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Postharvest Biology and Technology 45 (2007) 73–80

Chlorophyll a fluorescence measurements to evaluate storage time andtemperature of Valeriana leafy vegetables

Antonio Ferrante ∗, Tommaso MaggioreDip. Produzione Vegetale, University of Milan, via Celoria 2, 20122 Milan, Italy

Received 25 August 2006; accepted 12 February 2007

bstract

The quality of leafy vegetables has to be guaranteed for consumers for the whole postharvest period, usually limited to 5–7 days. The qualityf vegetables during storage is difficult to determine. The aim of this work was to evaluate the quality status of leafy vegetables by means ofhlorophyll a fluorescence measurements. Experiments were performed on Valeriana lettuce stored at 4 or 10 ◦C for 15 days. The quality of theettuce was evaluated by measuring anthocyanins, chlorophyll, carotenoids, phenols and chlorophyll a fluorescence. JIP analysis was performedt the intermediate points of the fluorescence induction curve. Results show that the higher storage temperature affected the lettuce leaf quality.ignificant chlorophyll reduction was observed after only 5 days of storage in leaves stored at 10 ◦C. Total carotenoids significantly decreasedfter 8 days at both storage temperatures. Anthocyanins and total phenols did not change statistically during the entire experimental period. Fv/Fmnd Fm measurements were able to be used to show changes that took place during the storage period, but were not to discriminate between the

wo storage temperatures. Among the calculated JIP indices, only PI, DIo/CS, ABS/DIo, ETo/DIo and RC/CSm were able to highlight differencesuring storage and between the two storage temperatures, and may be used as markers to evaluate the status of leaf during leafy vegetable storage.he highest value of R2 was found for ETo/DIo versus storage time. 2007 Elsevier B.V. All rights reserved.

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eywords: Anthocyanins; Chlorophyll; Carotenoids; Lamb’s lettuce; Postharve

. Introduction

In recent years, consumption of leafy vegetables has beenncreasing, especially as a result of changes in the consumerife style. This is particularly the case with ready-to-eat or min-mally processed fruit and vegetables (Ragaert et al., 2004).

ost of these products are sold within 1 week, 5–7 days, after

ackaging (Rolle and Chism, 1987). The postharvest techniquesor preserving the quality of fresh-cut vegetables are aimed ataintaining external colour, improving hygiene, and preventing

Abbreviations: ABS/CS, absorbed energy flux per cross-section; ABS/DIo,atio between absorbed energy flux and dissipation energy per cross-section;S, cross-section; DIo/CS, dissipation of energy per CS; Fo, fluorescence levelhen plastoquinone electron acceptor pool (Qa) is fully oxidised; Fm, fluo-

escence level when Qa is transiently fully reduced; Fv, variable fluorescenceFm − Fo); Fv/Fm, maximum quantum efficiency of photosystem II; PI, perfor-ance index; TRo/CS, trapped energy flux per CS; ETo/CS, electron transportux per CS; RC/CSo, density of reaction centres (equals F50 �s dark of theontrols); RC/CSm, density of reaction centres (Fm)∗ Corresponding author. Tel.: +39 02 50316589; fax: +39 02 50316575.

E-mail address: antonio.ferrante@unimi.it (A. Ferrante).

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925-5214/$ – see front matter © 2007 Elsevier B.V. All rights reserved.oi:10.1016/j.postharvbio.2007.02.003

enols; Storage

issue browning and the reduction of the internal phytonutrientontent (Brecht et al., 2004). The colour is extremely importantecause it defines the appearance of the vegetables and influ-nces consumer choice (Ferrante et al., 2004). Loss of colours due to degradation of the leaf pigments (chlorophyll andarotenoids) or tissue browning. These physiological processesccur when cell membranes lose their integrity and releasenzymes, which come into contact with their substrates, gen-rating postharvest disorders. The most important parameter forreserving produce quality and inhibiting pathogen developmenturing the postharvest life, is an adequate storage tempera-ure (Jacxsens et al., 1999, 2002). It is well known that lowemperatures slow down plant metabolic processes such as res-iration, ethylene production and, in general, enzyme activity.owever, low temperatures may induce chilling injury and com-romise produce quality. Correct storage temperature can varyrom species to species and cultivar to cultivar. The most fre-

uently used temperature is 4 ◦C, considered the optimal forany leafy vegetables (Jacxsens et al., 2002). However, a low

emperature must be maintained during the entire postharvesteriod to guarantee produce quality. Therefore, rapid methods

