Quality characteristics of Newfoundland cultured blue mussels (Mytilus edulis) at pre- and post-harvest stages

Khan, Muhammad Ahmad (2005) Quality characteristics of Newfoundland cultured blue mussels (Mytilus edulis) at pre- and post-harvest stages. Doctoral (PhD) thesis, Memorial University of Newfoundland.

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Abstract

Despite the rapid increase in production of Newfoundland cultured blue mussels in the last few years and publication of various studies addressing aspects of culturing and production, information with regard to the quality of cultured blue mussels at pre- and post-harvest stages is scarce and fragmented in the literature. In order to produce, process, package, transport, distribute, market, store and consume blue mussels with superior quality as well as to fill an important gap in the scientific literature regarding the quality of Newfoundland blue mussels, this research was designed to: (1) enumerate bacteria from cultured blue mussels from Newfoundland using different forms of agar; (2) evaluate changes in shell size, meat content, microbial quality, fatty acids, sterols and lipid composition of blue mussels during their growth at two aquaculture sites; (3) evaluate the effect of ice storage on proximate composition and quality of mussels; (4) assess the use of bacterial fatty acids as microbial quality indicators; and (5) examine the effects of mechanical handling and ascorbic acid treatment on lipid oxidation and quality of blue mussels. -- Results indicate that marine agar is better than plate count agar to evaluate microbial quality of bivalves. Ocean water temperatures at the aquaculture site affected chlorophyll a content or algae forms and their fatty acid compositions, as well as microbial quality of water, which in tum affected microbial quality, lipid and fatty acid composition, meat content and shell size of cultivated mussels. The measurement of n-3 polyunsaturated fatty acids (PUFA) and phytosterols in Newfoundland cultured mussels may add to there market value. Cultured mussels can reach their commercial size within a year following cultivation. Their optimum harvest time would be either spring or fall of each year. Meanwhile, microbial growth and lipid oxidation of ice stored mussels leads to their spoilage and an increase in flavor deterioration index. Conventional agar was the best substrate to monitor microbial changes during ice storage. Other potential indicators would be the bacterial fatty acids ai15:0, i17:0 or total bacterial fatty acids as determined by H₂SO₄-MeOH transmethylation reagent. Ice stored mussels were more susceptible to lipid oxidation than the fresh mussels as reflected in their high 2-thiobarbituric acid reactive substances (TBARS) values. However, the current rapid mechanized handling practice in the blue mussel industry, which includes washing, sorting, washing again and packaging, should not affect their oxidative status. Furthermore, exposing live blue mussels to specific concentrations of ascorbic acid may control lipid oxidation during their ice storage for only 5 days. Thereafter, the remaining ascorbic acid may become a pro-oxidant in ice stored mussels.

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