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Effect of chitosan coating combined with pomegranate peel extract on the quality of Pacific white shrimp during iced storage
Food Control 59 (2016) 818e823
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Food Control journal homepage: www.elsevier.com/locate/foodcont
Effect of chitosan coating combined with pomegranate peel extract on the quality of Pacific white shrimp during iced storage Gaofeng Yuan, Hua Lv, Wenyan Tang, Xiaojuan Zhang, Haiyan Sun* Key Laboratory of Health Risk Factors for Seafood of Zhejiang Province, Zhejiang Ocean University, Zhoushan, Zhejiang 316022, China
a r t i c l e i n f o
a b s t r a c t
Article history: Received 24 March 2015 Received in revised form 9 July 2015 Accepted 10 July 2015 Available online 13 July 2015
The effect of chitosan coating combined with pomegranate peel extract (PPE) on the melanosis and quality of Pacific white shrimp (Litopenaeus vannamei) during 10 days of iced storage was investigated. The melanosis and changes of total color difference (DE values) were significantly retarded, and the texture parameters and sensory scores were significantly improved in shrimp treated by chitosan coating, PPE and chitosan coating combined with PPE, compared with the control. The increase in total aerobic plate counts, pH and total volatile basic nitrogen values were significantly inhibited in shrimp treated with chitosan coating, PPE and chitosan coating combined with PPE. The melanosis and sensory scores, total volatile basic nitrogen values, and total aerobic plate counts of shrimp treated by chitosan coating combined with PPE were lower than those treated by chitosan coating or PPE alone during the later stage of iced storage, suggesting that there is a synergistic effect between chitosan coating and PPE. © 2015 Elsevier Ltd. All rights reserved.
Keywords: Pacific white shrimp Melanosis Quality Chitosan Pomegranate peel extract
1. Introduction Due to the high market value and nutrition value, shrimp is a very important food resource all over the world. Pacific white shrimp (Litopenaeus vannamei) is native to the Pacific coast of Mexico and now a variety of prawn of the world commonly caught or farmed for food. To date, the world's main producer of Pacific white shrimp is China with production levels of approximately 1,120,000 tons in 2010 (Wang et al., 2014). However, the shelf life of shrimp was limited due to melanosis and microbiological deterioration of shrimp during storage. Melanosis or blackening, the formation of black spots in crustaceans, such as shrimp and crabs during postmortem storage, severely damage the market value and usually caused economical loss of these seafoods (Kim, Marshall, & Wei, 2002). To retard the melanosis in crustaceans and ensure perishables have a longer shelf life, antimelanosic agents, such as 4-hexyl-1,3benzenediol (4-hexylresorcinol), sulphite-based compounds, and phosphates, have been intensively studied and proved to be effective to inhibit melanosis (Martinez-Alvarez, Lopez-Caballero, Montero, & Gomez-Guillen, 2005; Thepnuan, Benjakul, &
* Corresponding author. Key Laboratory of Health Risk Factors for Seafood of Zhejiang Province, Zhejiang Ocean University, Zhoushan, Zhejiang 316022, China. E-mail address: [email protected] (H. Sun). http://dx.doi.org/10.1016/j.foodcont.2015.07.011 0956-7135/© 2015 Elsevier Ltd. All rights reserved.
Visessanguan, 2008). However, the use of synthetic compounds to inhibit melanosis in seafood is limited due to increasing regulatory attention and their potential toxicity (McEvily, Iyengar, & Otwell, 1991). Due to the potential health hazards of chemical additives, natural products, especially natural antioxidants and antimicrobial agents, have been intensively examined as safe alternatives to synthetic compounds (Encarnacion, Fagutao, Hirono, Ushio, & Ohshima, 2010; Maqsood, Benjakul, & Shahidi, 2013). Recently, a series of studies conducted on the utilization of natural extracts to delay melanosis formation and extend the shelf life of seafood (Fang, Sun, Huang, & Yuan, 2013; Nirmal & Benjakul, 2011a, 2011c; Sun, Lv, Yuan, & Fang, 2014). It has been reported that pomegranate peel and peel extract (PPE) had significant free radical scavenging, anti-microbial, antiatherogenic and antimutagenic properties (Akhtar, Ismail, Fraternale, & Sestili, 2015; Hasnaoui, Wathelet, & Jimenez-Araujo, 2014). PPE also inhibited the formation of melanosis and improve the quality of Pacific white shrimp during iced storage (Basiri, Shekarforoush, Aminlari, & Akbari, 2015; Fang et al., 2013). These findings have led to increased interest in PPE. Chitosan, a cationic polysaccharide consisting of (1,4)-linked-2amino-deoxy-b-D-glucan, is the deacetylated form of chitin. Chitosan, which has attracted attention as a potential food preservative of natural origin, has been classified as a GRAS by the US FDA in 2001 (Sagoo, Board, & Roller, 2002). Chitosan has been broadly applied to the preservation of seafood products including oysters,
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sardine, salmon, sea bass, and silver carp duo to its non-toxic feature, antimicrobial and antifungal activities, biodegradability and biocompatibility, film-forming property (Cao, Xue, & Liu, 2009; Mohan, Ravishankar, Lalitha, & Gopal, 2012; Qiu, Chen, Liu, & Yang, 2014; Ramezani, Zarei, & Raminnejad, 2015). Chitosan also has been found to be effective in enhancing the quality and shelf life of shrimp (Huang, Chen, Qiu, & Li, 2012; Wang et al., 2014; Wu, 2014). However, to our knowledge, there is no literature reported the influence of chitosan coating combined with PPE on the shelf life and quality of seafood. The purpose of the present study was to evaluate the effect of chitosan coating combined with PPE (chitosan coating þ PPE) on the quality of Pacific white shrimp during iced storage. 2. Materials and methods 2.1. Preparation of pomegranate peel extract and coating solution The dried pomegranate peel was powdered using a mixer grinder and 200-g portions of finely-powdered pomegranate peel was blended with 50% ethanol for 2 h at 40 C in a shaking water bath. The ratio pomegranate peel powder: solvent was 1:10 (w/v). The extracts were through Waterman No. 1 filter paper (SigmaeAldrich Co., St. Louis, MO, USA) and concentrated under vacuum with a rotary evaporator (Eyela, Rikakikai, Tokio, Japan). The concentrate was dried overnight in an oven at 40 C to form powder which was stored at 4 C until further use. The 1.5% of PPE dipping solution was prepared by dissolving PPE in distilled water. Chitosan were purchased from Shanghai Jinsui Biotechnology Company (Shanghai, China). The degree of deacetylation of chitosan was 90% and the average molecular weight of chitosan was 25 kDa. Chitosan (10 g) was added to 1000 mL of 1% acetic acid and stirred for 1 h at room temperature to obtain 1% of w/w chitosan/ acetic acid solutions. 2.2. Shrimp collection and treatments Pacific white shrimp with the size of 50e55 shrimps/kg were purchased from a local market in Zhoushan, China. The shrimp were kept alive and transported to our laboratory. The shrimp were randomly assigned into five groups including the control (uncoated) group, PPE group, chitosan coating group, chitosan coating þ PPE group and sodium metabisulfite (SMS) group. The shrimp in the PPE group and chitosan group were dipped into the 1.5% of PPE and 1% of chitosan solutions at a shrimp/solution ratio of 1:2 (w/v) at 4 C for 30 min, respectively. After dipping, the shrimp were drained at ambient temperature for 3 min. The shrimp in the chitosan coating þ PPE group were immersed into the 1.5% of PPE at a shrimp/solution ratio of 1:2 (w/v) at 4 C for 30 min. After that, they were dipped into 1% of chitosan solutions at a shrimp/ solution ratio of 1:2 (w/v) at 4 C for 30 min, and then were drained at ambient temperature for 3 min. Another portion of shrimp was treated in 1.25% of SMS dissolved in distilled water at a ratio of 1:2 (w/v) for 1 min at 4 C. The samples from each treatment were covered in plastic bags and stored in ice using a shrimp/ice ratio of 1:2 (w/w). To maintain the shrimp/ice ratio, molten ice was removed and replaced with an equal amount of ice every 2 d. 2.3. Melanosis assessment Melanosis assessment of Pacific white shrimp was conducted through visual inspection by six panelists using ten-point scoring according to the method of Montero, Avalos, and Perez-Mateos (2001). Panelists were asked to give the melanosis score (0e10) for shrimp, where 0 ¼ absent; 2 ¼ slight (up to 20% of shrimps'