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4 A. Ferrante, T. Maggiore / Postharvest

or evaluating leafy vegetable quality during or at the end of theistribution chain should be developed. Among the non-invasivend highly sensitive tools for evaluating plant stress under dif-erent conditions, chlorophyll a fluorescence measurement ishe most important method (Strasser et al., 1995; Lazar, 1999).hlorophyll a fluorescence has been used for evaluating chill-

ng injury in different cultivars of basil (Meir et al., 1997). Thev/Fm ratio, one of the parameters that can be derived fromhlorophyll a fluorescence measurement, which represents theaximum quantum yield from PSII, showed a positive cor-

elation between the progress of senescence in broccoli andtorage time (Toivonen and DeEll, 2001). In apples, chloro-hyll a fluorescence was correlated with internal fruit qualityarameters such as mealiness. Unfortunately, in this case resultsere not always satisfactory, because of the high variability

mong cultivars (Moshou et al., 2005). In cucumber, chlorophyllfluorescence was used to determine the optimal storage tem-

erature and the related fluorescence parameters (Fv/Fm ratio,v, Fm) were able to show differences at the different temper-tures (Lin and Jolliffe, 2000). Also, in cut roses, Fv/Fm wassed for monitoring low temperature injury, but it did not leado a practical application because the changes in Fv/Fm valuesere not correlated with vase life of the flowers (Pompodakis et

l., 2005).In iceberg lettuce, chlorophyll a fluorescence was first used

o evaluate if it could be used as an indicator of storage poten-ial. Results showed that chlorophyll measured at harvest cane satisfactorily correlated with postharvest quality even if theettuce is grown in different locations (Schofield et al., 2005).

The availability of an instrument that allows us to estimateroduct quality or the change in health status during the storageeriod, may have a wide number of practical applications. Theim of this work was to evaluate the quality changes of Vale-iana lettuce at two storage temperatures, and if chlorophyll auorescence measurements can be used as a rapid diagnosticethod to monitor leaf quality during the storage period. More-

ver, analyses of the fluorescence transient and the intermediateata points were performed to evaluate leafy vegetable storageime, storage temperature and to evaluate how they may be useds accurate quality markers.

. Materials and methods

.1. Plant material and storage treatments

Lamb’s lettuce (Valeriana olitoria L. [Valeriana locusta]) cv.rofy was grown in a floating hydroponic system. Seeds wereirectly sown in trays containing perlite. After emergence, allhe trays containing seedlings were placed in floating tanks con-aining nutrient solution: (concentrations are expressed in mM)3 N-NO3, 1.5 P, 8 K, 3.5 Ca, 1.7 Mg, 9.5 Na, 8.0 Cl, 2.7 S, 0.04e and Hoagland’s concentration for micronutrients.

The experiment was repeated in spring, summer and winter

February, March, July, September). Valeriana leaves wereashed with 20 mg L−1 sodium hypochlorite (5–10 min),

lightly dried and the whole leaves were placed in sealed plasticags (high-density polyethylene film) for storage simulation.

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gy and Technology 45 (2007) 73–80

he packed leafy vegetables were stored at 4 or 10 ◦C in darkonditions. Each plastic bag was filled with 400 g lettuce,nd the bag capacity was 500 mL. Five bags were opened atach sampling time, with a total of 25 bags for each storageemperature.

