Improvement of the microbial quality, antioxidant activity, phenolic and flavonoid contents, and shelf life of smoked herring (Clupea harengus) during frozen storage by using chitosan edible coating

Smoked herring is a very popular traditional fish product widely consumed in Egypt. Nonetheless, rapid mould growth and lipid oxidation, with consequent short shelf life and loss of the essential characteristics, including the smoking color and flavor, are emerged as adverse problems during storage of this product. This study was aimed to improve the quality and lipid stability of smoked herring using chitosan coating. To achieve this goal, smoked herrings were collected from local producers and divided into 5 groups, including two controls (water-dipped and 0.5% lactic acid-dipped samples) and three treated groups (2%, 3% and 4% chitosan-coated samples) followed by storage at -18 degrees C for 3 months during which microbiological, physicochemical, and sensorial analyses, besides determination of phenolics, flavonoids, and the antioxidant activity were carried out. The results revealed that chitosan-coated (3% and 4%) samples exhibited more than 4 log10 CFU/g reduction in aerobic plate count, along with complete suppression of psychrotrophic, Enterobacteriaceae, yeast and mould counts, which were all under the detectable levels (2 log10 CFU/g). Chitosan improved and maintained the phenolic and flavonoid compounds along with the free radical scavenging activity in chitosan-coated smoked fish during frozen storage. Moreover, chitosan coating induced significant improvement of the physiochemical quality including; pH, total volatile base nitrogen, trimethylamine, thiobarbituric acid values, free fatty acid %, acid number, together with the sensory attributes, compared to control uncoated ones. The study concluded that chitosan coating can be a good choice for fish industry to overcome the problems that arise in smoked fish.