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1 Food Chemistry 124 (211) Contents lists ville t ScienceDirect Food Chemistry journl homepge: Effect of edile cotings on enzymes, cell-memrne integrity, nd cell-wll constituents in reltion to rittleness nd firmness of Hunghu pers (Pyrus pyrifoli Nki, cv. Hunghu) during storge Rn Zhou, Yunfei Li, Liping Yn c, Jing Xie, * College of Food Science nd Technology, Shnghi Ocen University, Shnghi, Chin Deprtment of Food Science & Technology, Shnghi Jio Tong University, Shnghi, Chin c Deprtment of Economics nd Mngement, Go n Cmpus of Yichun University, Go n, Chin rticle info strct Article history: Received 5 Octoer 29 Received in revised form 25 April 21 Accepted 21 June 21 Keywords: Fruit Edile film Texture properties Qulity To investigte the effects of edile cotings, such s shellc nd (sucrose-polyester sed coting) on the rittleness nd firmness of Hunghu pers (Pyrus pyrifoli Nki, cv. Hunghu), the chnges in the cell-memrne permeility nd cell-wll constituents, such s totl pectin (TP), N 2 CO 3 -solule pectin (NSP), CDTA-solule pectin (CSP), wter-solule pectin (WSP), hemicellulose nd cellulose were periodiclly mesured, for up to 6 dys of cold storge (4 C) fter hrvesting. The ctivities of peroxidse (POD), pectinesterse (PE), polyglcturonse (PG), nd cellulose were lso ssyed. The dt suggested tht high POD ctivity nd low ctivity of cell-wll-degrding enzymes, such s PE, PG, nd cellulse in the coted pers were ssocited with high integrity of the cell memrne nd few chnges in the cell-wll constituents, which contriuted to high levels of rittleness nd firmness in the pers during storge; further, the shellc coting provided etter effect thn coting. Ó 21 Pulished y Elsevier Ltd. 1. Introduction * Corresponding uthor. Tel./fx: E-mil ddress: jxie@shou.edu.cn (J. Xie). Hunghu pers (Pyrus pyrifoli Nki, cv. Hunghu), which re well known for their thin peel, delicte flesh, rich juice, nd good tste re one of the importnt fruits endemic to Chin (Zhou, Su, Yn, & Li, 27). These re some of the min per cultivrs in Shnghi nd re populrly known s Shnghimi pers. However, these pers ripen t mid-summer; the rpid posthrvest physiologicl chnges ccount for short posthrvest ripening period, nd pose mrketing chllenge (Zhou et l., 28). Softening chnges, including loss of rittleness nd firmness, re the most importnt chrcteristics indicting the deteriortion of Hunghu pers; these chnges directly influence the qulity of the fruits, s well s their storge life, trnsportility, nd mrketing. Fruit softening is generlly oserved during ripening in vrious types of fruits (Murym, Ktsumt, Endou, Fukushim, & Skuri, 26). Loss of turgor pressure nd degrdtion of the cell wll in climcteric fruits, such s Hunghu pers, contriutes to the decrese in rittleness nd firmness (Khin, Zhou, & Yeo, 27; Zhou et l., 28). The integrity of the cell memrne of fruits, which is involved in the mintennce of turgor pressure, cn e destroyed y peroxides produced during storge. An efficient ntioxidnt system cn postpone the senescence process even though nti-oxidtive ctivity in fruits decreses with geing (Zheng, Tin, Meng, & Li, 27). Peroxidse (POD), one of importnt ntioxidnt enzymes, is involved in the oxy-rdicl detoxifiction process in plnt tissues (Yun, Sun, Yun, & Wng, 21). The disssemly nd degrdtion of cell wll structure nd composition hve een ttriuted to the ction of enzymes (mong other things), such s pectin methylesterse (PE) nd polyglcturonse (PG) nd cellulse on polyscchrides, such s pectin, hemicellulose, nd cellulose present in the cell wll (Cheng et l., 29; Freye et l., 27; Lohni, Trivedi, & Nth, 24; Zhou et l., 27). However, the precise role of these enzymes in ltering the cell memrne nd cell wll, nd the importnce of relted fruit-softening enzymes in Hunghu pers re little known. Edile cotings, like modified tmosphere pckging, hve een known to retrd softening chnges in fruits y inhiiting