EFFECT OF POSTHARVEST SHORT HOT-WATER RINSING AND BRUSHING TREATMENT ON DECAY AND QUALITY OF STRAWBERRY FRUIT

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1 jfq_ EFFECT OF POSTHARVEST SHORT HOT-WATER RINSING AND BRUSHING TREATMENT ON DECAY AND QUALITY OF STRAWBERRY FRUIT W. JING 1,K.TU 1,3, X.F. SHAO 1, Z.P. SU 1, Y. ZHAO 1,S.WANG 2 and J. TANG 2 1 Key Laboratory of Food Proessing and Quality Control of Ministry of Agriulture College of Food Siene and Tehnology Nanjing Agriultural University Nanjing , P. R. China 2 Department of Biologial Systems Engineering Washington State University PO Box , Pullman, WA Reeived for Publiation February 18, 2008 Aepted for Publiation November 18, 2008 ABSTRACT Strawberry (Fragaria ananassa) v. Feng xiang was treated with hot water rinsing and brushing (HWRB) at 20C (ontrol), 55C (HWRB-55), 60C (HWRB-60) and 65C (HWRB-65) for 20 s. The effet of these heat treatments on fruit deay and quality was investigated after either ambient temperature storage (20C) for 3 days or old storage (0C) for 12 days. Results showed that HWRB treatments ould signifiantly redue the epiphyti mirobial population on fruit surfae, deay development and weight loss. Fruits treated with HWRB-65 had the lowest deay inidene and deay index, but about 60% of the treated fruits showed heat damage and beame ommerially unaeptable. Fruits treated with HWRB-60 showed less deay than the ontrol fruits, and old storage ould enhane the effet of HWRB treatments. There were no negative effets of HWRB-60 on fruit surfae olor, firmness, soluble solids ontent and titratable aidity. PRACTICAL APPLICATIONS This researh investigated the effets of hot water rinsing and brushing (HWRB) treatments on deay and quality of strawberry fruit, whih was suseptive of deay. HWRB treatments at 60C for 20 s signifiantly redued 3 Corresponding author. TEL: ; FAX: ; kangtu@ njau.edu.n 262 Journal of Food Quality 33 (2010) DOI: /j x 2010 Wiley Periodials, In.

2 DECAY AND QUALITY OF STRAWBERRY 263 fruit deay, did not affet its quality and ould be suggested as a potential postharvest heat treatment on strawberry fruit. On a ommerial sale, this short HWRB treatment would be a desirable method for treating freshly harvested produe to maintain fruit quality during postharvest period. Future work on exploring HWRB tehnology to a broader range of freshly harvested ommodities with improved fruit quality and meeting the quarantine requirements, will help the fruit industry to develop environmentally friendly and tehnially effetive HWRB tehnologies, and possibly redue the urrent extensive reliane on hemial pestiides. INTRODUCTION Strawberry (Fragaria ananassa) is an important berry fruit beause of its high nutritional and ommerial value. The disadvantage of that fruit inludes short storage life, a result of deay aused by fungi pathogens and quik softening rate. The suseptibility of freshly harvested strawberries to postharvest diseases inreases during storage and enables pathogens to develop in the fruits (Viente et al. 2006). Currently, the harvested fruit are ommonly treated by a variety of fungiides to maintain the produt quality. With several negative effets of hemial fungiides on food safety and environment, there is an urgent need to develop an alternative nondamaging physial treatment to hemial fungiides. Postharvest heat treatment offers a pestiide-free method to kill or weaken plant pathogens, ontrol inset infestations and maintain fruit storage quality (Barkai-Golan and Phillips 1991; Shao et al. 2007). A new tehnology has been proposed for simultaneously leaning and disinfeting fruits using hot water rinsing and brushing (HWRB). Reently, HWRB treatments are studied extensively beause of their higher temperature and shorter exposure time than traditional hot water immersions or dips. HWRB treatments ould not only remove the heavy dirt, pestiides and fungal spores on the freshly harvested produe, but ould also improve general produt appearane and maintain produt quality (Fallik 2004). Beause this tehnology has been designed to be a part of the ommerial paking house sorting line and suessfully used on the postharvest fresh-keeping treatment of sweet pepper (Fallik et al. 1999) and mango (Prusky et al. 1999), HWRB treatments would be desirable for treating freshly harvested produe on a ommerial sale (Porat et al. 2000a). There have been many studies on the appliation of hot water immersions and dips on strawberry to ontrol deay and maintain fruit quality (Garía et al. 1995; Couey and Follstad 1996; Viente et al. 2003). To our knowledge, however, there is little report on the effet of HWRB treatments on strawberry

