Effect of chlorine dioxide on the control of postharvest diseases and quality of litchi fruit

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1 Africn Journl of Biotechnology Vol. 10(32), pp , 4 July, 2011 Avilble online t DOI: /AJB ISSN Acdemic Journls Full Length Reserch Pper Effect of chlorine dioxide on the control of posthrvest diseses nd qulity of litchi fruit Bin Wu 1,2, Xueping Li 1, Huigng Hu 1, Aiyun Liu 1 nd Weixin Chen 1 * 1 Gungdong Key Lbortory for Posthrvest Science nd Technology of Fruits nd Vegetbles, College of Horticulture, South Chin Agriculturl University, Gungzhou , Chin. 2 College of Chemistry nd Chemicl Engineering, XinJing University, Urumqi, , Chin. Accepted 8 April, 2011 Litchi (Litchi chinensis Sonn.) is n importnt subtropicl fruit crop with high mrket vlue. However, rpid pericrp browning nd decy of litchi fruits cused by infection of microorgnisms during storge cn result in up to 50% of posthrvest loss prior to consumption. New methods re urgently needed for effectively overcoming these problems. In this study, we tested the efficcy of chlorine dioxide for the control of posthrvest diseses of litchi fruit. Inctivtion kinetics of litchi nthrcnose by solution concentrtions rnging from 5, 10, 20, 40, 60, 80 nd 120 mg/l ws lso studied. The fruits of the cultivr Huizhi were first treted with 80 nd 120 mg/l nd then stored t 20 C for 7 dys. The effect of the tretments on the posthrvest physiology ws investigted. The results showed tht 5 mg/l solution could significntly inhibit litchi nthrcnose spore germintion. In ddition, tretments with 80 nd 120 mg/l of significntly reduced posthrvest decy nd peel browning of the fruit, inhibited polyphenol oxidse (PPO) nd peroxidse (POD) ctivity, retined totl soluble solids (TSS) nd titrtble cidity (TA) content, nd incresed phenyllnine mmonilyse (PAL) ctivity nd mlondildehyde (MDA) content. However, solution did not significntly influence CO 2 nd C 2 H 4 production of the fruits, compred with those in the untreted control. Overll, 120 mg/l solution tretment ws effective in inhibiting posthrvest diseses nd improving the qulity of litchi fruits. Key words: Litchi, chlorine dioxide, Colletotrichum spp, polyphenol oxidse, peroxidse. INTRODUCTION Litchi (Litchi chinensis Sonn.) is n importnt subtropicl fruit crop with high mrket vlue. However, rpid pericrp browning nd decy of litchi fruits during storge re the min problems tht result in gret loss of its mrket vlue (Li et l., 2006). Posthrvest loss of litchi is estimted to be 20 to 30% of the hrvested fruit, even s high s 50% prior to consumption, minly due to the decy cused by infection of microorgnisms such s *Corresponding uthor. E-mil: wxchen@scu.edu.cn. Tel: Fx: Abbrevitions:, Chlorine dioxide; PPO, polyphenol oxidse; POD, peroxidse; PAL, phenyllnine mmonilyse; MDA, mlondildehyde; SO 2, sulphur dioxide; TA, titrtble cidity; BI, browning index; DI, disese incidence. Peronophythor lithci, Penicillium spp., Colletotrichum spp. (Jing et l., 2002; Jing et l., 2001). Currently, sulphur dioxide (SO 2 ) fumigtion is widely used to control the decy cused by some of these fungi such s Penicillium spp nd Colletotrichum spp. Infection of litchi fruits by these fungi cn become mjor problem in litchi export industry, becuse SO 2 fumigtion or SO 2 fumigtion followed by cid dip tretment with HCl to regin ppeling red colour, which is prcticed in some pckhouses, brings undesirble SO 2 nd residues, lters the fvorble fruit tste nd cuses hzrds for consumers nd pckhouse workers (Lichter et l., 2004; Sivkumr et l., 2008). In recent yers, there re growing concerns regrding SO 2 residue present in the fruits, especilly from import countries such s those in Europe, U.S. nd Jpn. The Europen community currently permits mximum limit of sulfur residue