metolic processes (Conforti & Zinck, 22; Prk, 1999). However, to our knowledge, there is no ville scientific literture regrding the effect of edile cotings on retining the texture of Hunghu pers during storge. Shellc wx nd sucrose polyesters re widely used s edile cotings for fruit; these cotings hve een successfully used in retining the texture of fruits like pples (Bi, Bldwin, & Hgenmier, 22), cherries (Ymn & Byoindirli, 22), nd quinces (Yurdugül, 25). Thus, in the present study, we selected nd designed two types of cotings, nmely, shellc /$ - see front mtter Ó 21 Pulished y Elsevier Ltd. doi:1.116/j.foodchem

2 57 R. Zhou et l. / Food Chemistry 124 (211) wx nd (sucrose-polyester sed coting), which hd different coting chrcteristics for gs exchnge, nd exmined the effects of edile cotings on mintining the qulity of Hunghu pers. The im of this work ws to (1) investigte the effects of coting tretments on POD ctivity nd cell-memrne integrity of pers, (2) investigte chnges in the hydrolse ctivity nd cell-wll constituents during storge, nd (3) clrify the contriutions of chnges cused y edile cotings to fruit softening nd determine the most pproprite edile coting to preserve Hunghu pers. 2. Mterils nd methods 2.1. Fruit nd cotings Hunghu pers (Pyrus pyrifoli Nki, cv. Hunghu) tht hd reched commercil mturity, which ws determined on the sis of fruit skin colour nd hrvest dte, were hnd-hrvested from n orchrd in Fengxin, Shnghi, Chin. The fruits were selected on the sis of uniform colour nd sence of ruises nd disese. Then, the pers were trnsported to the lortory within 2 h. We used two types of experimentl cotings. Shellc coting ws prepred using refined, dewxed, leched, nd food-grde shellc (14.3 g/1 ml; KFull-6715; Kunming Kfull Biotechnology Co. Ltd., Kunming, Chin), NH 3 (.8 g/1 ml wter), nd food-grde polydimethylsiloxne ntifom (.1 g/1 ml wter; XP1; Runqi Food Technology Co. Ltd., Shnghi, Chin). The preprtion steps of shellc coting were shown s follows: riefly, the shellc wx sed on the rtio ws homogenised with the heted mmoni wter (65 C), nd filtered through 4 lyers of cotton guze (Shnghi Honglong Medicl Supplies Equipment Co. Ltd., Shnghi, Chin). Food-grde polydimethylsiloxne ntifom (.1 g/1 ml wter) ws homogenised with the filtrte. Then, the mixture ws plced overnight nd filtered gin y following the forementioned procedure. coting ( ; AgriCot Industries Co. Ltd., Englnd; distriuted y HongYunXinD Co. Ltd., Beijing, Chin) ws cquired s liquor concentrte (5 g/1 ml wter), prepred from croxymethyl cellulose nd sucrose esters, nd glycerides of ftty cids. The rw liquor ws diluted with distilled wter to otin concentrtion pproprite for pers (1. g/1 ml wter), which is the recommended specifiction of the rw liquid. All other chemicls were of nlyticl grde. The fruits were then coted y dipping in the shellc nd solutions for 15 s, nd then suspended y their stems nd ir dried using fns. The pers dipped in distilled wter, following the sme procedure, were used s controls. Then, ll of pers were pre-cooled (7 C, 12 h) fter tretments. Finlly, ll pers were stored t 4 C nd pproximtely 95% reltive humidity (RH) Mesurement of rittleness nd firmness The rittleness nd firmness of the pers were determined on the sis of texture profile nlysis (TPA) curves of the fruits. TPA ws performed using TA-XT2i texture nlyser (Stle Micro Systems Ltd., UK) with stndrd compression plten (SMS P/1). Five pers from ech tretment group were used for the nlysis. The fruits were peeled, nd cylindricl plugs of 1-mm dimeter were otined from the equtoril region using cork orer; these plugs were then cut into 1-mm thick slices. From the equtoril region of ech fruit, four plugs were otined from four opposite sides. Brittleness ws mesured s the distnce (in mm) covered y the proe to rech the first pek of the TPA curve (Khin et l., 27), nd firmness ws defined s the second pek in the TPA curve, expressed s N Memrne