Abstract
Edible coatings have recently been developed and applied to different food matrices, due to their numerous benefits, such as increasing the shelf life of foods, improving their appearance, being vehicles of different compounds, such as extracts or oils of various spices that have antioxidant and antimicrobial activity, as well as being friendly to the environment. The objective of this research was to develop a new edible coating based on chitosan enriched with peppermint extract and to evaluate its effectiveness to inhibit microbial development in vitro and improve both the quality and shelf life of common carp (Cyprinus carpio) during refrigerated storage (4 ± 1 °C). Three treatments were used: edible coating (C + EC), edible coating +, 5% chitosan (C + ECCh) and edible coating + 1.5% chitosan + 10% peppermint (C + ECChP). Prior the coating carp fillets; the antibacterial activity and antioxidant capacity were evaluated in the peppermint extract and coating solutions. After coating and during storage, the following were determined on the fillet samples: microbiological properties, observed for ECP, an inhibition halo of 14.3 mm for Staphylococcus aureus, not being the case for Gram-negative species, for ECCh, inhibition halos of 17.6 mm, 17.1 mm and 16.5 mm for S. aureus, Salmonella typhimurium and Escherichia coli, respectively; for the ECChP, inhibition halos for S. aureus, S. typhimurium and E. coli of 20 mm, 17 mm and 16.8 mm, respectively. For the physicochemical characteristics: an increase in solubility was observed for all treatments during storage, reaching 46.7 mg SN protein/mg total protein for the control, and values below 29.1 mg SN protein/mg total protein (p < 0.05), for fillets with EC (C + EC > C + ECCh > C + ECChP, respectively at the end of storage. For the pH, maximum values were obtained for the control of 6.4, while for the fillets with EC a maximum of 5.8. For TVB-N, the fillets with different CE treatments obtained values (p < 0.05) of 33.3; 27.2; 25.3 and 23.3 mg N/100 g (control > C + E C > C + ECCh > C + ECChP respectively). Total phenolic compounds in the aqueous peppermint extract were 505.55 mg GAE/100 g dried leaves, with 98.78% antioxidant capacity in the aqueous extract and 81.88% in the EC. Biomolecule oxidation (hydroperoxide content) had a significant increase (p < 0.05) in all treatments during storage, 1.7 mM CHP/mg protein in the control, to 1.4 in C + EC, 1.27 in C + ECCh and 1.16 in C + ECChP; TBARS assay values increased in the different treatments during refrigerated storage, with final values of 33.44, 31.88, 29.40 and 29.21 mM MDA/mg protein in the control; C + EC; C + ECCh and C + ECChP respectively. In SDS -PAGE a protective effect was observed in the myofibrillar proteins of fillets with ECChP). The results indicate that the C + ECCh and C + ECChP treatments extend the shelf life of 3–5 days with respect to microbiological properties and 4–5 days with respect to physicochemical characteristics. A reduction in lipid and protein oxidation products was also observed during refrigerated storage. With these findings, this is considered a promising method to increase the shelf life of fish fillets combined with refrigeration and we are able to recommend this technology for the fish processing industry.
Highlights
Biopolymers have become an alternative for synthetic packaging that is non-biodegradable and has a negative impact on the environment
In ECChP, a synergistic effect was observed on S. aureus since a large zone of growth inhibition (20 mm) was found, unlike S. typhimurium and E. coli which had inhibition zones of 17 to 16.8 mm
Results of the present study show that independent of the type of coating, edible coatings (ECs) have a protective activity on muscle proteins, with C + ECChP exerting the best protective effect during refrigerated storage, preventing loss of structural
Summary
Biopolymers have become an alternative for synthetic packaging that is non-biodegradable and has a negative impact on the environment. Biopolymer-based edible coatings (ECs) can increase the shelf life and quality of food, acting as selective barriers against humidity and oxygen, lipid oxidation and loss of volatile aromatic compounds [1,2]. Because of its non-toxic character, antifungal and antimicrobial activity, biodegradability, and biocompatibility as well as film-forming and antioxidant properties, chitosan has been widely applied in the preservation of meat products such as beef, chicken, mutton and fish [3,4,5,6,7,8,9,10]. Decomposition of fish muscle is the result of biological reactions such as lipid and protein oxidation which are due to the enzymatic activity characteristic of the species or the metabolic activity of the microorganisms present. Rajalakshmi et al [18,19] demonstrated that the extracted chitosan exhibits potent antioxidant activity and free radical scavenging activity, including activity toward DPPH radicals, hydrogen peroxide and superoxide anion radicals, and López-Caballero et al [4] concluded that the chitosan-gelatin solution employed allowed cold preparation of a coating that was suitable for preventing fish spoilage, Kanatt et al [19] suggested using peppermint extracts as coadjuvants in this activity
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