Sayavedra-Soto v Mongomery, 1986), bng cch gim o-quinon diphenols (nguyn Golan-Goldhirsh v Whitaker, 1984, Richard-Qun et al, 1992) hoc Cu2 + cho Cu + (al Hsu v cng s, 1988) do s tng tc vi s hnh thnh ca cc sn phm o-quinone.. (Embs v Markakis, 1965; Sanchez-Ferrer et al. 1989) hoc bng cch gim s hp thu ca O2 cho phn ng (Embs v Markakis, 1965;. Chen v cng s, 1991a). Mt s thuc c ch phn ng xc tc PPO c th hot ng bi nhiu hn mt c ch. Thiol hp cht, v d, c th hot ng bng cch gim Cu2

PPO trang web hot ng + cho Cu + l d dng hn mt t PPO (Osuga v Whitaker, 1995), nhng hnh ng c ch trc tip trn PPO (Dudley v Hotchkiss, nm 1989; Robert et al, 1996. ), gim quinone-o (Kahn, 1985; Richard-Qun et al, 1992) hoc bng cch to phc vi quinon hnh thnh cc hp cht khng mu (Richard et al, 1991;.. Richard-Qun et al, 1992).. Ascor-giam bt hnh vi nh mt tc nhn lm gim t hiu qu hn cysteine (Janovitz-Klapp et al., 1990) v chuyn i o-quinon tr li tng ng o ca h-diphenols. N cng bt hot PPO trc tip, v trong s hin din ca cc mc thp ca ng, aerobically c th ph hy d lng histidine ca PPO, gii phng ng bng mt c ch gc t do (Osuga v Whitaker, 1995). Sodium erythorbate cho thy khng c tc dng c ch PPO, nhng n phng chng nu l do gim quinon hnh thnh trong phn ng enzym tr li cc hp cht phenolic gc (Gopalan v cng s, 1999.). Benzoic acid, kojic acid [5-hydroxy-2(hydroxymethyl)--pyrone] axit v cacboxylic cinnamic ca lot cng c chng minh cho thy tc dng c ch PPO trong tri cy v rau qu (Vamos-Vigyazo, 1981; Chen et s, 1991b).. Hiu qu c ch canxi xut hin c lin quan n vic bo tn cu trc mem-brane hoc c ch trc tip ca PPO. Thn mu nu trong rau dip c th c gim bng cch ra gc a vi cc gii php clorua canxi l 0,3 M, 0.1 mM 2,4 -. Acid dichlorophenoxyacetic (2,4-D) hoc M 0,5 acetic acid (Thomas-Barberan et al, 1997). Canxi cng gy ra s st gim 60% trong hot ng PAL nhng khng c nh hng ng k v s tch t ca cc hp cht phenolic. Khng ging nh acid acetic m khng th phc hi c ch hot ng PAL, 2,4-D c mt s c ch 60%. N cng c tc dng inhibitive v sinh tng hp cc hp cht phenolic. Mt hn hp gim v dung dch axt acetic cng c th c s dng ngn nga s i mu mng rau dip (Castaner et al., 1996). Cysteine, resorcinol, EDTA v axt citric cng c hiu qu trong cng tc phng chng rau dip nu trong lu tr. Kahn (1985) th hin s bt lc ca thy phn casein v albumin huyt thanh b c ch nm (Agaricus bisporus) hot ng PPO. L-Lysine, glycine, L-histidine v Lphenylalanine ( tng hiu qu) c ch activ-ITY ln n 60%; L-cysteine l 0.4 mM c ch hon ton. Glycine, diglycine v triglycine (theo th t tng) c hiu qu trong vic gim mc cui cng ca melanin mu c hnh thnh bi cc hnh ng ca PPO nm trn dehydroxyphenylalanine. iu tr nm vi hexylresorcinol-4 c bo co to ra s i mu ca nm-phng. S kt hp ca 4,5 erythorbate natri%, 0,1% cysteine HCl v 100 ppm EDTA, iu chnh pH 5.5, c kh hiu qu trong vic ngn nga nu (Sapers et al.,

1995). Monophenolase v cc hot ng diphenolase ca PPO nm l c ch bi agaritine [-N-(-L (+)-glutamyl)-4-hydroxymethylphenylhydrazine]. Hiu qu c ch l khng nhiu nh tropolone nhng l tng ng vi cc acid L-mimosine v benzoic, v mnh hn axit azeliac (Cabanes et al, 1996.). Agaritine, mt hp cht phong ph v c trng t cc chi Agaricus cng loi b cc enzyme to ra o-quinon. N nh vy c th c cho rng agaritine ng mt vai tr trong c th trong quy ch ni sinh ca hot ng PPO nm v nng o-quinone (Espin v cng s, 1998a.). Sau y l mt nh gi gn y (Beaulieu v Gorny, 2002) v hiu qu ca mt s hp cht chng nu trn tri cy ti ct. Ascorbic acid c tm thy c hiu qu hn trong vic ngn nga acid erythorbic b mt mu nu trong 'Winesap' v 'Red Delicious' to cm c lu tr 24 gi nhit phng, v 1% acid citric nng cao hiu qu ca h (Sapers v Zoilkowski, 1987). Browning hn ch hiu qu trong lu tr (4,4 C) chn khng ng gi lt carambola c iu tr bng 1 hoc 2,5% acid citric cng vi 0,25% acid ascorbic (Weller v cng s, 1997.). Ascorbic acid 2-phosphate v ascorbic acid phng php iu tr-2-triphosphate cng gim nu trong phch cm to "Red Delicious 'trong 24 gi nhit phng (Sapers et al., 1989). to 'Fuji' lt iu tr bng 2% acid ascorbic khng c mu nu ng k hoc mt cht lng hnh nh cho n 15 ngy, khi bo qun 10 C trong O2 0,25 kPa (Gil v cng s, 1998.). Canxi, kt hp vi acid ascorbic (c hai thng p dng nh chm 1%), c hiu qu cao trong vic ngn nga s i mu ca qu to ti ct