2 Wu et l concentrtion t s low s only 10 mg/l in the edible portion of the fruits (Pull et l., 1998; Sivkumr et l., 2010). Therefore, replcement for SO 2 with the sfer, environmentlly friendly nd economicl fungicide tretments would be preferred. Chlorine dioxide ( ) is one of the disinfectnts, which hs been used to control microbiologicl growth in different industries. The U.S. Environmentl Protection Agency (EPA) hs pproved the use of s disinfectnt for potble wter tretment with 1.0 mg/l limit to chlorite ion in the treted wter (US FDA, 2000). Aqueous hs been pproved by FDA s n ntimicrobil gent for wshing fruits nd vegetbles t residul concentrtion of 3.0 mg/l (US FDA, 1995). Aqueous offers severl dvntges for food snitiztion, especilly for processing vegetbles nd fruits. solutions hve shown to be efficient in inhibiting pthogens inoculted to different fruits nd vegetbles, such s pple, cntloupe, strwberry, tomto nd blueberries (Gomez-Lopez et l., 2009; Lee et l., 2006; Wu nd Kim, 2007), lthough, no complete elimintion hs been obtined. This study ws conducted to investigte the effect of solution on controlling Colletotrichum spp spore germintion, pericrp browning nd the shelf life of litchi fruits. The ctivities of browning relted enzymes including PPO, POD nd PAL, s well s MDA content were lso evluted in litchi fruits during storge with 7 dys of post-storge t 20 C. MATERIALS AND METHODS Strins nd spore germintion Litchi nthrcnose (Colletotrichum spp) ws provided by Plnt Pthology Deprtment, College of Horticulture, South Chin Agriculturl University Gungzhou, Chin. The pthogens were cultured for 6 dys on potto sucrose gr (PSA: 1 L of distilled wter contining 200 ml of extrct of boiled pottoes, 20 g of sucrose nd 20 g of gr) pltes t 26 C. The spores were prepred by wshing pltes with wter gr. Conidil suspensions were then djusted to 3.0 to spores/l using hemcytometer counts of conidi. A 0.1 ml liquot of conidil suspension ws dded to 10 ml (0, 5, 10, 20, 40 nd 60 mg/l) C1O 2 solutions nd incubted for 24 h t 26 to 28 C. The spore germintion rte ws checked by microscopic exmintion t 40 mgnifiction nd colonies were counted. Axioskop 2 plus electron microscope (Crl Zeiss Jen, Germny) ws used for the observtion of Colletotrichum spp spore micro-morphology (Clvo et l., 2007). Plnt mterils nd tretment Litchi (L. chinensis Sonn.) fruits of the cultivr Huizhi t 80 to 90% mturity were obtined from commercil orchrd in Gungzhou. Fruits with uniform size nd colour were selected nd dipped into different solutions (0, 80, 120 mg/l) for 3 min nd then ir-dried. Ech 1000 g of the treted fruits ws pcked into plstic punnet nd wrpped with 0.03 mm thick polyethylene bg nd then stored in room t 20±1 C with 80 to 90% reltive humidity (RH). During the storge, enzyme ctivity nd overll visul qulity were mesured t one-dy intervl. Fruits treted with tp wter were used s the control for simultion of the commercil conditions. A stbilized powder product (Beijing Strtech Science nd Technology Co. Ltd, Chin) ws used in this reserch. After ctivted by tp wter, solution (10,000 mg/l) ws further diluted with tp wter to specific concentrtions. concentrtion in seled test bottles ws mesured over time t 360 nm using UV-2450 spectrophotometer (Shimdzu, Jpn) (Ruffell et l., 2000). Fruit qulity evlution Posthrvest decy ws ssessed on 1 to 5 scle, describing the severity of posthrvest fungl decy (1 = no decy; 2 = 