Chitosan as an edible film for protection of seafood quality

Yatiyana Vidana Arachchilage, Janak Kamil (2000) Chitosan as an edible film for protection of seafood quality. Masters thesis, Memorial University of Newfoundland.

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Abstract

Preservation of seafood quality against oxidation of highly unsaturated lipids, autolysis reactions and microbial activities is important. Chitosan, a deacetylated form of chitin, has been identified as a versatile biopolymer for a broad range of food applications. However, very little information is available about the use of chitosan as an edible coating material for preservation of seafood quality and virtually nothing is known regarding the effect of viscosity of chitosan on its preservative efficacy for seafood. Effect of chitosan coating for extension of shelf-life of two different fish species, Atlantic cod (Gadus morhua) as a lean fish, and herring (Clupea harengus) as a fatty fish, was evaluated during a 12-days storage at refrigerated temperature (4 ± 1°C). Three chitosan preparations from snow crab (Chinoecetes opilio) processing wastes, differing in viscosities and molecular weights, were prepared and used in this study. The apparent viscosity of chitosans was dependent on the deacetylation time of their chitin precursors and were 14, 57 and 360 cP for samples prepared over a 20, 10 and 4 h period, respectively. -- Prepared chitosan samples were used as edible coating material on the surface of the fish muscle and the quality of the coated samples were monitored. This was achieved by monitoring relative moisture loss (%) and peroxide value (PV), conjugated dienes (CD), 2-thiobarbituric acid-reactive substances (TBARS) and headspace (HS) volatiles, all which are related to lipid oxidation. Furthermore, total volatile basic nitrogen (TVB-N), trimethylamine (TMA) and hypoxanthine (Hx), which are related to chemical spoilage, as well as total plate count (TPC) related to microbial spoilage were monitored. A significant (p ≤ 0.05) reduction in relative moisture loss, by 37, 29, 29, 40, and 32%, over that of uncoated cod samples was observed for those coated with 360 cP chitosan after 4, 6, 8, 10, and 12 days of storage, respectively. Chitosan coating significantly (p ≤ 0.05) reduced lipid oxidation, chemical spoilage and growth of microorganisms in both fish model systems compared to uncoated samples. The preservative efficacy and the viscosity of chitosan were inter-related; the efficacy of chitosans with a viscosity of 57 and 360 cP was superior to that with a 14 cP viscosity. -- In another study, antioxidant efficacy of different viscosity chitosans in cooked comminuted herring and cod systems was investigated. Oxidative stability of treated fish species was determined and compared to those treated with conventional antioxidants such as butylated hydroxyanisole (BHA), butylated hydroxytoluene (BHT) and tert-butylhydroquinone (TBHQ) at a level of 200 ppm. Progression of oxidation was monitored by employing peroxide value and TBARS tests. In general, all chitosans exhibited varying antioxidant activities in both types of fish model systems investigated. Formation of hydroperoxides and TBARS in herring samples containing 200 ppm 14 cP chitosan was reduced after day-8 of storage by 61 and 52%, respectively. -- The mechanism of action of chitosan coating for extension of shelf-life of seafood appears to be due to chelation of metal ions contained in fish muscle proteins, controlling of gas exchange, particularly oxygen, between fish meat and the surrounding environment, and bactericidal effect of chitosan itself. Edible superficial chitosan coatings provide supplementary and sometimes essential means to control physiological, microbiological and physicochemical changes in seafood products. The active edible chitosan coatings may thus be extended to new fully adapted superficial or internal applications for seafood products.

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