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Shelf-life extension of crucian carp (Carassius auratus) using natural preservatives during chilled storage
Food Chemistry 135 (2012) 140–145
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Shelf-life extension of crucian carp (Carassius auratus) using natural preservatives during chilled storage Tingting Li a,b, Jianrong Li a,c,⇑, Wenzhong Hu b, Xuguang Zhang a, Xuepeng Li c, Jin Zhao a,d a
College of Food Science and Biotechnology, Zhejiang Gongshang University, Hangzhou 310035, China College of Life Science, Dalian Nationalities University, Dalian 116600, China c Bohai University, Jinzhou 121013, China d Zhejiang Marine Food Processing Quality Control Techniques and Instrumentation Engineering Laboratory, College of Life Science, China Jiliang University, Hangzhou 310018, China b
a r t i c l e
i n f o
Article history: Received 22 December 2011 Received in revised form 6 April 2012 Accepted 18 April 2012 Available online 27 April 2012 Keywords: Crucian carp Tea polyphenols Rosemary extract Quality characteristics Shelf-life
a b s t r a c t The effect of the natural preservatives, tea polyphenols and rosemary extract, on microbiological [total viable count (TVC)], chemical [pH, total volatile base nitrogen (TVB-N), K-value and thiobarbituric acid (TBA) values], texture and sensory changes of air-packaged whole crucian carp (Carassius auratus) stored at 4 ± 1 °C was investigated for 20 days. The shelf-life of crucian carp was found to be 7–8 days for untreated group (control), 13–14 days for tea polyphenols group and 15–16 days for rosemary extract treated group according to sensory assessment results, for which the corresponding microbiological assessment also showed an increased shelf-life. Meanwhile, the increases of pH, TVB-N, K-value and TBA values were significantly delayed in both treated groups of samples compared to the control group. Thus, either tea polyphenols or rosemary extract could be used as potential preservatives to extend the shelf-life of crucian carp during chilled storage. Ó 2012 Elsevier Ltd. All rights reserved.
1. Introduction Crucian carp (Carassius auratus) is one of the most economically important freshwater-cultured fish species. It is popular in China due to its fast growth rate, palatability, and the nutritional quality of its flesh (Zeng, Huang, Li, & Huang, 2001). In China, production of crucian carp reached nearly 2,000,000 tons in 2009 (Fishery Bureau of Department of Agriculture of China., 2011). However, fish are usually more perishable than other muscle foods, and a considerable number of fish are spoiled due to lack of good preservation. Crucian carp is an easily perishable product because of its relatively high quantities of volatile basic nitrogen as well as free amino acids, high water activity, and presence of autolytic enzymes (Duan, Jiang, Cherian, & Zhao, 2010). Xiao, Kang, and Xin (2007) reported the freshness variation of crucian carp (Carassius auratus) during chilled storage, while Yue, Shen, and Ou (2002) studied the effect of coatings with different molecular weight chitosan on crucian carp quality. The spoilage of fish is a complicated process in which microbiology, physical and chemical changes interact. Activities of the fish’s own enzymes and chemical reactions are usually responsible for the initial loss of fish freshness, whereas the metabolic activities ⇑ Corresponding author at: College of Food Science and Biotechnology, Zhejiang Gongshang University, Hangzhou 310035, China. Tel./fax: +86 416 3400008. E-mail addresses: [email protected] (T. Li), [email protected]. edu.cn (J. Li). 0308-8146/$ - see front matter Ó 2012 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.foodchem.2012.04.115
of microorganisms are involved in the whole spoilage (Sallam, Ahmed, Elgazzar, & Eldaly, 2007). The inherent quality of seafood makes it more susceptible to food-borne hazards. Therefore, effective methods for extending shelf-life and improving quality of fresh crucian carp are necessary. The application of good manufacturing practices (GMP), good hygienic practices (GHP), and hazard analysis of critical control point (HACCP) is essential in the production, distribution, storage and retailing of refrigerated foods. Because of consumer desire for fresh chilled foods with extended shelf-life, numerous studies have been directed toward using diverse preservation strategies to preserve or prolong the shelf-life of fresh foods including fishery products to ensure product safety (Sallam, 2007). Natural preservatives, such as tea polyphenols and rosemary extract, have been widely used in the food industry because of their good preservative effect (Li et al., 2012; Ozogul et al., 2010; Fan, Chi, & Zhang, 2008; Georgantelis, Ambrosiadis, Katikou, Blekas, & Georgakis, 2007; Tironi, Tomás, & Añón, 2009; Yi, Zhu, Fu, & Li, 2010). The preservative effect of tea polyphenols and rosemary extract is mainly due to the inhibition of some enzymes’ activities, as well as the free radical scavenging ability and therefore prevention of lipid oxidation (Bubonja-Sonje, Giacometti, & Abram, 2011; Fan et al., 2008). In addition, their antimicrobial properties are also important (Georgantelis et al., 2007; Yi et al., 2010). Limited data, however, are available with regard to the application of tea polyphenols and rosemary extract for extension of the shelf-life of crucian carp. Thus, the objective of the present
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study was to evaluate the potential effects of tea polyphenols and rosemary extract as antioxidants on the quality and shelf-life of crucian carp during chilled storage.
2. Materials and methods 2.1. Fish sample preparation Fifty live commercial-sized crucian carp with an average weight of 360 ± 10 g were purchased from Dalian Aquatic Market in September (Dalian, Liaoning province, China). They were transferred to the Food Processing Laboratory of Dalian Nationalities University within 0.5 h and kept alive before being processed. The fish were killed by slurry ice and kept whole and ungutted at 0 °C before use.
2.2. Natural antioxidants and chemicals Tea polyphenols was purchased from Zhejiang University Tea Scientific Co., Ltd. (purity P 98%, Hangzhou, Zhejiang province, China). Rosemary extract containing 22 ± 4% phenolic diterpenes (carnosic acid, carnosol, rosmarinic acid, as stated by the manufacturer) was bought from Guizhou Red Star Development Duyun Luyou Co., Ltd. (Duyun, Guizhou province, China). The two extracts were packed in polyethylene bags and stored at 4 ± 1 °C before using.
2.3. Preparation of fish samples The whole fish were washed under running tap water and divided into three groups. First group was used as the control, second group was immersed in a solution of 2 g of tea polyphenols in 1 L of distiled water (4 ± 1 °C) for 60 min (0.2% TP), and the third was immersed in a solution of 2 g of rosemary extract in 1 L of distiled water (4 ± 1 °C) for 60 min (0.2% R), then the three groups of fish were kept on a plastic net for 2 h to drain at 4 ± 1 °C. After that, they were packed in air-proof polyethylene pouches and stored at 4 ± 1 °C for subsequent quality assessment. Microbiological, chemical, and sensory analyses were performed at 5-day intervals, each analysis was repeated three times with three fish and the averages were used to measure the overall quality of fish.