3 264 W. JING ET AL. under different storage onditions. Thus, the purpose of our study was to examine the effet of HWRB treatments on the deay and quality of strawberry fruits and determine whether HWRB treatments are suitable to be used as pratial postharvest treatments and ommerial implementations for strawberry fruit. MATERIALS AND METHODS Materials and Treatments Strawberries (F. ananassa Feng xiang ) were harvested from a ommerial orhard in Nanjing, Jiangsu Provine, China. The fruits were then paked into fiberboard artons and transferred to the laboratory on the same day. Uniform size and damage-free fruits at the ripening stage, with 50~70% of the fruit surfae showing red, were piked out and randomly distributed into four bathes; eah bath ontained 200 fruits. Three bathes of fruits were applied with HWRB treatment at 55C (HWRB-55), 60C (HWRB-60) and 65C (HWRB-65), respetively, for 20 s, and then allowed to dry in air as desribed by Fallik (2004). As a ontrol, the fourth bath of fruits was rinsed and brushed with tap water (20C) for 20 s. After HWRB treatments, one-half of eah bath of fruits was kept at 20 1C for 3 days (ambient temperature storage) and another half was kept at 0 1C for 12 days (old storage). The relative humidity (RH) was 90 5% at both storage onditions. The epiphyti mirobial population of strawberry fruits surfaes was assessed immediately after HWRB treatments. Fruit deay inidene, deay index, weight loss, firmness, soluble solids ontent (SSC), titratable aidity (TA) and olor values of L*, a* and H were assessed before and after storage. Effet of HWRB Treatments on Epiphyti Mirobial Population The epiphyti mirobial population was measured as desribed by Fallik et al. (2000). After HWRB treatments, three fruits were piked out from eah bath of ontrol, HWRB-55, HWRB-60 and HWRB-65 to examine for the epiphyti mirobial population. Eah fruit was immersed into 150 ml of sterile distilled water ontaining 0.03% Tween-20 and inubated for 10 min on a shaker (TY-80; Nanda Biologial Development Company, Jiangsu, China). Serial dilutions up to 10-5 were prepared and 100 ml of eah dilution were plated in Petri dishes ontaining potato dextrose agar amended with 250 mg/l of hlorampheniol to inhibit baterial growth. The number of olony-forming units (CFU) was expressed as log 10 fu/fruit.