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surface affected); 4 ¼ moderate (20%e40% of shrimps' surface affected); 6 ¼ notable (40%e60% of shrimps' surface affected); 8 ¼ severe (60%e80% of shrimps' surface affected); 10 ¼ extremely heavy (80%e100% of shrimps' surface affected). Samples were taken for each treatment every 2 d up to 10 d for melanosis assessment. 2.4. Color measurements of shrimp shells The color of shrimp was measured by using an automatic color difference meter (DC-P3, Shanghai Go On Chemical Co., Ltd., Shanghai, China) according to the method of Zhang, Ma, Deng, Xie, and Qiu (2015). L* (lightness) represents the brightness on a scale of 0 (dark) to 100 (white), a* (redness) scale ranges from negative values for green to positive values for red and b* (yellowness) scale ranges from negative values for blue to positive values for yellow. Color was determined in three zones (head, body and tail) on the shrimp shell. For each sample, triplicate measurements were taken at each shell zone and the average values of six samples were recorded. Total color differences (DE values), which indicate the magnitude of color difference between shrimps at the beginning of storage and after the storage period, were calculated using following equation: DE ¼ [(L* L*0)2 þ (a* a*0)2 þ (b* b0*)2]1/2, where L*0, a*0, and b*0 are the values of L*, a*, and b* color parameters at the beginning of storage. 2.5. Texture profile analysis A texture analyzer (TMS-PRO, FTC, Sterling, VA, USA) was used to evaluate the texture (hardness and springiness) of shrimp muscle samples according to the method of Zhang et al. (2015). The texture profile analysis (TPA) at room temperature (25 C) and performed under the following conditions: constant test speed, 1.0 mm/s; sample deformation, 50%; hold time between cycles, 3 s; and trigger force, 0.05 N. Texture analysis parameters were calculated using FTC-PRO software from the forceetime curves generated from each sample. All measurements were carried out on six different single shrimp specimens, and the average value was obtained. 2.6. Sensory evaluation Sensory evaluation of shrimp samples was performed by a group of six trained panelists according to the methods of Wu (2014). Panelists were regular consumers of shrimp and had no allergies to shrimp. Panelists were asked to evaluate appearance, odor, texture, flavor, and overall acceptability of shrimp samples. A rating was assigned separately for each parameter on a 1 to 9 descriptive hedonic scale, with 9 as the highest-quality sample. 2.7. Chemical analyses The pH values were measured in shrimp according to the method of Lopez-Caballero, Martinez-Alvarez, Gomez-Guillen, and Montero (2007). Total volatile basic nitrogen (TVB-N) was determined on steam distillation of trichloroacetic acid-shrimp extract with the Kjeltec 8400 Automatic Kjeldahl Nitrogen Determination apparatus (Foss, Sweden) in triplicates. The TVB-N values were expressed as mg N/100 g shrimp meat. 2.8. Microbiological analysis Microbiological analysis was performed according to the Chinese National Standard (GB4789.2-2010) by measurement of the total bacteria amounts indicated as total aerobic plate counts
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(TPC). Twenty-five grams of shrimp were homogenized with 225 mL of 0.85% of sterile saline water at 8000 rpm for 1 min. Samples were serially diluted logarithmically in 0.85% of sterile saline water. TPC was determined by spread plating samples on nutrient agar and incubating at 36 C for 48 h. Microbial colonies were counted and reported as log CFU/g of fresh weight. 2.9. Statistical analysis Statistical analysis was performed using the SPSS package program version 11.5 (SPSS inc. Chicago, IL, USA). Data was analyzed by one-way ANOVA, followed by Turkey's HSD multiple comparison test. The values are reported as means with their standard error for all results. Differences were considered significant at p < 0.05. 3. Results and discussion 3.1. Melanosis Fig. 1 shows the melanosis scores of Pacific white shrimp. The melanosis in all treatments was significantly increased during iced storage. This result indicated that there was rapid loss in visual quality occurred in Pacific white shrimp during iced storage, which is similar to our previous studies (Fang et al., 2013; Sun et al., 2014). The melanosis in Pacific white shrimp treated by chitosan coating, PPE and chitosan coating þ PPE was significantly inhibited (p < 0.05), compared with the control. In addition, the score of melanosis of Pacific white shrimp treated by chitosan coating þ PPE was less than those treated by PPE or chitosan coating alone. Previous studies have shown that natural extracts or natural compounds could inhibit the melanogenesis of shrimp during iced storage (Encarnacion et al., 2010; Encarnacion et al., 2011; Fang et al., 2013; Nirmal & Benjakul, 2009b, 2010, 2011b). Our previous study showed that melanosis was significantly inhibited in the Pacific white shrimp treated with various concentration of PPE (Fang et al., 2013). Recently, Basiri et al. (2015) also observed that PPE-treated shrimp obtained lower melanosis score during 6 days of storage under refrigeration. The present study further confirmed that PPE had inhibition effect on the melanosis of Pacific white shrimp.
Fig. 1. Combined effect of chitosan and pomegranate peel extract on melanosis scores of Pacific white shrimp during iced storage. Each data is the mean values per treatment and time point (mean ± standard error). SMS, sodium metabisulfite; PPE, pomegranate peel extract.
The present findings are in agreement with those of Huang et al. (2012) and Wang et al. (2014) who reported that the application of chitosan coatings was effective to retard melanosis in shrimp during storage. The retard of melanosis in shrimp treated by chitosan coating may be attributed to certain chitosan functional properties, such as being an antioxidant, an antimicrobial agent, and an oxygen barrier (Huang et al., 2012). In addition, chitosan coating þ PPE was more effective than chitosan coating or PPE alone in the retard of melanosis in shrimp, suggesting that there is a synergistic effect between chitosan coating and PPE.
3.2. Color Color is one of the quality parameters for freshness. DE values， which indicate the magnitude of color difference between shrimps at the beginning of storage and after the storage period, are shown in Fig. 2. Generally, there was a gradual increase in the DE values of shrimp among the five groups with the storage time increasing. Interesting, a significantly fluctuated DE values in shrimp treated during the whole storage by chitosan coating were observed (p < 0.05) wherein the data spread exhibited a wavelike pattern, which is in agreement with that of Okpala, Choo, and Dykes (2014). The DE values in shrimp treated by chitosan coating, PPE and chitosan coating þ PPE were significantly lower (p < 0.05) than that in control shrimp during iced storage. Thus, treatments with chitosan coating, PPE and chitosan þ PPE coating could delay the change of color of shrimp in the present study. However, there was no significant difference on the DE values of shrimp treated by chitosan coating, PPE and chitosan coating þ PPE, besides the DE value in shrimp treated by chitosan coating at the 6th day of storage was significantly lower than that treated by PPE and chitosan coating þ PPE.
