| Summary: | 碩士 === 國立臺灣海洋大學 === 食品科學系 === 97 === The raw shucked oyster began to shrink in shape and darken in color after storage at 4℃ for 3 days. Drained liquid also increased and K value reached 45%. After 7-day storage the darkened color and liquid loss became more serious. K value and volatile basic nitrogen reached 77% and 25.76 mg/100 g, respectively. Results showed the shelf-life of refrigerated oyster was less than 7 days. In addition, the supply and quilty of raw oyster is unstable. Therefore this study was carried out to develop frozen oyster products and to upgrade their quality for the benefit of oyster production and marketing.
The products treated with slow freezing (-18℃), I.Q.F. (individual quick freezing) (-40℃, 35 min) and T.P. (tray-packing type, liquid N2 freezing) (-110℃, 18 min) gradually became brown in color during frozen storage. The rupture of some tissues such as gills and digestive glands was found in slow freezing and I.Q.F. products after thawing. The drained liquid in T.P. product was the highest. There were no remarkable differences in solid and glycogen content among three products. Slow freezing product had the highest values of VBN, hypoxanthine and K value. The loss of free amino acids (FAA) including taurine and glutamic acid was more serious in T.P. product.
Shucked oyster meat were immersed with distilled water, brine (1.5%) and phosphate solution (0.3%), and then frozen storage at -18℃ for 3 months. The thawed products showed their solid, glycogen and FAA remained lower than those of control group without treatment. The brown color was also found in the thawed products.
The oyster meat treated with blanching procedure (80℃, 70 sec) and then I.Q.F. (-40℃, 35 min) freezing showed no occurrence of broken products. This procedure also reduced drip loss and bacteria counts including aerobic plate count, E. coli and coliforms. The shelf-life of the blanched product was 24 hrs during storage at 4℃, and 5 months for that of frozen (-18℃) storage. This study provided useful information for the seafood industry to produce the high quality frozen products at oyster season and provided them in the market at oyster off-season to stabilize the price and the quality of oyster products.
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