4 DECAY AND QUALITY OF STRAWBERRY 265 Effet of HWRB Treatments on Fruit Deay Inidene and Deay Index After the ambient temperature or old storage, the perentage of deayed fruits and deay severity was determined. Fruit deay inidene was represented as the perentage of deayed fruits over 30 fruits in total in eah treatment. Whole fruit deay originating from quiesent infetions was evaluated subjetively by a modifiation of the method of Fallik et al. (1993) and sored as 0 (no deay development); 1 (one to three small spots of berry deayed); 2 (one-quarter to one-half of berry deayed); 3 (one-half to threequarters of berry deayed); and 4 (three-quarters to whole fruit rotted). Results were expressed as deay index: Deay index = ( 0 fruit number of 0+ 1 fruit number of fruit number of 2+ 3 fruit number of fruit number of 4) 30 Effet of HWRB Treatments on Fruit Quality Attributes Thirty fruits of eah bath were used for measurement of weight loss. The fruits were weighted and the results were expressed as perentage of weight loss over the initial value (Viente et al. 2003). Ten fruits of eah treatment were used to measure both olor and firmness. Two readings per fruit were taken on opposite heks of the strawberry. Firmness was measured with a tester (FT-327, Fruit Pressure Tester, Alfonsine, Italy) using a 0.78-m diameter tip. Results were expressed as kg/m 2. External olor of fruit was measured with a Minolta Chromameter (Model CR-300; Minolta, Tokyo, Japan) in CIE L* a* b* mode under CIE Standard Illuminant C. Changes in hue angle ( H) were alulated as H = artan b*/a* ( ). SSC and TA were measured with juie obtained from 30 fruits per treatment by a method modified from Lara et al. (2006). SSC was determined with a hand refratometer (WYT-4; Quanzhou Optial Instrument Co. Ltd, Quanzhou, China), and results were expressed as perent soluble solids in juie at 20C. A 10-mL aliquot of the filtered fruit juie was diluted with 50 ml distilled water, and the dilution was titrated with 0.1N NaOH to ph 8.1. TA results were expressed as perent of itri aid. Statistial Analysis All the tests were repeated three times and the means with standard errors of the three experimental results were presented. Results were analyzed using one-way analysis of variane and Dunan s multiple range test at P = 0.05 with SAS 8.2 (SAS institute, Cary, NC).

5 266 W. JING ET AL. RESULTS AND DISCUSSION Effets of HWRB Treatments on Epiphyti Mirobial Population, Deay Inidene and Deay Index of Strawberry Fruits Compared with the ontrol, all the HWRB treatments signifiantly redued the epiphyti mirobial populations on the fruit surfae and an additional 0.31, 1.52 and 1.71 log redutions in the population of epiphyti miroorganisms were observed after hot water rinsing and brushing at 55, 60 and 65C, respetively (Fig. 1) (P < 0.05). Other studies (Fallik et al. 2000) found that HWRB ould simultaneously lean the disinfeted Galia melon, resulting in surfae free from spores and dust partiles. Moreover, in organi itrus fruit subjeted to HWRB treatments, platelets flattened while rak and most stomata appeared partially or ompletely plugged by melted wax, thereby providing a mehanial barrier against wound pathogens (Porat et al. 2000a). HWRB treatments showed different effets on reduing deay inidene (Fig. 2). After ambient temperature storage, 70.0% of ontrol fruits deayed, while 63.3%, 51.7% and 53.3% of HWRB treated fruits deayed at 55C, 60C and 65C, respetively. After old storage, all HWRB treated fruits showed a b Log 10 CFU/Fruit Control HWRB-55 HWRB-60 HWRB-65 Treatment FIG. 1. EFFECT OF HWRB TREATMENTS ON THE EPIPHYTIC MICROBIAL POPULATIONS (fu) OF STRAWBERRBY FRUITS AFTER TREATMENT FOR 20 S AT 20C (CONTROL), 55 (HWRB-55), 60C (HWRB-60) OR 65C (HWRB-65) Means of three independent treatments followed by the same letter are not signifiantly different at P = 0.05 aording to analysis by Dunan s multiple range tests. Vertial bars represent standard errors of the mean over three independent repliates. HWRB, hot water rinsing and brushing.