25% decyed; 3 = 50% decyed; 4 = 75% decyed nd 5 = entire fruit decyed) (Sivkumr nd Korsten, 2006). The severity of browning ws ssessed visully s: 1 = no browning; 2 = 1 2 brown spots, cceptble mrketbility; 3 = some spots with browning, limited mrketbility; 4 = 50% of the fruit surfce with browning; 5 = 75% entire fruit surfce with browning, no mrketbility. The browning index (BI) ws clculted s (browning scle percentge of corresponding fruit within ech scle) (Zhng et l., 2001). A set of twenty-four (24) fruits were rndomly selected from ech tretment, the pulp were pressed mnully through lyers of guze nd the totl soluble solids (TSS) ws determined with digitl refrctometer (Atgo, Jpn). Percentge of titrtble cidity (TA) ws determined by titrtion with 0.01 M NOH nd clculted s citric cid equivlents from 10 g of pulp obtined from 10 fruit. Three groups of smples with 20 fruits per group were enclosed in 1.9 L continer nd incubted for 2 h t 20 C. A 1.0 ml of gs smple ws withdrwn from the hedspce nd the concentrtions of C 2H 4 nd CO 2 were mesured using GC2014/G-3900 gs chromtogrph (Shimdzu/Hitchi Corp. Ltd, Jpn) equipped with porpk-q column nd flme ioniztion/therml conductivity detectors (FID/TCD). Helium ws used s the crrier gs with hed pressure of 180 kp. The oven temperture ws mintined t 80/50 C, both the injector nd detector tempertures were kept t 150 C. The results were expressed s µl C 2H 2 /kg h nd mg CO 2/kg h, respectively. PPO, POD nd PAL ctivities One grm of pericrp tissue from 10 fruits ws homogenized in 5 ml of 0.05 M phosphte buffer (ph 7.0) nd 0.5 g of polyvinylpyrrolidone (PVP insoluble) t 4 C. After centrifugtion for 20 min t 19,000 g t 4 C, PPO ctivity ws ssyed by mesuring the oxidtion of 4-methylctechol s the substrte, ccording to the method of Dong et l. (2004). One unit of enzyme ctivity ws defined s the mount tht cused chnge of in the bsorbnce per minute. POD ctivity, using guicol s substrte, ws ssyed by the method of Zhng et l. (2005) in rection mixture (3 ml) contining 25 µl of enzyme extrct, 2.78 ml of 0.05 M phosphte buffer (ph 7.0), 0.1 ml of 1% H 2O 2 nd 0.1 ml of 4% guicol. The increse in the bsorbnce t 470 nm due to the guicol oxidtion ws recorded for 2 min. One unit of enzyme ctivity ws defined s the mount tht cused chnge of 0.01 in the bsorbnce per minute. PAL ws extrcted ccording to the methods of Sun et l., (2009). All steps were performed t 4 C. Litchi pericrp tissue (1 g) ws homogenized in 5 ml of 0.05 M sodium borte buffer (ph 8.8) contining 5 mm mercptoethnol nd 0.1 g of PVP. The enzyme

3 6032 Afr. J. Biotechnol. nd 0.4 g of PVP (insoluble) t 4 C nd centrifuged t 10,000 g for 15 min. A 1 ml of superntnt ws dded to 3.0 ml of 0.5% (w/v) thiobrbituric cid in 10% (w/v) trichlorocetic cid. The mixture ws heted t 100 C for 30 min nd then quickly cooled on ice. After centrifugtion t 10,000 g for 10 min, A532, A600 nd A440 of the superntnt were recorded. The vlue for non-specific bsorption t 600 nm ws subtrcted nd stndrd curve of sucrose (from 2.5 to 10 µmol/ml) ws used to rectify the results from the interference of soluble sugrs in smples, reding A532 nd A440. MDA content ws clculted using its bsorption coefficient of 157 /mmol cm nd expressed s µmol MDA /mg (DW) Sttisticl nlysis The entire experiment ws done three times with three replictes for ech time. Dt were plotted using Sigm Plot10.0 softwre nd one-wy nlysis of vrince (ANOVA) nd Duncn s multiple rnge test (P < 0.05, P < 0.01) using SPSS Version Dt were presented s men ± stndrd error (SE). RESULTS AND DISCUSSION Micro-morphology nd germintion rte of Colletotrichum spp spores Figure 1. Effect of on the Colletotrichum spp spore growth fter 24 h incubtion. The growth of hyphe dipped in 20 mg/l solution ws significntly inhibited (A), when compred with the control (B). 