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EFFECT OF NANO-PACKING COMBINED CONTROLLEDATMOSPHERE ON POSTHARVEST PHYSIOLOGY ANDBIOCHEMISTRY OF GYNURA BICOLOR D.CLI JIANG, JUAN JIANG, HAIBO LUO and ZHIFANG YU1

Key Laboratory of Food Processing and Quality Control of MOA (Ministry of Agriculture), College of Food Science and Technology, Nanjing

Agricultural University, Nanjing, Jiangsu 210095, Peoples Republic of China

1Corresponding author.

TEL: +86-25-84399098;

FAX: +86-25-84395618;

EMAIL: [email protected]

Received for Publication August 15, 2012

Accepted for Publication December 10, 2012

doi:10.1111/jfpp.12078

ABSTRACT

Effect of nano-packing combined controlled atmosphere (CA + NP) on posthar-vest physiology and biochemistry of Gynura (Gynura bicolor D.C) was investi-gated during 20-day storage at 0C. The results showed that the CA + NP had aquite beneficial effect on physicochemical and sensory quality of Gynura com-pared with nano-packing (NP) or normal polyethylene packaging with a con-

trolled atmosphere (CA). After 20-day storage, decay index was increased to 8.97%for CA + NP, 9.23% for NP and 9.64% for CA, respectively. Relative leakage rate,O2- production and MDA content of CA + NP were significantly inhibited. Mean-while, CA + NP effectively reduced the activities of PPO, and enhanced the activi-ties of the enzymes POD, CAT and SOD. These results indicated that CA + NPcould provide a promising alternative for extending storage life and improvingpostharvest quality of Gynura.

PRACTICAL APPLICATIONS

Gynura, a Chinese herbal medicine, has also been used as food substancesthroughout Asia for centuries. Since the main pharmacological composition on it

has not been determined, the fresh Gynura demand increases gradually. However,postharvest decay of Gynura is the main limitation to market acceptance, thisstudy has given an experimental evidence that CA + NP could provide a promis-ing alternative for extending storage life and improving postharvest quality ofGynura. Furthermore, these nano-packing materials have the advantages of simpleprocessing and industrial feasibility in contrast with other storages, some of whichare time-consuming and costly.

INTRODUCTION

Gynura bicolor D.C (Gynura), a perennial wild leafy veg-

etable belonging to Composite Gynura Cass, is found in bothsubtropics and temperate zone, and widely distributed insouthern China (Wang et al. 2004). It has been commonlyused as herbs, herbal tea, folk medicines, antioxidant andnatural pigment as well as flavorant for thousands of years(Li et al. 2002).

However, postharvest decay of Gynura leaves is the mainlimitation to market acceptance. Much attention had beenpaid to effective storage techniques of vegetables, includingheat treatments (Murata et al. 2004), edible coatings (Tay

and Perera 2004) and high-pressure processing (Huang andHu 2006). However, most of these strategies are expensiveand time-consuming. Thus, there is an urgent need to have

alternative technologies to inhibit undesirable physico-chemical and physiological changes of Gynura leaves duringstorage.

The potential of controlled atmosphere (CA) to extendshelf life of many fruits has been well documented (Chenet al. 2001; Ahn et al. 2005; Escalona et al. 2007). Low levelsof O2- were able to significantly reduce the respiration rate,with the benefit of delaying senescence, thus extending thestorage life of the fresh produce (Saltveit 2003). In recent

years, nanomaterials have attracted increasing attention

Journal of Food Processing and Preservation ISSN 1745-4549

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because of their potential impact on a wide range of indus-tries and markets (Chen et al. 2001; Zhai et al. 2005; Lianget al. 2006; Janardhanan et al. 2009). Silver ions haveattracted the interest of antibacterial activity (Janardhananet al. 2009) and TiO2 has been the focus of photocatalystsunder UV irradiation because of its physical and chemical

stability, low cost, ease of availability and nontoxicity(Sobana et al. 2006).

