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Postharvest Biology and Technology 46 (2007) 20–28

Effect of transport vibration levels on mechanical damage and physiologicalresponses of Huanghua pears (Pyrus pyrifolia Nakai, cv. Huanghua)

Ran Zhou a, Shuqiang Su b, Liping Yan c, Yunfei Li b,∗a Institute of Refrigeration & Cryogenic Engineering, Shanghai Jiao Tong University, Shanghai, China

b Department of Food Science & Technology, Shanghai Jiao Tong University, Shanghai, Chinac College of Forestry Engineering, Inner Mongolia Agricultural University, Hohhot, China

Received 7 October 2006; accepted 15 April 2007

bstract

The effect of transport vibration on the quality of Huanghua pears (Pyrus pyrifolia Nakai, cv. Huanghua) during commercialization (roomemperature) after transport was tested. Different vibration levels on the front and rear floors in a 2-tonne truck with leaf-spring suspensionsere evaluated for their effect on mechanical damage to fruit during transport. Changes in color and cell membrane permeability of pear

kin, flesh firmness, hydrolase activities and cell wall constituents were examined in fruit stored for up to 36 days after transport. Our datauggest that the damage levels of pears loaded on different positions in the truck were significantly different (p < 0.05) and pears in top con-ainers of columns were damaged more heavily than this in bottom containers (p < 0.05). Physical and chemical results showed that mechanical

amage caused by different vibration levels to pears affected plasma membrane integrity of skin cells and contents of the polysaccharide com-onents in the cell walls of pear tissue, which contributed to color change and softening of pears during subsequent commercialization afterransport. 2007 Elsevier B.V. All rights reserved.

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eywords: Pears; Fruit; Vibration; Mechanical damage; Bruise; Firmness; Enz

. Introduction

The loss of fresh fruit and vegetables during transport and dis-ribution has been estimated to be above 30% in China (Zhang,000), particularly of firm and crisp fruit, given their sensi-ivity to mechanical injury. The presence of physical injuriesesults in the rejection of such fruit, with consequent commer-ial and monetary loss. Huanghua Pears (Pyrus pyrifolia Nakai,v. Huanghua), widely planted in the South of China, are easilyffected by mechanical damage from excessive vibration duringistribution because of their firm, crisp and juicy nature whenipe.

Much research has been carried recently out on assessing theffect of transport vibration on farm produce. The frequencies of

ransport vibration have been monitored for trucks carrying freshruit (Hinsch et al., 1993; Jarimopas et al., 2005). Moreover,uch attention has been paid to assessing mechanical damage

∗ Corresponding author. Tel.: +86 21 64783085; fax: +86 21 64783085.E-mail address: yfli@sjtu.edu.cn (Y. Li).

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925-5214/$ – see front matter © 2007 Elsevier B.V. All rights reserved.oi:10.1016/j.postharvbio.2007.04.006

Hydrolase; Cell wall; Electrical conductivity

o different species of fruit and vegetables during transport, suchs potatoes (Turczyn et al., 1986), peaches (Vergano et al., 1991),pples (Timm et al., 1996; Van Zeebroeck et al., 2006), loquatsBarchi et al., 2002), and pears (Berardinelli et al., 2005). It ishus well known that one of the major causes of mechanicalamage to fresh fruit is vibration duing transport between farmsnd retail outlets (Remon et al., 2003).

Huanghua pears are judged to be acceptable mainly on theasis of two criteria: appearance and texture. Severe mechanicalamage can seriously affect fruit appearance and lead to mois-ure loss from fruit and invasion of decay organisms, furthereducing the quality of the injured fruit (Sommer, 1957; Gentryt al., 1965; Slaughter et al., 1998). Sometimes, the mechanicalounds on fruit cannot be detected visually. Moreover, phenyl-ropanoid metabolism and subsequent tissue browning of pearsave been shown to be induced by visible and invisible injuriesAmiri and Bompeix, 2004). Wang and Mellenthin (1973) sug-

ested that the exposure of cell contents to the atmosphereaused by mechanical damage was probably the reason for fric-ion discoloration of pears. Additionally, vibration treatment,ven though without obvious damage, can result in changes in

gy and Technology 46 (2007) 20–28 21

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Table 1Main characteristics of the 2-tonne truck

Characteristics Truck

Model CHANGCHUNSuspension Leaf-springThe number of spring leaves of the rear axles 30 sheetsThe number of axles 2LT

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espiration and cell membrane composition of fruit (Ying et al.,998). However, little detailed information is available about theffects of different levels of transport vibration on the changes inhe acceptability of the pears in subsequent commercializationfter transport.