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(Ponting et al, 1972.) V l (Gorny v cng s, 1998;. Rosen v Kader, 1989). Browning chm trong hi 'Bartlett' di chn v 'd'Anjou' l c iu tr bng erythorbate natri, CaCl2 v 4-hexylresorcinol sau 14 ngy k t ngy lu tr 4 C, tuy nhin, ti ct 'Bosc' qu l v nhiu b khng phn bit mu nu-inhib itor iu tr (Sapers v Miller, 1998). Mt nhng sau ct vi 0,01% 4-hexylre-sorcinol, acid ascorbic 0,5% v 1% canxi lactate m rng thm cuc sng ca 'Anjou, 'Bartlett v qu l' Bosc 'lt cho 15 n 30 ngy (Dong v cng s, 2000.). to "Red Delicious 'lt iu tr bng mt dip chng nu kt hp (4-hexylresorcinol, isoascor-BIC acid, N acetylcystein v calcium propionate) v c t chc ti 5 C duy tr cht lng hnh nh trong nm tun, nhng vi sinh vt phn hy l hin nhin sau khi bn tun (Buta et al.,

1999). Phn tch ca cc axit hu c v cc loi ng chnh cho thy rng cc slices c iu tr vi cc kt hp ca cc hp cht chng nu gi li cp cao hn ca axit malic v khng c s suy gim lng ng trong lc 5 v 10 C, ch ra rng cht lng cao c duy tr trong thi gian lu tr. Browning gim ng k ti ct lt chui x l bng axt citric (0,5 M) v N-acetylcysteine (0,05 M) c lu tr ti 5 C hoc 15 C trong vng by ngy, v khng c su vi sinh vt c quan st trong by ngy lu tr (Moline et al, 1999.). Mt s kt hp ca geenan-Jerzy Dudek 0,5% v 0,5% acid citric cng c ch nu trong lu ct nh 'Granny Smith' v to 'Red Delicious' cho 7-9 ngy ti 3 C (Tng v Hicks, 1991). Khi cysteine c s dng nh mt cht c ch enzym nu trn qu to ct lt (Walker v c mu, 1964) hay qu l (Sapers v Miller, 1998), hng nht, off-mu com-pao c hnh thnh do phenol ti sinh vi s hnh thnh mu sc su ( Richard-Qun et al, 1992).. Nu hnh off-mu sc c th c ngn chn, cysteine c th chng minh l mt thay th hiu qu bisulfites, bi v cysteine l mt axit amin t nhin c GRAS tnh trng s dng nh l mt iu bt (M s ca Lin bang Regu-lations 21:184.1271 v 21 : 184,1272). Browning c gim xung ch mt ngy 0 C trong "Golden Delicious" qu to ti ct c iu tr bng cysteine 0,1% (Nicoli et al., 1994). Thiu hiu qu ca vic iu tr cysteine l do qu trnh oxy ha trong cc gi v c c th do nng thp c p dng. Gn y, Gorny et al. (2000) bo co rng mt dip sau ct (pH 7) ca axt ascorbic 2%, canxi 1% lactate, cng vi 0,5% (w / v) cysteine ng k ko di thi hn s dng ca cc lt qu l 'Bartlett "bi mt c ch ca cng slice v ngn nga ct b mt mu nu. Ngi tiu dng khng th phn bit gia cc lt qu l c iu tr bng cc gii php bo qun v kim sot lt qu l. Sau 10 ngy k t ngy lu tr trong khng kh 0 C, 82% ngi tiu dng nh gi iu tr lt qu l c chp nhn trong xut hin, v 70% nh gi hng v c chp nhn. Khi s dng kt hp vi acid ascorbic, 4 hexylresorcinol- c bo co l mt cht c ch rt hiu qu ca mt ct nu trn nhiu loi tri cy ti ct, bao gm c to v l c bit (Dong v cng s, 2000;. Luo v Barbosa-Cnovas, 1996, 1997; Moline v cng s, 1999;.. Monslave-Gonzalez v cng s, 1993; Sapers v Miller, 1998). Gia 1 v ppm 7 / hexylresorcinol d-4 l cn thit ngn chn nu trn qu l ti lt ct, lu tr ln n 14 ngy 2-5 C (ng et al, 2000.). Mc d hexylresorcinol-4 c hiu qu trong vic ngn nga mt ct lt qu l mu nu trong sch-ct, n khng phi l hin ang xem xt GRAS ca FDA v c th khng hin ang c s dng thng mi trn cc sn phm tri cy ti ct. Tuy nhin, 4hexylresorcinol cng c th truyn t mt off-hng v khng th chp nhn cc sn

phm tri cy.

