Lipid Deterioration and Its Inhibition of Japanese Oyster Crassostrea gigas during Frozen Storage

Abstract

Lipid deterioration and its inhibition in the Japanese oyster Crassostrea gigas during frozen storage were investigated. The shelled oyster were treated with antioxidants such as dibutylhy-droxytoluene and natural vitamin E, and then stored at -20°C for 12 months and the effect of deoxygenizer was examined similarly. Untreated oyster were also stored either at -20°C or at -35°C. During storage, changes in TBA value, POV, and fatty acid and class compositions of lipids were determined to evaluate the quality of oyster. The color and taste of cooked oysters were also evaluated.
POV in all the samples increased gradually with the duration of storage. Contents of phos-phatidylcholine (PC) and triglyceride decreased in varied degrees, while those of free fatty acid, lyso-PC (LPC) increased. These changes in lipid classes proceeded at a higher rate in the samples stored at -20°C than in the sample stored at -35°C. Percentages of polyenoic acids in lipids decreased in all the samples during storage, whereas those of saturated and monoenoic acids in-creased. Decreasing rates in the percentages of polyenoic acids were highest in the untreated sample (-20°C) and lowest in the sample with enclosed deoxygenizer. Sensory scores of the untreated sample (-35°C) and the sample with enclosed deoxygenizer almost did not decrease during storage over 12 months. These results clearly indicated that the lipid deteriorations of oyster were inhibited effectively by storing at -35°C as well as by storing with enclosed deoxygenizer at -20°C.