The objectives of the present work were to: (1) investigateibration levels of a leaf-spring truck on different kinds of roadonditions and the extent of damage to Huanghua pears at dif-erent positions in the truck during transport; (2) examine theffects of different transport vibration levels on the appearancend firmness of the pears during commercial storage (23 ◦C), aituation which is relatively common in the Chinese fruit trade;3) assay changes in hydrolase activity and cell wall constituentso try to clarify changes in pear firmness during storage afterransport.

. Materials and methods

.1. Fruit selection and packaging conditions

Huanghua pears (P. pyrifolia Nakai) at commercial maturity,ere harvested according to color from an orchard in Fengxian,hanghai, China. Pears were packaged in new, reusable plas-

ic containers (RPCs), measuring 505 mm × 350 mm × 300 mmnd weighing approximately 22.5 kg. Each column consisted ofix superposed RPCs (approximately 1.8 m high).

In order to compare the effects of different vibration levelsn mechanical damage, the RPC columns of pears were placedn the front and rear of the truck trailer as previous research hasuggested that vertical acceleration can be different betweenhe front and rear positions of the truck trailer (Berardinelli etl., 2005). The positions of RPC columns are shown in Fig. 1.he remainder of the truck was loaded with ballast to minimize

esearch costs. Twenty pears in each RPC at the top and bottomf the columns were randomly selected and tagged on their stemo evaluate vibration damage during transport. The remainingears (not including the tagged pears) in the same RPC weresed to determine physiological changes of pears during storagefter transport. Some of the pears were picked and transported

irectly to the laboratory within 15 min drive. These fruit weresed as control samples as they did not suffer prolonged transitime.

ig. 1. Positions of the accelerometers on the truck. RPC columns were placedt the front and rear positions of the truck floor.

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.2. Vibration levels in transit

Detailed characteristics of the two-ton truck with leaf-springuspensions used in this study are shown in Table 1. Huanghuaears were transported from the orchard to the wholesale markethen returned to the laboratory over a variety of different roadonditions. The driving distance was approximately 500 km, uti-izing highways, arterial roads, secondary roads, tertiary roads,nd laterite roads (rutted, pothole-filled lanes on hardened clay,ommonly used in Chinese villages).

Two accelerometers (JF-102, Xingcheng Corp., Shanghai,hina) were connected to a shock recorder (Model VIB-0, Xingcheng Corp., Shanghai, China). Vibration data wereecorded in real time for 2 s for every 3 min of road travel. Theotal recording time was 320 s for about 8 h driving. As shownn Fig. 1, the two accelerometers were fixed on the truck floort two different positions (front and rear) to measure vibrationevels of the front and rear positions of the truck floor duringransport. Every sample provided frequency information in theange 2–200 Hz. Vibration data were transferred to a computeror analysis using VIB-30 software (Xingcheng Corp., Shang-ai, China). Data are presented as power density (PD) spectratilizing fast Fourier transformation (FFT) algorithms.

.3. Evaluation of vibration damage to pears

The 20 tagged pears of each treatment were unloaded, storedt 23 ◦C for 24 h, and arrayed (four lines by five rows) with theevere damaged side of each pear placed face-up on the table.he tagged fruit from each container were then photographed

Canon powershot A80, 4 megapixel of effective Pixels) afterruises from the tagged pears were counted three times perear. Pictures were transferred to a computer to calculate theercentage of bruises utilizing Leica QWin software (Leicaicrosystems Imaging Solutions Ltd., Cambridge, UK).