Polyphenol oxidase trong rau qu Apple Hydroxycinnamic dn xut acid (caffeoyl, coumaroyl v feruloyl) l nhng phenolics quan trng nht trong cc ging to vo ngy o hn (Amiot et al, 1992.). Apple qu c c trng bi mt u th ca axit chlorogenic hoc axit 5'caffeoylquinic. Flavan-3ols (catechin v procyanidins) l quan trng th hai. S tin tng i ca cc hp cht ny c tng quan vi PPO gy ra mu nu-ing trong to (Vamos-Vigyazo, 1981;. Amiot et al, 1992). Cc hp cht phenolic v polyphenol oxidase (PPO) hot ng trong cc loi tri cy ca 11 ging to, trc v sau khi bm tm, cho thy mc ca mu nu lin quan cht ch vi s lng phenol (cht dn xut hydroxycinnamic v flavan-3ols) b xung cp. Trng thnh dng nh khng nh hng ng k s pht trin ca mu nu (Amiot et al., 1992). Prabha v Patwardhan (1986), tuy nhin, lu rng trong qu trnh chn, PPO lm tng hot ng trong cc m v nhng gim trong tht qu. Barrett et al. (1991) bo co rng nhng thay i v tr subcellular ca PPO xy ra trong thi gian lu tr kh quyn kim sot (CA) ca to 'ngon'. Nhng thay i xy ra sm hn nhng qu to c lu tr trong iu kin CO2 cao (2,5-6% O2, 8-12% CO2) hn so vi bnh thng c lu tr di iu kin CA (2% O2, 3% CO2). PPO cc phn phn on thu c bng cch ly tm mc 4000 g v 100.000 g gim, trong khi ha tan v 200 g phn s tng ln vi lu tr. m hnh isozyme ca PPO cng a dng trong cc phn phn on khc nhau subcellular. Da chut PPO hot ng trong qu da chut ch hin din trong da, khng ging nh hot ng POD ca tri cy ch n l hin ti trong da v xc tht, mc d POD hot ng cao hn trong da. C hai enzym trong Optima da chut pH trin lm gn 7,0 nhng cuc trin lm Optima nhit khc nhau v thermostabilities (Miller v cng s, 1990.). PPO hot ng tng quan vi kh nng chng nm mc mai (Yun et al, 1995.) V Pseudoperono-spora cubensis trong da chut (Li et al., 1991).

Rau dip Ethylene PAL gy ra hot ng l mt yu t d bo tt p ca cuc sng ti ct lu tr rau dip (Couture v cng s, 1993.). PPO enzyme trong rau dip vi mt trng lng phn t khong 56 kDa nhanh chng b xi ha axit chlorogenic (5-caffeoyl quinic acid) v (-) - epicatechin. PH ti u ca chlorogenic acid oxidase v (-) cc hot ng oxidaseepicatechin c 4,5 v 7,8, tng ng, v c hai hot ng c n nh trong khong pH 6-8 ti 5 C trong 20 gi (Fujita et al, 1991.). Heimdal et al. (1994), tuy nhin, thy rng PPO quang trong cc m v mch mu ca rau dip c trng lng phn t c ngun gc khong 150 v 136 kDa, tng ng. Cc enzyme trong cc m mch mu v quang trong rau dip c phn loi nh l mt 1,2-benzenediol: oxidoreductase oxy (EC 1.10.3.1). Ngoi ra, hai ban nhc PPO-hot ng (40 v kDa 46), c th tiu n v ca enzym, c tm thy trong cc m c mch ch. im isoelectric cho PPO rau dip l 3.6. PPO gy ra mu nu ca rau dip c th tng quan

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vi ni dung phenolic ha tan (Ke v Saltveit, 1989b). Cc m quang c mt ni dung cao hn phenolic hn m midrib. i vi c hai loi t bo, tng hot ng PPO xy ra trong lu tr. Cc m quang trong rau dip, tuy nhin, dng nh thch nghi tt hn cho ti ct ch bin (Castaner et al, 1999.). Kim sot kh quyn c cha khng kh + CO2 11% gy ra tn thng m v hot ng gy ra PAL trong m tng bng midrib rau dip. Thng tch triu chng bao gm vt mu nu (mu nu ca m biu b) v chm m khu vc biu b (pitting) mt vi mm ng knh. R xy ra trong mi trng CO2 cao ti 5 C khng tng trong ni dung phenolic, nhng mu nu khng pht trin cho n khi m c chuyn giao cho khng kh 25 C. Rau dip m tip xc vi 1,5% ca O2 + 11% CO2 gim hot ng PAL v ha tan thp hn hm lng phenolic hn so vi rau dip tip xc vi khng kh + CO2 11% (Ke v Saltveit, 1989b). Cc PPO c ch hot ng nh ca O2 thp xut hin c lin quan n s c ch ca hnh ng ethylene, tip vin tc ng trn s trao i cht phenolic v cc hot ng oxidase IAA (Ke v Saltveit, 1989a). Mt mi trng CO2 cao c ch hot ng cinnamic acid-4-hydroxylase trong rau dip, c l do c ch sn xut ca cc hp cht phenolic (Siriphanich v Kader, 1985). Tuy nhin, tnh nhy cm vi CO2 thng tch khc nhau vi cy trng. 'Climax' rau dip trng by cc