3.3. Texture profile analysis Hardness is the most critical textural attribute in meat or seafood. In general, the hardness of Pacific white shrimp in all five treatments was significantly decreased during iced storage (Fig. 3A). However, the hardness of shrimp treated by PPE, chitosan coating and chitosan coating þ PPE at the 6th, 8th and 10th day of
Fig. 2. Combined effect of chitosan and pomegranate peel extract on the DE values of Pacific white shrimp during iced storage. Means in the same storage day with different letter are significantly different (p < 0.05). Key: see the caption for Fig. 1.
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at the 8th and 10th day of storage was significantly improved (p < 0.05) as compared with that of the control shrimp. Compared with control shrimp, the highest springiness values (p < 0.05) were also observed in that treated by chitosan coating þ PPE at the 10th day of storage. The change of texture parameters was one of the major components of acceptability and influenced by several factors, such as the rate and extent of postmortem pH decline, muscular protein arrangement. The principal muscle components responsible for the texture change are the myofibrillar and connective tissue proteins in shrimp. The present findings are in agreement with that of Wang et al. (2014) who observed that application of chitosan coatings was effective to retard the change of texture parameters in shrimp during storage. The bonds between chitosan and myofibrillar proteins could be associated with the improvement of texture properties in shrimp muscle, with the final structure formed by both covalent and noncovalent interactions. In addition, the textural effect in seafood is also due to microbiological processes caused by the death of the seafood, which bring degradation of myofibrillar protein, following softening of the muscle. Li, Li, Hu, and Li (2013) showed that grape seed extract and tea polyphenols, which are rich in polyphenolic compounds, could extend the shelf life and improve the textural parameter of red drum. In the present study, the hardness and springiness of Pacific white shrimp treated by PPE, chitosan coating þ PPE was also significantly improved. 3.4. Sensory evaluation
Fig. 3. Combined effect of chitosan and pomegranate peel extract on the change of texture of Pacific white shrimp during iced storage. A. hardness; B, springness. Key: see the caption for Fig. 1.
storage was significantly improved (p < 0.05) as compared with that of the control shrimp (see Fig. 3A). The springiness defines the distance measured when food recovers its height during the time that elapsed between the end of first bite and start of second bite in the TPA. In general, the springiness of shrimp in all five treatments was significantly decreased during iced storage (Fig. 3B). However, the springiness of shrimp treated by PPE, chitosan coating and chitosan coating þ PPE
Fig. 4 shows the change in sensory quality of Pacific white shrimp. All samples had the score higher than 9 at the beginning of iced storage, and no differences in likeness of samples were found between all treatments. In general, the sensory scores of shrimp showed a tendency to decrease during iced storage. The sensory score of control shrimp was 5.19 at the 6th day of iced storage, which reached unacceptable level according to the Chinese National Standard (GB2741-94). The decrease of sensory scores in shrimp treated by PPE, chitosan coating, chitosan coating þ PPE were significantly lower than that of the control shrimp. In addition, the decrease of sensory score in shrimp treated by chitosan coating þ PPE was significantly lower than that treated by PPE or chitosan coating alone at the 8th and 10th day of storage (p < 0.05), which were coincidental with the melanosis formation and the change of color and textural parameters. These results suggested that treatment with chitosan coating þ PPE could improve the sensory properties of shrimp. 3.5. Chemical analyses
Fig. 4. Combined effect of chitosan and pomegranate peel extract on sensory scores of Pacific white shrimp during iced storage. Key: see the caption for Fig. 1.
Fig. 5A shows the change in pH of Pacific white shrimp. pH of the fresh shrimp at the beginning of storage was 7.24. In general, the rise of pH of shrimp in all treatments was observed during iced storage. However, the rise of pH was highest in the control shrimp for all the sampling days (p < 0.05). The pH change in shrimp was due to the accumulation of basic compounds because of activity of bacteria or enzymatic actions (Lopez-Caballero et al., 2007). The increase of pH in shrimp was significantly inhibited by chitosan coating þ PPE or chitosan coating alone in the present study, similar to that of Huang et al. (2012). However, the inhibition in rise of pH of shrimp was less effective than SMS in the present study (p < 0.05). These results suggested that chitosan coating þ PPE might play a role in retarding quality loss of shrimp, in which the spoilage or decomposition could be lowered. TVB-N, which includes ammonia; primary, secondary, and tertiary amines; and products of protein breakdown, has been used as
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demonstrated synergism in retarding of TVB-N value when used in combination with PPE. 3.6. Microbiological analysis
Fig. 5. Combined effect of chitosan and pomegranate peel extract on chemical changes of Pacific white shrimp during iced storage. A. pH; B. the total volatile basic nitrogen content. Key: see the caption for Fig. 1.
a common and important parameter of the seafood quality because the rise of TVB-N value in seafood is related to microbial and chemical spoilage. Fig. 5B shows the changes in TVB-N values of Pacific white shrimp. In general, the TVB-N values of shrimp in all five treatments were significantly increased during 10 days of iced storage, whereas the increase of TVB-N values varied among five treatments. The increase in TVB-N values was highest in control shrimp and that was significantly inhibited in shrimp treated by PPE, chitosan coating, chitosan coating þ PPE at the 2nd, 4th, 8th and 10th day of storage, respectively (p < 0.05). In addition, the TVB-N values in shrimp treated by chitosan coating þ PPE were significantly less than those treated by PPE or chitosan coating alone at the 8th and 10th day of storage (p < 0.05). According to the Chinese National standard (GB2741-94), the TVB-N value of fresh shrimp should be < 300 mg/100 g. The initial TVB-N value of Pacific white shrimp was 8.86 mg/100 g. For the control shrimp, the TVB-N value was 33.54 mg/100 g at the 8th day of storage and exceeded the spoilage limit of shrimp. However, the TVB-N value of shrimp treated by chitosan coating þ PPE was 23.66 mg/100 g at the end of iced storage (10th day). Above results are in agreement with those of previous studies which reported that the TVB-N values of Pacific white shrimp treated with ferulic acid, cinnamaldehyde and grape seed extract were significantly decreased (Mu, Chen, Fang, Mao, & Gao, 2012; Nirmal & Benjakul, 2009a; Sun et al., 2014). The increase of TVB-N value of shrimp treated by chitosan coating was also inhibited in comparison with the control, which is in agreement with those of Huang et al. (2012) and Wu (2014). In addition, the increase of TVB-N value of shrimp treated by chitosan coating þ PPE was significantly less than those treated by PPE or chitosan coating alone, suggesting that chitosan coating
The TPC of Pacific white shrimp during iced storage are shown in Fig. 6. In general, an increasing tendency of TPC in all samples was observed throughout the storage for 10 days. The increase in TPC was highest in control shrimp for all the sampling days, whereas that was significantly inhibited in shrimp treated by PPE, chitosan coating, chitosan coating þ PPE, respectively. The increase in TPC of shrimp treated by PPE þ chitosan was significantly less than that treated by PPE or chitosan coating alone at the 6th, 8th and 10th day of storage (p < 0.05). PPE are considered rich sources of polyphenolic compounds including punicalagin A, punicalagin B, gallic acid, ellagic acid, chlorogenic acid, caffeic acid, catechin, epicatechin, rutin, quercetin, and galangal, which show antioxidant and antimicrobial effects (Akhtar et al., 2015; Li et al., 2015). Several studies have shown that PPE exhibited antimicrobial activity both in vitro (agar diffusion) and in situ (food) (Al-Zoreky, 2009; Kanatt, Chander, & Sharma, 2010; Negi & Jayaprakasha, 2003). Addition of PPE to popular chicken meat products enhanced its shelf life by 2e3 weeks during chilled storage (Kanatt et al., 2010). PPE also showed in situ inhibition of Listeria monocytogenes in meat pate at different temperatures (Hayrapetyan, Hazeleger, & Beumer, 2012). In the present study, PPE also exert the antimicrobial activity in Pacific white shrimp during iced storage. Chitosan is well known for its broad spectrum of antimicrobial activities against both gram-positive and gram-negative bacteria. The antimicrobial activity of chitosan could be mediated by the interactions between the positively charged chitosan and negatively charged microbial cell membranes, which induces the leakage of cellular proteins and other intracellular constituents (No, Meyers, Prinyawiwatkul, & Xu, 2007). Chitosan also inhibits the microbial growth by the chelation of nutrients and essential metals, spore components, as well as the penetration of the nuclei of the microorganisms, which leads to the interference with protein synthesis by binding with DNA. Chitosan coatings act as an oxygen barrier and can inhibit the growth of aerobic bacteria (Devlieghere, Vermeulen, & Debevere, 2004). Previous studies have reported the use of chitosan coating to improve the shrimp quality (Huang et al.,
Fig. 6. Combined effect of chitosan and pomegranate peel extract on total aerobic plate counts of Pacific white shrimp during iced storage. Key: see the caption for Fig. 1.