Nano-technology has been widely applied to the foodindustry. Green tea, with nano-packing, had better mainte-nance of vitamin C, chlorophyll, polyphenols and aminoacids than with normal packing (Huang and Hu 2006).Chinese jujube with nano-packing preservation agents hadgood quality according to the research of Li et al. (2009).Since the CA extended shelf life of fruits and vegetables, theobjective of this work was to investigate the effect of nano-packing combined controlled atmosphere (CA + NP) onpreservation quality of Gynura during 0C storage.

MATERIALS AND METHODS

Materials

Gynura. Gynura were harvested in June 2009, at a com-mercial farmland in Shanghai, China. The Gynura were pre-cooled to 25C and transferred to the laboratory byrefrigerated vehicle within 3 h. Leaves without defects (pest-damaged, bruised and defective) were selected and ran-domly divided into three treatments (three replicate of eachtreatment, 500 g leaves per replicate): (1) packed by normalpolyethylene packing combined a CA of 3% O2 and 97% N2

(CA, 15 bags); (2) packed by NP with fresh air (NP, 15bags); and (3) packed by NP combined a CA of 3% O 2 and97% N2 (CA + NP, 15 bags). All treatments were stored at0C (without chilling injured) for 20 days. Three bags ofeach treatment were used to analyze each index every 5 days(0, 5, 10, 15 and 20 days) during the storage.

The Performance was Repeated

NP Material. Nano-powder (nano-Ag 35%, nano-TiO240%, kaolin 25%) (30%), polyethylene (56%) and cross-link reagents (14%) were blended to uniformity for 1 h

using a high-speed mixer. After cooling for 12 min, themixture was extruded by a twin-screw extruder and cut intonano-granules. Then, 1.5 kg of nano-granules and 38.5 kgof polyethylene granules were blended for 0.5 h, and after-wards made into film of 40-mm thickness. Finally, the filmwas made into bags of 30 45 cm using a microcomputer-controlled high-speed bag making machine (FBD 300 W,JiaQi Packaging Machiner Co., Zheijang, China). Polyethyl-ene bags of the same thickness and size without nano-powder served as controls.

Methods

For decay analysis, about 500 g leaves from each treatmentwere used, and decay degrees were visibly divided into fourlevels: 0, no decay; 1, decay< l/3; 2, 1/32/3 decay; 3, >2/3decay. The decay index was calculated according to the fol-

lowing formula:

Decay index N N N 3 N(%) [ ] [ ]= + + ( )1 1 2 2 3 3 100

where N is the total number of leaves showing the differentdegrees of decay.

Relative leakage rate was determined according to themethod of Li (2000). The content of malondialdehyde(MDA) and superoxide anion radical (O2-) production wasmeasured following the method of Tao et al. (2007) andWang and Lou (1990), while the activities of polyphenoloxi-dase (PPO), peroxidase (POD), catalase (CAT) and super-oxide dismutase (SOD) were assayed following the method

of Xu and Ye (1989), Zheng et al. (2007), Candan andTarhan (2003) and Zheng and Tian (2006), respectively.

Statistical Analysis

The experiments were conducted in a completely random-ized design. All analyses were carried out in triplicate anddata were expressed as means standard deviation. One-way analysis of variance was performed to calculate the sig-nificant differences among the treatments, and multiplecomparisons were done by the least significant differencetest with Statistical Package for the Social Sciences 8.0 statis-

tical software (SPSS Inc., Chicago, IL). Different lettersin the same testing index indicate significant differences(P< 0.05).