permeility of per cells The memrne permeility of per cells ws expressed in terms of reltive electricl conductivity. The electricl conductivity of pers during storge ws ssyed using digitl conductometer (DDB-62; Shnghi Leici Apprtus, Shnghi, Chin) with DJS-1 type electrode. The ssys were performed ccording to the procedure descried y Feng, Yng, nd Li (25) with slight modifictions. Five pers were rndomly selected from ech tretment group, rinsed with doule-distilled deionized wter, nd then lightly wiped with filter pper. We otined 14.5-mm flesh smples from the equtoril region of pers using cork orer, nd then cut them into 2-mm thick wfers. Next, 5-g flesh smples were collected from ech tretment group, rinsed three times with doule-distilled deionized wter, nd immersed in 1 ml doule-distilled deionized wter for 1 h. The initil electrolyte lekge ws mesured. Susequently, the smples were oiled for 5 min, nd the totl electrolyte lekge ws ssyed fter the smples reched room temperture. The reltive electricl conductivity ws clculted s the percentge of the totl electrolyte lekge. All the experiments were repeted three times Enzyme extrction nd ssys The extrction method of POD ws dpted from Dong, Cheng, Tn, Zheng, nd Jing (24), with slight modifiction. The flesh of five pers ws mixed nd ground rpidly in n ice th with mortr nd pestle. Fruit tissue (1 g) ws otined nd homogenised with 4 ml of.5 M phosphte uffer (ph 6.8), nd then filtered through two lyers of middle-speed quntittive filter pper (Hngzhou Specil Pper Industry Co. Ltd., Hngzhou, Chin). The filtrte ws centrifuged t 1,g for 2 min nd the superntnt ws used for further ssys. POD ctivity ws determined ccording to the method descried y (Jung et l., 24). The rection mixture comprised of 5 ll of.2 M guicol, 2.8 ml of.1 M phosphte uffer (ph 6.8), nd.1 ml of enzyme superntnt. Next, we dded 4 ll of.4 M H 2 O 2 into the mixture, nd immeditely determined the rection time. The chnges in sornce t 47 nm were recorded for 3 min. One unit of enzyme ctivity ws defined s the mount of enzyme contriuting to chnge of.1 units in sornce per minute. The PE, PG, nd cellulse ctivities were ssyed ccording to the procedure descried in previous studies (Zhou et l., 27). Similrly, the flesh of 5 pers ws mixed nd ground in n ice th. For PE extrction, 1 g fruit flesh ws otined nd homogenised with 1 ml of.5 M Tris HCl (ph 8.) nd centrifuged (8g, 1 min) t 4 C. The Tris HCl solution contined 1 mm cyclohexne-trns-1, 2-diminetetr-cetic cid (CDTA), 5% (w/v) polyvinylpyrrolidone, nd 2 M NCl. PE ctivity in the superntnt ws ssyed y n cid se titrtion method descried y Ngel nd Ptterson (1967). One unit of enzyme ctivity ws the mount of the enzyme required to hydrolyse 1 lmol ester per minute, per grm of the originl fresh flesh of pers. For PG nd cellulose extrction, fruit flesh (1 g) ws homogenised with 1 ml of.1 M phosphte uffer (ph 7.) nd centrifuged (8g, 1 min). The phosphte uffer contined 1 mm CDTA, 5% (w/v) polyvinylpyrrolidone, nd.5 M NCl. The PG ctivity in the superntnt ws ssyed y mesuring the reducing groups relesed from citrus pectin (Sigm Chemicl Co., St. Louis, Mo.), ccording to the method descried y Zhou et l. (27). One unit of enzyme ctivity ws defined s 1 lmol of reducing groups relesed per hour, per grm of the originl fresh flesh of pers. The cellulse ctivity ws ssyed y mesuring the reducing groups relesed from croxymethyl cellulose (Zhou et l., 27). One unit of enzyme ctivity ws the mount of the enzyme