.4. Storage conditions

The Huanghua pear is a climacteric fruit, which changesolor and becomes soft easily after harvest (Lin et al., 2003).n this research, pears were stored at room temperature (23 ◦C).esearch has suggested that during transport, the top container

n a column suffers the most severe vibration (Slaughter et al.,993). To obtain the most effects of transport vibration on theuality of Huanghua pears, the assays were focused on the fruitn the top RPCs of the columns loaded on the front and rear

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ruck floor. Pears not exposed to long-time transit were used asontrols. Pears were analyzed at five time points: 1, 9, 18, 27nd 36 days after storage. The physical and chemical tests wereetermined on 5 pears per treatment per test day (a total of 25ears per treatment during storage).

.4.1. ColorPears were rinsed with distilled water and lightly wiped with

lter paper. Each batch of five fruit was randomly chosen fromhe three examined groups. Color values of each fruit were

easured from four opposite sides (not including the bruisingreas) at the equatorial region. A color difference meter (Model

SC-S, Shanghai Precision & Scientific instrument co., Ltd,hanghai, China) was used with a 20 mm viewing aperture.he CIE L*a*b* color space was used to record color measure-ents. The instrument was calibrated with a white reference

ile and a black trap and L*, a* and b* color coordinates wereecorded. Here, L* defines the lightness; h* (hue angle) was cal-ulated as h* = arctan(b*/a*), and C* (chromatic correction) as* = (a*2 + b*2)1/2 (Diaz-Perez et al., 2000).

.4.2. Relative electrical conductivityPears were rinsed with double distilled deionized water and

ightly wiped with filter paper before examination. Slice samplesf Huanghua pear skin were taken with a cork borer, diameter4.5 mm, from a batch of 5 pears at a time, weighing 5 g (1 g sliceample per pear, not including the bruise areas). Electrical con-uctivity of the slice samples of fruit skin was assayed using aigital conductometer (DDB-6200, Shanghai Leici Apparatus,hanghai, China) with a DJS-1 conductivity immersion elec-

rode. The assaying method was that described by Feng et al.2005). Five grams slice samples were immersed in 100 mLouble distilled deionized water for 1 h. The first measurementas then made and the samples subsequently boiled for 5 min,

he total electrical conductivity then re-assayed after the sampleeached room temperature. The measurement of each treatmentas repeated three times. The percent value of relative elec-

rical conductivity was calculated as electrolyte leakage by therst result (electrical conductivity after 1 h in 100 mL distilledater) divided by the second result (electrical conductivity afteroiling).

.4.3. Flesh firmnessFlesh firmness was measured using a TA-XT2i texture Ana-

yzer (Stable Micro Systems Ltd., UK) with a 5 kg load cellnd a 2 mm diameter cylinder probe. The test was performedith a pre-test and test speed of 5 mm/s, a post-test speedf 10 mm/s, and auto-25 g trigger force. Each batch of fiveruit was randomly picked from the three treatment groups andeeled. Then, firmness was measured on four opposite sides ofach fruit at the equatorial region. All data for one batch wereooled.

.4.4. Enzyme extraction and assaysThe enzyme assays were adapted from the procedure

escribed by Deng et al. (2005a). The flesh of five pears ofach group (rear top, front top and control) was mixed and

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and Technology 46 (2007) 20–28

round rapidly in an ice bath. Fruit flesh (10 g) was taken outnd homogenized with 10 mL of 0.5 M Tris–HCl (pH 8.0) forectinesterase (PE) extraction, and with 10 mL of 0.1 M phos-hate buffer (pH 7.0) for polygalacturonase (PG) and cellulaset 4 ◦C. Tris–HCl solution was comprised of 1 mM CDTA,% polyvinylpyrrolidone (w/v) and 2 M NaCl; phosphateuffer contained 1 mM CDTA, 5% polyvinylpyrrolidone (w/v)nd 0.5 M NaCl. The mixtures were centrifuged at 8000 × gor 10 min at 4 ◦C. The supernatants were used for furtherssays.

Enzyme activities were determined immediately followingxtraction. Pectinesterase was assayed by the acid–base titra-ion procedure (Nagel and Patterson, 1967). One unit of enzymectivity was the amount of the enzyme required to hydrolyse�mol ester per min per g of original fresh flesh of pears.olygalacturonase activity was determined by measuring theeducing groups set free from citrus pectin (Sigma) accordingo the method described by Deng et al. (2005a). One unit ofnzyme activity was the amount of the enzyme required to form�mol of reducing groups per h per g of original fresh flesh ofears. Cellulase activity was assayed by measuring the reduc-ng groups released from carboxymethyl cellulose according tohe technique of Deng et al. (2005a). One unit of enzyme activ-ty was the amount of the enzyme required to form 1 �mol ofeducing groups per h per g of the original fresh weight of pearesh.