triu chng tn thng nghim trng hn CO2 hn 'Salinas' v 'Winterhaven' ging (Siriphanich v Kader, 1986). Trung bnh chn khng ng gi (MVP) trong 80 m polyethylene c ch enzym nu trn lu tr 10 ngy ti 5 C. Khi ng gi trong 80 O2%, CO2 20% (80/20), nhiu mu nu xy ra SL3-ti (59 m nhiu lp p n ng b phim) hn trong cc ti polyethylene. Ascorbic acid ni sinh khng hiu qu nh l mt cht chng oxy ha trong vic tr hon nu (Heimdal et al, 1995.). Cc sinh l ban u cc thuc tnh ca tm ging rau dip ('Calmar', 'El Toro,' 'bin xanh', 'Thi Bnh Dng,' 'Monterey,' 'Salinas 88,' 'Salinas 86-13,' v 'Nerone') v ba giai on trng thnh (cha trng thnh, trng thnh v overmature) khng tng quan vi cht lng lu tr khi ch bin rau dip c gi trong khng kh hoc khng kh cng vi ethylene cho 1-4 ngy trc khi khng kh lu tr ti 2,5-20 C. Tuy nhin, ethylene gy ra PPO v PAL hot ng v cng ng k nu corre-lated vi cht lng hnh nh cui cng ca rau dip ethylene c iu tr ti thiu x l, sau 6-10 ngy k t ngy lu tr (Couture v cng s, 1993.).

Mango C v nh bo tr cht lng ca xoi ti, ct gim nhiu hn lin quan n s kt hp c bit ca cc cht chng nu hn l to ra bu khng kh thay i bn trong gi. S kt hp ca cc cht chng nu kt qu trong mt gim suy thoi nu v xoi ti ct c lu tr 10 C v c nhiu hiu qu hn so vi nhng ng dng ring (GonzalezAguilar v cng s, 2000.). Phng php iu tr c cha 4-hexylresorcinol v kali sorbat, hoc acid D-isoascorbic gim thay i mu sc v vi khun pht trin v khng nh hng n c tnh cm quan ca xoi ti ct.

Nm Nm c th mu nu enzyme nng trong x l v lu tr v c th khng p ng tt vi iu tr bng thuc c ch chm nu. Ra v

p dng cc th trng yu lm tng thm mau hng, ch yu l do kt qu ca s hp th

nc trong thi gian iu tr m tng mt mi trng ni b thun li cho vi khun pht trin (Sapers et al, 1995.). Tng mu nu ca nm nhit lu tr cao hn cng xy ra do nh hng trc tip ca nhit hot ng ca enzym. Catechol oxidase hot ng trong nm nt 15 C l gn nh gp i ti 10 v 5 C (Rai v cng s, 1989.). Cc m da c tyrosinase hot ng ln hn v nng protein cao hn v phenol hn so vi cc m tht (Burton v cng s, 1993.).

Da gang Lamikanra v Watson (2001) xc nh rng ni dung PPO cc da cantaloupe b tng i yu so vi nhng ngi trong to v rau dip. Ca tri cy ni dung ca cc hp cht phenolic oxidizable cng khng ng k. iu ny gii thch vic thiu phn ng ng k nu trong da cantaloupe ct (Lamikanra et al, 2000.).

L pH ti u cho PPO bo co t nhiu l 4,3-7,0 (et al Espin nm 1997;. Saddiq v cng s, 1994;. Zhou v Feng, nm 1991; Haruta v cng s, 1999.). enzyme ny cho thy hot ng monophenolase (Espin et al, 1997.), v s hin din ca PPO ht rng buc trong qu l c chng minh bng cc mu nu gim trong lc v ly tm cc loi nc p qu l (Sapers, 1992). Bc sut-hn ch trong c ch phn ng monophenolase trong qu l v to dng nh l mt cuc tn cng i lc ht nhn ca nguyn t oxy thuc nhm hydroxyl nguyn t cacbon v tr-4 trn cc nguyn t ng ca trang web hot ng ca enzyme (Espin et s, 1998b).. Catechol, 4-methyl catechol v dopamine l PPO l cht tt, nhng monohydroxy cht cho thy khng c hot ng (Siddiq v cng s, 1994.). enzyme ny c th c kho nghim mt phng php specto-trc quang lin tc bng cch s dng p-hydroxyphenyl axt prpionic (PHPPA) vi 3-methyl2-benzothiazolinone hydrazone (MBTH) (Espin et al, 1997.). Tht mu nu gy ra bi iu tr CO2 c cht ch lin quan ti PPO v PAL hot ng trong qu l 'Niitaka' (Park, 1999). PPO, PAL v 4 hydroxylase cinnamate-(CA4H) hot ng trong xc tht l cao hn ng k trong tri cy c lu tr trong O2 2% + 2,5% hoc 5% CO2 hn khng kh hoc O2 2% ti 5 C, nhng khng c s khc bit trong cc hot ng enzyme 0 C. Ni dung tng phenolics trong tht tng ln ng k vi bu kh quyn lm giu CO2.