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2012; Wang et al., 2014; Wu, 2014). The present finding further confirmed that chitosan coating could inhibit the microbial growth in shrimp. Moreover, the efficacy of chitosan coating to retard microbial growth was increased, when chitosan coating was used in combination with PPE. The results suggested that chitosan coating demonstrated synergism in antimicrobial activity when used in combination with PPE. 4. Conclusions The results presented in this study indicated that chitosan coating combined with PPE could inhibited the melanosis and change of color difference, and improved the sensory quality, hardness and springiness of Pacific white shrimp during 10 days of iced storage. The chitosan coating combined with PPE also inhibited the increase in the TPC, pH and TVB-N content in Pacific white shrimp. These results suggested that chitosan coating combined with PPE could be used as an effective natural alternative to synthetic antimelanosic agents to inhibit postmortem melanosis and improve the quality of shrimp during iced storage. Acknowledgment This work was supported by Key Laboratory of Health Risk Factors for Seafood of Zhejiang Province (No. 2014E10002). References Akhtar, S., Ismail, T., Fraternale, D., & Sestili, P. (2015). Pomegranate peel and peel extracts: chemistry and food features. Food Chemistry, 174, 417e425. Al-Zoreky, N. S. (2009). Antimicrobial activity of pomegranate (Punica granatum L.) fruit peels. International Journal of Food Microbiology, 134(3), 244e248. Basiri, S., Shekarforoush, S. S., Aminlari, M., & Akbari, S. (2015). The effect of pomegranate peel extract (PPE) on the polyphenol oxidase (PPO) and quality of Pacific white shrimp (Litopenaeus vannamei) during refrigerated storage. LWT e Food Science and Technology, 60(2, Part 1), 1025e1033. Cao, R., Xue, C. H., & Liu, Q. (2009). Changes in microbial flora of Pacific oysters (Crassostrea gigas) during refrigerated storage and its shelf-life extension by chitosan. International Journal of Food Microbiology, 131(2e3), 272e276. Chinese National Standard (GB2741-94). (1994). Hygienic standard for sea shrimp. Beijing: Chinese National Hygiene Ministry. Chinese National Standard (GB4789.2-2010). (2010). Microbiological examination of food hygiene: Detection of aerobic bacterial count. Beijing: Chinese National Hygiene Ministry. Devlieghere, F., Vermeulen, A., & Debevere, J. (2004). Chitosan: antimicrobial activity, interactions with food components and applicability as a coating on fruit and vegetables. Food Microbiology, 21(6), 703e714. Encarnacion, A. B., Fagutao, F., Hirayama, J., Terayama, M., Hirono, I., & Ohshima, T. (2011). Edible mushroom (Flammulina velutipes) extract inhibits melanosis in Kuruma shrimp (Marsupenaeus japonicus). Journal of the Science of Food and Agriculture, 76(1), C52eC58. Encarnacion, A. B., Fagutao, F., Hirono, I., Ushio, H., & Ohshima, T. (2010). Effects of ergothioneine from mushrooms (Flammulina velutipes) on melanosis and lipid oxidation of Kuruma shrimp (Marsupenaeus japonicus). Journal of Agricultural and Food Chemistry, 58(4), 2577e2585. Fang, X. B., Sun, H. Y., Huang, B. Y., & Yuan, G. F. (2013). Effect of pomegranate peel extract on the melanosis of Pacific white shrimp (Litopenaeus vannamei) during iced storage. Journal of Food Agriculture and Environment, 11(1), 105e109. Hasnaoui, N., Wathelet, B., & Jimenez-Araujo, A. (2014). Valorization of pomegranate peel from 12 cultivars: dietary fibre composition, antioxidant capacity and functional properties. Food Chemistry, 160, 196e203. Hayrapetyan, H., Hazeleger, W. C., & Beumer, R. R. (2012). Inhibition of Listeria monocytogenes by pomegranate (Punica granatum) peel extract in meat pate at different temperatures. Food Control, 23(1), 66e72. Huang, J. Y., Chen, Q. C., Qiu, M., & Li, S. Q. (2012). Chitosan-based edible coatings for quality preservation of postharvest whiteleg shrimp (Litopenaeus vannamei). Journal of the Science of Food and Agriculture, 77(4), C491eC496. Kanatt, S. R., Chander, R., & Sharma, A. (2010). Antioxidant and antimicrobial activity of pomegranate peel extract improves the shelf life of chicken products. International Journal of Food Science and Technology, 45(2), 216e222. Kim, J., Marshall, M. R., & Wei, C. (2002). Polyphenoloxidase in seafood enzymes: utilization and influence on postharvest seafood quality. In N. Haard, & B. Simpson (Eds.), Seafood Enzymes (pp. 271e315). New York: Marcel Dekker Inc.