RESULTS AND DISCUSSION

Decay Index

Vegetables decay includes browning, yellowing and putres-cence. Browning of fresh vegetables during storage oftenleads to quality loss, and this has become one of the impor-tant factors responsible for its short shelf life and unfavor-

able marketability (Murata et al. 2004; Zheng and Tian2006). In this study, the relative humidity of each treatmentwas more than 94%, which lead to the low weightless andhigh browning. And also browning is the only complicationof Gynura leaves decay during cold storage. As shown inTable 1, the decay index of leaves increased in all treatmentduring storage. The leaves stored with CA started decayingon day 1, and reached a maximum of 9.64% on day 20during cold storage. Meanwhile, in the case of NP andCA + NP groups, less decay was observed during the

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storage, and decay indices of 9.23% and 8.97% were signifi-cantly lower than that of the CA on day 20 (P< 0.05). Incontrast with NP treatments, the combination of NP andCA could be able to inhibit leaves decaying leaves (8.97%)more effectively. This may be related to the higher mainte-nance of cell membrane integrity, which could enhanceresistance of the leaves against infection and lesion. Our

result was in agreement with the report that different pack-aging may significantly change the decay indices of Flam-mulina velutipes (Yang et al. 2009). According to Li et al.s(2009) report, antibacterial nano-Ag may be another reasonto reduce decay.

Relative Leakage Rates

The degradation of cell wall components, mainly pectins,was prompted by some specific enzymes. The membranepermeability is associated to relative leakage rates. Duringstorage, the relative leakage rates of all treatments increased

with storage time (Table 2). Moreover, the relative leakagerates of CA + NP leaves were always lower than that of theNP or CA. On day 20, the relative leakage rates reached40.34% for CA + NP leaves, 43.48% for NP and 48.69% for

CA, respectively, suggesting that the CA + NP could keepthe relative leakage rate of leaves at lowest level.

The Content of MDA and O2-

Lipid peroxidation usually occurs when plant cells senesceor was wound by external factors, which would result in theaccumulation of MDA. Therefore, MDA content was oftenserved as an indicator of lipid peroxidation resulting fromoxidative stress. As shown in Table 2, MDA content, the oxi-dative enzymic product, in NP and NA + CA leaves, weresignificantly lower than that of CA leaves after the 20-daystorage. No significantly different MDA content wasobserved between CA and NP groups on day 10 and day 15.However, MDA accumulation was significantly increased inNP packages than that in CA leaves on day 20, while no sig-nificant difference between the NP and CA + NP after the20-day storage. This result showed the MDA content wassignificantly inhibited by NP.

The increase of O2- production was one of the indicesrelated to tissue senescence (Tao et al. 2007). The O2- pro-duction of stored leaves tended to increase rapidly duringstorage (Table 2). Compared with CA, NP significantly

TABLE 1. EFFECT OF NANO-PACKING COMBINED MODIFIED ATMOSPHERE PACKAGING ON THE DECAY INDEX OF GYNURA BICOLOR D.C

Testing index Treatment

Storage time (days)*

0 5 10 15 20

Decay index (%) CA 0Ae 2.76 0.05Ad 3.85 0.08Ac 5.92 0.03Ab 9.64 0.03Aa

NP 0Ae 2.47 0.03Bd 3.27 0.13Bc 5.36 0.01Bb 9.23 0.01Ba

CA + NP 0Ae 2.15 0.06Cd 3.19 0.02Cc 5.04 0.04Cb 8.97 0.03Ca

* Each value is the mean for three replicates and vertical bars indicate the standard deviation of each mean value (n = 3). Means within the same

column or row followed by the same uppercase or lowercase letter are not significantly different by the least significant difference test (P 0.05).

CA, controlled atmosphere; NP, nano-packing.

TABLE 2. EFFECT OF NANO-PACKING COMBINED MODIFIED ATMOSPHERE PACKAGING ON THE RELATIVE LEAKAGE RATE, O2- AND MDA

OF GYNURA BICOLOR D.C



0 5 10 15 20

Relative leakage rate (%) CA 15.13 0.13Ae 19.75 0.01Ad 22.21 0.14Ac 29.49 0.35Ab 48.69 0.22Aa

NP 15.13 0.13Ae 19.09 0.08Bd 20.56 0.24Bc 27.41 0.13Bb 43.48 0.05Ba

CA + NP 15.13 0.13Ae 16.29 0.17Cd 18.69 0.13Cc 25.47 0.20Cb 40.34 0.23Ca

O2- (mmol/g prot/h) CA 357.85 8.54Ae 455.38 6.90Ad 622.47 11.01Aa 591.61 10.10Bb 554.41 8.22Ac

