Introduction

It is well known that many undesirable changes such as microbial spoilage and lipid oxidation can be occurred during refrigerated storage of meat. Minimizing contamination and retarding or inhibiting the growth of spoilage is very important for improving fresh meat shelf life and quality [1]. Fish contain high protein sources, hydrosoluble and liposoluble vitamins, minerals, polyunsaturated fatty acids (PUFAs) and relatively large quantities of free amino acids. Unsaturated fatty acids are highly susceptible to oxidation, resulting in off-flavors and structural changes which are unappealing to consumers [2,3]. Some complex process such as chemical, microbiological and physical changes have occurred during storage of fish. These reactions are usually responsible for the initial loss of freshness, obvious spoilage and thereby degrade product shelf life and quality of fish [4,5]. Nevertheless, toxicological effects [6] together with consumer preference for natural products have resulted an increased interest in the search and utilize for natural antioxidants in fruits and vegetables that maybe help attenuate oxidative processes [7]. Plants contain high antioxidant capacity and some phytochemicals such as polyphenols, mainly phenolic acids and flavonoids that exhibited antioxidant activity [8]. The deleterious effect of lipid oxidation on food is retarded with the application of antioxidant agents and natural preservation. Furthermore, lipid oxidation can be effectively reduced by choosing films and coatings of limited oxygen permeability [9]. Recently, natural antioxidants and preservation have become very popular for food application and are preferred by consumers than synthesized antioxidants. Among these, pomegranate fruit and its derivate products have been shown to be effective in retarding the process of lipid oxidation in both in vitro and in vivo assays [10-12]. It is reported that pomegranate peel is rich source of tannins and other phenolic and flavonoids compounds which have remarkable antimicrobial and antioxidant activity [13-16]. The antioxidant activity exhibited by phenolic compounds has been reported in fresh as well as in processed meat in terms of reduced lipid oxidation [17-20]. The antimicrobial activity of pomegranate fruits and its peel extract have been demonstrated for several pathogens such as Escherichia coli, Staphylococcus aureus, including several methicillin resistant strains, Vibrio cholerae and Bacillus subtilis [21-30]. The objectives of this study were to evaluate the effects of edible coating containing pomegranate peel extract on the quality and shelf life of silver carp fillet during refrigerated storage.

Material and Methods

Preparation of samples

Preparation of treatments: Fresh silver carp (Hypophthalmichthys molitrix) were purchased from a local market in Zabol, Iran and transported to fishery lab during 30 min in ice. Samples were washed, cleaned, gutted and the filleted into needed slices (100 g/average weight/fillet) by hand. Then the mixture of edible coating was prepared (60% cool water + 30% wheat flour + 10% corn flour). First thin layer of edible coating mixture spread on fillets by hand and then the concentrations of 5% and 10% of PPE spray on fillets by syringe. Three treatments were prepared: control (fillet treated with edible coating and no antioxidants); fillet treated with edible coating and 5% PPE (T1) and fillet treated with edible coating and 10% PPE (T2). 21 fillets from each sample were prepared, and then all of samples were packed and placed in the refrigerator. For each treatment three replicates were considered.

Preparation of pomegranate peel powder:

Mature pomegranate fruit, variety “shishe kap”, having no visible external cuts or spoilage was purchased from the central fruit market (Mashhad, Iran). To obtain the pomegranate peel, the pomegranate fruits were peeled manually and dried in air for 48 h. Dried pieces were powdered in heavy duty kitchen grinder and stored in freezer(-18°C).