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Effect of cinnamaldehyde on melanosis and spoilage of Pacific white shrimp (Litopenaeus vannamei) during storage. Journal of the Science of Food and Agriculture, 92(10), 2177e2182. Negi, P. S., & Jayaprakasha, G. K. (2003). Antioxidant and antibacterial activities of Punica granatum peel extracts. Journal of Food Science, 68(4), 1473e1477. Nirmal, N. P., & Benjakul, S. (2009a). Effect of ferulic acid on inhibition of polyphenoloxidase and quality changes of Pacific white shrimp (Litopenaeus vannamei) during iced storage. Food Chemistry, 116(1), 323e331. Nirmal, N. P., & Benjakul, S. (2009b). Melanosis and quality changes of Pacific white shrimp (Litopenaeus vannamei) treated with catechin during iced storage. Journal of Agricultural and Food Chemistry, 57(9), 3578e3586. Nirmal, N. P., & Benjakul, S. (2010). Effect of catechin and ferulic acid on melanosis and quality of Pacific white shrimp subjected to prior freeze-thawing during refrigerated storage. Food Control, 21(9), 1263e1271. Nirmal, N. P., & Benjakul, S. (2011a). Inhibition of melanosis formation in Pacific white shrimp by the extract of lead (Leucaena leucocephala) seed. Food Chemistry, 128(2), 427e432. Nirmal, N. P., & Benjakul, S. (2011b). Inhibitory effect of mimosine on polyphenoloxidase from cephalothoraxes of Pacific white shrimp (Litopenaeus vannamei). Journal of Agricultural and Food Chemistry, 59(18), 10256e10260. Nirmal, N. P., & Benjakul, S. (2011c). Retardation of quality changes of Pacific white shrimp by green tea extract treatment and modified atmosphere packaging during refrigerated storage. International Journal of Food Microbiology, 149(3), 247e253. No, H. K., Meyers, S. P., Prinyawiwatkul, W., & Xu, Z. (2007). Applications of chitosan for improvement of quality and shelf life of foods: a review. Journal of the Science of Food and Agriculture, 72(5), R87eR100. Okpala, C. O. R., Choo, W. S., & Dykes, G. A. (2014). Quality and shelf life assessment of Pacific white shrimp (Litopenaeus vannamei) freshly harvested and stored on ice. LWT e Food Science and Technology, 55(1), 110e116. Qiu, X., Chen, S., Liu, G., & Yang, Q. (2014). Quality enhancement in the Japanese sea bass (Lateolabrax japonicas) fillets stored at 4 C by chitosan coating incorporated with citric acid or licorice extract. Food Chemistry, 162, 156e160. Ramezani, Z., Zarei, M., & Raminnejad, N. (2015). Comparing the effectiveness of chitosan and nanochitosan coatings on the quality of refrigerated silver carp fillets. Food Control, 51, 43e48. Sagoo, S., Board, R., & Roller, S. (2002). Chitosan inhibits growth of spoilage microorganisms in chilled pork products. Food Microbiology, 19(2e3), 175e182. Sun, H. Y., Lv, H., Yuan, G. F., & Fang, X. B. (2014). Effect of grape seed extracts on the melanosis and quality of Pacific white shrimp (Litopenaeus vannamei) during iced storage. Food Science and Technology Research, 20(3), 671e677. Thepnuan, R., Benjakul, S., & Visessanguan, W. (2008). Effect of pyrophosphate and 4-hexylresorcinol pretreatment on quality of refrigerated white shrimp (Litopenaeus vannamei) kept under modified atmosphere packaging. Journal of the Science of Food and Agriculture, 73(3), S124eS133. Wang, Y., Liu, L., Zhou, J., Ruan, X., Lin, J., & Fu, L. (2014). Effect of chitosan nanoparticle coatings on the quality changes of postharvest whiteleg shrimp, Litopenaeus vannamei, during storage at 4 C. Food and Bioprocess Technology, 8(4), 907e915. Wu, S. J. (2014). Effect of chitosan-based edible coating on preservation of white shrimp during partially frozen storage. International Journal of Biological Macromolecules, 65, 325e328. Zhang, B., Ma, L. K., Deng, S. G., Xie, C., & Qiu, X. H. (2015). Shelf-life of pacific white shrimp (Litopenaeus vannamei) as affected by weakly acidic electrolyzed water ice-glazing and modified atmosphere packaging. Food Control, 51, 114e121.
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Effect of chitosan coating combined with pomegranate peel extract on the quality of Pacific white shrimp during iced storage Gaofeng Yuan, Hua Lv, Wenyan Tang, Xiaojuan Zhang, Haiyan Sun* Key Laboratory of Health Risk Factors for Seafood of Zhejiang Province, Zhejiang Ocean University, Zhoushan, Zhejiang 316022, China
a r t i c l e i n f o
a b s t r a c t
Article history: Received 24 March 2015 Received in revised form 9 July 2015 Accepted 10 July 2015 Available online 13 July 2015
The effect of chitosan coating combined with pomegranate peel extract (PPE) on the melanosis and quality of Pacific white shrimp (Litopenaeus vannamei) during 10 days of iced storage was investigated. The melanosis and changes of total color difference (DE values) were significantly retarded, and the texture parameters and sensory scores were significantly improved in shrimp treated by chitosan coating, PPE and chitosan coating combined with PPE, compared with the control. The increase in total aerobic plate counts, pH and total volatile basic nitrogen values were significantly inhibited in shrimp treated with chitosan coating, PPE and chitosan coating combined with PPE. The melanosis and sensory scores, total volatile basic nitrogen values, and total aerobic plate counts of shrimp treated by chitosan coating combined with PPE were lower than those treated by chitosan coating or PPE alone during the later stage of iced storage, suggesting that there is a synergistic effect between chitosan coating and PPE. © 2015 Elsevier Ltd. All rights reserved.
Keywords: Pacific white shrimp Melanosis Quality Chitosan Pomegranate peel extract
1. Introduction Due to the high market value and nutrition value, shrimp is a very important food resource all over the world. Pacific white shrimp (Litopenaeus vannamei) is native to the Pacific coast of Mexico and now a variety of prawn of the world commonly caught or farmed for food. To date, the world's main producer of Pacific white shrimp is China with production levels of approximately 1,120,000 tons in 2010 (Wang et al., 2014). However, the shelf life of shrimp was limited due to melanosis and microbiological deterioration of shrimp during storage. Melanosis or blackening, the formation of black spots in crustaceans, such as shrimp and crabs during postmortem storage, severely damage the market value and usually caused economical loss of these seafoods (Kim, Marshall, & Wei, 2002). To retard the melanosis in crustaceans and ensure perishables have a longer shelf life, antimelanosic agents, such as 4-hexyl-1,3benzenediol (4-hexylresorcinol), sulphite-based compounds, and phosphates, have been intensively studied and proved to be effective to inhibit melanosis (Martinez-Alvarez, Lopez-Caballero, Montero, & Gomez-Guillen, 2005; Thepnuan, Benjakul, &
* Corresponding author. Key Laboratory of Health Risk Factors for Seafood of Zhejiang Province, Zhejiang Ocean University, Zhoushan, Zhejiang 316022, China. E-mail address: [email protected] (H. Sun). http://dx.doi.org/10.1016/j.foodcont.2015.07.011 0956-7135/© 2015 Elsevier Ltd. All rights reserved.
Visessanguan, 2008). However, the use of synthetic compounds to inhibit melanosis in seafood is limited due to increasing regulatory attention and their potential toxicity (McEvily, Iyengar, & Otwell, 1991). Due to the potential health hazards of chemical additives, natural products, especially natural antioxidants and antimicrobial agents, have been intensively examined as safe alternatives to synthetic compounds (Encarnacion, Fagutao, Hirono, Ushio, & Ohshima, 2010; Maqsood, Benjakul, & Shahidi, 2013). Recently, a series of studies conducted on the utilization of natural extracts to delay melanosis formation and extend the shelf life of seafood (Fang, Sun, Huang, & Yuan, 2013; Nirmal & Benjakul, 2011a, 2011c; Sun, Lv, Yuan, & Fang, 2014). It has been reported that pomegranate peel and peel extract (PPE) had significant free radical scavenging, anti-microbial, antiatherogenic and antimutagenic properties (Akhtar, Ismail, Fraternale, & Sestili, 2015; Hasnaoui, Wathelet, & Jimenez-Araujo, 2014). PPE also inhibited the formation of melanosis and improve the quality of Pacific white shrimp during iced storage (Basiri, Shekarforoush, Aminlari, & Akbari, 2015; Fang et al., 2013). These findings have led to increased interest in PPE. Chitosan, a cationic polysaccharide consisting of (1,4)-linked-2amino-deoxy-b-D-glucan, is the deacetylated form of chitin. Chitosan, which has attracted attention as a potential food preservative of natural origin, has been classified as a GRAS by the US FDA in 2001 (Sagoo, Board, & Roller, 2002). Chitosan has been broadly applied to the preservation of seafood products including oysters,
