Effects of natural preservatives on shrimp ( Penaeus vannamei) during cold storage

Shrimps ( Penaeus vannamei) were preserved by 0.05% lysozyme, 0.1% phytic acid, 0.5% citric acid, 0.15% ascorbic acid, 0.5% L- cysteine and 1.5% chitosan respectively to improve the quality of shrimps during cold storage. In order to evaluate the effect of these preservatives on quality changes of shrimps, sensory evaluation, pH, total bacteria count, total volatile basic nitrogen and relative activity of polyphenol oxidase were determined. Results showed that 1.5% chitosan was effective to retard the decline of sensory quality and inhibit the growth of microbes.0.5% citric acid showed stronger inhibition on total volatile basic nitrogen and activity of polyphenol oxidase.0.5% L- cysteine could restrain the activity of polyphenol oxidase and melanosis. However, 0.05% lysozyme, 0.1% phytic acid and 0.15% ascorbic acid seldom improved the quality of shrimps.