3 R. Zhou et l. / Food Chemistry 124 (211) required to form 1 lmol of reducing groups per hour, per grm of the originl fresh flesh of the pers Extrction nd frctiontion of cell-wll constituents Extrction nd seprtion of cell-wll constituents in per flesh ws performed ccording to the method descried in previous studies (Deng, Wu, & Li, 25; Murym et l., 26) with slight modifictions. The flesh of 5 pers ws ground with mortr nd pestle in n ice cold th. Next, 5 g of flesh ws treted with 8% (v/v) oiling ethnol (1 ml, 2 min) to eliminte scchrides nd inctivte enzymes, nd then the flesh ws cooled to room temperture. The smple ws centrifuged t 2g for 1 min, nd the residue ws re-extrcted twice in 8% (v/v) ethnol y following the forementioned procedure. The residue contining cell-wll mteril ws dissolved in 15 ml of 9% (v/v) dimethylsulfoxide (DMSO) t 4 C for 15 h, to remove strch. Susequently, it ws wshed twice with 1 ml of solute ethnol nd twice with 1 ml of solute cetone, nd finlly dried overnight t 4 C. The dry smple ws dispersed in 1 ml of 5 mm sodium cette uffer (ph 6.5), mechniclly shken for 6 h, nd centrifuged t 4 C (1,g, 1 min). The sediment ws re-extrcted twice y following the forementioned procedure. The three superntnts were comined nd designted s wter-solule pectin (WSP). The sediment from this step ws suspended in 1 ml of 5 mm sodium cette (ph 6.5) contining 5 mm CDTA, mechniclly shken for 6 h, nd centrifuged (1,g, 1 min). This extrction procedure ws repeted twice. The three superntnts were comined s CDTA-solule pectin (CSP). The sediment from this step ws dispersed in 1 ml of 5 mm N 2 CO 3 contining 2 mm CDTA y shking for 6 h, nd centrifuged t 4 C (1,g, 1 min). The smple ws re-extrcted twice y the ovementioned procedure. The three superntnts were comined s N 2 CO 3 -solule pectin (NSP). The remining residue ws re-suspended in 1 ml of 4 M NOH contining 1 mm NBH 4, mechniclly shken for 6 h, nd centrifuged t 4 C (1,g, 1 min). This procedure ws repeted twice nd the three superntnts were comined s hemicellulose. The remining residue ws wshed with doule-distilled deionized wter until neutrlistion, nd ws designted s cellulose. The pectin contents in the frction were determined y the m-hydroxydiphenyl method. Glcturonic cid (Fluk) ws used s the stndrd. The totl pectin (TP) content ws otined y dding WSP, CSP, nd NSP vlues. The hemicellulose nd cellulose contents were determined y the nthrone method, with D(+)-glucose s the stndrd Sttisticl nlysis The SAS 8. softwre ws used to perform sttisticl nlysis. The results were nlysed using vrince nlysis (p <.5). Duncn s multiple rnge tests were used to determine the men differences. The dt re represented s the men with stndrd devition (SD); these were clculted from physicl nd chemicl experiments, which were performed in triplicte. 3. Results nd discussion 3.1. Brittleness nd firmness As shown in Fig. 1, the rittleness nd firmness of pers showed vrying degrees of reduction over time. By dy 6, the rittleness nd firmness of the coted smples were higher ( times nd times, respectively) thn those of the control smples (p <.5). It ws cler tht the texture of coted pers ws etter retined thn tht of the control pers during storge. Similr findings were reported for pples nd cherries (Bi et l., 22; Ymn & Byoindirli, 22). In ddition, shellc-coted pers hd higher rittleness thn -coted pers y dy 6 (p <.5). There were no significnt differences in firmness etween the shellc-coted pers nd the -coted pers (p <.5), however, the men firmness vlues of the shellc-coted pers were reltively higher thn the men firmness vlues of the -coted pers during storge. Apprently, compred to coting, shellc coting ws more effective in decresing the texture chnges (especilly for rittleness) in the per flesh during storge (Fig. 1) Reltive electricl conductivity The reltive conductivity of ll the smples incresed during storge, s shown in Fig. 2. This phenomenon cn e ttriuted to the instility nd the susequent loss of integrity of the plsm () 5 4 Shellc ()15 12 Shellc rittleness (mm) 3 2 c Firmness,N Dys fter hrvest Dys fter hrvest Fig. 1. Chnges in the rittleness () nd firmness () of Hunghu pers treted with different cotings during 6 dys of storge t 4 C. : control smples; shellc: pers coted with shellc; nd : pers coted with. The vlues hving different letters within the sme dy were significntly different (p <.5).