.2. Chlorophyll and carotenoid content determination

Total chlorophyll and total carotenoid contents were deter-ined by extraction using 99.9% methanol as solvent. Samplesere kept in a dark, cold room at 4 ◦C for 24 h. Quantita-

ive chlorophyll and carotenoid determinations were carried outmmediately after extraction. Absorbance readings were per-ormed at 665.2 and 652.4 nm for chlorophyll pigments and70 nm for total carotenoids. Total chlorophyll and carotenoidontents were calculated using Lichtenthaler’s formula (1987).

.3. Determination of anthocyanin and total phenolbsorbance

Samples of the frozen tissue (100 mg) were ground in a pre-hilled mortar and extracted into methanolic HCl (1%). Samplesere incubated overnight at 4 ◦C in darkness. The concentrationf anthocyanins was expressed in cyanidin-3-glucoside equiv-lents determined spectrophotometrically at 535 nm using anxtinction coefficient of 29,600 (ε).

Phenolic compounds were extracted from 30 to 50 mg ofeaves using 5 mL 1.2 M HCl in 99% methanol. Absorbance

easurements were taken after overnight incubation at 4 ◦C.otal phenolics were estimated by measuring absorbance at20 nm using an UV–vis spectrophotometer (Ke and Saltveit,989). The amount of total phenols was expressed as gallic acidquivalents.

.4. Chlorophyll a fluorescence

The fluorescence of chlorophyll a was determined on darkdapted leaves, randomly taken from the stored boxes andncubated for 40 min at room temperature. Chlorophyll a flu-rescence (expressed in relative units) was measured using aortable Handy Plant Efficiency Analyser (PEA, Hansatech,K). Leaf fluorescence was determined after illumination with a

ight intensity of 3000 �mol m−2 s−1. The fluorescence param-ters were calculated automatically: Fv/Fm or (Fm − Fo)/Fm.IP analysis was performed to determine the following indices:erformance index (PI), absorbed energy flux per cross-sectionABS/CS), trapped energy flux per CS (TRo/CS), electronransport flux per CS (ETo/CS), dissipation of energy per CSDIo/CS), density of reaction centres at O stage (RC/CSo) andensity of reaction centres at P stage (RC/CSm).

.5. Statistical analysis

The data are reported as mean values with a standard errorS.E.). The data were subjected to one-way or two-way anal-sis of variance and the differences among treatments wereetermined by Tukey’s test (P < 0.05). Each treatment consisted

A. Ferrante, T. Maggiore / Postharvest Biology and Technology 45 (2007) 73–80 75

Fig. 1. Total chlorophyll (A) and total carotenoids (B) in Valeriana leaves storeda ◦ws

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Fig. 2. Total anthocyanins (expressed as cyaniding-3-glucoside mg g−1 FW)(A) and total phenols (expressed gallic acid equivalents mg g−1 FW) (B) inValeriana leaves stored at 4 or 10 ◦C. Mean values are accompanied by standardem

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mstodecreased with the increase in storage time, in both storageconditions (Fig. 3).

t 4 or 10 C. Mean values are accompanied by standard errors (n = 5). Dataere subjected to one-way ANOVA and different letters mean that values are

tatistically different P < 0.05.

f five replicate samples. Data were subjected to simple lin-ar regression analysis using Excel statistical tools (Microsoftoftware).

. Results

.1. Chlorophyll, carotenoids, anthocyanins and totalhenolics

Storage treatments showed that the total chlorophyll con-ent in Valeriana leaves significantly decreased at both storageemperatures. After 5 days of cold storage, the common com-

ercial selling period of Valeriana salad, the chlorophyll contentecreased only in leaves stored at 10 ◦C, by 13% with respecto the initial value (Fig. 1A). After 8 days, chlorophyll lossesere observed in leaves stored at both storage temperatures and

mounted to 22% at 4 ◦C and 35% at 10 ◦C. However, after 15ays, no additional chlorophyll losses were noted in either treat-ent (Fig. 1A). Total carotenoids also decreased significantly

t both storage temperatures. However, differences were statis-ically significant after 8 days of storage. Longer storage, asith the results obtained with chlorophyll, did not induce any

dditional decrease (Fig. 1B).Anthocyanin content showed the same trend in both treat-

ents even if greater variability was observed in leaves stored◦

t 10 C (Fig. 2A). Analogous results were obtained for the total

henol content. In fact, total phenols did not show significanthanges between the two storage conditions (Fig. 2B). How-ver, both anthocyanins and total phenols showed an increase ineaves after 5 days of storage at 10 ◦C.

