solid soluble in tomato products official method
TRANSCRIPT
42.1.10AOAC Of fi cial Method 970.59
Solids (Sol u ble)in To mato Prod ucts
Re frac tive In dex MethodFirst Ac tion 1970Fi nal Ac tion 1973
A. Ap pa ra tus and Re agents
(a) Fil ters.—Cut stems off of 75 mm id glass or plas tic fun nels ca
1 cm from apex at 90° an gle and firepolish ends of glass funnels. Setfun nels in 150 mL jars, ca 55 mm id. If 150 mL beak ers are used,close pour ing spout with tape to pre vent evap o ra tion. In sert foldedpa per, Whatman No. 2V, 12.5 cm, or equiv a lent, in fun nel.
(b) Refractometer.—Readability to 0.0001 n.
(c) Ul tra cen tri fuge.—Cen tri fuge should pro duce force of ca
150 000 ´ g (lesser force may be sat is fac tory for some products).In ter na tional Equipment Co. No. B-20A (re place ment ModelB-22M) is sat is fac tory.
(d) Pec tic en zyme.—(1) Dry prep a ra tion.—In diatomaceousearth base, e.g., Klerzyme® an a lyt i cal (Gist-Brocades USA, PO Box 241068, Char lotte, NC 28224-1068, USA), or Spark-L® (Bayer,1127 Myr tle St, PO Box 70, Elkhart, IN 46514, USA) or equivalent.(2) So lu tion.—Pre pare 0.4–1% aque ous so lu tion of (1); mixthor oughly and let set tle. Use clear supernate. Liq uid prep a ra tionsare also avail able com mer cially; di lute, if nec es sary, be fore use.Also available from Presque Isle Wine Cellars (9440 W. Main Rd,North East, PA 16428, USA; http://shop.piwine.com/shopsite/prwc.product54.html).
B. Prep a ra tion of Sam ple
(a) Fil tra tion with out di lu tion.—Weigh 100 g test por tion atroom tem per a ture and add weighed amount (0.2–1.0 g) dry en zymeprep a ra tion. Im me di ately mix with spoon or spat ula to avoidevap o ra tion and trans fer to fil ter. Tamp so test por tion is in closecon tact with pa per and cover with Petri dish (top or bot tom por tion)to form loose seal with top of fun nel. Dis card tests that do not fil ter in rea son able length of time (<1 h). Mix 0.2–1.0 g dry en zymeprep a ra tion with 100 g fresh test por tion, seal in closed con tainer,
and in cu bate 30–60 min at ca 40°C. Cool nearly to room tem per a ture be fore open ing con tainer, remix test por tion, and trans fer to fil ter.For test sam ples that still do not fil ter within 1 h pro ceed as in (b).
(b) Fil tra tion with di lu tion.—[Ap pli ca ble to test sam ples
con tain ing ³35% sol ids that will not fil ter when treated as in (a).]Add 100 g en zyme so lu tion to 100 g test por tion and im me di atelymix with spoon or spat ula to avoid evap o ra tion. (Me chan i cal mixer[e.g., Osterizer] with sealed blend ing con tainer may be used.)Al ter nately blend and shake to dis lodge and break up lumps stick ingto con tainer. Ex am ine mix ture care fully for lumps and con tinuemix ing un til ho mo ge neous. Trans fer to fil ter and cover with Petridish.
(c) Centrifugation.—(Ap pli ca ble to all test sam ples.) Cen tri fugetest sam ple in ul tra cen tri fuge un til rea son ably clear se rum isob tained (se rum of some test sam ples may be slightly tur bid and/orred from pres ence of finely di vided par ti cles of pig ment). Add dryen zyme as in (a) to de crease cen tri fug ing time. Pro tect test sam plefrom evap o ra tion dur ing cen tri fug ing and be fore read ing inrefractometer.
C. De ter mi na tion
(a) With fil tra tion.—Ad just refractometer for re frac tive in dex
(nD) of 1.3330 with H2O at 20°C. Let test sam ple fil ter into jar orbeaker un til fil trate is clear (some color and tur bid ity may betol er ated). Quickly re move fun nel and trans fer large drop of fil tratedi rectly from fun nel to refractometer prism. (Tip of fun nel may touchrefractometer prism but should not scratch prism.) Re place fun nel in
jar. Read refractometer, pref er a bly at 20°C, but if hu mid ity causescon den sa tion of mois ture on prism, make mea sure ments at roomtem per a ture and cor rect read ings to stan dard tem per a ture as in990.36A (see Appendix C). Read n or % su crose on refractometer. IfnD is read, con vert to % su crose from 990.35A (see Appendix C).
Let test sam ple fil ter sev eral min more. Re peat read ing byre mov ing fun nel and trans fer ring drop of fil trate to refractometerprism. The 2 read ings should agree within 0.0002nD or 0.1%su crose. If not, re peat read ings on suc ces sive por tions of fil trateun til agree ment is ob tained. Er ratic read ings in di cate evap o ra tion orfaulty mix ing and/or fil tra tion tech nique.
Read clear supernate of 1% so lu tion of dry en zyme on refractometer
and con vert to % su crose. Sub tract 1.15 ́ B ́ C from di rect read ing ontest sam ple (as % su crose); where 1.15 = cor rec tion for in sol u ble sol idsin weighed test por tion, as sum ing 12.5% to tal sol ids to be in sol u blesol ids; B = % en zyme prep a ra tion added to test por tion; and C = read ing as su crose ob tained on 1% so lu tion.
If di luted test sam ple is used, sub tract 0.55 ´ D ´ C from read ingon test por tion (as % su crose); 0.55 = cor rec tion for in sol u ble sol ids,as above, and D = % en zyme prep a ra tion added to di lu tion H2O.Mul ti ply cor rected read ing for di luted test sam ple by 2 and addad di tional cor rec tion ac cord ing to Ta ble 970.59.
(b) With centrifugation.—Re move se rum from ro tor orcen tri fuge tube with pipet or med i cine drop per, and trans fer torefractometer prism; avoid in clud ing solid par ti cles as much aspos si ble. If sharp line is not ob tained on refractometer be cause ofsus pended sol ids, in crease cen tri fug ing time or speed, or adden zyme to test sam ple be fore cen tri fug ing. Cal cu late sol u ble sol idsas above.
(c) Cor rec tion for added salt.—(Use only when test samplecon tains added salt and R > S.) Cor rect refractometer read ing
ex pressed as % su crose at 20°C for added salt by fol low ing for mula:
S = (R - N) ´ 1.016 = to tal sol u ble sol ids as su crose ex clu sive ofadded salt; where S = refractometer read ing as su crose cor rected foradded NaCl, R = to tal sol u ble sol ids as su crose, and N = % to talchlo rides ex pressed as NaCl [de ter mined by 939.10B (see 42.1.14)or 971.27 (see 42.1.15)].
Ref er ences: JAOAC 52, 1050(1969); 55, 809(1972).
Re vised: March 2002
ã 2005 AOAC IN TER NA TIONAL
Table 970.59. Re frac tive in dex cor rec tion values
Nat u ral to mato sol u ble sol ids as %su crose cor rected for en zyme ´ 2 Cor rec tion
25.0 0.3
30.0 0.4
35.0 0.5
40.0 0.7
45.0 0.8
50.0 0.9
2006 AOAC INTERNATIONAL