4 572 R. Zhou et l. / Food Chemistry 124 (211) Reltive electicl conductivity, % Shellc Dys fter hrvest Fig. 2. Chnges in the reltive electricl conductivity of Hunghu pers treted with different cotings during 6 dys of storge t 4 C. : control smples; shellc: pers coted with shellc; nd : pers coted with. The vlues hving different letters within the sme dy were significntly different (p <.5). c memrne of the per cells with incresing the storge time (Feng et l., 25). The coted pers showed reltively lower levels of electrolyte lekge thn the control smples did (Fig. 2). After 6 dys of cold storge, the reltive conductivities of the fruits coted with shellc nd were only 66.2% nd 79.%, respectively, of the vlues for the control smples; this difference ws significnt (p <.5). Furthermore, the reduction in the plsm-memrne integrity of the fruit cells during storge contriuted to the loss of cell turgor, which ws relted to the chnges in the rittleness nd firmness of the fruits during storge (Khin et l., 27; Zhou et l., 28). The reltive electricl conductivity of shellc-coted fruits ws much lower thn tht of the control fruits nd the -coted fruits (Fig. 2), which showed tht the cell memrne of the shellc-coted fruits hd lower permeility. Thus, the reltively etter-integrted cell memrne of the shellc-coted fruits could hve reduced the liquid infiltrtion from the intrcellulr spce to the intercellulr gp nd mintined the cell turgor of per flesh, therey ensuring etter texture of the pers during storge Enzymtic ctivity In plnt tissues, POD, which is n iron-contining enzyme, cn oxidise n extensive rnge of phenolic compounds in the presence () Peroxidse ctivity,units / g FW Shellc () 3. Shellc Pectinesterse ctivity, units / g FW Dys fter hrvest. Dys fter hrvest (c) 1.5 Shellc (d) 1.6 Shellc Polyglcturonse ctivity, units / g FW Cellulse ctivity,units / g FW.8.4. Dys fter hrvest. Dys fter hrvest Fig. 3. Chnges in the peroxidse (), pectinesterse (), polyglcturonse (c), nd cellulse (d) ctivities of Hunghu pers treted with different cotings during 6 dys of storge t 4 C., control smples; shellc, pers coted with shellc;, pers coted with. The vlues hving different letters within the sme dy were significntly different (p <.5).

5 R. Zhou et l. / Food Chemistry 124 (211) of peroxides, nd this phenomenon hs contriuted to the specultion tht POD my e relted to multiple chnges ffecting the texture, flvour, nd colour of fruits nd vegetles (Oms-Oliu, Odriozol-Serrno, Soliv-Fortuny, & Mrtín-Belloso, 28; Ons, Sri, Selmt, & Bkr, 24). As shown in Fig. 3, the POD ctivity in ll the smples decresed grdully, nd the POD ctivity in coted fruits ws generlly higher thn tht of the control fruits over the time of storge. Especilly on dys 15, 3 nd 45, the POD ctivity in the shellc-coted smples ws significntly higher thn tht in the control smples (p <.5). Higher ctivity of POD, which is n ntioxidnt enzyme, my generlly fcilitte conditions tht cn dely senescence in fruits (Yun et l., 21). Clerly, in this study, the coting tretments delyed the senescence of pers y inducing higher ctivity of POD. These findings were similr to the dt from the oxlic cid tretment of pech (Zheng et l., 27) nd the 1-methylcyclopropene tretment of roccoli florets (Yun et l., 21). During storge, peroxides, such s superoxide ðo 2 Þ nd H 2O 2 (hydrogen peroxide), ccumulted in fruit flesh cusing lipid peroxidtion nd loss of the plsm-memrne integrity of fruit cells (Oms-Oliu et l., 28). Peroxidtion cused y the peroxides in the plsm memrne cn contriute to memrne injury, nd produce hrmful sustnces, such s ethylene nd mlondildehyde (Yun et l., 21); in turn, these sustnces increse memrne dmge, therey incresing memrne permeility. POD hs specific peroxide demnds nd cn e thought of s peroxide scvenger (Ons et l., 24). Thus, the shellc-coted fruits showed etter memrne integrity due to higher POD ctivity, therey contriuting to the enhnced retention of rittleness nd firmness of pers during storge (Figs. 1 3). Fig. 3 shows the chnges in PE ctivity of pers during storge. The PE ctivity in ll tretments incresed, peked, nd then decresed. These findings were similr to the results on prickly pers (Hernández-Pérez, Crrillo-López, Guevr-Lr, Cruz-Hernández, & Predes-López, 25), ut were different