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rrors (n = 5). Data were subjected to one-way ANOVA and different lettersean that values are statistically different P < 0.05.

.2. Fluorescence measurements and linear regression

Chlorophyll a fluorescence was used as a rapid diagnosticethod to determine the health of Valeriana leaves. Results

howed that the fluorescence induction curve is lowered withhe increase in storage time at both 4 and 10 ◦C (Fig. 3). The flu-rescence JIP induction curve showed that the Fm significantly

ig. 3. Chlorophyll a fluorescence induction curve in Valeriana leaves storedt 4 or 10 ◦C at the beginning of the experiment and after 15 days of storage.ean values are accompanied by standard errors (n = 5). Data were subjected to

ne-way ANOVA and different letters mean that values are statistically different< 0.05.

7 Biology and Technology 45 (2007) 73–80

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6 A. Ferrante, T. Maggiore / Postharvest

Differences in the polyphasic increase in fluorescence tran-ients became evident at I intermediate step that normally occurst 30 ms (Fig. 3). The Fo values did not change statisticallyuring storage, while Fv and Fv/Fm slowly decreased, but sig-ificant differences between the two storage temperatures werenly observed for the Fv (Fm − Fo) parameter at the end ofhe storage period (data not shown). However, both decreasedtatistically with time, especially the Fv/Fm ratio.

JIP analysis performed on the intermediate data points aserived indices changed during storage at both storage temper-tures. The mean initial PI value was 3.4, and decreased to 1.6−53%) and 0.8 (−76%) at the end of the storage period in Vale-iana leaves stored at 4 and 10 ◦C, respectively (Table 1). The PIlso changed in relation to cultivation period, the lowest beingn July (2.94 ± 0.075) and the highest in February–September3.37 ± 0.12).

The ABS/CS values of Valeriana leaves stored at 4 ◦C didot change during the first 8 days of storage, after which theyncreased significantly. Those stored at 10 ◦C, instead, showedn earlier increase in ABS/CS values after 8 days and subse-uently a decrease until they reached the same values recordedt the beginning of the experiment (Fig. 4A). The TRo/CS val-es increased at 4 ◦C during the first 8 days of storage, thenecreased slightly. The TRo/CS index of leaves stored at 10 ◦Cid not change statistically during the first 8 days of storage,hen decreased (Fig. 4B). The DIo/CS index showed a linearncrease in leaves stored at both storage temperatures, even ifhe DIo/CS values were statistically higher in leaves stored at◦C after 8 days of storage (Fig. 4C). The ETo/CS index slightly

ncreased in leaves stored at 4 ◦C after 8 days, but at the end ofhe experiment the values were not statistically different. TheTo/CS of leaves stored at 10 ◦C progressively decreased afterdays of storage (Fig. 4D). The RC/CSo and RC/CSm had the

ame trend, both progressively decreased with the increase inhe storage time (data not shown).

The linear regression analysis between the storage time (upo 15 days) and each index was calculated. The higher R2 valuesere found for PI, DIo/CS, ABS/DIo, ETo/DIo and RC/CSmersus storage time (Fig. 5). Other indices, with a significantinear regression coefficient, were ABS/CSo (only at 10 ◦C)nd RC/CSo. The combined indices such as ABS/DIo (energyux and dissipation energy per cross-section ratio) and ETo/DIoelectron transport flux and dissipation energy per cross-sectionatio) were also able to show differences between the two storageemperatures immediately after 5 days of storage with higher R2

alues (Table 1 and Fig. 5).