2.4. Proximate composition analyses A proximate composition analysis was performed on five fish on day 0 of preservation. Proximate analyses (moisture content, total crude protein, lipid content and ash content) of the fish samples were based on the procedures set by the AOAC (1997).
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2.6. Chemical analyses 2.6.1. pH and Total volatile basic nitrogen (TVB-N) The pH values were measured to illustrate the hygienic standard of fish and other aquatic products according to the GB/T of the Chinese standard (GB/T 5009.45-2003). A 10.0-g sample of fish muscle was mixed with 90 ml of distiled water and the mixture was filtered. After 30 min, the pH of the filtrate was measured using a digital 320 pH metre (Mettler Toledo, Zurich, Switzerland). Total volatile basic nitrogen (TVB-N) value was estimated by the FOSS. (2002). The microdiffusion method was mensurated by distillation after adding MgO to the homogenised samples. TVB-N values were determined with a Kjeltec 2300 (FOSS, Hiller, Denmark). TVB-N values were expressed in mg nitrogen kg1 (mg N kg1) fish sample. 2.6.2. K-value ATP and its breakdown products were measured according to the modified method of Özogul, Özden, Özog˘ul, and Erkan (2010). Five grams of minced fish flesh without skin were extracted with 25 ml of 0.6 M perchloric acid using an Ultra-Turrax (T25 basic; IKA-Werke, Staufen, Germany) for 1 min in an ice bath. The extraction mixture was centrifuged at 1940g for 10 min and after that, 10 ml of supernatant were quickly adjusted to pH 6.5–6.8 using 1 M KOH. The neutralised supernatant was allowed to stand for 30 min in an ice bath to precipitate most of the potassium perchlorate, which was then removed by centrifuging at 1940g for 10 min. The supernatant solution was made up to 20 ml and then stored at 80 °C until HPLC analysis. The identification of nucleotides, nucleosides and bases was determined and calculated by comparing their retention times with those of commercially obtained standards and by adding or spiking of standards. The K-value was defined as the per cent ratio of inosine (HxR) and hypoxanthine (Hx) to the sum of ATP and degradation products as follows:
K% ¼ ½ðHxR þ HxÞ=ðATP þ ADP þ AMP þ IMP þ HxR þ HxÞ 100:
2.6.3. Thiobarbituric acid reactive substances (TBARS) The thiobarbituric acid value was determined colorimetrically by the method of Porkony and Dieffenbacher, as described by Kirk and Sawyer (1991). A portion (200 mg) of sample was weighed into a 25-ml volumetric flask. An aliquot (1 ml) of 1-butanol was added to dissolve the sample. The mixture was made to volume and mixed. A portion (5.0 ml) of the mixture was pipetted into a dry stoppered test tube and 5 ml of TBA reagent (prepared by dissolving 200 mg of 2-TBA in 100 ml 1-butanol, filtered, stored at 4 °C for not more than 7 days) were added. The test tubes were stoppered, vortexed and placed in a water bath at 95 °C for 120 min, then cooled. Absorbance (As) was measured at 530 nm against water blank. A reagent blank was run and absorbance (Ab) recorded. TBA value (mg of malonaldehyde equivalents/kg of tissue) was obtained by the formula:
50 ðAs Ab Þ 200
2.5. Bacteriological analyses
TBA ¼
Fish samples were taken aseptically in a vertical laminar-flow cabinet and 10 g were transferred to a stomacher bag; 90 ml of 0.1% peptone water with salt (NaCl, 0.85%, w/v) were added and homogenised for 60 s with a stomacher. From this dilution, other decimal dilutions were obtained and 1 ml of three dilutions was transferred in triplicate to Petri dishes containing 15 ml commercial plate count agar (PCA, Base Bio-Tech, Hangzhou, China). Total viable counts (TVC) were determined by counting the number of colony-forming units after incubation at 25 °C for 48 h.
2.6.4. Texture measurements Texture profile analyses (TPA) were carried out according to Sigurgisladottir et al. (1999). The TA.XT texture analyser (Stable Micro Systems Ltd., Godalming, UK) was used. A flat-ended cylinder that simulated the human finger was used. Constant penetration depth of 2.5 mm was applied on the fillets of about 15 mm thickness after testing penetrations in the range of 2–5 mm. This penetration depth was chosen as the maximum distance which could be
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applied without influencing the muscle structure by damaging it and leaving a mark on the fillet. Three sampling points were selected in each fillet [dorsal, tail (8 mm from the edge of tail) and between dorsal and tail. Double compression was applied to construct the texture profile analyses (TPA) parameters. The flat-ended cylinder (20 mm diameter) approached the sample at the speed of 3 mm/s and penetrated 0.5 mm into the fillet. Then the force was reduced and the fillet was allowed to rebound 10 s with the cylinder just touching the surface. After this, the cylinder was pressed on the fillet a second time. Hardness of the fish flesh was obtained by analysing the first force peak of the TPA curve, and the obtained values were expressed as gram. Six fillets from three fish were used for analysis. 2.7. Sensory evaluation Sensory scores of raw fish were calculated using the quality index method (QIM) by seven member trained panellists from the laboratory staff (two females and five males between 26 and 46 years old). The QIM is based on the freshness quality grading system developed by Nielsen and Hyldig (2004). Each assessor scored for eyes, gill, skin, body surface, body surface slime and colour of belly from 0 to a maximum of 3, where 0 represented the freshest quality and the scores increased according to spoilage up to 3 for each parameter. Scores of separate characteristics were summed to give a comprehensive sensory score. Panellists were asked to describe whether the fish were acceptable or not. This was used to determine the shelf-life of the fish. 2.8. Statistical analysis Data are expressed as mean values (n = 3) accompanied by the standard errors of means. Analyses were performed with SPSS software (Version 14.0; SPSS, Chicago, IL). Descriptive statistics (mean, standard deviation, and coefficient of variation), one-way ANOVA, multiple comparison with the Tukey test, and linear regression analysis were applied. Significance level was set at 5%. 3. Results and discussion 3.1. Proximate composition Proximate analysis was determined in the initial fish samples before being treated with preservatives. The mean (±SD) compositional contents of moisture, lipid, protein, and ash (g/100 g fish muscle) in the raw crucian carp were 77.61 ± 1.53%, 3.22 ± 0.14%, 17.40 ± 0.85%, and 1.01 ± 0.08%, respectively. The proximate composition of crucian carp reported in different studies (Moon et al., 2006) indicated some differences, especially for the lipid content and protein. Such differences in the composition of fish are strongly related to their nutrition, catching season (spawning cycles), environment, fish size and gender (Sallam, 2007). The compositional variations may lead to the changes in sensory attributes, and also can affect the microbial growth. In addition, the farming patterns of fish usually influence their lipid content. The compositional variation will induce differences in the sensory attributes, including aroma, taste, colour, surface appearance, and texture of the fish, which influence its acceptability.
