Effects of Individual and Block Freezing on the Quality of Pacific Oyster ( Crassostrea gigas ) during Storage under Different Pretreatment Conditions

• Published in: Sustainability
• Main Authors: Hsin-Shan Tsai, Yu-Tien Hsiao, Yih-Ming Weng
• Format: Article in Journal/Newspaper
• Language: English
• Published: MDPI AG 2022
• Subjects: shucked oyster; ice-glazing; individual freezing; drip loss; water holding capacity; total aerobic plate count (TAPC); Environmental effects of industries and plants; TD194-195; Renewable energy sources; TJ807-830; Environmental sciences; GE1-350; Pacific; Crassostrea gigas; Pacific oyster
• Online Access: https://doi.org/10.3390/su14159404; https://doaj.org/article/61b8bd5412144289a7aa1d23a958143c

In this study, a series of pretreatments, including ice-glazing, polyphosphate impregnated, and both ice-glazing and polyphosphate impregnated, were employed to pretreat shucked oysters in order to explore the optimal processing conditions for long-time storage. The effect of repeated freezing-thawing cycles on the quality of oysters was evaluated. Several quality indicators were used to investigate the effects of pretreatment. For the VBN (volatile salt-based nitrogen) value, the lowest value was 9.1 ± 0.2 of BPG (block oyster with polyphosphate impregnated and ice-glazing), which was significantly lower than 9.6 ± 0.2 of IPG (individual oyster with polyphosphate impregnated and ice-glazing). In terms of drip loss, there was no significant difference between the IPG (21.0 ± 0.2%) and the BPG (20.8 ± 0.2%). In addition, the highest WHC% (water holding capacity) was IPG (65.5 ± 0.5%) which was slightly lower than BPG (67.6 ± 0.6%). As compared to the experimental control, the IPG and BPG had the best appearance and color. In terms of TAPC (total aerobic plate count), with the increase of freezing storage time, each group showed a slight downward trend, but the difference was not statistically significant. After repeated freezing-thawing of block frozen oysters, there were significant differences in drip loss, WHC, and cooked taste with the increasing number of times, and there was a trend of deterioration ( p < 0.05). Repeated freezing and thawing can seriously degrade the quality of oysters, so individual freezing (especially IPG) should be the most appropriate processing method.