.3. Correlation analyses and linear regression betweeneaf pigments and fluorescence parameters

The JIP indices were also analysed and correlated with inter-al leaf quality parameters such as chlorophyll, carotenoids,nthocyanins and total phenols. Chlorophyll and carotenoids

howed significant correlations with the most important fluores-ence indices, while anthocyanins and total phenols did not showignificant correlations. Total chlorophyll was positively and sig-ificantly correlated with PI index with an r of 0.499 (P < 0.05)

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ured on Valeriana leaves stored at 4 or 10 ◦C. Mean values are accompanied bytandard errors (n = 5). Data were subjected to two-way ANOVA and differentetters mean that values are statistically different P < 0.05.

uring storage at 4 ◦C, while at 10 ◦C the correlation coefficientwas 0.824 (P < 0.0001). The correlation between carotenoidsnd PI was significant with a coefficient value of 0.523 (P < 0.05)t 4 ◦C and 0.733 (P < 001) at 10 ◦C. The correlation analy-is between chlorophyll and ABS/DIo was significant at both

torage temperatures. Analogous results were observed for theorrelation between total carotenoids and ABS/DIo. The cor-elation value between chlorophyll and Fv/Fm was 0.599 at◦C (P < 0.01) and 0.645 at 10 ◦C (P < 0.05); similar values

A. Ferrante, T. Maggiore / Postharvest Biology and Technology 45 (2007) 73–80 77

Table 1Indices derived by the OJIP analysis: PI, ABS/DIo and ETo/DIo calculated on the intermediate steps of chlorophyll a fluorescence measured on Valeriana leavesstored at 4 or 10 ◦C

Day PI ABS/DIo ETo/DIo

4 ◦C 10 ◦C 4 ◦C 10 ◦C 4 ◦C 10 ◦C

0 3.4 ± 0.27 a 3.4 ± 0.27 a 6.46 ± 0.119 a 6.46 ± 0.119 a 3.15 ± 0.064 a 3.15 ± 0.064 a5 2.0 ± 0.24 b 2.4 ± 0.25 b 5.51 ± 0.054 b 5.58 ± 0.101 ab 2.47 ± 0.045 b 2.69 ± 0.056 a8 1.9 ± 0.17 be 1.3 ± 0.19 c 5.15 ± 0.190 b 5.13 ± 0.184 b 2.41 ± 0.106 b 2.07 ± 0.090 c

15 1.6 ± 0.28 ce 0.8 ± 0.11 d 4.52 ± 0.090 c 4.29 ± 0.244 c 2.02 ± 0.076 c 1.42 ± 0.160 c

Mean values are accompanied by standard errors (n = 5). Data were subjected to two-way ANOVA and different letters mean that values are statistically differentP < 0.05.

Fig. 5. Linear regression analysis between storage time and PI at 4 ◦C (A), PI at 10 ◦C (B), RC/CSm at 4 ◦C (C), RC/CSm at 10 ◦C (D), ETo/DIo at 4 ◦C (E), ETo at10 ◦C (F), ABS/DIo at 4 ◦C (G) or ABS/DIo at 10 ◦C (H) calculated from chlorophyll a fluorescence measured from Valeriana leaves during storage.

78 A. Ferrante, T. Maggiore / Postharvest Biology and Technology 45 (2007) 73–80

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ig. 6. Linear regression and correlation analysis between chlorophyll and ABSI at 4 or 10 ◦C (C), carotenoids and PI at 4 or 10 ◦C (D), chlorophyll and Fv/rom chlorophyll a fluorescence measured from Valeriana leaves during storage

ere found between carotenoids and Fv/Fm at both storageemperatures (Fig. 6A–F) with a P < 0.05. The higher storageemperature showed higher correlation values between leaf pig-

ents and fluorescence parameters.