20 mg/l tretment. Red br: 50 µm. extrct ws centrifuged t 12,000 g for 15 min nd then the superntnt ws collected to determine PAL ctivity. The rection mixture consisted of 1.9 ml of 0.05 M sodium borte buffer (ph 8.8), 1 ml of 20 mm L-phenyllnine nd 0.1 ml of enzyme solution, with finl volume of 3 ml. Enzyme smples were incubted for 1 h t 37 C. In the control smple, the enzymtic extrct ws replced by 1 ml of 0.05 M sodium borte buffer (ph 8.8). The rection ws stopped by the ddition of 0.2 ml of 6 M trichlorocetic cid. One unit of enzymtic ctivity ws defined s the mount of the enzyme tht cused chnge of 0.01 in the bsorbnce t 290 nm per hour. Mlondildehyde (MDA) determintion MDA content ws mesured following the method of Sofo et l., (2004) nd expressed s µmol per grm dry weight. Litchi pericrp tissue (1 g) ws dded to 5.0 ml of 0.05 M phosphte buffer (ph 7.8) The spore micro-morphology of Colletotrichum spp is shown in Figure 1. Microscopic exmintion of the fungus cultured under sustined 20 mg/l confirmed the lck of sporultion in Colletotrichum spp. solution completely inhibited Colletotrichum spp spore growth. The hyphe in the control cultures were highly brnched nd lcked spores. After 24 h incubtion, the verge hyphl length reched plteu (300±50 µm) in the control (Figure 1), wheres in the treted group, the verge hyphl length ws 50±10 µm (Figure 1b). The spore germintion rte of Colletotrichum spp is shown in Tble 2. The inctivtion effect of on Colletotrichum spp spore incresed s concentrtions were incresed. Spores were inctivted when the concentrtion ws s low s 5 mg/l. At concentrtion of 20 mg/l, spore germintion rte ws 0.00%, compred with 95% in the control. These results clerly indicted tht, tretment significntly (P < 0.01) decresed the germintion rte of Colletotrichum spp spore of litchi fruits. Cell membrne hs been identified s the primry trget of on microbil cells. Beucht et l. (2004) found tht, tretment of Bcillus cereus nd Bcillus thuringiensis spores in medium in which cells hd grown nd produced spores with n equl volume of lkline (ph 12.1) (400 mg/l) for 30 min reduced spore popultions by 4.6 nd 5.2 log cfu/ml. Lee et l. (2004) reported tht, Alicyclobcillus cidoterrestris spore number ws reduced by > 4.8 log with 120 mg/l free chlorine dioxide tretment for only 1 min. Po et l. (2007) demonstrted significntly snitizing bility of 20 mg/l ginst Slmonell enteric nd Erwini crotovor inoculted onto the surfce of

4 Wu et l Tble 1. Effect of on TSS nd TA of litchi fruit during storge t 20 C. Prmeter Dy of storge Control 18.86± ±0.10 c 17.36±0.05d 17.03±0.20d TSS ± ±0.13 b 18.26±0.05 b 18.23±0.06 b ± ±0.11 b 17.90±0.12 c 17.63±0.06 d TA Control 0.84± ±0.04 c 0.53±0.04 f 0.40±0.02 h ± ±0.05 b 0.57±0.10 e 0.49±0.02 g ± ±0.03 b 0.64±0.03 d 0.58±0.04 e Mens within column between control nd tretment followed by the sme letter re not significntly different t the 5% level. Ech dt point represents the men ± S.E. (n = 3). tomto fruits. These results support tht solutions cn significntly reduce fungl popultion in litchi fruits. Chnges in pericrp browning nd disese index (DI) of -treted litchi fruits Posthrvest decy is one of the mjor problems tht reduce the commercil vlue of litchi fruits. A wide rnge of fungi, such s Aspergillus, Penicillium nd Rhizopus, cn cuse decy of litchi fruits, occurring during nd fter hrvest through skin injury, wheres Colletotrichum nd