viable counts (TVC) during the 20-day storage are presented in Fig. 1. The results showed that microbiological growth was significantly (p < 0.05) influenced by the addition of the two natural preservatives and especially rosemary extract. The initial TVC was 2.84 log CFU/g, indicating that the crucian carp studied was of good quality. The fish muscle is sterile when caught, but is quickly contaminated by surface as well as intestinal bacteria, along with contamination from the aquatic environment, equipment, human handling and storage conditions. Because of these reasons, the TVC values of the three groups increased gradually with storage. The fish of the control group attained a TVC value of 6.97 log CFU/g on day 10, which was close to the microbiological acceptability limit of 7 log CFU/g for raw fish (Ojagh, Rezaei, Razavi, & Hosseini, 2010), indicating a microbiological shelf-life about 9– 10 days for the control samples. In comparison, a shelf-life of less than 10 days has been measured for salmon stored at 1 °C (Sallam, 2007). Dipping crucian carp into 0.2% aqueous solutions of tea polyphenols and rosemary extract obviously delayed microbial growth and extended the shelf-life of the fish. Neither treated group samples reached the microbiological acceptability limit during the 15-day storage and had significantly lower TVC values than the control group (p < 0.05), especially the rosemary extract group. Tea polyphenols, with effective antimicrobial and antioxidant activities, could significantly delay microbial growth and have been widely applied as a natural food preservative. Yi et al. (2010) confirmed that shelf-life of vacuum-packed Collichthys fish balls could be prolonged for an additional 6 days during 0 °C storage by adding tea polyphenols. Many studies have proved that tea polyphenols show broad antimicrobial properties and could effectively inhibit most foodborne pathogens and spoilage organisms, such as Bacillus cereus, Staphylococcus aureus, Pseudomonas aeruginosa, Listeria monocytogenes, and Pseudomonas fluorescens (Yi et al., 2010; Friedman, Henika, Levin, Mandrell, & Kozukue, 2006). Rosemary also has been shown to present possess antioxidant and antibacterial activity (Georgantelis et al., 2007).
3.3. Chemical analyses 3.3.1. pH value and total volatile basic nitrogen (TVB-N) Changes in the pH values of crucian carp muscle during storage are shown in Fig. 2. The initial pH value of the fish samples was 6.61 ± 0.03, which was similar to the result reported by Kristoffersen et al. (2006) for Atlantic cod (Gadus morhua L), but was slightly
3.2. Microbiological analyses It has been estimated that about one-third of the world’s food production is lost annually on account of microbial spoilage. Microorganisms associated with aquatic products usually reflect the microbial population in their environment. Changes of total
Fig. 1. Changes in total viable counts (TVC) of crucian carp during chilled storage (TP = tea polyphenols, R = rosemary oil).
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carp in tea polyphenols and rosemary extract, and TVB-N value level was significantly lower for the treated samples than for the control samples.
Fig. 2. Changes in pH and TVB-N values of crucian carp during chilled storage (TP = tea polyphenols, R = rosemary oil).
higher than the value reported by Fan et al. (2008) for silver carp. Differences in the initial values of pH may due to the species, diet, seasons, and the level of activity or stress during the catch as well as the type of muscle. During storage, the pH values decreased in the early stages and then increased gradually. The initial decrease of pH might be related to the accumulation of lactic acid, a product of glycolysis, while the increase in late storage may be caused by the growth of spoilage bacteria leading to the accumulation of alkaline components (e.g., ammonia and trimethylamine). Similar results were obtained by Duan et al. (2010) and Fan et al. (2008). The pH values of both treated group samples were consistently lower than that of the control (p < 0.05) during storage, which might result from the antimicrobial characteristics of tea polyphenols and rosemary extract. However, no significant difference was found between the tea polyphenols treated group and rosemary extract treated group (p > 0.05). The TVB-N value is one of the most widely used indicators of seafood deterioration. It is a general term which includes the calculation of trimethylamine (produced by spoilage bacteria), dimethylamine (produced by autolytic enzymes during chilled preservation), ammonia (produced by the deamination of aminoacids and nucleotide catabolites) as well as other volatile basic nitrogenous compounds correlated with seafood spoilage. Changes in TVB-N values in fish samples during chilled storage are shown in Fig. 2. The results showed that the values increased gradually in all samples during the 20-day storage. TVB-N values increased from an initial value (mg N per 100 g of fish) of 6.89 ± 0.22–42.9 ± 0.59 for control sample, to 33.5 ± 3.34 for tea polyphenols treated group, and to 30.4 ± 2.62 for rosemary extract treated group at the end of storage (Day 20). The two treated sample groups maintained a significantly (p < 0.05) lower TVB-N value than that of the control. When considering a TVB-N value level of 25 mg N/100 g fresh fish as the acceptable limit proposed by Ojagh et al. (2010), the shelf-life of the control and the treated groups were about 11 and nearly 18 days, respectively. Since TVB-N is produced mainly by bacterial decomposition of fish muscle, the initial TVB-N value was related to the relatively low TVC value, and higher values of TVC for the control samples compared with treated samples after 11 days storage could account for the higher TVB-N values of the control samples. Fan et al. (2008) reported that during the storage of silver carp, using tea polyphenols dip could be conducive to either a more rapidly reduced bacterial population or decreased capability of bacteria for oxidative deamination of non-protein nitrogen compounds, or both. Similarly, microbial growth was effectively inhibited by dipping crucian
3.3.2. K-value The pathway of adenosine triphosphate (ATP) catabolism in fish flesh has been widely documented as a catabolite sequence to adenosine diphosphate (ADP), adenosine monophosphate (AMP), inosine monophosphate (IMP), inosine (INO) and hypoxanthine (Hx), and has been used frequently as a basis to calculate the K-value or freshness index in many species (Ocaño-Higuera et al., 2011; Özogul et al., 2010). Changes in K-values of crucian carp during chilled storage are shown in Fig. 3. A gradual increase in K-values was observed with storage time. The initial K-value in fish samples was 3.62%, which was in agreement with that of Li, Luo, Feng, and Yao (2011), who reported the initial K-value in crucian carp was 3%. The K-value of the control group rose continuously and reached 54.58% on day 20 of storage. The changes of K-value in tea polyphenols treated group and rosemary extract treated group showed the same tendency as did those in the control group. Saito, Arai, and Matsuyoshi (1959) depicted fishing products with K-values lower than 20% as very fresh ones, with less than 50% as moderately fresh, and higher than 70% as not fresh. Based on these K-value categories, the three groups of fish samples could be considered very fresh till at least the fifth day, and moderately fresh at the end of storage. Moreover, the K-values of treated groups were lower than that of the control, indicating that tea polyphenols and rosemary extract could inhibit the degradation of ATP and maintain the quality of fish. 3.3.3. Thiobarbituric acid reactive substances (TBARS) Lipid oxidation in fish flesh depends on numerous factors (the species, preservation temperature, fat composition, etc.). TBA value has been broadly used to describe the degree of lipid oxidation, and the presence of TBA reactive substances is due to second stage auto-oxidation, during which peroxides are oxidised to aldehydes and ketones. In this study, TBA values of different treated groups during chilled storage are shown in Fig. 4. The results showed that TBA values of three groups increased gradually from an initial 0.19 ± 0.01 mg MDA/kg to 0.84 ± 0.01, 0.71 ± 0.03 and 0.75 ± 0.01 mg MDA/kg during storage for the control, tea polyphenols treated group and rosemary extract treated group, respectively. The TBA values of the fish treated with tea polyphenols and rosemary
Fig. 3. Changes in K values of crucian carp during chilled storage (TP = tea polyphenols, R = rosemary oil).
