The Effect of Corn Zein Edible Coating Containing Coriander Extract on The Quality and Durability of Silver carp (Hypophthalmichthys molitrix)

Abstract
Introduction: Silver carp fishing is in large quantities during the production season and supplied fresh or frozen, therefore maintaining the quality and durability of this type of fish is very important. The use of new packaging methods and the use of natural additives in food is expanding, because consumers want a healthy product with a longer durability (Aavidson and Zivanivic, 2003). One of the methods of food coating is the use of food coatings that cover the surface of the food in a thin layer and protect it from adverse changes (Krochta, 1997). These films are biodegradable and cannot be seen by the naked eye. Food coatings, as a secondary skin, have the properties of sticking to food, antibacterial and antioxidant, which are inside the material. They penetrate food by covering the surface of the product with these films, it is possible to prevent the decrease of humidity and the penetration of oxygen and improve the appearance of the product. Edible films, which are like preservatives to prevent the growth of microbes and corruption on the product surface, are a good substitute for them (Seifzadeh, 2007). In ancient times, plant and natural essential oils were used as fertilizers. Today, with the progress of science, it has been shown that these substances have antimicrobial and antioxidant activities (Hosseini et al., 2009). Although the use of artificial preservatives has a great effect to prevent bacterial growth and maintain the optimal quality of food, but because the adverse effects of such substances on the body have been identified in recent years, consumers prefer the use of natural substances and essential oils to synthetic substances and They prefer chemical (Satihivel, 2005). Therefore, the use of edible films is a method that, considering the problems related to food production and consumption, especially issues such as safety, quality, health and hygiene, improving the appearance and proper packaging, and finally paying attention to the economy of production, can play an effective role in the development Have a food industry (Gennadios, 2002). Given the increasing consumer preference for natural ingredients and the prohibition of chemical preservatives, the use of corn zein protein as a protein with a not-so-high price and the use of coriander extract, which is abundant in Iran, and the optimal use of combining these two by-products can be considered new research in the field of food preservation.
Material and methods: The present study was conducted with the aim of evaluating the effect of 10% corn protein coating containing coriander extract on the shelf life and quality maintenance of Silver carp fish at refrigerated temperature. Fresh Silver carp fish were obtained from fish farming ponds located in Gorgan city, filleted by hand and stored in sterile nylon bags in a refrigerator (4°C) until coating. A 10% corn zein protein coating was prepared and glycerol (2.5%) was used as a plasticizer. In addition to samples containing 10% zein protein, samples containing coriander extract were also prepared (Janes et al., 2002). Fish samples coated with corn zein without extract and with coriander extract were treated separately, and the uncoated sample was used as a control sample. The samples were stored at 4°C and evaluated at three-day intervals for 15 days for microbial (total microorganism count and psychrophilic bacteria count), lipid oxidation, qualitative (TBA, TVN, FFA, pH) and sensory (odor, color, and overall acceptance) tests (Parveneh, 2007). In order to determine the pH of fish meat, 10 grams of meat was ground into a paste using a blender and homogenized in 90 ml of distilled water using a homogenizer at a speed of 1000 rpm. The pH was measured by inserting a pH meter electrode into the resulting mixture. Sensory evaluation was performed on the basis of the Five Point Hedonic Scale in three separate sections. Fresh and dried fish samples were coded, then a questionnaire was prepared and the dessert was given to a trained panelist. 15 students and laboratory experts were selected as panelists. The panelists rated the color, aroma, texture, and overall acceptability on a scale of 1 to 5 (1 being very bad and 5 being very good) (Parveneh, 2007).
Results and discussion: The results of the microbial study showed that at the beginning of storage (time zero), the total number of microorganisms was 1.71 Log cfu/g, which increased rapidly during storage, reaching 7.88 on the 12th day of storage for the control sample, while the sample coated with corn zein protein without extract and containing extract had 6.74 and 5.97 Log cfu/g of microorganisms, respectively. Fish coated with corn zein protein and coriander leaf extract had a lower number of microorganisms during the storage days, as coriander extract reduced the growth of microorganisms on all days of storage. The number of psychrophilic bacteria also increased during storage, so that on the final day of storage, the logarithm of the number of psychrophilic bacteria per gram of Silver carp fish samples of control, coated with corn zein protein without extract and containing coriander leaf extract was 6.55, 6.14 and 5.57 (Log cfu/g), respectively. By comparing the results of the number of psychrophilic bacteria of Silver carp fish coated with the control sample, coriander leaf extract played a more effective role in preventing the growth of the number of Silver carp fish bacteria as well as the total number of microorganisms. Here it can be concluded that the corn zein coating containing coriander extract caused a three-day delay in the growth of microorganisms and delayed the microbial spoilage of Silver carp fish. The total count of microorganisms per gram of Silver carp fish samples containing coriander extract on the 15th day was 21.7 (Log cfu/g), which was much lower compared to the control sample. The amount of free fatty acids in Silver carp fish after 15 days was determined to be 41.2% in the control sample. Protein coating and coriander extract had a significant and significant effect on the amount of fatty acids produced by fish. At the end of storage, this amount was determined to be 97.1 and 96.1% for fish coated with corn zein protein without extract and with coriander leaf extract, respectively. A significant difference was observed between the amount of volatile nitrogen bases in the control sample and the coated samples on all days of storage. The minimum and maximum amount of TBA in this study were 0.45 mg of Malondialdehyde on day 0 and 1.51 mg of Malondialdehyde in the control treatment on day 15 per kilogram of fish meat, respectively. Coating and extract had a significant effect on the production of Malondialdehyde in fish during the last days of storage. The lowest TBA level in this study was related to the treatment with corn zein protein containing coriander extract, which was probably due to the richness of coriander extract in polyphenolic compounds and its role in reducing fat oxidation in fish (Parveneh, 2007).
Conclusion: Based on the results of microbial tests (total count of microorganisms and psychrophilic bacteria), coriander leaf extract played a more effective role in preventing the growth of Silver carp fish bacteria. Based on the results, the use of corn zein protein coating in Silver carp fish samples reduced the amount of TBA compared to other samples, which is probably due to the richness of coriander extract in polyphenolic compounds and its role in reducing fat oxidation in fish. The pH value was also lower in the coated sample than in other samples and remained constant during the storage period, which is probably due to the buffering properties of proteins in the coating. The samples coated with corn zein protein and coriander extract also maintained the pH constant to a greater extent and more effectively during storage, which is probably due to the phenolic compounds and antimicrobial properties in the composition of coriander extract. According to the results, the sensory characteristics and overall acceptance of Silver carp fish decreased over time. In general, samples coated with corn zein protein without extract showed very good results on the final day. These results show that fish spoilage has a direct relationship with the sensory properties of the product, and that as spoilage progresses, the sensory properties of the product are greatly reduced, and by controlling spoilage, a product with more desirable sensory properties can be produced during storage. In general, the results of this study showed that the effect of corn zein protein coating and coatings containing coriander extract on Silver carp fish maintains appropriate quality and increases their shelf life during storage in refrigerated conditions.