. Discussion

Colour change during the selling period is very importantecause it affects produce attractiveness to consumers (Ferrantet al., 2004). However, internal qualities such as the antioxi-ant components are also important for human health because ofheir nutritional value. Chlorophyll and carotenoids are tightlyorrelated with each other because the latter have to protecthe chlorophyll from photo-oxidation during growth (Biswall,995). During postharvest life the leaf pigments undergo degra-ation that leads to leaf discolouration. Total chlorophyll andarotenoid contents start to decline a few days after harvest.

his phenomenon has been observed in many leafy vegetables.mong carotenoids, �-carotene, which is the most important

ntioxidant in vegetables, is the most sensitive component toegradation (Negi and Roi, 2004).

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at 4 or 10 ◦C (A), carotenoids and ABS/DIo at 4 or 10 ◦C (B), chlorophyll andtio at 4 or 10 ◦C (E) carotenoids and Fv/Fm ratio at 4 or 10 ◦C (F) calculated

The decrease in the chlorophyll content during storage isemperature-dependent and this process has been observed in

any fresh-cut vegetables such as rocket, Swiss chard andpinach (Vina and Chaves, 2003; Ferrante et al., 2004). In ourxperiments, both chlorophyll and carotenoids showed a signif-cant decrease after 5–8 days, that is longer than the normalelling period of 5–6 days in most cases. Total phenols andnthocyanin variability suggests that inter-conversions amonghe many groups of polyphenols may occur. These results weren accordance with previous experiments performed on Swisshard (Ferrante et al., 2004).

Anthocyanin and total phenol contents did not change linearlyith storage time. Therefore, they cannot be used to estimate theealth status of leafy vegetables during storage. Moreover, theetermination of these compounds requires quite a long time forxtraction and assessment procedures. In other words, it was notossible to estimate how long the leafy vegetables were storedy only monitoring chlorophyll, carotenoid, anthocyanin and

otal phenol changes.

On the contrary, chlorophyll a fluorescence measurementsan be easily and promptly determined. It is a non-invasive andighly sensitive, fast and easy to perform method to determine

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tress conditions (Lazar, 1999, 2006). Chlorophyll a fluores-ence has been widely used in photosynthesis research, such aso monitor the progress of natural flag leaf senescence of field-rown wheat or rice plants (Lu et al., 2002; Weng et al., 2005).owever, chlorophyll a fluorescence parameters, such as Fo,m and Fv/Fm, do not always give satisfactory results. In par-

icular, the Fv/Fm ratio that indicates the maximal efficiency ofSII photochemistry did not significantly change during natu-al senescence (Bjorkman and Demmig, 1987; Lu et al., 2002).he Fv/Fm ratio represents the PSII functional status, which

s not always correlated with leaf chlorophyll content (Krausend Weis, 1991; Maxwell and Johnson, 2000; Lazar, 2006). Thisatio is an indicator of stress; leaf values below 0.83 are generallyonsidered indicative of stressed plants (Maxwell and Johnson,000). A decline in Fv/Fm might be due to an increase in pro-ective non-radiative energy dissipation or to photoinhibitoryamage to the PSII reaction centre (Maxwell and Johnson,000).

In our experiments, the Fv and Fo were not good markersor estimating leaf health status during storage. On the contrary,v/Fm and Fm were able to show differences with increasingtorage time, but unfortunately they were not able to differenti-te the storage temperature. Analogous results were observedn cut roses stored at temperatures ranging from 1 to 10 ◦CPompodakis et al., 2005).

In order to investigate the effect of storage on electron trans-ort at the acceptor side of PSII, JIP analysis was performed. TheIP test is used to explain the stepwise flow of energy throughSII at the reaction centre (RC) level. This test has been used fortudying a wide range of physiological processes such as CO2ssimilation, chlorophyll fluorescence in dark chilling condi-ions and nitrogen fixation in soybean (Lin and Jolliffe, 2000;an Heerdena et al., 2003). The effect of light treatment in Mon-tera and Philodendron, was also evaluated using the JIP testhat showed how some parameters were able to describe theifferences among treatments better than others (Force et al.,003).