6 DECAY AND QUALITY OF STRAWBERRY 267 Deay inidene % a b a b Control HWRB-55 HWRB-60 HWRB After 3 days' ambient temperature storage After 12 days' old storage d FIG. 2. EFFECTS OF HWRB TREATMENTS ON DECAY INCIDENCE OF STRAWBERRY FRUITS FOR 20 S AT 20C (CONTROL), 55 (HWRB-55), 60C (HWRB-60) OR 65C (HWRB-65) AFTER AMBIENT TEMPERATURE OR COLD STORAGE Means of three independent treatments followed by the same letter are not signifiantly different at P = 0.05 aording to analysis by Dunan s multiple range tests. Vertial bars represent standard errors of the mean over three independent repliates. HWRB, hot water rinsing and brushing. lower deay inidene (0 22.2%) as ompared with 58.6% of ontrol fruits. Similarly, HWRB treatments ould signifiantly (P < 0.05) redue the deay index (Fig. 3). The deay development was signifiantly redued after a 20 s HWRB treatment at 55C, and the prevention effet of deay was enhaned by 60C and 65C HWRB treatments (P < 0.05) (Fig. 3). This was probably beause the HWRB treatment effetively disinfeted the fruit from pathogeni fungi through high temperatures at 60 65C. On the other hand, HWRB treatments also made a lear redistribution of the epiutiular wax layer, whih prevented the pathogen penetration. The exposure time of fruit to HWRB treatments lasted only seonds, rather than minutes or hours of traditional heat treatments, yet these former treatments were suffiient to indue heat resistane of ertain fruits against pathogen infetion. Porat et al. (2000b) reported that 59C or 62C 20 s HWRB indued aumulation of pathogen-related proteins suh as hitinase, b-1, 3-gluanase and heat shok proteins (Fallik et al. 1993). Further studies are still needed to explore whether there existed other indued heat resistane on strawberry fruit by HWRB treatments.

7 268 W. JING ET AL. 3 a b Control HWRB55 HWRB60 HWRB65 2 Deay index a 1 b 0 After 3 days' ambient temperature storage b After 12 days' old storage FIG. 3. EFFECTS OF HWRB TREATMENTS ON DECAY INDEX OF STRAWBERRY FRUITS FOR 20 S AT 20C (CONTROL), 55 (HWRB-55), 60C (HWRB-60) OR 65C (HWRB-65) AFTER AMBIENT TEMPERATURE OR COLD STORAGE Means of three independent treatments followed by the same letter are not signifiantly different at P = 0.05 aording to analysis by Dunan s multiple range tests. Vertial bars represent standard errors of the mean over three independent repliates. HWRB, hot water rinsing and brushing. Results of our study showed that 20 s HWRB treatment at 65C damaged about 60% of strawberry fruits, in whih shrinking of the outer layers epiarps ourred, while fruits treated with 55C or 60C HWRB treatment had no heat damage. This was in good agreement with the observed heat damage on HWRB-treated fruit generally at temperatures above 60C (Fallik 2004). High temperatures of treatment might ause surfae damage in speifi suseptible itrus ultivars (Mulas et al. 1997; Shirra and D hallewin 1997; Porat et al. 2000a), but it may have some positive effets (Fallik et al. 2000; Porat et al. 2000b), and these diverse responses of fruits to heat treatments might be aused by differenes among heating proedures and ultivars. Effets of HWRB Treatments on Postharvest Quality of Strawberry Fruits HWRB treatments signifiantly redued the weight loss of fruits after ambient temperature storage (P < 0.05), but there was no signifiant differene between HWRB-treated and ontrol fruits after old storage (P > 0.05) (Table 1).