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Fig. 4. Changes in TBA values of crucian carp during chilled storage (TP = tea polyphenols, R = rosemary oil). Fig. 6. Changes in sensory of crucian carp during chilled storage (TP = tea polyphenols, R = rosemary oil).
extract were lower than that of the control (p < 0.05). The results showed that lipid oxidation could be inhibited by tea polyphenols and rosemary extract, suggesting that both have antioxidant activity, in agreement with Li et al. (2012) and Fan et al. (2008). The TBA values in this study were lower than those reported for whole fish with higher fat contents stored under similar circumstances, such as silver carp (Fan et al., 2008). In addition to fat content, oxidative rancidity may be influenced by other factors, such as storage states. Since a fillet has a large surface space exposed to oxygen, it is prone to oxidation more than the whole fish (without being gutted).
3.3.4. Texture The muscle texture of fish depends on intrinsic biological factors, such as the content of fat and collagen, and the microbiological and autolytic processes caused by the death of the fish, which induce degradation of myofibrillar protein integration and eventual softening of the muscle. The firmness of crucian carp decreased gradually as the storage time increased (Fig. 5). The two treatments showed good effects in retarding the softening of fish meat. The hardness of the fish samples treated with tea polyphenols or rosemary extract was higher than that of the control.
3.4. Sensory attributes An objective freshness assessment system is the Quality Index Method (QIM). QIM is a scientific sensory method based on meaningful sensory parameters for raw fish and a score system from zero to one to two or three demerit points (Nielsen & Hyldig, 2004). The scores for all the characteristics are then aggregated to give an overall sensory score, the so-called Quality Index. QIM gives scores of zero to very fresh fish with increasing values as the fish decay. The changes in the sensory score of crucian carp in different treated groups during the whole storage are shown in Fig. 6. Zero represented absolutely fresh and 22 defined completely deteriorated, as determined by test panellists who gave the advice that the fish were not acceptable. The scores of the sensory assessment showed a similar tendency of increasing unacceptability for the flesh samples of the control, tea polyphenols treated group and rosemary extract treated group. The fish treated with tea polyphenols and rosemary extract gave lower sensory scores and showed better characteristics for appearance, flavour, relative to the control. Both groups of fish had less fishy smells and kept a firmer texture; the fish with rosemary extract treatment were preferred by the panellists. Until Day 10 all samples received sensory scores in the range of 7–13. The observed shelf-life of crucian carp was about 7–8 days for control samples, 13–14 days for tea polyphenols treated group and 15–16 days for rosemary extract treated group. Fish spoilage gives rise to strongly fishy, rancid and putrid odours. Treating with tea polyphenols or rosemary extract could retain good quality characteristics and extend the shelflife of crucian carp by 6–8 days compared to the control samples. These conclusions agreed well with the results for microbiological and chemical quality analyses.
4. Conclusion
Fig. 5. Changes in texture of crucian carp during chilled storage (TP = tea polyphenols, R = rosemary oil).
The present study showed that a dipping treatment with either 0.2% tea polyphenols or 0.2% rosemary extract could effectively retard microbial growth, delay chemical deterioration, maintain or improve sensory attributes and extend the shelf-life of crucian carp for 6–8 days during refrigerated storage. Natural preservatives such as tea polyphenols and rosemary extract can be used as a safe method for storage of crucian carp.
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Acknowledgements This study was supported by a Grant from the National Key Technologies R&D Program of China during the 12th 5-Year Plan Period (No. 2012BAD29B06) and the National Natural Science Foundation of China (No. 31071514).