Da Cc isozyme PPO chnh t da dng nh l mt tetramer ca tiu n v ging ht nhau, mi ln vi mt khi lng phn t l 25 kDa. Cc chui amino acid ca isozyme ny cho thy s hin din ca mt hm lng cao ca acid glutamic, glycine v serine v ni dung mc thp ca lu hunh cha cc axit amin. Cc PPO khng cho thy hot ng creolase, v cc cht nn thch c diphenols. Ascorbic acid v L-cysteine l cht c ch mnh da PPO (Das v cng s, 1997.). Mt ri lon sinh l thng do lnh hoc acid gibberellic (GA-3) x l ton b da l mu nu bn trong ca tri cy c gi l blackheart

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hoc ni sinh nu ti ch. iu ny ch yu l do qu trnh oxy ha ca cc hp cht phenolic xc tc bi PPO to thnh cc sn phm mu nu. Nhit thp hoc GA-3 tng ng k PPO v PAL hot ng v ni dung ca catechol, chlorogenic acid v acid caffeic (Chu, Tn, 1992). Mi quan h gia ni dung PPO v kch thc qu vi tnh nhy cm vi mu nu bn trong da "Smooth Cayenne ' c chng minh bi Botrel et al. (1993). Tri cy d b nu ha ni b l nhng ngi trong nhm ln th hai (15001799 g) v trng lng v nhng hin th cc hot ng PPO cao nht. Cc loi tri cy nh nht l nhng ngi t nht l nhy cm. Hoa qu nht chng nu ni b c mt hm lng cao ca cc hp cht phenolic v cc hot ng POD cao. X l nhit ca tri cy trong mt lng p (32-50 C trong 24 gi) tip theo l lu tr trong mt cn phng lnh 15 C gim PPO, POD, ascorbic acid, chua v t l h hng. Ngm qu trong nc nng (55 C trong 10 pht) tip theo l lu tr 15 C cng lm gim s pht trin ca mt mt mu nu nhng do ni b ca cng v trng lng trong cc giai on sau ca lu tr (Selvarajah v cng s, 1998.). Tri cy Prunus PPO t nm Prunus loi tri cy (o, mai, hnh nhn, qu mn v anh o) cho thy khong pH ti u 4-5,5, v cc enzym khng xy ra trong mt hnh thc tim n (Fraignier et al, 1995.). Nhiu hnh thc hot ng xy ra nh l kt qu ca s phn gii protein ca mt dng chnh. Trong iu kin bin tnh, cc hot ng v proteolyzed hnh

thc chnh l tng ng, monome s 63 v 43 kDa. Peach enzyme PPO hnh vi ch yu vo cu hnh orthodihydroxy vi khong pH ti u ca 4,0-6,0 (Reyes v Luh, 1960; Haruta v cng s, 1999.). Mt s tng quan gia kiu gen tn ti cho ni dung o phenolic v nu enzyme (Gradziel v Wang, 1993). Bn isozyme PPO vi stabilities nhit khc nhau c phn lp t o trai ao chua. Khng c cc isozyme hot ng monophenolase, v chng khc nhau c trng ca h cho mt vi diphenols (Wong v cng s, 1971a.). Trong mt nghin cu xc nh nh hng ca cht c ch phloroglucinol PPO v resorcinol trn tion trai ao chua o PPO xc tc-oxida ca methylcatechol-4, Wong et al. (1971b) xc nh rng trong khi PPO xc tc s hnh thnh ca 4-methyl-quinone-o, n khng ng mt vai tr trong phn ng vi resorcinol, phloroglucinol, d catechin-hoc orcinol. Phn ng gia phenol, 4-methyl-o quinone- sn xut mu nu din ra nonenzymatically. Chlorogenic acid ni dung gim nhanh chng trong nu enzyme, nhng nhy cm nu dng nh mnh m hn na tng quan vi s tin ban u ca flavan-3-ols trong mt s ging cy trng mai. Chlorogenic v cc acid neochlorogenic, (+)-catechin v (-) epicatechin-, v Rutin (hoc quercetin-3-rutinoside) l nhng hp cht phenolic ln trong m (Radi v cng s, 1997.). Pectic enzym lm mm tri cy v rau enzim pectic nhn c s ch ng k v s tham gia ca h trong qu trnh chn v lm mm cc thnh phn vch t bo. Duy tr cng l mt tham s cht lng quan trng trong tri cy ti ct v sn phm thc vt (Agar v cng s, 1999;. Gorny