8 DECAY AND QUALITY OF STRAWBERRY 269 TABLE 1. EFFECTS OF HWRB TREATMENTS ON POSTHARVEST QUALITY OF STRAWBERRY FRUITS FOR 20 S AT 20C (CONTROL), 55 (HWRB-55), 60C (HWRB-60) OR 65C (HWRB-65) BEFORE STORAGE OR AFTER AMBIENT TEMPERATURE OR COLD STORAGE Storage ondition Treatments Weight loss (%) Firmness (kg/m 2 ) SSC (%) TA (%) Before storage Control 0.00 a 1.80 a 7.69 a 1.16 b HWRB a 1.73 a 7.96 a 1.23 b HWRB a 1.74 a 7.89 a 1.21 b HWRB a 1.78 a 7.76 a 1.32 a 3 days ambient storage Control 1.61 a a 1.15 a HWRB b 2.00 a 7.06 a 1.12 ab HWRB b 1.90 b 6.91 a 1.12 ab HWRB a 7.11 a 1.11 a 12 days old storage Control 1.86 ab 1.95 a 6.69 ab 0.94 ab HWRB a 2.06 a 6.99 ab 1.11 a HWRB ab 2.05 a 6.99 ab 1.07 a HWRB b 2.01 a 7.16 a 1.11 a Means of three independent samples within a olumn and within a day followed by the same letter are not signifiantly different at P = 0.05 aording to analysis by Dunan s multiple range tests. HWRB, hot water rinsing and brushing; SSC, soluble solids ontent; TA, titratable aidity. After HWRB treatments, the heat-treated fruits showed low firmness when ompared with the ontrol, but the differene was not signifiant before storage (P > 0.05) (Table 1). The firmness of ontrol fruits had no obvious hanges after storage, but those of heat-treated fruits had higher firmness than ontrol after ambient temperature storage (P < 0.05). There was no signifiant differene of firmness between the three treatments after old storage (P > 0.05) although they were slightly higher than the ontrol. Thus, HWRB treatments inreased fruit firmness after ambient storage and these results were in aordane with hot water-dipped strawberry (Garía et al. 1995). The higher firmness value of heat-treated fruit ould be due to the diminution of ell wall degrading enzymes, aused in turn by the delay of ripening (Pan et al. 2004). Lara et al. (2006) also reported that heat treatments preserved strawberry fruit firmness. There was no signifiant differene of SSC, TA and superfiial olor indexes (L*, a* and H) between ontrol and HWRB-treated fruits before and after storage (P > 0.05) (Table 2). Consequently, these results suggested that HWRB treatments signifiantly redued fruits deay by reduing the epiphyti mirobial population, espeially at HWRB-60 and HWRB-65 treatments. HWRB treatments also inhibited fruits weight loss, but 60% of HWRB-65 treated fruits showed heat damage and lost ommerial value. On the other hand, HWRB-60 treated

9 270 W. JING ET AL. TABLE 2. EFFECTS OF HWRB TREATMENTS ON COLOR INDEX OF STRAWBERRY FRUITS FOR 20 S AT 20C (CONTROL), 55 (HWRB-55), 60C (HWRB-60) OR 65C (HWRB-65) BEFORE STORAGE OR AFTER AMBIENT TEMPERATURE OR COLD STORAGE Storage ondition Treatments Value of L* Value of a* Value of H Before storage Control ab b a HWRB ab ab ab HWRB b b a HWRB a b b 3 days ambient storage Control a a a HWRB a a a HWRB a a a HWRB a a a 12 days old storage Control a a a HWRB b a a HWRB b a a HWRB b a a Means of three independent samples within a olumn and within a day followed by the same letter are not signifiantly different at P = 0.05 aording to analysis by Dunan s multiple range tests. HWRB, hot water rinsing and brushing. fruits had lower deay development than ontrol and HWRB-55 treated fruits, and did not affet fruits external quality and ontents of SSC and TA. This suggested that the HWRB treatment at 60C for 20 s provided a potential heat treatment for postharvest deay ontrolling of strawberry fruits. ACKNOWLEDGMENTS The authors are grateful to National Siene Foundation of China (NSFC) Projet for the finanial support of this researh. REFERENCES BARKAI-GOLAN, R. and PHILLIPS, D.J Postharvest heat treatment of fresh fruits and vegetables for deay ontrol. Plant Dis. 75, COUEY, H.M. and FOLLSTAD, M.N Heat pasteurization for ontrol of postharvest deay in fresh strawberries. Phytopathology. 56, FALLIK, E Prestorage hot water treatment (immersion, rinsing and brushing). Postharvest. Biol. Tehnol. 32,

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