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Moon, J. Y., Kim, Y. B., Lee, S. I., Song, H., Choi, K., & Jeong, G. H. (2006). Distribution characteristics of polychlorinated biphenyls in crucian carp (Carassius auratus) from major rivers in Korea. Chemosphere, 62, 430–439. Nielsen, D., & Hyldig, G. (2004). Influence of handling procedures and biological factors on the QIM evaluation of whole herring (Clupea harengus L.). Food Research International, 37, 975–983. Ocaño-Higuera, V. M., Maeda-Martínez, A. N., Marquez-Ríos, E., CanizalesRodríguez, D. F., Castillo-Yáñez, F. J., Ruíz-Bustos, E., Graciano-Verdugo, A. Z., & Plascencia-Jatomea, M. (2011). Freshness assessment of ray fish stored in ice by biochemical, chemical and physical methods. Food Chemistry, 125, 49–54. Ojagh, S. M., Rezaei, M., Razavi, S. H., & Hosseini, S. M. H. (2010). Effect of chitosan coatings enriched with cinnamon oil on the quality of refrigerated rainbow trout. Food Chemistry, 120, 193–198. Ozogul, Y., Ayas, D., Yazgan, H., Ozogul, F., Boga, E. K., & Ozyurt, G. (2010). The capability of rosemary extract in preventing oxidation of fish lipid. International Journal of Food Science & Technology, 45, 1717–1723. Özogul, F., Özden, Ö., Özog˘ul, Y., & Erkan, N. (2010). The effects of gammairradiation on the nucleotide degradation compounds in sea bass (Dicentrarchus labrax) stored in ice. Food Chemistry, 122, 789–794. Saito, T., Arai, K., & Matsuyoshi, M. (1959). A new method for estimating the freshness of fish. Bulletin of the Japanese Society of Scientific Fisheries, 24, 749–750. Sallam, K. I. (2007). Antimicrobial and antioxidant effects of sodium acetate, sodium lactate, and sodium citrate in refrigerated sliced salmon. Food Control, 18, 566–575. Sallam, K. I., Ahmed, A. M., Elgazzar, M. M., & Eldaly, E. A. (2007). Chemical quality and sensory attributes of marinated Pacific saury (Cololabis saira) during vacuum-packaged storage at 4 °C. Food Chemistry, 102, 1061–1070. Sigurgisladottir, S., Hafsteinsson, H., Jonsson, A., Lie, Ø., Nortvedt, R., Thomassen, M., & Torrissen, O. (1999). Textural properties of raw salmon fillets as related to sampling method. Journal of Food Science, 64, 99–104. Tironi, V., Tomás, M., & Añón, M. (2009). Lipid and protein changes in chilled sea salmon (Pseudopercis semifasciata): Effect of previous rosemary extract (Rossmarinus officinalis L.) application. International Journal of Food Science & Technology, 44, 1254–1262. Xiao, F., Kang, H. B., & Xin, L. (2007). Freshness variation of crucian carp (Carassius auratus) during chilled storage. Food Science, 28, 501–511 (in Chinese). Yi, S. M., Zhu, J. L., Fu, L. L., & Li, J. R. (2010). Tea polyphenols inhibit Pseudomonas aeruginosa through damage to the cell membrane. International journal of food microbiology, 144, 111–117. Yue, X. H., Shen, Y. X., & Ou, J. (2002). Coating with different molecular weight chitosan on the quality of crucian carp (Carassius auratus) during chilled storage. Science and Technology of Food Industry, 23, 69–71 (in Chinese). Zeng, M. Y., Huang, H., Li, Y. H., & Huang, Y. F. (2001). Quality changes of crucian (Carassius auratus) during partial freezing. Journal of Ocean University of Qingdao, 31, 351–355 (in Chinese).
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Shelf-life extension of crucian carp (Carassius auratus) using natural preservatives during chilled storage Tingting Li a,b, Jianrong Li a,c,⇑, Wenzhong Hu b, Xuguang Zhang a, Xuepeng Li c, Jin Zhao a,d a
College of Food Science and Biotechnology, Zhejiang Gongshang University, Hangzhou 310035, China College of Life Science, Dalian Nationalities University, Dalian 116600, China c Bohai University, Jinzhou 121013, China d Zhejiang Marine Food Processing Quality Control Techniques and Instrumentation Engineering Laboratory, College of Life Science, China Jiliang University, Hangzhou 310018, China b
a r t i c l e
i n f o
Article history: Received 22 December 2011 Received in revised form 6 April 2012 Accepted 18 April 2012 Available online 27 April 2012 Keywords: Crucian carp Tea polyphenols Rosemary extract Quality characteristics Shelf-life
a b s t r a c t The effect of the natural preservatives, tea polyphenols and rosemary extract, on microbiological [total viable count (TVC)], chemical [pH, total volatile base nitrogen (TVB-N), K-value and thiobarbituric acid (TBA) values], texture and sensory changes of air-packaged whole crucian carp (Carassius auratus) stored at 4 ± 1 °C was investigated for 20 days. The shelf-life of crucian carp was found to be 7–8 days for untreated group (control), 13–14 days for tea polyphenols group and 15–16 days for rosemary extract treated group according to sensory assessment results, for which the corresponding microbiological assessment also showed an increased shelf-life. Meanwhile, the increases of pH, TVB-N, K-value and TBA values were significantly delayed in both treated groups of samples compared to the control group. Thus, either tea polyphenols or rosemary extract could be used as potential preservatives to extend the shelf-life of crucian carp during chilled storage. Ó 2012 Elsevier Ltd. All rights reserved.
1. Introduction Crucian carp (Carassius auratus) is one of the most economically important freshwater-cultured fish species. It is popular in China due to its fast growth rate, palatability, and the nutritional quality of its flesh (Zeng, Huang, Li, & Huang, 2001). In China, production of crucian carp reached nearly 2,000,000 tons in 2009 (Fishery Bureau of Department of Agriculture of China., 2011). However, fish are usually more perishable than other muscle foods, and a considerable number of fish are spoiled due to lack of good preservation. Crucian carp is an easily perishable product because of its relatively high quantities of volatile basic nitrogen as well as free amino acids, high water activity, and presence of autolytic enzymes (Duan, Jiang, Cherian, & Zhao, 2010). Xiao, Kang, and Xin (2007) reported the freshness variation of crucian carp (Carassius auratus) during chilled storage, while Yue, Shen, and Ou (2002) studied the effect of coatings with different molecular weight chitosan on crucian carp quality. The spoilage of fish is a complicated process in which microbiology, physical and chemical changes interact. Activities of the fish’s own enzymes and chemical reactions are usually responsible for the initial loss of fish freshness, whereas the metabolic activities ⇑ Corresponding author at: College of Food Science and Biotechnology, Zhejiang Gongshang University, Hangzhou 310035, China. Tel./fax: +86 416 3400008. E-mail addresses: [email protected] (T. Li), [email protected]. edu.cn (J. Li). 0308-8146/$ - see front matter Ó 2012 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.foodchem.2012.04.115
of microorganisms are involved in the whole spoilage (Sallam, Ahmed, Elgazzar, & Eldaly, 2007). The inherent quality of seafood makes it more susceptible to food-borne hazards. Therefore, effective methods for extending shelf-life and improving quality of fresh crucian carp are necessary. The application of good manufacturing practices (GMP), good hygienic practices (GHP), and hazard analysis of critical control point (HACCP) is essential in the production, distribution, storage and retailing of refrigerated foods. Because of consumer desire for fresh chilled foods with extended shelf-life, numerous studies have been directed toward using diverse preservation strategies to preserve or prolong the shelf-life of fresh foods including fishery products to ensure product safety (Sallam, 2007). Natural preservatives, such as tea polyphenols and rosemary extract, have been widely used in the food industry because of their good preservative effect (Li et al., 2012; Ozogul et al., 2010; Fan, Chi, & Zhang, 2008; Georgantelis, Ambrosiadis, Katikou, Blekas, & Georgakis, 2007; Tironi, Tomás, & Añón, 2009; Yi, Zhu, Fu, & Li, 2010). The preservative effect of tea polyphenols and rosemary extract is mainly due to the inhibition of some enzymes’ activities, as well as the free radical scavenging ability and therefore prevention of lipid oxidation (Bubonja-Sonje, Giacometti, & Abram, 2011; Fan et al., 2008). In addition, their antimicrobial properties are also important (Georgantelis et al., 2007; Yi et al., 2010). Limited data, however, are available with regard to the application of tea polyphenols and rosemary extract for extension of the shelf-life of crucian carp. Thus, the objective of the present
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study was to evaluate the potential effects of tea polyphenols and rosemary extract as antioxidants on the quality and shelf-life of crucian carp during chilled storage.