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sardine, salmon, sea bass, and silver carp duo to its non-toxic feature, antimicrobial and antifungal activities, biodegradability and biocompatibility, film-forming property (Cao, Xue, & Liu, 2009; Mohan, Ravishankar, Lalitha, & Gopal, 2012; Qiu, Chen, Liu, & Yang, 2014; Ramezani, Zarei, & Raminnejad, 2015). Chitosan also has been found to be effective in enhancing the quality and shelf life of shrimp (Huang, Chen, Qiu, & Li, 2012; Wang et al., 2014; Wu, 2014). However, to our knowledge, there is no literature reported the influence of chitosan coating combined with PPE on the shelf life and quality of seafood. The purpose of the present study was to evaluate the effect of chitosan coating combined with PPE (chitosan coating þ PPE) on the quality of Pacific white shrimp during iced storage. 2. Materials and methods 2.1. Preparation of pomegranate peel extract and coating solution The dried pomegranate peel was powdered using a mixer grinder and 200-g portions of finely-powdered pomegranate peel was blended with 50% ethanol for 2 h at 40 C in a shaking water bath. The ratio pomegranate peel powder: solvent was 1:10 (w/v). The extracts were through Waterman No. 1 filter paper (SigmaeAldrich Co., St. Louis, MO, USA) and concentrated under vacuum with a rotary evaporator (Eyela, Rikakikai, Tokio, Japan). The concentrate was dried overnight in an oven at 40 C to form powder which was stored at 4 C until further use. The 1.5% of PPE dipping solution was prepared by dissolving PPE in distilled water. Chitosan were purchased from Shanghai Jinsui Biotechnology Company (Shanghai, China). The degree of deacetylation of chitosan was 90% and the average molecular weight of chitosan was 25 kDa. Chitosan (10 g) was added to 1000 mL of 1% acetic acid and stirred for 1 h at room temperature to obtain 1% of w/w chitosan/ acetic acid solutions. 2.2. Shrimp collection and treatments Pacific white shrimp with the size of 50e55 shrimps/kg were purchased from a local market in Zhoushan, China. The shrimp were kept alive and transported to our laboratory. The shrimp were randomly assigned into five groups including the control (uncoated) group, PPE group, chitosan coating group, chitosan coating þ PPE group and sodium metabisulfite (SMS) group. The shrimp in the PPE group and chitosan group were dipped into the 1.5% of PPE and 1% of chitosan solutions at a shrimp/solution ratio of 1:2 (w/v) at 4 C for 30 min, respectively. After dipping, the shrimp were drained at ambient temperature for 3 min. The shrimp in the chitosan coating þ PPE group were immersed into the 1.5% of PPE at a shrimp/solution ratio of 1:2 (w/v) at 4 C for 30 min. After that, they were dipped into 1% of chitosan solutions at a shrimp/ solution ratio of 1:2 (w/v) at 4 C for 30 min, and then were drained at ambient temperature for 3 min. Another portion of shrimp was treated in 1.25% of SMS dissolved in distilled water at a ratio of 1:2 (w/v) for 1 min at 4 C. The samples from each treatment were covered in plastic bags and stored in ice using a shrimp/ice ratio of 1:2 (w/w). To maintain the shrimp/ice ratio, molten ice was removed and replaced with an equal amount of ice every 2 d. 2.3. Melanosis assessment Melanosis assessment of Pacific white shrimp was conducted through visual inspection by six panelists using ten-point scoring according to the method of Montero, Avalos, and Perez-Mateos (2001). Panelists were asked to give the melanosis score (0e10) for shrimp, where 0 ¼ absent; 2 ¼ slight (up to 20% of shrimps'
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surface affected); 4 ¼ moderate (20%e40% of shrimps' surface affected); 6 ¼ notable (40%e60% of shrimps' surface affected); 8 ¼ severe (60%e80% of shrimps' surface affected); 10 ¼ extremely heavy (80%e100% of shrimps' surface affected). Samples were taken for each treatment every 2 d up to 10 d for melanosis assessment. 2.4. Color measurements of shrimp shells The color of shrimp was measured by using an automatic color difference meter (DC-P3, Shanghai Go On Chemical Co., Ltd., Shanghai, China) according to the method of Zhang, Ma, Deng, Xie, and Qiu (2015). L* (lightness) represents the brightness on a scale of 0 (dark) to 100 (white), a* (redness) scale ranges from negative values for green to positive values for red and b* (yellowness) scale ranges from negative values for blue to positive values for yellow. Color was determined in three zones (head, body and tail) on the shrimp shell. For each sample, triplicate measurements were taken at each shell zone and the average values of six samples were recorded. Total color differences (DE values), which indicate the magnitude of color difference between shrimps at the beginning of storage and after the storage period, were calculated using following equation: DE ¼ [(L* L*0)2 þ (a* a*0)2 þ (b* b0*)2]1/2, where L*0, a*0, and b*0 are the values of L*, a*, and b* color parameters at the beginning of storage. 2.5. Texture profile analysis A texture analyzer (TMS-PRO, FTC, Sterling, VA, USA) was used to evaluate the texture (hardness and springiness) of shrimp muscle samples according to the method of Zhang et al. (2015). The texture profile analysis (TPA) at room temperature (25 C) and performed under the following conditions: constant test speed, 1.0 mm/s; sample deformation, 50%; hold time between cycles, 3 s; and trigger force, 0.05 N. Texture analysis parameters were calculated using FTC-PRO software from the forceetime curves generated from each sample. All measurements were carried out on six different single shrimp specimens, and the average value was obtained. 2.6. Sensory evaluation Sensory evaluation of shrimp samples was performed by a group of six trained panelists according to the methods of Wu (2014). Panelists were regular consumers of shrimp and had no allergies to shrimp. Panelists were asked to evaluate appearance, odor, texture, flavor, and overall acceptability of shrimp samples. A rating was assigned separately for each parameter on a 1 to 9 descriptive hedonic scale, with 9 as the highest-quality sample. 2.7. Chemical analyses The pH values were measured in shrimp according to the method of Lopez-Caballero, Martinez-Alvarez, Gomez-Guillen, and Montero (2007). Total volatile basic nitrogen (TVB-N) was determined on steam distillation of trichloroacetic acid-shrimp extract with the Kjeltec 8400 Automatic Kjeldahl Nitrogen Determination apparatus (Foss, Sweden) in triplicates. The TVB-N values were expressed as mg N/100 g shrimp meat. 2.8. Microbiological analysis Microbiological analysis was performed according to the Chinese National Standard (GB4789.2-2010) by measurement of the total bacteria amounts indicated as total aerobic plate counts
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(TPC). Twenty-five grams of shrimp were homogenized with 225 mL of 0.85% of sterile saline water at 8000 rpm for 1 min. Samples were serially diluted logarithmically in 0.85% of sterile saline water. TPC was determined by spread plating samples on nutrient agar and incubating at 36 C for 48 h. Microbial colonies were counted and reported as log CFU/g of fresh weight. 2.9. Statistical analysis Statistical analysis was performed using the SPSS package program version 11.5 (SPSS inc. Chicago, IL, USA). Data was analyzed by one-way ANOVA, followed by Turkey's HSD multiple comparison test. The values are reported as means with their standard error for all results. Differences were considered significant at p < 0.05. 3. Results and discussion 3.1. Melanosis Fig. 1 shows the melanosis scores of Pacific white shrimp. The melanosis in all treatments was significantly increased during iced storage. This result indicated that there was rapid loss in visual quality occurred in Pacific white shrimp during iced storage, which is similar to our previous studies (Fang et al., 2013; Sun et al., 2014). The melanosis in Pacific white shrimp treated by chitosan coating, PPE and chitosan coating þ PPE was significantly inhibited (p < 0.05), compared with the control. In addition, the score of melanosis of Pacific white shrimp treated by chitosan coating þ PPE was less than those treated by PPE or chitosan coating alone. Previous studies have shown that natural extracts or natural compounds could inhibit the melanogenesis of shrimp during iced storage (Encarnacion et al., 2010; Encarnacion et al., 2011; Fang et al., 2013; Nirmal & Benjakul, 2009b, 2010, 2011b). Our previous study showed that melanosis was significantly inhibited in the Pacific white shrimp treated with various concentration of PPE (Fang et al., 2013). Recently, Basiri et al. (2015) also observed that PPE-treated shrimp obtained lower melanosis score during 6 days of storage under refrigeration. The present study further confirmed that PPE had inhibition effect on the melanosis of Pacific white shrimp.