.4.5. Pectin and cellulose contentsThe extraction of pear pectin was based on the method

escribed by previous studies (Fang et al., 1991; Peng et al.,004) with little modification. The flesh of 5 pears was groundapidly in an ice cold bath with a mortar and pestle. Pearesh (5 g) was homogenized in 80% boiling ethanol (50 mL,0 min) using a blender to eliminate saccharides and to inacti-ate enzymes, then filtered with filter paper. The residue washen washed with 10 mL 95% ethanol and acetone, mixedith distilled water (40 mL), heated in a water bath (50 ◦C,0 min) and centrifuged (8000 g, 10 min). The content of water-oluble pectin was measured in the supernatant. 100 mL of 0.5 M2SO4 were added to the sediment and mixed. Then the mix-

ure was heated in a boiling water bath (1 h) and centrifuged8000 × g, 10 min); the content of protopectin was measuredn the supernatant. Total pectin content was obtained by addi-ion of protopectin and the water-soluble pectin. Pectin contentas determined by the m-hydroxydiphenyl method (Kintner andan Buren, 1982). Galacturonic acid (Fluka) was used as thetandard.

Cellulose extract was obtained as previously describedNing, 1998). Briefly, pear flesh (10 g) was removed fromhe mortar and stirred in 150 mL of 2% (v/v) hydrochlo-ic acid. The suspension was heated with a reflux exchanger3 h) to remove saccharides, hemicellulose and starch. Theesidue was consecutively washed with hot distilled water,

bsolute ethyl alcohol and ether to remove chloride ions andther compounds, then air-dried. Cellulose content was deter-ined utilizing the anthrone method, with d(+)-glucose as the

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.5. Statistical analysis

Statistical analyses were carried out using SAS 8.0. Variancenalysis was conducted for the root mean square (RMS) accel-ration of the front and rear positions of the truck floor. Leastignificant difference (LSD) was performed for the damaged

reas of pears, determined at the 95% level. Values are givens the average with standard deviation (S.D.) calculated fromhysical and chemical experiments in which each sample wasssayed for three replicates.

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ig. 2. Power density (PD) spectra at the two positions in the truck on highways (a),

d Technology 46 (2007) 20–28 23

. Results and discussion

.1. Vibration levels in transit

Fig. 2 and Table 2 show the main characteristics of vibrationevels of the front and rear truck floor along the entire route.

ccording to the results, the PD spectra of the two positions

n the truck were characterized by peaks in the 2.5–4 Hz rangend a second but lower peak between 15 and 40 Hz, with higheralues noted for the rear position in the truck and lower values

arterial roads (b), secondary roads (c), tertiary roads (d), and laterite roads (e).

24 R. Zhou et al. / Postharvest Biology and Technology 46 (2007) 20–28

Table 2Main route characteristics and frequency of peak values of power density (PD) spectra at the front and rear positions of the truck floor during transport

Type of road Speed (km/h) Duration (min) The frequency of peak in PD spectra (2–200 Hz) (Hz)

Average Max. Front position Rear position

Highway 70 80 60 4 3.5Arterial road 70 75 150 3 3STL

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or the front position. These data were confirmed by the spectraf different road conditions during transport. The peak in the.5–4 Hz range is in agreement with measurements of Hinscht al. (1993) and Slaughter et al. (1993) of vibrations at the bot-om boxes containing ‘Bartlett’ pears for loaded trucks equippedith steel-spring suspensions, even though these authors did noteasure peaks higher than 3.5 Hz for boxes at the bottom posi-

ion. A second peak around 9 Hz and a third peak around 18 Hzas only measured for boxes at the top position. However, the

econd peak between 15 and 40 Hz in our data (Fig. 2) is notresent in the results of Hinsch et al. (1993). Previous studiesave indicated that the PD spectra above 15 Hz for a loaded truckith leaf-spring suspensions mainly represents the responsesf tires, road roughness, the structure (floor), and drive trainJarimopas et al., 2005; Singh et al., 2006). The differences inur experiment conditions could contribute to the differences inhe vibration responses between 15 and 40 Hz.