2. Materials and methods 2.1. Fish sample preparation Fifty live commercial-sized crucian carp with an average weight of 360 ± 10 g were purchased from Dalian Aquatic Market in September (Dalian, Liaoning province, China). They were transferred to the Food Processing Laboratory of Dalian Nationalities University within 0.5 h and kept alive before being processed. The fish were killed by slurry ice and kept whole and ungutted at 0 °C before use.
2.2. Natural antioxidants and chemicals Tea polyphenols was purchased from Zhejiang University Tea Scientific Co., Ltd. (purity P 98%, Hangzhou, Zhejiang province, China). Rosemary extract containing 22 ± 4% phenolic diterpenes (carnosic acid, carnosol, rosmarinic acid, as stated by the manufacturer) was bought from Guizhou Red Star Development Duyun Luyou Co., Ltd. (Duyun, Guizhou province, China). The two extracts were packed in polyethylene bags and stored at 4 ± 1 °C before using.
2.3. Preparation of fish samples The whole fish were washed under running tap water and divided into three groups. First group was used as the control, second group was immersed in a solution of 2 g of tea polyphenols in 1 L of distiled water (4 ± 1 °C) for 60 min (0.2% TP), and the third was immersed in a solution of 2 g of rosemary extract in 1 L of distiled water (4 ± 1 °C) for 60 min (0.2% R), then the three groups of fish were kept on a plastic net for 2 h to drain at 4 ± 1 °C. After that, they were packed in air-proof polyethylene pouches and stored at 4 ± 1 °C for subsequent quality assessment. Microbiological, chemical, and sensory analyses were performed at 5-day intervals, each analysis was repeated three times with three fish and the averages were used to measure the overall quality of fish.
2.4. Proximate composition analyses A proximate composition analysis was performed on five fish on day 0 of preservation. Proximate analyses (moisture content, total crude protein, lipid content and ash content) of the fish samples were based on the procedures set by the AOAC (1997).
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2.6. Chemical analyses 2.6.1. pH and Total volatile basic nitrogen (TVB-N) The pH values were measured to illustrate the hygienic standard of fish and other aquatic products according to the GB/T of the Chinese standard (GB/T 5009.45-2003). A 10.0-g sample of fish muscle was mixed with 90 ml of distiled water and the mixture was filtered. After 30 min, the pH of the filtrate was measured using a digital 320 pH metre (Mettler Toledo, Zurich, Switzerland). Total volatile basic nitrogen (TVB-N) value was estimated by the FOSS. (2002). The microdiffusion method was mensurated by distillation after adding MgO to the homogenised samples. TVB-N values were determined with a Kjeltec 2300 (FOSS, Hiller, Denmark). TVB-N values were expressed in mg nitrogen kg1 (mg N kg1) fish sample. 2.6.2. K-value ATP and its breakdown products were measured according to the modified method of Özogul, Özden, Özog˘ul, and Erkan (2010). Five grams of minced fish flesh without skin were extracted with 25 ml of 0.6 M perchloric acid using an Ultra-Turrax (T25 basic; IKA-Werke, Staufen, Germany) for 1 min in an ice bath. The extraction mixture was centrifuged at 1940g for 10 min and after that, 10 ml of supernatant were quickly adjusted to pH 6.5–6.8 using 1 M KOH. The neutralised supernatant was allowed to stand for 30 min in an ice bath to precipitate most of the potassium perchlorate, which was then removed by centrifuging at 1940g for 10 min. The supernatant solution was made up to 20 ml and then stored at 80 °C until HPLC analysis. The identification of nucleotides, nucleosides and bases was determined and calculated by comparing their retention times with those of commercially obtained standards and by adding or spiking of standards. The K-value was defined as the per cent ratio of inosine (HxR) and hypoxanthine (Hx) to the sum of ATP and degradation products as follows:
K% ¼ ½ðHxR þ HxÞ=ðATP þ ADP þ AMP þ IMP þ HxR þ HxÞ 100:
2.6.3. Thiobarbituric acid reactive substances (TBARS) The thiobarbituric acid value was determined colorimetrically by the method of Porkony and Dieffenbacher, as described by Kirk and Sawyer (1991). A portion (200 mg) of sample was weighed into a 25-ml volumetric flask. An aliquot (1 ml) of 1-butanol was added to dissolve the sample. The mixture was made to volume and mixed. A portion (5.0 ml) of the mixture was pipetted into a dry stoppered test tube and 5 ml of TBA reagent (prepared by dissolving 200 mg of 2-TBA in 100 ml 1-butanol, filtered, stored at 4 °C for not more than 7 days) were added. The test tubes were stoppered, vortexed and placed in a water bath at 95 °C for 120 min, then cooled. Absorbance (As) was measured at 530 nm against water blank. A reagent blank was run and absorbance (Ab) recorded. TBA value (mg of malonaldehyde equivalents/kg of tissue) was obtained by the formula:
50 ðAs Ab Þ 200
2.5. Bacteriological analyses
TBA ¼
Fish samples were taken aseptically in a vertical laminar-flow cabinet and 10 g were transferred to a stomacher bag; 90 ml of 0.1% peptone water with salt (NaCl, 0.85%, w/v) were added and homogenised for 60 s with a stomacher. From this dilution, other decimal dilutions were obtained and 1 ml of three dilutions was transferred in triplicate to Petri dishes containing 15 ml commercial plate count agar (PCA, Base Bio-Tech, Hangzhou, China). Total viable counts (TVC) were determined by counting the number of colony-forming units after incubation at 25 °C for 48 h.