from other reserches on vovdos (Brmore & Rouse, 1976) nd Flor de Invierno fresh-cut pers (Alndes, Pérez-Munuer, Llorc, Quiles, & Hernndo, 29). The differences in storge conditions, tretment methods nd fruit species in our experiments could contriute to the differences in chnges in PE ctivity during storge. According to Fig. 3, the highest nd lowest PE ctivities were noted in the control smples nd the pers treted with shellc coting, respectively. At dy 3 nd dy 45 of storge in prticulr, the PE ctivity of shellccoted pers ws reltively lower thn tht of the control pers (p <.5). In ll the three tretments, the PG ctivity showed similr progressive increse during the storge process, with the exception of the -coted smples on dys 45 nd 6, during which the PG ctivity decresed slightly ut not significntly (p <.5) (Fig. 3c). The PG ctivity in the shellc-coted pers ws lower thn tht in the -coted pers during storge. However, no differences in the PG ctivity were noted etween the two kinds of coted pers, with the exception of ssys performed on dy 45, in which the shellc-coted pers displyed lower PG ctivity (p <.5). Pectin-degrding enzymes re closely relted to chnges in pectins, which ply significnt role in the softening chnges in fruit nd vegetle tissues (Au-Goukh & Bshir, 23). In higher plnts, PE hydrolyses pectins, which re the min constituents of the middle lmell nd primry cell wll of the fruit, to generte demethylted pectins tht cn e more esily hydrolysed y PG; in ddition, PG ctlyses the hydrolysis of (1? 4) glcturonn linkges of demethylted pectins nd releses shorter chins, therey cusing the depolymeriztion nd dissolution of pectins (Brummell & Hrpster, 21; Singh & Dwivedi, 28). In this study, the reltively lower ctivities of PE nd PG in the shellc-coted pers contriuted to the enhnced retention of rittleness nd firmness during storge (Figs. 1 nd 3 nd c). As shown in Fig. 3d, the cellulse ctivity in shellc-coted pers ws significntly lower thn tht in the control smples t dy 15, dy 3 nd dy 45 of storge (p <.5). Cellulse cn degrde oth cellulose nd the -1,4-glucn ckone of xyloglucn, hemicellulosic polyscchride tht is prominently found in the cell wlls of dicotyledons (Sethu, Prh, & Thrnthn, 1996). Our results showed tht the overll response of cellulose-ctivity levels for pers reflected the softening chnges in the flesh (Figs. 1 nd 3d). Similr results hve een reported for nns (Lohni et l., 24) nd grpes (Deng et l., 25). Cellulse hs different effects on softening chnges in different fruits. Especilly, in the cse of Hunghu pers, cellulse plys n importnt role in fruit softening during ripening. The results of this study supported the ssumption tht the lower levels of cellulse ctivity in shellccoted pers during storge fvored the retention of rittleness nd firmness of the fruit flesh Cell-wll constituents In ll the tretment groups, the pectin (TP, CSP, nd NSP), hemicellulose, nd cellulose contents showed vrying degrees of reduction, which ccompnied the loss of rittleness nd firmness over storge time (Figs. 4 nd 1). The dt showed tht the softening of Hunghu pers during storge could e prtly ttriuted to n increse in depolymeriztion nd degrdtion of the cell-wll polyscchrides contining pectin, hemicellulose, nd cellulose. Softening-relted chnges in pectin, hemicellulose, nd cellulose during posthrvest ripening hve lso een reported in mngoes (Roe & Bruemmer, 1981), ppy (Mnrique & Ljolo, 24), nn (Dun et l., 28), nd grpe (Deng et l., 25). The results of our experiments indicte tht y dy 6, the decline in the rittleness nd firmness were ccompnied y drmtic reductions in the levels of NSP ( %), CSP ( %), nd TP ( %); moderte reduction ( %) in hemicellulose levels; nd reltively smll reductions in cellulose levels ( %) (Figs. 4 nd 1). The drmtic chnges in the pectin contents cn e ttriuted to the fct tht pectin is most suject to enzymtic chnges nd shows the highest wter soluility mong these polyscchrides during ripening nd storge (Freye et l., 27). Further, the reltively lower loss of cellulose content cn e ttriuted to the crystlline nture of cellulose, which endows the cellulose molecule with high degree of resistnce to enzymtic degrdtion (Deng et l., 25; Zhou et l., 27). Generlly, the formtion of the cellulose