v cng s, 1999;. Ji v Gross, 1998; Senesi v Pastine, 1996). vt liu pectic c to thnh t chui t 1-4 n v acid D-galacturonic lin kt thng c este ha vi mc khc nhau vi methanol. Cc men ny c th c lin kt ngang trong nhiu cch khc nhau, v chng th hin mt lot cc solubilities t ha tan cao, rng ri cc phn t lin kt cho ca protopectin bn a d dng ha tan trong chui ngn, cnh ca trng lng phn t thp (El-Ashwah et al. , 1977; Legentil v cng s, 1995; Martin-Cabrejas et al, 1995)... Pectins l nhng thnh phn quan trng ca thnh t bo v phin knh trung bnh trong cc nh my cao hn. H ch yu l tuyn tnh -1 ,4-galacturonan chui vi mt s nhm carboxyl este ha. Cc dy chuyn l b gin on bi lin kt 1, 2 - D lng rhamnose, v covalently ngoi quan arabinose v galactose l -1 arabinan-,5 v -1 ,4-chui bn galactan lin kt vi rhamnose, tng ng (Pressey, 1986). S tin tnh cht, tng i ca phn nhnh ti pectin khc nhau t mt ngun khc (Fischer et al, 1994;. Massiot v cng s, 1988;. Hoff v Castro, 1969; Ross v cng s, 1993.). Nhnh ca galacturonan cc thng xy ra nhiu hn trong cc bc tng t

bo hn so vi phin knh trung bnh (Fischer et al, 1994;. MacDougall v cng s, 1997;. Gi v cng s, 1975.). axit cacboxylic min ph trong axit glacturonic tham gia vo cc mi lin kt gia cc phn ng vai tr nh qua cu c nh hng n t bo thnh sc mnh. Canxi xut hin c tham gia vo vic hnh thnh cc cy cu gia cc phn do s tng tc vi cc nhm Vit cacboxyl ca axit pectic polymer to thnh mui khng ha tan to thnh lin kt ion gia cc phn t pectin (Kohn, 1969; McFeeters v Fleming, 1991). Pectin xy ra hu ht cc nguyn liu thc vt, c bit trong m nh v tri cy, v l mt thnh phn ch yu ca thnh t bo. Pectin phn t tham gia vo lin kt ngang polysaccharides khc v cc protein trong t bo (Cutsem v cng s, 1993;. K v cng s, 1995.). Cc t bo trong tri cy v rau qu c kt ni thng qua cc phin knh gia l pectinous trong t nhin. Pectin tc ng vng chc cho nh my c quan bng cch cung cp kt dnh thnh t bo juxtaposed trong phin knh trung bnh (Chen v cng s, 1998a;. Crooks v Grierson, 1983; Luza v cng s, 1992;.. Rihouey et al, 1995). Mt trong nhng thay i r rng nht xy ra trong qu trnh lm mm cc loi tri cy v rau qu l tin b v ha tan depolymerization ca ph pectic-lp trng (Aspinall, 1980; McNeil v cng s, 1984;. Bacic et al, 1988.). Cc ion canxi v cc enzym pectic vai tr quan trng trong qu trnh lm mm. C mt s cch m theo cc ion canxi c th nh hng lm mm. Mt canxi t gia phin knh c th lm gim cc mi lin kt ion gia cc phn t pectin (Femenia et al., Nm 1998; Hng v cng s, 1995;.. Tandon v cng s, 1984), v thay i cng ion, dn n thit hi canxi, c th lm gim hot ng qun l ca mnh trn hydrolase vch t bo (Almeida v Huber, 1999), gim turgor t bo (Stow nm 1993;. Mignani et al, 1995) v, do , tnh cht ca n n nh trn mng (Shackel v cng s, 1991;. Picchioni et al, 1995).. Cell turgor quy nh vic cng thng m, nh hng n kt cu vng chc. Enzyme phn hy pectins trong c chua nh hng n s tin tng i ca canxi lin kt vi pericap cc, nhau thai v gel nhu m (Burns v Pressey, 1987). C hai loi chnh ca cc enzyme chu trch nhim v s xung cp pectin trong rau qu. y l nhng depolymerases (polygalacturonaza v pectic lyase) v pectinesterase, cn c gi l pectinmethylesterase, pectase hoc pectinmethox ylase-. Depolymerizers thy phn cc lin kt glycosidic (hydrolases) hoc ph v chng bng cch loi b- (lyases). Pectinesterase (EC 3.1.1.11) xc tc de-esterifica-tion ca pectin.

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Hnh 6,4 chia ca tri phiu glycosidic trong pectin do thy phn (polygalacturonaza) v loi b- (pectate lyase v pectin lyase) (Pilnik v Voragen, 1989).