2.6.4. Texture measurements Texture profile analyses (TPA) were carried out according to Sigurgisladottir et al. (1999). The TA.XT texture analyser (Stable Micro Systems Ltd., Godalming, UK) was used. A flat-ended cylinder that simulated the human finger was used. Constant penetration depth of 2.5 mm was applied on the fillets of about 15 mm thickness after testing penetrations in the range of 2–5 mm. This penetration depth was chosen as the maximum distance which could be
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applied without influencing the muscle structure by damaging it and leaving a mark on the fillet. Three sampling points were selected in each fillet [dorsal, tail (8 mm from the edge of tail) and between dorsal and tail. Double compression was applied to construct the texture profile analyses (TPA) parameters. The flat-ended cylinder (20 mm diameter) approached the sample at the speed of 3 mm/s and penetrated 0.5 mm into the fillet. Then the force was reduced and the fillet was allowed to rebound 10 s with the cylinder just touching the surface. After this, the cylinder was pressed on the fillet a second time. Hardness of the fish flesh was obtained by analysing the first force peak of the TPA curve, and the obtained values were expressed as gram. Six fillets from three fish were used for analysis. 2.7. Sensory evaluation Sensory scores of raw fish were calculated using the quality index method (QIM) by seven member trained panellists from the laboratory staff (two females and five males between 26 and 46 years old). The QIM is based on the freshness quality grading system developed by Nielsen and Hyldig (2004). Each assessor scored for eyes, gill, skin, body surface, body surface slime and colour of belly from 0 to a maximum of 3, where 0 represented the freshest quality and the scores increased according to spoilage up to 3 for each parameter. Scores of separate characteristics were summed to give a comprehensive sensory score. Panellists were asked to describe whether the fish were acceptable or not. This was used to determine the shelf-life of the fish. 2.8. Statistical analysis Data are expressed as mean values (n = 3) accompanied by the standard errors of means. Analyses were performed with SPSS software (Version 14.0; SPSS, Chicago, IL). Descriptive statistics (mean, standard deviation, and coefficient of variation), one-way ANOVA, multiple comparison with the Tukey test, and linear regression analysis were applied. Significance level was set at 5%. 3. Results and discussion 3.1. Proximate composition Proximate analysis was determined in the initial fish samples before being treated with preservatives. The mean (±SD) compositional contents of moisture, lipid, protein, and ash (g/100 g fish muscle) in the raw crucian carp were 77.61 ± 1.53%, 3.22 ± 0.14%, 17.40 ± 0.85%, and 1.01 ± 0.08%, respectively. The proximate composition of crucian carp reported in different studies (Moon et al., 2006) indicated some differences, especially for the lipid content and protein. Such differences in the composition of fish are strongly related to their nutrition, catching season (spawning cycles), environment, fish size and gender (Sallam, 2007). The compositional variations may lead to the changes in sensory attributes, and also can affect the microbial growth. In addition, the farming patterns of fish usually influence their lipid content. The compositional variation will induce differences in the sensory attributes, including aroma, taste, colour, surface appearance, and texture of the fish, which influence its acceptability.
viable counts (TVC) during the 20-day storage are presented in Fig. 1. The results showed that microbiological growth was significantly (p < 0.05) influenced by the addition of the two natural preservatives and especially rosemary extract. The initial TVC was 2.84 log CFU/g, indicating that the crucian carp studied was of good quality. The fish muscle is sterile when caught, but is quickly contaminated by surface as well as intestinal bacteria, along with contamination from the aquatic environment, equipment, human handling and storage conditions. Because of these reasons, the TVC values of the three groups increased gradually with storage. The fish of the control group attained a TVC value of 6.97 log CFU/g on day 10, which was close to the microbiological acceptability limit of 7 log CFU/g for raw fish (Ojagh, Rezaei, Razavi, & Hosseini, 2010), indicating a microbiological shelf-life about 9– 10 days for the control samples. In comparison, a shelf-life of less than 10 days has been measured for salmon stored at 1 °C (Sallam, 2007). Dipping crucian carp into 0.2% aqueous solutions of tea polyphenols and rosemary extract obviously delayed microbial growth and extended the shelf-life of the fish. Neither treated group samples reached the microbiological acceptability limit during the 15-day storage and had significantly lower TVC values than the control group (p < 0.05), especially the rosemary extract group. Tea polyphenols, with effective antimicrobial and antioxidant activities, could significantly delay microbial growth and have been widely applied as a natural food preservative. Yi et al. (2010) confirmed that shelf-life of vacuum-packed Collichthys fish balls could be prolonged for an additional 6 days during 0 °C storage by adding tea polyphenols. Many studies have proved that tea polyphenols show broad antimicrobial properties and could effectively inhibit most foodborne pathogens and spoilage organisms, such as Bacillus cereus, Staphylococcus aureus, Pseudomonas aeruginosa, Listeria monocytogenes, and Pseudomonas fluorescens (Yi et al., 2010; Friedman, Henika, Levin, Mandrell, & Kozukue, 2006). Rosemary also has been shown to present possess antioxidant and antibacterial activity (Georgantelis et al., 2007).
3.3. Chemical analyses 3.3.1. pH value and total volatile basic nitrogen (TVB-N) Changes in the pH values of crucian carp muscle during storage are shown in Fig. 2. The initial pH value of the fish samples was 6.61 ± 0.03, which was similar to the result reported by Kristoffersen et al. (2006) for Atlantic cod (Gadus morhua L), but was slightly
3.2. Microbiological analyses It has been estimated that about one-third of the world’s food production is lost annually on account of microbial spoilage. Microorganisms associated with aquatic products usually reflect the microbial population in their environment. Changes of total
Fig. 1. Changes in total viable counts (TVC) of crucian carp during chilled storage (TP = tea polyphenols, R = rosemary oil).
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carp in tea polyphenols and rosemary extract, and TVB-N value level was significantly lower for the treated samples than for the control samples.
Fig. 2. Changes in pH and TVB-N values of crucian carp during chilled storage (TP = tea polyphenols, R = rosemary oil).