Fig. 1. Combined effect of chitosan and pomegranate peel extract on melanosis scores of Pacific white shrimp during iced storage. Each data is the mean values per treatment and time point (mean ± standard error). SMS, sodium metabisulfite; PPE, pomegranate peel extract.
The present findings are in agreement with those of Huang et al. (2012) and Wang et al. (2014) who reported that the application of chitosan coatings was effective to retard melanosis in shrimp during storage. The retard of melanosis in shrimp treated by chitosan coating may be attributed to certain chitosan functional properties, such as being an antioxidant, an antimicrobial agent, and an oxygen barrier (Huang et al., 2012). In addition, chitosan coating þ PPE was more effective than chitosan coating or PPE alone in the retard of melanosis in shrimp, suggesting that there is a synergistic effect between chitosan coating and PPE.
3.2. Color Color is one of the quality parameters for freshness. DE values， which indicate the magnitude of color difference between shrimps at the beginning of storage and after the storage period, are shown in Fig. 2. Generally, there was a gradual increase in the DE values of shrimp among the five groups with the storage time increasing. Interesting, a significantly fluctuated DE values in shrimp treated during the whole storage by chitosan coating were observed (p < 0.05) wherein the data spread exhibited a wavelike pattern, which is in agreement with that of Okpala, Choo, and Dykes (2014). The DE values in shrimp treated by chitosan coating, PPE and chitosan coating þ PPE were significantly lower (p < 0.05) than that in control shrimp during iced storage. Thus, treatments with chitosan coating, PPE and chitosan þ PPE coating could delay the change of color of shrimp in the present study. However, there was no significant difference on the DE values of shrimp treated by chitosan coating, PPE and chitosan coating þ PPE, besides the DE value in shrimp treated by chitosan coating at the 6th day of storage was significantly lower than that treated by PPE and chitosan coating þ PPE.
3.3. Texture profile analysis Hardness is the most critical textural attribute in meat or seafood. In general, the hardness of Pacific white shrimp in all five treatments was significantly decreased during iced storage (Fig. 3A). However, the hardness of shrimp treated by PPE, chitosan coating and chitosan coating þ PPE at the 6th, 8th and 10th day of
Fig. 2. Combined effect of chitosan and pomegranate peel extract on the DE values of Pacific white shrimp during iced storage. Means in the same storage day with different letter are significantly different (p < 0.05). Key: see the caption for Fig. 1.
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at the 8th and 10th day of storage was significantly improved (p < 0.05) as compared with that of the control shrimp. Compared with control shrimp, the highest springiness values (p < 0.05) were also observed in that treated by chitosan coating þ PPE at the 10th day of storage. The change of texture parameters was one of the major components of acceptability and influenced by several factors, such as the rate and extent of postmortem pH decline, muscular protein arrangement. The principal muscle components responsible for the texture change are the myofibrillar and connective tissue proteins in shrimp. The present findings are in agreement with that of Wang et al. (2014) who observed that application of chitosan coatings was effective to retard the change of texture parameters in shrimp during storage. The bonds between chitosan and myofibrillar proteins could be associated with the improvement of texture properties in shrimp muscle, with the final structure formed by both covalent and noncovalent interactions. In addition, the textural effect in seafood is also due to microbiological processes caused by the death of the seafood, which bring degradation of myofibrillar protein, following softening of the muscle. Li, Li, Hu, and Li (2013) showed that grape seed extract and tea polyphenols, which are rich in polyphenolic compounds, could extend the shelf life and improve the textural parameter of red drum. In the present study, the hardness and springiness of Pacific white shrimp treated by PPE, chitosan coating þ PPE was also significantly improved. 3.4. Sensory evaluation
Fig. 3. Combined effect of chitosan and pomegranate peel extract on the change of texture of Pacific white shrimp during iced storage. A. hardness; B, springness. Key: see the caption for Fig. 1.
storage was significantly improved (p < 0.05) as compared with that of the control shrimp (see Fig. 3A). The springiness defines the distance measured when food recovers its height during the time that elapsed between the end of first bite and start of second bite in the TPA. In general, the springiness of shrimp in all five treatments was significantly decreased during iced storage (Fig. 3B). However, the springiness of shrimp treated by PPE, chitosan coating and chitosan coating þ PPE
Fig. 4 shows the change in sensory quality of Pacific white shrimp. All samples had the score higher than 9 at the beginning of iced storage, and no differences in likeness of samples were found between all treatments. In general, the sensory scores of shrimp showed a tendency to decrease during iced storage. The sensory score of control shrimp was 5.19 at the 6th day of iced storage, which reached unacceptable level according to the Chinese National Standard (GB2741-94). The decrease of sensory scores in shrimp treated by PPE, chitosan coating, chitosan coating þ PPE were significantly lower than that of the control shrimp. In addition, the decrease of sensory score in shrimp treated by chitosan coating þ PPE was significantly lower than that treated by PPE or chitosan coating alone at the 8th and 10th day of storage (p < 0.05), which were coincidental with the melanosis formation and the change of color and textural parameters. These results suggested that treatment with chitosan coating þ PPE could improve the sensory properties of shrimp. 3.5. Chemical analyses
Fig. 4. Combined effect of chitosan and pomegranate peel extract on sensory scores of Pacific white shrimp during iced storage. Key: see the caption for Fig. 1.
Fig. 5A shows the change in pH of Pacific white shrimp. pH of the fresh shrimp at the beginning of storage was 7.24. In general, the rise of pH of shrimp in all treatments was observed during iced storage. However, the rise of pH was highest in the control shrimp for all the sampling days (p < 0.05). The pH change in shrimp was due to the accumulation of basic compounds because of activity of bacteria or enzymatic actions (Lopez-Caballero et al., 2007). The increase of pH in shrimp was significantly inhibited by chitosan coating þ PPE or chitosan coating alone in the present study, similar to that of Huang et al. (2012). However, the inhibition in rise of pH of shrimp was less effective than SMS in the present study (p < 0.05). These results suggested that chitosan coating þ PPE might play a role in retarding quality loss of shrimp, in which the spoilage or decomposition could be lowered. TVB-N, which includes ammonia; primary, secondary, and tertiary amines; and products of protein breakdown, has been used as
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demonstrated synergism in retarding of TVB-N value when used in combination with PPE. 3.6. Microbiological analysis
Fig. 5. Combined effect of chitosan and pomegranate peel extract on chemical changes of Pacific white shrimp during iced storage. A. pH; B. the total volatile basic nitrogen content. Key: see the caption for Fig. 1.