Botryodiplodi infects fruits either in the field or through the cut stem end during hrvest or hndling (Jing et l., 2002; Scott et l., 1982). In this study, the posthrvest diseses were observed to be significntly reduced by solution t 80 nd 120 mg/l (Figure 2b). Additionlly, the browning index of the fruits treted with solution t 80 nd 120 mg/l were significntly lower thn tht of the control fter 5 dys of hrvest (Figure 2). Compring the inhibitory efficiency of vrious concentrtions on browning, we found tht 120 mg/l of ws the most effective concentrtion for litchi, cv. Huizhi. It is worth noting tht, following the incresing of the disese index, the browning index of the fruits incresed grdully in ll the tretments (Figure 2). This observtion is similr to those mde by Li et l. (2005) who reported tht the incidence of nthrcnose of the fruits ws closely relted to the browning of the pericrp, the infection of nthrxcnose fungus ccelerted the pericrp browning nd lesion lrging. These observtions indicte tht the incresed browning index is possibly ssocited with the disese index development. In this study, we observed tht tht the pericrp browning ws mrkedly delyed by tretments. This inhibitory effect my contribute to lower disese index of litchi fruits during storge t 20 C. Respirtion rte nd ethylene production Litchi fruit is non-climcteric nd does not continue to ripen fter hrvest (Holcroft nd Mitchm, 1996). Respirtion rte incresed from 2 dys fter tretment nd peked on dy 7 (Figure 3). In contrst to the control, the respirtion rte of the fruit treted with 80 mg/l ws decresed. However, no significnt difference ws found in the respirtion rte between untreted nd treted smples on dy 7 (P < 0.05), which were ±0.024, ± nd ± g/h g, respectively. Another study reported significnt reduction in the respirtion rte t 10 C fter fumigting green bell pepper with 20 nd 50 mg/l gs for 40 dys (Du et l., 2007). Furthermore, Gomez-Lopez found n increse in the respirtion rte of shredded white cbbge by 22% with gs, but did not ffect the respirtion rte of grted crrots nd shredded iceberg lettuce (Gomez-Lopez et l., 2007, 2008). These contrdictory results could be due to the differences of concentrtion, exposure time or possibly in ssocition with the disese development fter hrvest. The pttern of ethylene production ws similr to tht of respirtion rte, where it incresed from 3 to 6 dys during storge t 20 C, peked t dy 6 nd then decreesed (Figure 3b). tretments incresed the ethylene production but no significnt difference ws found between untreted nd treted smples (P < 0.05). This result might be ssocited with skin browning nd rotting of litchi fruit. Totl soluble solids nd titrtble cidity Totl soluble solids (TSS) nd titrtble cidity (TA) re importnt fctors in the ssessment of the flvor nd nutrition of litchi fruit. Litchi fruit does not continue to ripen nd ccumulte sugrs fter hrvest, so the TSS increses during fruit ripening, while the TA remrkbly decreses (Sivkumr et l., 2010). As shown in Tble 1, the concentrtions of TA nd TSS decresed over time during the shelf life evlution. TSS in -treted fruit generlly decresed during storge time from (dy

5 6034 Afr. J. Biotechnol. 90 Disese incidence % CK -80mg/l -120mg/l ( A) Browning index 100 ( B ) CK -80mg/l Diseses index % mg/l b b c b b b b Time (Dys) Figure 2. Effect of on browning index with disese incidence (A) nd disese index (B) of litchi fruit during storge t 20 C. Ech vlue is presented s the men ± SE (n = 3). The sme letters re not significntly different t P < 0.05 level within the sme group. BI, Browning index; DI, disese incidence.