higher than the value reported by Fan et al. (2008) for silver carp. Differences in the initial values of pH may due to the species, diet, seasons, and the level of activity or stress during the catch as well as the type of muscle. During storage, the pH values decreased in the early stages and then increased gradually. The initial decrease of pH might be related to the accumulation of lactic acid, a product of glycolysis, while the increase in late storage may be caused by the growth of spoilage bacteria leading to the accumulation of alkaline components (e.g., ammonia and trimethylamine). Similar results were obtained by Duan et al. (2010) and Fan et al. (2008). The pH values of both treated group samples were consistently lower than that of the control (p < 0.05) during storage, which might result from the antimicrobial characteristics of tea polyphenols and rosemary extract. However, no significant difference was found between the tea polyphenols treated group and rosemary extract treated group (p > 0.05). The TVB-N value is one of the most widely used indicators of seafood deterioration. It is a general term which includes the calculation of trimethylamine (produced by spoilage bacteria), dimethylamine (produced by autolytic enzymes during chilled preservation), ammonia (produced by the deamination of aminoacids and nucleotide catabolites) as well as other volatile basic nitrogenous compounds correlated with seafood spoilage. Changes in TVB-N values in fish samples during chilled storage are shown in Fig. 2. The results showed that the values increased gradually in all samples during the 20-day storage. TVB-N values increased from an initial value (mg N per 100 g of fish) of 6.89 ± 0.22–42.9 ± 0.59 for control sample, to 33.5 ± 3.34 for tea polyphenols treated group, and to 30.4 ± 2.62 for rosemary extract treated group at the end of storage (Day 20). The two treated sample groups maintained a significantly (p < 0.05) lower TVB-N value than that of the control. When considering a TVB-N value level of 25 mg N/100 g fresh fish as the acceptable limit proposed by Ojagh et al. (2010), the shelf-life of the control and the treated groups were about 11 and nearly 18 days, respectively. Since TVB-N is produced mainly by bacterial decomposition of fish muscle, the initial TVB-N value was related to the relatively low TVC value, and higher values of TVC for the control samples compared with treated samples after 11 days storage could account for the higher TVB-N values of the control samples. Fan et al. (2008) reported that during the storage of silver carp, using tea polyphenols dip could be conducive to either a more rapidly reduced bacterial population or decreased capability of bacteria for oxidative deamination of non-protein nitrogen compounds, or both. Similarly, microbial growth was effectively inhibited by dipping crucian
3.3.2. K-value The pathway of adenosine triphosphate (ATP) catabolism in fish flesh has been widely documented as a catabolite sequence to adenosine diphosphate (ADP), adenosine monophosphate (AMP), inosine monophosphate (IMP), inosine (INO) and hypoxanthine (Hx), and has been used frequently as a basis to calculate the K-value or freshness index in many species (Ocaño-Higuera et al., 2011; Özogul et al., 2010). Changes in K-values of crucian carp during chilled storage are shown in Fig. 3. A gradual increase in K-values was observed with storage time. The initial K-value in fish samples was 3.62%, which was in agreement with that of Li, Luo, Feng, and Yao (2011), who reported the initial K-value in crucian carp was 3%. The K-value of the control group rose continuously and reached 54.58% on day 20 of storage. The changes of K-value in tea polyphenols treated group and rosemary extract treated group showed the same tendency as did those in the control group. Saito, Arai, and Matsuyoshi (1959) depicted fishing products with K-values lower than 20% as very fresh ones, with less than 50% as moderately fresh, and higher than 70% as not fresh. Based on these K-value categories, the three groups of fish samples could be considered very fresh till at least the fifth day, and moderately fresh at the end of storage. Moreover, the K-values of treated groups were lower than that of the control, indicating that tea polyphenols and rosemary extract could inhibit the degradation of ATP and maintain the quality of fish. 3.3.3. Thiobarbituric acid reactive substances (TBARS) Lipid oxidation in fish flesh depends on numerous factors (the species, preservation temperature, fat composition, etc.). TBA value has been broadly used to describe the degree of lipid oxidation, and the presence of TBA reactive substances is due to second stage auto-oxidation, during which peroxides are oxidised to aldehydes and ketones. In this study, TBA values of different treated groups during chilled storage are shown in Fig. 4. The results showed that TBA values of three groups increased gradually from an initial 0.19 ± 0.01 mg MDA/kg to 0.84 ± 0.01, 0.71 ± 0.03 and 0.75 ± 0.01 mg MDA/kg during storage for the control, tea polyphenols treated group and rosemary extract treated group, respectively. The TBA values of the fish treated with tea polyphenols and rosemary
Fig. 3. Changes in K values of crucian carp during chilled storage (TP = tea polyphenols, R = rosemary oil).
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Fig. 4. Changes in TBA values of crucian carp during chilled storage (TP = tea polyphenols, R = rosemary oil). Fig. 6. Changes in sensory of crucian carp during chilled storage (TP = tea polyphenols, R = rosemary oil).
extract were lower than that of the control (p < 0.05). The results showed that lipid oxidation could be inhibited by tea polyphenols and rosemary extract, suggesting that both have antioxidant activity, in agreement with Li et al. (2012) and Fan et al. (2008). The TBA values in this study were lower than those reported for whole fish with higher fat contents stored under similar circumstances, such as silver carp (Fan et al., 2008). In addition to fat content, oxidative rancidity may be influenced by other factors, such as storage states. Since a fillet has a large surface space exposed to oxygen, it is prone to oxidation more than the whole fish (without being gutted).
3.3.4. Texture The muscle texture of fish depends on intrinsic biological factors, such as the content of fat and collagen, and the microbiological and autolytic processes caused by the death of the fish, which induce degradation of myofibrillar protein integration and eventual softening of the muscle. The firmness of crucian carp decreased gradually as the storage time increased (Fig. 5). The two treatments showed good effects in retarding the softening of fish meat. The hardness of the fish samples treated with tea polyphenols or rosemary extract was higher than that of the control.
3.4. Sensory attributes An objective freshness assessment system is the Quality Index Method (QIM). QIM is a scientific sensory method based on meaningful sensory parameters for raw fish and a score system from zero to one to two or three demerit points (Nielsen & Hyldig, 2004). The scores for all the characteristics are then aggregated to give an overall sensory score, the so-called Quality Index. QIM gives scores of zero to very fresh fish with increasing values as the fish decay. The changes in the sensory score of crucian carp in different treated groups during the whole storage are shown in Fig. 6. Zero represented absolutely fresh and 22 defined completely deteriorated, as determined by test panellists who gave the advice that the fish were not acceptable. The scores of the sensory assessment showed a similar tendency of increasing unacceptability for the flesh samples of the control, tea polyphenols treated group and rosemary extract treated group. The fish treated with tea polyphenols and rosemary extract gave lower sensory scores and showed better characteristics for appearance, flavour, relative to the control. Both groups of fish had less fishy smells and kept a firmer texture; the fish with rosemary extract treatment were preferred by the panellists. Until Day 10 all samples received sensory scores in the range of 7–13. The observed shelf-life of crucian carp was about 7–8 days for control samples, 13–14 days for tea polyphenols treated group and 15–16 days for rosemary extract treated group. Fish spoilage gives rise to strongly fishy, rancid and putrid odours. Treating with tea polyphenols or rosemary extract could retain good quality characteristics and extend the shelflife of crucian carp by 6–8 days compared to the control samples. These conclusions agreed well with the results for microbiological and chemical quality analyses.
4. Conclusion
Fig. 5. Changes in texture of crucian carp during chilled storage (TP = tea polyphenols, R = rosemary oil).
The present study showed that a dipping treatment with either 0.2% tea polyphenols or 0.2% rosemary extract could effectively retard microbial growth, delay chemical deterioration, maintain or improve sensory attributes and extend the shelf-life of crucian carp for 6–8 days during refrigerated storage. Natural preservatives such as tea polyphenols and rosemary extract can be used as a safe method for storage of crucian carp.
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Acknowledgements This study was supported by a Grant from the National Key Technologies R&D Program of China during the 12th 5-Year Plan Period (No. 2012BAD29B06) and the National Natural Science Foundation of China (No. 31071514).
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