Polygalacturonaza Poly--1 ,4-galacturonide glycanohydrolase, thng c gi l onase-polygalactur (PG), thy phn lin kt glucosidic nh trong hnh 6.4. Polygalactur-onases c c th cho galactoronans de este ha. T l v mc thy phn l ph thuc vo mc este ha pectin (Jain v cng s, 1990;. L-Cam et al. 1994). Polygalacturonases c th c phn loi vo endozymes rng ngu nhin tch tri phiu ca cc axit pectic glycosidic v polygalacturonates trong phn t ti cc -1, 4 lin kt v exozymes rng xc tc thy phn tng bc ca acid galacturonic t cui nonreducing ca chui. Endopolygalacturonases (EC 3.2.1.15) xy ra trong tri cy v si nm nhng khng c trong nm men hay vi khun (Baldwin v Pressey, Nm 1988; Hadfield v cng s, 1998; Kawano et al, 1999)... Exopolygalacturonases (EC 3.2.1.67) xy ra trong nm, vi khun v thc vt (Bartley v u gi, 1982; Downs et al. Nm 1992;. Konno v cng s, 1986; Tae et al, 1997).. Nhn chung, endopolygalacturonase (endo-PG) enzyme ti khon cho hu ht cc hot ng polygalacturonaza trong tri cy chn (Brady, 1987; Downs v cng s, 1992;.. Nogata et al, 1993), mc d c hai endo-exo-enzym v ang hot ng trong mt s loi tri cy chn (Bartley v u gi, 1982; Nogata et al, 1993).. Endo-PG xut hin xc tc ha tan ca pectins trong cc t bo tip theo l thy phn xa hn bng cch PG-exo (Pressey v Avants, 1973, 1976). Mt s loi tri cy mm ng k trong qu trnh chn (v d, l, o a khi) cha khng ch endo-PG m cn exo-PG. tri cy khc (v d, to v o trai ao chua) c cha ch exo-PG, ph hp vi c im mm chm. mc thp ca PG-exo c tm thy trong nhiu m thc vt v lu tr (Pressey, 1986).

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LYASES Poly (methoxygalacturonide) lyase (pectin lyase; EC 4.2.2.10) v pectate eliminase xuyn (pectate lyase; EC 4.2.2.2) tch nhng lin kt -1 ,4-galacturonosidic bi loi b xuyn ca hydro trn carbon 5 ca acid galacturonic vi oxy trn tri phiu glycosidic. Mt tri phiu CC cha bo ha c to ra gia 4 - v 5-v tr ca cc d lng acid galacturonic vo cui nonreducing ca on pht hnh (Hnh 6.4). tri phiu glycosidic trong pectin rt nhy cm vi phn ng ny. Pectin lyase depolymerizes este ha cao pectin carboxyl bng cch chia cc mi lin kt glycosidic bn cnh nhm cacboxyl methyl este ha bng loi b-, trong khi cc cuc tn cng pectate lyase mi lin kt glycosidic cnh mt nhm cacboxyl t do. Hu ht lyases Tuy nhin, c th cho galacturonans este ha (Bruchlmann, nm 1995; Chen et al. 1998b). Cc enzym l hu nh ch t cc vi sinh vt, mc d c nhng du hiu cho thy s xut hin t nhin trong mt s loi tri cy (Albersheim v Killias, 1962; Medina-Escobar v cng s, 1997).. Lyases sn xut khng bo ha monome sp xp li cc acid 2-keto-uronic (Glover v Brady, 1995; Renard et al, 1991; Rng v cng s, 1994..). PECTINESTERASE Pectinesterase (PE), cn c gi l hydrolase pectin-pectyl, xc tc cc lation-demethy ca pectin este ha (Hnh 6.5). Nhng enzym thy phn c bit cc nhm methylester ca cc v tr C6 ca acid galacturonic v ng mt vai tr quan trng trong s suy thoi ca thnh t bo thc vt bc cao, lm cho polymerized pectin cao d b suy thoi hn na bi PG (Fischer v Bennett, 1991). V d, trong c chua, tin x l ca bc tng vi tinh tng PE kt xut t tt c cc giai on chn u nhy cm vi PG (Koch, 1989). Ging c chua chn sm cng cho thy PG cao hn v hot ng PE tt c cc giai on, so vi cc ging chn mun, ni PG v lm tng hot ng PE trong qu trnh chn (Young, nm 1995; Thakur v

Hnh 6,5 Fragment ca phn t pectin v cc im ca cuc tn cng ca enzim pectic (Pilnik v Voragen, 1989).

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Pandey, 1999). Khng ging nh PG, PE l thng hin din trong s lng ln trong tri cy cha chn (Tucker v Grierson, 1982). PE cng c th chun b mt cht nn cho cc hot ng lyase pectate. enzyme ny c c th cho este polygalacturonide v s khng thy phn este methyl nongalacturonide hoc nhng ngi trong galacturonans chui ngn n mt mc ln. Chng c kch hot bi cc cation hoa tri hai hoc monovalent nng cao v c tm hot ng ti u ca pH 5-8 (Pressey, 1977). S phn b ca cc nhm methoxy r rng nh hng n tc phn ng ca enzyme. nhm methoxy gip vi nhm carboxyl min ph c loi b vi mt tc nhanh hn nhng ngi bn cnh d lng este ha trn cc phn t pectin (MacMillian v Sheiman, 1974). PE hot ng presum-ably yu cu mt nhm carboxyl min ph bn cnh mt nhm este ha trong chui galacturonide v tin tuyn tnh nh cc nhm methoxy c loi b trong chui pectin cho n khi tc nghn mt l t. Khi ca cc nhm t do carboxyl c nh vy l kt qu ca hnh ng PE (Contreras-Esquivel v cng s, 1999;. Grasdalen v cng s, 1996;. Hou v Chang, 1997; Kohn v cng s, 1985.).