hemicellulose network with hydrogen-ond crosslinks etween hemicelluloses nd cellulose microfirils proly provides strength (rigidity) to the cell wll (Cheng et l., 29). Pectin is one of the min components of the middle lmell nd primry cell wlls, nd mjor dhesive mteril for pectic polyscchrides nd other cell wll components in plnt tissues (Redgwell et l., 1997; Dun et l., 28). CSP my minly exist in etween cell wlls (i.e., middle lmell) or on the outside surfce of the cell-wll mterils; further, NSP is likely to exist throughout the primry cell wll (Redgwell et l., 1997). The degrdtion of pectin nd hemicellulose cuses the disssemly of the cellulose hemicellulose network nd induces fruit softening (Cheng et l., 29; Dun et l., 28). However, the results of this study my support the suggestion tht the rpid degrdtion of NSP nd CSP plys more importnt role in chnging the rittleness nd firmness of Hunghu pers during storge (Figs. 4 nd 1). As shown in Fig. 4d, in ll the tretments, the WSP content of the pers peked nd then decresed during storge. This result ws consistent with tht of the previous study on peches (Kng, Yu, & Lu, 25). The increse in WSP content is ttriuted to the ction of PG, which cts in tndem with PE nd other glycosidses

6 574 R. Zhou et l. / Food Chemistry 124 (211) () 4 Totl pectin (mg/gfw) Shellc () Sodium cronte-solule pectin (mg/gfw) Shellc Dys fter hrvest. Dys fter hrvest (c) 2.4 Shellc (d) 1.6 Shellc CDTA-solule pectin (mg/gfw) c Wter-solule pectin (mg/gfw).8.4. Dys fter hrvest. Dys fter hrvest (e) 12 Shellc (f) 8 Shellc Hemicelluloses (mg/gfw) Cellulose,mg/gFW Dys fter hrvest Dys fter hrvest Fig. 4. Chnges in totl pectin (), N 2 CO 3 -solule pectin (), CDTA-solule pectin (c), wter-solule pectin (d), hemicellulose (e), nd cellulose (f) contents of Hunghu pers treted with different cotings during 6 dys of storge t 4 C., control smples; shellc, pers coted with shellc;, pers coted with. The vlues hving different letters within the sme dy were significntly different (p <.5). (Deng et l., 25); the decrese in the WSP content in fruit cn e ttriuted to the norml ctolism-relted reduction in WSP levels (Kng et l., 25). At the 3th dy, the WSP content in the control fruits ppered s the highest pek nd then decresed t rte fster thn tht in the coted smples (Fig. 4d). This finding indicted tht coting tretments could decelerte the production of WSP nd dely the destruction of WSP-sed sustnces. In comprison with the tretment, the shellc tretment ws more effective in mintining stle content of WSP over storge time (Fig. 4d).

7 R. Zhou et l. / Food Chemistry 124 (211) Furthermore, the levels of cell-wll constituents, such s pectin (TP, CSP, nd NSP), hemicellulose, nd cellulose in the control smples were generlly lower thn those in the coted pers, especilly the shellc-coted pers (Fig. 4). These results suggested tht the coting tretments ffected chnges in the cell-wll constituents y ctully inhiiting the hydrolytic enzymes, including PE, PG, nd cellulse of pers during storge (Fig. 3 d), therey reducing the rte of metolic processes in the fruit during ripening nd storge (Conforti nd Zinck, 22). However, the mechnism of the suppression of enzymtic ctolism in coted pers could not e elucidted nd merits further investigtion. In totlity, since the chnges in rittleness nd firmness re significntly relted to chnges in cell-wll constituents, the lower reductions in the levels of pectin (TP, CSP, nd NSP), hemicellulose, nd cellulose nd the fewer chnges in the ppernce of WSP in shellc-coted pers, in comprison to the corresponding chnges in the coted smples, would fcilitte the inhiition of softening chnges in Hunghu pers, therey enhncing fruit storge. 4. Conclusions The current study reveled tht shellc coting ws more effective thn the coting in retining texture (especilly for rittleness) of pers. The use of shellc coting lso mintined higher POD ctivity nd lower ctivities of cell wll hydrolses such s PE, PG, nd cellulse in pers during storge thn the coting. Different levels of enzymtic ctivity influenced the integrity of the cell memrne nd the depolymeriztion nd degrdtion of cell-wll constituents, which further ffected the chnges in rittleness nd firmness of pers. 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