NP 357.85 8.54Ad 371.51 5.25Bd 468.92 8.09Bc 622.47 11.81Aa 499.78 7.22Bb

CA + NP 357.85 8.54Ad 365.16 4.75Bd 434.38 8.39Cb 387.63 5.02Cc 512.58 4.23Ba

MDA (nmol/g) CA 8.49 0.12Ae 23.12 0.21Aa 17.29 0.04Bb 14.73 0.71Ac 13.00 0.34Ad

NP 8.49 0.12Ae 21.71 0.51Ba 17.30 0.28Bb 14.25 0.15ABc 12.04 0.10Bd

CA + NP 8.49 0.12Ae 21.11 0.42Ca 18.14 0.41Ab 13.76 0.18Bc 11.86 0.22Bd


column or row followed by the same uppercase or lowercase letter are not significantly different by the least significant difference test (P 0.05).

CA, controlled atmosphere; MDA, malondialdehyde; NP, nano-packing.

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reduced the production of O2- (P< 0.05). On day 20, theO2- production of stored leaves reached to 554.41 mmol/gprot/h for the CA, 499.78 mmol/g prot/h for the NP and512.58 mmol/g prot/h for the NA + CA, respectively. Never-theless, there was no significant difference in O2- produc-tion between NP and CA + NP leaves. The previouslymentioned results suggest that NP reduced the productionof O2- (P< 0.05), but CA on the NP had no more effect onreducing the O2- production of leaves.

PPO ActivityPPO plays a key role in regulating the melanogenesispathway (Kim and Uyama 2005), and catalyzing the oxida-tive reaction associated with undesirable browning ofdamaged tissues in fresh fruits and vegetables (Fujita et al.2002). As shown in Table 3, PPO activity in all treatmentswere continuously decreased during storage and reached to19.28 103 U/min/g for CA, 18.40 103 U/min/g for NPand 13.04 103 U/min/g for CA + NP. CA + NP signifi-cantly reduced the PPO activity in comparison with NP orCA, and this inhibition might be related to application ofCA + NP. Similar results has been reported by Tian et al.

(2005), who found that low O2 atmosphere was able todecrease PPO activity in litchi fruit. This suggested thatCA + NP could effectually decrease the decay and extendedthe storage time.

Activities of Antioxidant Enzymes

POD is an important enzyme present in the active oxygen-scavenging system of plants, which can reduce H2O2 with avariety of co-reducing agents available to the cell (Shen

et al. 2006). Once the cell wall components degraded, PODmight participate in the oxidation and accumulate phenolicsubstances during the postharvest decay, which would resultin browning of the leaves. POD activity was related to therelative leakage rate during storage (Table 3). On day 5,POD activity of CA + NP reached 21.24 103 U/min/g,which was much higher than others. Meanwhile, alongwith the increased relative leakage rate, POD activity ofCA + NP (30.43 103 U/min/g) was significantly lower thanCA or NP treatments (34.48 103 U/min/g for CA and38.52 103 U/min/g for NP, respectively) on day 20 and

there was no significant difference between NP and CA. Sothe effect of CA + NP on browning of Gynura duringstorage was partly due to a relative decrease of POD activityin the leaves.

High CAT activity would fasten the decomposition ofH2O2 and delay tissue senescence. CAT activity in theGynura leaves increased at the beginning of storage andreached maximum activity on day 10, then markedlydeclined toward the termination of storage. As shown inTable 3, the leaves packed by CA + NP presented a relativelyhigher CAT activity during storage in comparison with theothers. On day 20, the CAT activity in CA + NP reached

8.24 103

U/min/g, which was 1.34 times and 1.72 timeshigher than that in NP and CA, respectively. The previouslymentioned results suggested that application of CA + NPcould maintain the preservation quality of Gynura leaves ata higher level.