Pectic enzym c trong rau qu Apple Cc hot ng sinh l t bo enzyme tng xung cp trong to c PE, exo-PG, -galactosidase v -1, 4 glucanase (Pollard, 1975; u gi nm 1993; Abeles v Takeda, 1990). Endo-PG vng mt trong qu. iu ny lm cho c ch ca s chn khc nhau t loi tri cy nh o v l, trong endo-exo v PG-c hin din trong tri cy trng thnh. Lm mm cc m v no ca to chn thng c c trng bi s mt mt ca d lng galactose t thnh t bo v tng pectin ha tan. Apple PG exo-c pH ti u ca 4,5-5, b c ch bi EDTA v citrat v c kch hot bi Ca2 v, n mt mc thp hn, bi SR2. Cc enzyme trong c mt trng lng phn t khong 58 kDa, lm gim cc ch phm t bo v to tng, releas-ing thp trng lng phn t acid uronic v cn polyuronide (Bartley, 1978). Soft-ening to trong qu trnh bo qun lnh c i km vi PG gia tng v cc hot ng Cx (Mahajan, 1994). Trn cy, tuy nhin, qu trnh

ny xy ra ng thi vi s gim st trong hot ng Cx (Abeles v Takeda, 1990). Dung mi hu c chit xut t to c ch -galactosidase (Dick v cng s, 1984;. Lidseter et al, 1985.). Cc hp cht ny c ch -galactosidase c xc nh l axit chlorogenic, catechin v glycosides quercetin (Dick v cng s, 1985.). -Galactosidase trong to c cho l chu trch nhim v s mt mt ca d lng galactose l kt qu ca s thy phn ca galactan ca thnh t bo s cp. polyuronide ha tan c ngun gc t khu vc gia phin knh ca bc tng (u gi, 1993). Ha tan ca polyuronides l hot ng suy thoi chnh c tng quan vi lm mm nhng tri to (Bartley v u gi, 1982). -Galactosidase hot ng tng ln, v t bo ni dung tng galactose gim trong qu trnh lm mm ca 'Lodi,' 'McIntosh,' 'Golden Delicious "v" quc York' to. S gim tng Tose-galac c, tuy nhin, t nht l trong 'Lodi,' trong c cc hot ng -galactosidase thp nht. 'York Imperial,' m lm mm chm nht, cho thy cc hot ng -galactosidase cao nht trong lu tr (Wallner, 1978). Vic thiu s tham gia ca PG nh l mt yu t quyt nh trong vic lm mm ca to cng c xut (Kang v cng s, 1999;. Yoshioka v cng s, 1992.). Kang et al. (1999) c tm thy

PG khng c pht hin trong qu trnh lm mm ca 'Fuji' v cc cy to "Tsugaru. cc hot ng ha tan enzyme tham gia th t gim dn l -mannosidase> -arabinosidase> -galactosidase> -galactosidase trong lm mm ca to 'Fuji', trong khi cc hot ng nm trong th t ca -galactosidase> -arabinosidase-mannosidase> > -galactosidase trong qu trnh lm mm ca to "Tsugaru. Trong , -galactosidase hot ng tng nhanh c hai ging. Yoshioka et al. (1992) cng pht hin khng c hot ng lm mm ca PG trong to v xut de-este ha ca polyuronides vi mt mc cao hn l methoxylation depolymerization ca polyuronides trong bilization-Solu ca polyuronides trong qu trnh chn ca qu. to chiu x (20 krd) tng tc phn hy pectin v lm tng hot ng gy ra lm mm PE sm ca tri cy (Flores et al, 1971.). Hai hnh thc PE c mt trong to. Chng khc nhau c v ph v trng lng phn t. khi lng phn t ca h l 55 v kDa 28, tng ng, v hnh thc nng hn l n nh ln n 40 C. Ti u hot ng trong khong pH 6,5-7,5 (et al Castaldo, 1989.). Lu tr ca to 38 C trong bn ngy v lu tr tip theo l 0 C gim mm ca to "Golden Delicious" mc d mc c th so snh PE vi nhm iu khin tri cy, cho thy vic thiu s tham gia ca PE trong qu trnh chn to v lm mm khi lm nng trc (Klein

v cng s, 1995.). X l nhit cng c ch hot ng PG nhng khng phi l ca PE. Vo cui thi k chn, to nng gi li nhiu pectin ha tan v c crisper hn iu khin (Lurie v Klein, 1991). Kiwi Kiwi (Actinidia deliciosa) cung cp mt gii php thay th hu ch cho c chua, trong hc lm mm tri cy. Sau khi thu hoch, c mt thi gian di, trong hu ht cc loi qu lm mm xy ra. Tinh bt xung cp v thay i thnh t bo xy ra, bao gm ha tan pectin, mt galactose t cc chui bn pectin, gim trng lng phn t ca xyloglucan v thnh t bo sng. th nghim ko t v nghin cu siu cu trc ch ra rng mt s mt mt ca t bo-t bo b