6 Wu et l Respirtion rte ( CO 2 mg kg -1 h -1 ) CK -80mg/l -120mg/l ( A ) Ethylene production ( ÌL Kg -1 h -1 ) CK -80mg/l -120mg/l ( B ) Dys fter poshrvest Figure 3. Effect of on ethylene production (A) nd respirtion rtes (B) of litchi fruits during storge t 20 C. Ech vlue is presented s the men ± SE (n = 3).

7 6036 Afr. J. Biotechnol. Tble 2. Effect of on spore germintion rte of Colletotrichum spp spore growth fter 24 h incubtion. concentrtion (%) 0 mg/l 5 mg/l 10 mg/l 20 mg/l 40 mg/l 60 mg/l Spore germintion rte 95.0±0.5 A 10.3±0.2 B 3.5±0.8 C 0 D 0 D 0 D *Results re shown s men ± stndrd devition men. Different letters within the sme line indicte sttisticl significnce t P < ) to (dy 7). TSS nd TA contents in fruit treted with 80 nd 120 mg/l were significntly higher thn the control fter 7 dys. Conversely, Du et l. (2007) reported tht, tretment did not influence TA nd TSS contents of green bell peppers. In this study, the higher levels of TSS nd TA in the pulp with tretment my be due to the reduced posthrvest diseses of litchi fruit, but this needs further investigtion. Effect of on PPO, POD nd PAL ctivity As shown in Figure 4, PPO ctivity in litchi fruit incresed t the beginning of storge nd peked t 6 dys fter hrvest nd then mrkedly declined. The fruit treted with presented reltively lower POD ctivity during storge in comprison to the control. Both 80 nd 120 mg/l tretments showed the bility to significntly inhibit the PPO ctivity. Pericrp browning due to decy or desicction is medited by PPO ctivity (Jing nd Fu, 1998). The browning index of litchi fruit pericrp ws ssocited with incresed PPO ctivity. A significntly higher incidence nd severity of browning nd PPO ctivity were observed in the control fruit, but moderte browning in the treted fruit. Similrly, n increse in POD ctivity ws pprent during the course of the storge. POD ctivity in the control fruit slowly incresed nd then rpidly incresed fter 5 dys of storge. tretment resulted in slight increse of POD ctivity throughout 7 dys of storge compred with the control fruit (Figure 4b). Peel browning of hrvested litchi fruit hs lrgely been ttributed to the rpid degrdtion of red nthocynin pigments. This process is ssocited with enzymtic oxidtion of phenolics by polyphenol oxidse (PPO) nd/or peroxidse (POD) nd formtion of polymeric browning pigments (o-quinones) (Jing et l., 2004; Sivkumr et l., 2010). Since is widely used s pulp bleching gent in the pper industry, Du et l. (2007) hypothesized tht, it might be useful to preserve color of vegetbles. These uthors demonstrted tht the PPO ctivities were inhibited with tretment during the storge of the pepper nd might relte to the oxidtion of mino cids nd/or disulfide bonds tht re involved in the ctive site in the PPO. It hs been reported tht could oxidize phenols (Npolitno et l., 2005). In this study, we showed tht the PPO ctivity ws reduced by during storge. This effect my be prtilly ttributed to the inhibition of posthrvest diseses nd/or rect with phenols. It is lso possible tht, hs direct impct on the PPO nd POD content. Further studies re needed to figure out the exct reson for this trend Figure 4c shows tht, PAL ctivity in the fruits with ll tretments incresed during storge (Figure 4c). There were significnt differences in PAL ctivity between the control nd the groups treted with 80 nd 120 mg/l (P < 0.05). PAL is the first enzyme in phenylpropnoid pthwy nd plys key role in the synthesis of phenolic