a common and important parameter of the seafood quality because the rise of TVB-N value in seafood is related to microbial and chemical spoilage. Fig. 5B shows the changes in TVB-N values of Pacific white shrimp. In general, the TVB-N values of shrimp in all five treatments were significantly increased during 10 days of iced storage, whereas the increase of TVB-N values varied among five treatments. The increase in TVB-N values was highest in control shrimp and that was significantly inhibited in shrimp treated by PPE, chitosan coating, chitosan coating þ PPE at the 2nd, 4th, 8th and 10th day of storage, respectively (p < 0.05). In addition, the TVB-N values in shrimp treated by chitosan coating þ PPE were significantly less than those treated by PPE or chitosan coating alone at the 8th and 10th day of storage (p < 0.05). According to the Chinese National standard (GB2741-94), the TVB-N value of fresh shrimp should be < 300 mg/100 g. The initial TVB-N value of Pacific white shrimp was 8.86 mg/100 g. For the control shrimp, the TVB-N value was 33.54 mg/100 g at the 8th day of storage and exceeded the spoilage limit of shrimp. However, the TVB-N value of shrimp treated by chitosan coating þ PPE was 23.66 mg/100 g at the end of iced storage (10th day). Above results are in agreement with those of previous studies which reported that the TVB-N values of Pacific white shrimp treated with ferulic acid, cinnamaldehyde and grape seed extract were significantly decreased (Mu, Chen, Fang, Mao, & Gao, 2012; Nirmal & Benjakul, 2009a; Sun et al., 2014). The increase of TVB-N value of shrimp treated by chitosan coating was also inhibited in comparison with the control, which is in agreement with those of Huang et al. (2012) and Wu (2014). In addition, the increase of TVB-N value of shrimp treated by chitosan coating þ PPE was significantly less than those treated by PPE or chitosan coating alone, suggesting that chitosan coating
The TPC of Pacific white shrimp during iced storage are shown in Fig. 6. In general, an increasing tendency of TPC in all samples was observed throughout the storage for 10 days. The increase in TPC was highest in control shrimp for all the sampling days, whereas that was significantly inhibited in shrimp treated by PPE, chitosan coating, chitosan coating þ PPE, respectively. The increase in TPC of shrimp treated by PPE þ chitosan was significantly less than that treated by PPE or chitosan coating alone at the 6th, 8th and 10th day of storage (p < 0.05). PPE are considered rich sources of polyphenolic compounds including punicalagin A, punicalagin B, gallic acid, ellagic acid, chlorogenic acid, caffeic acid, catechin, epicatechin, rutin, quercetin, and galangal, which show antioxidant and antimicrobial effects (Akhtar et al., 2015; Li et al., 2015). Several studies have shown that PPE exhibited antimicrobial activity both in vitro (agar diffusion) and in situ (food) (Al-Zoreky, 2009; Kanatt, Chander, & Sharma, 2010; Negi & Jayaprakasha, 2003). Addition of PPE to popular chicken meat products enhanced its shelf life by 2e3 weeks during chilled storage (Kanatt et al., 2010). PPE also showed in situ inhibition of Listeria monocytogenes in meat pate at different temperatures (Hayrapetyan, Hazeleger, & Beumer, 2012). In the present study, PPE also exert the antimicrobial activity in Pacific white shrimp during iced storage. Chitosan is well known for its broad spectrum of antimicrobial activities against both gram-positive and gram-negative bacteria. The antimicrobial activity of chitosan could be mediated by the interactions between the positively charged chitosan and negatively charged microbial cell membranes, which induces the leakage of cellular proteins and other intracellular constituents (No, Meyers, Prinyawiwatkul, & Xu, 2007). Chitosan also inhibits the microbial growth by the chelation of nutrients and essential metals, spore components, as well as the penetration of the nuclei of the microorganisms, which leads to the interference with protein synthesis by binding with DNA. Chitosan coatings act as an oxygen barrier and can inhibit the growth of aerobic bacteria (Devlieghere, Vermeulen, & Debevere, 2004). Previous studies have reported the use of chitosan coating to improve the shrimp quality (Huang et al.,
Fig. 6. Combined effect of chitosan and pomegranate peel extract on total aerobic plate counts of Pacific white shrimp during iced storage. Key: see the caption for Fig. 1.
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2012; Wang et al., 2014; Wu, 2014). The present finding further confirmed that chitosan coating could inhibit the microbial growth in shrimp. Moreover, the efficacy of chitosan coating to retard microbial growth was increased, when chitosan coating was used in combination with PPE. The results suggested that chitosan coating demonstrated synergism in antimicrobial activity when used in combination with PPE. 4. Conclusions The results presented in this study indicated that chitosan coating combined with PPE could inhibited the melanosis and change of color difference, and improved the sensory quality, hardness and springiness of Pacific white shrimp during 10 days of iced storage. The chitosan coating combined with PPE also inhibited the increase in the TPC, pH and TVB-N content in Pacific white shrimp. These results suggested that chitosan coating combined with PPE could be used as an effective natural alternative to synthetic antimelanosic agents to inhibit postmortem melanosis and improve the quality of shrimp during iced storage. Acknowledgment This work was supported by Key Laboratory of Health Risk Factors for Seafood of Zhejiang Province (No. 2014E10002). References Akhtar, S., Ismail, T., Fraternale, D., & Sestili, P. (2015). Pomegranate peel and peel extracts: chemistry and food features. Food Chemistry, 174, 417e425. Al-Zoreky, N. S. (2009). Antimicrobial activity of pomegranate (Punica granatum L.) fruit peels. International Journal of Food Microbiology, 134(3), 244e248. Basiri, S., Shekarforoush, S. S., Aminlari, M., & Akbari, S. (2015). The effect of pomegranate peel extract (PPE) on the polyphenol oxidase (PPO) and quality of Pacific white shrimp (Litopenaeus vannamei) during refrigerated storage. LWT e Food Science and Technology, 60(2, Part 1), 1025e1033. Cao, R., Xue, C. H., & Liu, Q. (2009). Changes in microbial flora of Pacific oysters (Crassostrea gigas) during refrigerated storage and its shelf-life extension by chitosan. International Journal of Food Microbiology, 131(2e3), 272e276. Chinese National Standard (GB2741-94). (1994). Hygienic standard for sea shrimp. Beijing: Chinese National Hygiene Ministry. Chinese National Standard (GB4789.2-2010). (2010). Microbiological examination of food hygiene: Detection of aerobic bacterial count. Beijing: Chinese National Hygiene Ministry. Devlieghere, F., Vermeulen, A., & Debevere, J. (2004). Chitosan: antimicrobial activity, interactions with food components and applicability as a coating on fruit and vegetables. Food Microbiology, 21(6), 703e714. Encarnacion, A. B., Fagutao, F., Hirayama, J., Terayama, M., Hirono, I., & Ohshima, T. (2011). Edible mushroom (Flammulina velutipes) extract inhibits melanosis in Kuruma shrimp (Marsupenaeus japonicus). Journal of the Science of Food and Agriculture, 76(1), C52eC58. Encarnacion, A. B., Fagutao, F., Hirono, I., Ushio, H., & Ohshima, T. (2010). Effects of ergothioneine from mushrooms (Flammulina velutipes) on melanosis and lipid oxidation of Kuruma shrimp (Marsupenaeus japonicus). Journal of Agricultural and Food Chemistry, 58(4), 2577e2585. Fang, X. B., Sun, H. Y., Huang, B. Y., & Yuan, G. F. (2013). Effect of pomegranate peel extract on the melanosis of Pacific white shrimp (Litopenaeus vannamei) during iced storage. Journal of Food Agriculture and Environment, 11(1), 105e109. Hasnaoui, N., Wathelet, B., & Jimenez-Araujo, A. (2014). Valorization of pomegranate peel from 12 cultivars: dietary fibre composition, antioxidant capacity and functional properties. Food Chemistry, 160, 196e203. Hayrapetyan, H., Hazeleger, W. C., & Beumer, R. R. (2012). Inhibition of Listeria monocytogenes by pomegranate (Punica granatum) peel extract in meat pate at different temperatures. Food Control, 23(1), 66e72. Huang, J. Y., Chen, Q. C., Qiu, M., & Li, S. Q. (2012). Chitosan-based edible coatings for quality preservation of postharvest whiteleg shrimp (Litopenaeus vannamei). Journal of the Science of Food and Agriculture, 77(4), C491eC496. Kanatt, S. R., Chander, R., & Sharma, A. (2010). Antioxidant and antimicrobial activity of pomegranate peel extract improves the shelf life of chicken products. International Journal of Food Science and Technology, 45(2), 216e222. Kim, J., Marshall, M. R., & Wei, C. (2002). Polyphenoloxidase in seafood enzymes: utilization and influence on postharvest seafood quality. In N. Haard, & B. Simpson (Eds.), Seafood Enzymes (pp. 271e315). New York: Marcel Dekker Inc.
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