Among the several indices that can be calculated withIP analyses, the PI, ABS/DIo ETo/DIo and RC/CSm werehe parameters that better highlighted the differences betweenreatments during cold storage of Valeriana leaves (Fig. 5).he PI, performance index, is calculated by multiplyingBS/CS × TRo/CS × ETo/CS (Strasser and Strasser, 1995).his index is a biophysical parameter and was useful in reveal-

ng differences in the response of PSII to dark stored leafyegetables.

In leaves of Valeriana stored at 4 ◦C, the absorbed energy fluxnd electron transport were not affected even if the dissipationnergy and the trapped energy flux increased. These results sug-est that the PSII antenna and reaction centres were not damagedy 4 ◦C storage temperature. On the contrary, the higher stor-ge temperature (10 ◦C) influenced the absorbed energy flux perross-section, that initially increased and then decreased. Thisscillation was accompanied by a decrease in the electron trans-

ort flux, indicating that the PSII was probably damaged by therolonged storage temperature. In fact, the non-trapped energynd the dissipation energy per cross-section (DIo/CS), in leaves

2d

ology and Technology 45 (2007) 73–80 79

tored at 10 ◦C, decreased and increased, respectively. Usuallyhese results indicate that part of the energy is transformed intoeat or transferred to other systems (Strasser and Strasser, 1995;orce et al., 2003). The RC/CSm, that represents the active reac-

ion centres at Fm, was also a good marker for evaluating thetorage time. The active reaction centres progressively decreasedt both storage temperatures, indicating that storage reduces theunctionality of PSII. Other JIP parameters that were calculatedere not useful for estimating the storage time, such as ABS/CS,Ro/CS and ETo/CS.

The ratio of absorbed energy flux and dissipated energy,hrough the cross-section, gives the ABS/DIo index, that wasvalid marker for evaluating the storage time (permanence) of

eafy vegetables. The combination of some indices derived fromhe JIP test was useful for studying the adaptation of Spirulinalatensis to salt stress (Lu and Vonshak, 1999).

ETo/DIo was the only derived index that significantlyhanged with time and was also able to show differences betweenhe two storage temperatures, after only 5 days of storageTable 1). Hence, it may be useful for evaluating changes duringhe storage period, and the temperature inside the cold room.

Fluorescence data analyses showed that during storage thenergy flux through the cross-section or the reaction centress mainly affected by storage time. The PSII of leaves withhe progression of storage is slowly impaired (especially atigher temperatures) and the conversion of energy at the reac-ion centres becomes less efficient with increasing dissipation ofnergy.

The correlation between leaf pigments (chlorophyll,arotenoids) and fluorescence parameters (ABS/DIo, PI, Fv/Fm)as significant during storage at both storage temperatures, even

f it became stronger at higher storage temperatures, indicatinghat chlorophyll a fluorescence can also be used for estimatingeaf internal quality.

. Conclusion

Storage time and temperature are the most important fac-ors that affect the quality of Valeriana leafy vegetables duringostharvest life. The PI, DIo/CS, ABS/DIo, ETo/DIo andC/CSm indices derived from the JIP analyses may be usefuls markers for evaluating the health status of leaves. Thereforehlorophyll a fluorescence and derived indices can be sug-ested as non-destructive methods for evaluating the quality ofeafy vegetables along the distribution chain and during storage.

oreover, further validation analyses should be performed foretting up a correlation graph that estimates the storage time andemperature during the whole distribution chain from the grow-rs to the retailers or end users. Chlorophyll a fluorescence canlso be used for prolonging the selling period of leafy vegetablesn the market shelves.

cknowledgment

The present work was funded by MIUR with PRIN004–2005 “Minimally processed horticultural products: pro-uction and quality improvement strategies (Prodotti orticoli

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