compounds in plnts (Pin nd Erre, 2008). These compounds cn be further converted to other phenolic compounds vi coumrte, such s flvonols, nthocynins, chlorogenic cid nd cffeic cid derivtives which re thought to serve s browning substrtes in some plnt tissues (Toms-Brbern et l., 1997). A lrge number of reports hve shown tht the increse of PAL ctivity ws relted to nthocynin ccumultion (Frgher nd Chlmers, 1977; Jing nd Joyce, 2003; Wng et l., 2000). In this study, the ctivtion of PAL ctivity in the litchi fruits reduced the decy index of litchi fruit treted with, might lso be beneficil in delying pericrp browning of the fruits. MDA content The mlondildehyde (MDA) content of both treted nd control fruits incresed during storge (Figure 5). Compred with the control, the MDA content of -treted fruits remined significntly lower throughout the storge (P < 0.05). A lter increse in MDA content fter hrvest is possibly ssocited with -inhibited post-hrvest disese of litchi fruits. MDA is the min product of lipid peroxidtion in plnt cells (Li nd Yu, 2001); there-fore, the lower MDA content might indicte tht higher membrne integrity ws mintined with tretment. In conclusion, this study investigted the shelf life of the litchi fruits fter 7 dys of storge t 20 C, in terms of skin browning nd disese development. We observed tht ppliction of delyed skin browning, inhibited posthrvest diseses nd mintined higher concentrtions of totl soluble solids nd titrtble cidity. Also, this tretment lso significntly reduced spore germintion of Colletotrichum spp. We observed lower PPO, POD nd higher PAL ctivity during storge fter tretment. The mechnism of the inhibition of PPO nd POD ctivity by requires further investigtion. Our results

8 Wu et l BI-CK BI-80mg/l ( A ) 8 PPO ctivity (U.g -1 FW) BI-120mg/l PPO-CK PPO-80mg/l PPO-120mg/l Browning index ( B ) 140 CK -80mg/l -120mg/l POD ctivity (U.g -1 FW) POD ctivity (U.g -1 FW) Dys fter hrvest Figure 4. Effect of on PPO ctivity nd browning index (A), POD ctivity; (B) PAL ctivity nd disese incidence; (C) in the pericrp of litchi fruit during storge t 20 C. Ech vlue is presented s the men ± SE (n = 3). PAL, Phenyllnine mmonilyse; DI, disese incidence. indicted tht, tretment might be suitble to retin better qulity of litchi fruits. Therefore, s non-toxic oxidizing gent during storge nd trnsporttion for mrketing chins, tretment could be used t lest s prtil lterntive to SO 2 fumigtion, for helth conscious consumers in domestic nd overses mrkets. Further reserch on the commercil pckhouses t different geogrphicl loctions prior to ppliction of

9 6038 Afr. J. Biotechnol. Figure 4. continued. Figure 5. Effect of on MDA content in the pericrp of litchi fruit during storge t 20 C Ech vlue is presented s the men ± SE (n=3). ppliction needs to be conducted t commerciliztion. nyhyzx nd nycytx-33) nd the Ministry of Science nd Technology of Chin (Project no. 2006BAD30B06). ACKNOWLEDGEMENTS This work ws funded by the Ntionl Nturl Science Foundtion of Chin (Project no. UO631004), the Nturl Science Foundtion of Gungdong Province (Project no ), the Ministry of Agriculture of Chin (Projects REFERENCES Beucht LR, Pettigrew CA, Trembly ME, Roselle BJ, Scouten AJ (2004). Lethlity of chlorine, chlorine dioxide, nd commercil fruit nd vegetble snitizer to vegettive cells nd spores of Bcillus cereus nd spores of Bcillus thuringiensis. J. Food Prot. 67:

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