Furthermore, SOD activity in all leaves decreased at thebeginning of storage and increased on day 5, then reachedmaximum activity on day 15 (Table 3). The levels of SODactivity in NP leaves were similar to the CA leaves, but thelevels of SOD activity in CA + NP leaves was significantly

TABLE 3. EFFECT OF NANO-PACKING COMBINED MODIFIED ATMOSPHERE PACKAGING ON THE ENZYME ACTIVITIES OF GYNURA BICOLOR D.C



0 5 10 15 20

PPO (103U/min/g) CA 33.20 0.32Aa 31.76 0.32Ab 22.40 0.48Ac 19.08 0.38Ad 19.28 0.25Ad

NP 33.20 0.32Aa 29.08 0.33Bb 20.92 0.39Bc 18.64 0.26Bd 18.40 0.14Bd

CA + NP 33.20 0.32Aa 24.36 0.58Cb 14.20 0.33Cc 14.04 0.23Cc 13.04 0.11Cd

POD (103/min/g) CA 21.08 3.56Ac 18.56 0.40Ad 30.68 0.45Bb 35.64 0.24Ce 34.48 0.22Ba

NP 21.08 3.56Ac 18.52 0.28Ad 33.24 0.27Ab 36.24 0.19Be 38.52 0.36Aa

CA + NP 21.08 3.56Ac 21.24 0.40Bc 25.00 0.34Cb 29.76 0.34Ad 30.43 0.27Ca

CAT (103/min/g) CA 3.13 0.03Ad 5.33 0.02Bb 7.73 0.07Ca 4.78 0.03Bc 4.78 0.04Cc

NP 3.13 0.03Ad 6.13 0.06Ab 8.50 0.04Ba 4.51 0.09Cc 6.14 0.03Bb

CA + NP 3.13 0.03Ae 4.90 0.08Cd 9.90 0.03Aa 7.31 0.03Ac 8.24 0.08Ab

SOD (U/h/g) CA 126.05 0.17Ab 122.9 1.35ABc 125.33 2.31Bb 129.67 1.07Ba 127.13 0.55Bb

NP 126.05 0.17Ab 121.39 1.82Bc 127.67 1.53Bab 130.00 1.43Ba 127.07 2.20Bb

CA + NP 126.05 0.17Ac 124.11 0.28Ac 130.33 1.53Ab 134.52 0.77Aa 129.60 1.20Ab


column or row followed by the same uppercase or lowercase letter are not significantly different by the least significant difference test

(P 0.05).the same uppercase or lowercase letter are not significantly different by the least significant difference test ( P 0.05). CA, controlled

atmosphere; CAT, catalase; NP, nano-packing; POD, peroxidase; PPO, polyphenoloxidase; SOD, superoxide dismutase.



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higher than in NP or CA on day 20. SOD is believed to playa crucial role in antioxidant defense, and a high level ofSOD in nonnetted muskmelon, combined with changes inthe three different classes of SOD during storage, contributeto delay the senescence process of fruit (Lacan and Baccou1998). Our results showed that CA + NP could enhance the

activities of the SOD in Gynura leaves and play a protectiverole in membrane integrity.

CONCLUSION

In this study, a novel NP material with higher barrier andmechanical properties, and CA packing was applied to thepreservation of Gynura during storage at 0C. Comparedwith other leafy vegetables (such as spinach, lettuce, Brusselssprouts), storage characteristics of Gynura are different andunique. The results showed that the CA + NP had quitebeneficial effects on physicochemical and physiological

quality compared with NP or CA. Therefore, the CA+

NPmay provide an attractive alternative to improve the preser-vation qualities of Gynura during storage. Furthermore,these NP materials have the advantages of simple processingand industrial feasibility in contrast with other storages,some of which are time-consuming and costly. Moreover,further research will be needed to explore the definitemechanism that CA + NP acts during storage to facilitatethe application of nano-technology over a broader range inthe future.

ACKNOWLEDGMENTS

This work was financially supported by the Strategic KeyProject of Jiangsu Provincial Science and Technology (BE2003347), Nanjing Agricultural University Innovation andTechnology Fund for Youths (KJ2011015) and the NationalBasic Research Program of China (2007AA100403).

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