Global RMS acceleration values were significantly differentp < 0.05) for the rear position of the truck floor (1.91 m/s2) andhe front position (1.62 m/s2) during the entire route, demonstrat-ng differences in vibration levels depending on the positions inhe truck. The differences in acceleration levels between the rearnd front truck floor were consistent with results of Berardinellit al. (2005), even though the truck they used was equipped withir-ride suspensions. Furthermore, during the entire route, theighest RMS acceleration value for the rear position in the truckas noted for tertiary roads (2.09 m/s2) and the lowest for high-ays (1.78 m/s2). However, the RMS acceleration value of the

ear position in the truck in this research was lower than theMS acceleration value measured by Hinsch et al. (1993) for

rucks with steel-spring suspensions during highway transport.his phenomenon could be due to the truck type, an important

actor which affects vibration levels of trucks during transportJarimopas et al., 2005); that used in this study was differentrom that which Hinsch et al. (1993) used.

.2. Evaluation of vibration damage to the pears

Table 3 gives the results of the evaluation of damage to pearsontained in the RPCs at the four positions in the truck afterransport. Darkened burnings of the skin and bruises with littler no penetration into the flesh were the main injuries to the

ruit during transport. The greatest damage was noted in pearsontained in the top RPC of the column at the rear position ofhe truck floor (p < 0.05). The average number of bruises and theercentage of damaged skin on the pears was still significantly

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ifferent between the rear top position and the front top positionp < 0.05). The results also showed that pears in top containersere more damaged than those in the bottom containers within

he same column (p < 0.05). According to Slaughter et al. (1993)his is due to the higher acceleration levels in the upper contain-rs. The accelerations in the upper containers were not measuredn our research.

.3. Color

Instrumental color measurements showed that L*, h* and C*

alues of the pears increased at the beginning of storage andnderwent a progressive decrease later during storage (Fig. 3).he skin color changed from a cyan and yellow color to a yellowolor, then to an orange and blue color in over-ripe samples.here was no significant difference in any color parameters of

he pears between the rear top and the front top positions inhe truck (p > 0.05). However, the control samples had betterolor maintenance, which higher L*, h* and C* values than thosehich suffered prolonged transit times. By day 36, the control

amples were 1.05–1.26 times higher in L* values, 1.43–1.49imes higher in h* values and 1.01–1.02 times higher in C* valueshan the pears in the rear top and the front top containers. Theseata demonstrated that fruit mechanically injured by transportibration had a higher rate of color change than intact fruit duringtorage in ambient temperatures.

.4. Relative electrical conductivity

Change in electrolyte leakage is an important indicator oflasma membrane integrity of cells which is related to the qualityf fruit (Deng et al., 2005b). The relative electrical conductivitiesf all the samples increased (Fig. 4), corresponding to the risen the electrolyte leakage from the skin cells of the pears duringtorage. The reason for the phenomenon was probably that thelasma membrane of fruit cells would tend to be unstable andonsequently lead to electrolyte leakage during storage (Feng etl., 2005).

Previous studies indicated that mechanical vibrationncreased the activities of malonyl dialdehyde (MDA) andipoxygenase, and accelerated tissue electrolyte leakage, whiched to over-ripe changes in kiwifruit during storage (Li et al.,

000). According to Fig. 4, higher levels of electrolyte leakagef the skin cells were noted with pears in the rear top containerhan pears in the front top container, supporting the idea that dif-erent vibration levels resulted in not only different degrees of

R. Zhou et al. / Postharvest Biology and Technology 46 (2007) 20–28 25

Table 3The average number of bruises and estimated percentage of damaged skin of Huanghua pears loaded in different positions of the truck after transport

Pears in the rear top RPC Pears in the rear bottom RPC Pears in the front top RPC Pears in the front bottom RPC

The average number of bruises 14.40 ± 0.45a 8.23 ± 0.50c 10.70 ± 0.22b 7.70 ± 1.22dThe percentage of damaged

skin on the pear surface (%)8.49 ± 0.24a 2.26 ± 0.11c 2.97 ± 0.23b 1.58 ± 0.08c

Values are expressed as mean ± S.D. Values within a line followed by the same letter

Fig. 3. Development of CIELAB values of pears during storage after transport.(a) Lightness (L*); (b) hue angle (h*); (c) chroma (C*). Control is the controlsamples, front top is pears contained in the front top RPC; rear top is pearscontained in the rear top RPC.

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are not significantly different (p > 0.05).

echanical damage, but different levels of cell content leakage inear skin during transport. Furthermore, it was expected that thencrease in cell leakage of fruit skin brings enzyme and substratesnto contact, which results in the browning of fruit (Jiang andhen, 1995). In that way, the cell leakage of pear skin affected

he appearance of fruit that experienced prolonged transit timeuring storage, although no clear differences in color parametersere observed between the pears contained in the front top and

ear top containers. Besides the cell leakage, the discolorationf fruit skin is also correlated to activities of polyphenoloxi-ase (PPO) and peroxidase (POD) and contents of anthocyanin,otal phenolics, and flavonoids (Zhang and Quantick, 1997).owever, the mechanism behind this phenomenon foruanghua pears is not well understood and is worth further

nvestigation.

.5. Firmness

The pear firmness decreased significantly during the periodquivalent to subsequent commercialization after transportFig. 5). The highest and lowest levels of firmness were notedith control samples and pears contained in the rear top con-

ainer, respectively. It was clear that fruit suffering less vibrationamage retained greater firmness. By day 36, the firmness ofhe control samples was 1.48–1.92 times higher than that of

hose experiencing prolonged transit times in the front-top andear-top RPC during storage. The firmness of fruit transportedn the rear top container had the fastest softening rate, losing2.5% of their firmness by day 18 while the fruit transported

ig. 4. Changes in electrolyte leakage of Huanghua pear skin during storagefter transport. Control is the control samples, front top is pears contained in theront top RPC; rear top is pears contained in the rear top RPC.

26 R. Zhou et al. / Postharvest Biology and Technology 46 (2007) 20–28

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ig. 5. Changes in firmness of Huanghua pears during storage after transport.ontrol is the control samples. Front top is pears contained in the front top RPC;

ear top is pears contained in the rear top RPC.

n the front top RPC lost only 20.1% of their firmness at theame time. These data demonstrated that more heavily injuredruit had a higher rate of softening during storage at ambientemperature.

.6. Activities of enzymes

During the subsequent storage after transport, enzyme activ-ties peaked then decreased (Fig. 6). The PE activity of the pearsndergoing severe transport vibration was higher than in the con-rol samples. After 27 days storage, the PE activity for the pearsransported in the rear top RPC was much higher than the activityf the pears contained in the front top RPC. Polygalacturonasectivity is responsible for pectin depolymerization and solubi-ization (Brummell and Harpster, 2001). In the current study,G activity of pears in the rear top RPC increased sharply in

he first 18 days storage and was higher than for other treatedruit. However, no clear differences in PG activity were observedetween the control samples and pears transported in the frontop RPC. Similarly, no clear differences in cellulase activity werebserved between control samples and the pears in the front topontainer, with the exception of assays performed on day 27, inhich pears that suffered heavier damage had higher cellulase

ctivity.Fruit softening during ripening has been attributed to the

ction of (among other things) pectic enzymes and cellulasen polysaccharides in the cell wall (Barnes and Patchett, 1976;an Buren, 1991; Lohani et al., 2004). Our data revealed thatigher vibration intensity during transport resulted in heav-er visible damage to fruit. Also, the data suggested thatechanical injuries to pears affected the hydrolase activity

Fig. 6). Additionally, the loss in firmness of all samples,uring storage, was found to vary consistently, and decrease

etween days 27 and 36, with the increase in enzyme activityFigs. 5 and 6), similar to what has been previously reported (Roend Bruemmer, 1981; Abu-Goukh and Bashir, 2003; Deng et al.,005a,b).

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ellulase (c) of Huanghua pears during storage after transport. Control is theontrol samples. Front top is pears contained in the front top RPC; rear top isears contained in the rear top RPC.

.7. Pectin and cellulose contents

The contents of protopectin, total pectin and cellulose

ecreased with increased storage time to varying degreesFig. 7). The decline in protopectin content was very fast, reach-ng 60.5–69.7% for all of the samples after 18 days storage.rotopectin levels were generally lower in pears in the rear top

R. Zhou et al. / Postharvest Biology an

Fig. 7. Changes in content of protopectin (a), total pectin (b), cellulose (c) ofHFt

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uanghua pears during storage after transport. Control is the control samples.ront top is pears contained in the front top RPC; rear top is pears contained in

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PC compared to those in the front top RPC or the controlamples. Total pectin content of pears in the rear top RPC wasenerally lowest. By day 36, the control fruit retained 1.17–1.98

imes higher content of total pectin than those of other sam-les. These results suggest that the exterior damage of pearsffected changes in the cell wall composition. Additionally, it islear that heavier damage levels caused by transport vibration

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d Technology 46 (2007) 20–28 27

esulted in faster catabolism of the pears. However, the influ-nces of transport vibration on the hydrolase activities of pearsere less convincing than their effects on the reduction in cellall contents during storage after transport.Softening during ripening in climacteric fruit, such as

uanghua pears, is generally attributed to degradation of theell wall and the decomposition of pectin (Lin et al., 2003;ohani et al., 2004). As shown in the results, the decline ofesh firmness was accompanied by the dramatic loss of pro-

opectin (87.4–91.1%), total pectin (65.7–79.1%) and cellulose19.2–22.6%) (Fig. 7). Previous studies indicated that there waslarge absence of protopectin as fruit softened and lost cohe-

ion in cell walls; the decrease of total pectin was positivelyorrelated with concomitant changes in tissue texture resultingrom catabolic enzyme activity (Nagel and Patterson, 1967; Roend Bruemmer, 1981; Van Buren, 1991). Moderate changes inhe cellulose content during storage after transport was probablyue to the fact that the crystalline nature of cellulose imparts aigh resistance to chemical or enzymatic degradation (Bartz andrecht, 2003; Deng et al., 2005a).

In the current research, the softening rate of Huanghuaears was associated with differences in external damage toears during transport, as well as with storage-related reduc-ion in protopectin, total pectin and cellulose. However, the

echanism responsible for the relationship between the vibra-ion damage to fruit during transport and the changes of fruitrmness in the subsequent storage is not clearly understood. Pre-ious researchers have stated that mechanical damage to fruitould affect quality appreciation of the consumer, and even amall bruise could provide a point of entry for decay organ-sms (Van Zeebroeck et al., 2006). The exposure of injury areaso the atmosphere has led us to suspect that oxidation (Wangnd Mellenthin, 1973), moisture loss and organisms might benvolved in fast deterioration of damaged fruit during storage.ing et al. (1998) indicated that transport vibration can affect

he physiological changes, further decreasing the quality of fruit.isible bruises and invisible cell-wall fractures caused by dif-

erent degrees of transport vibration induced changes in thectivity of hydrolases, which decomposed supporting materi-ls of cell walls. Depolymerization and degradation of cell wallolysaccharides in these fruit were accompanied by loss ofrmness.

. Conclusion

The current research showed that the vibration levels of theruck floor were different, and levels of the rear position wereigher than levels of the front floor along the entire route whichesulted in heavier damage to Huanghua pears loaded in theear top RPC than damage to the fruit in the front top RPCp < 0.05). Additionally, different levels of mechanical dam-ge to pears caused by different levels of transport vibrationffected the leakage of skin cells and cell wall decomposition

n tissue, which further influenced changes in appearance andrmness of the fruit and subsequent commercialization after

ransport. Given these data, we recommend the use of shockbsorption treatments to reduce mechanical damage to pears

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oaded at the rear position of the truck floor during transport andistribution.

cknowledgements

This work is the main part of the project ‘Research and Devel-pment of Fresh Produce Modern Logistics Technology andrading Demonstration’ (2004BA527B) financed by Ministry ofcience and Technology of China. The authors thank L. Wang, J.ang and T.T. Yin for assistance in performing the experiments.

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