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.

The main purpose of this study is to study the effect of live oysters on various quality indicators after alkaline electrolytic seawater depuration. The depuration treatments were carried out for 12 h at temperatures of 5 °C, 10 °C, 15 °C, and 20 °C, pH = 9, 10, and 11, respectively. The total aerobic plate count (TAPC) of oyster meat was reduced from about 5.2 ± 0.4 log CFU/g to below detection limits when the oysters were depurated in pH = 11 alkaline electrolytic seawater for 9 h at 5 °C and 12 h at 10 °C. At the same pH value, the lower the seawater temperature, the lower the amount of TAPC, and it decreased with the increase in depuration time. After the oyster had been depurated, the chemical components contained in the oyster meat, such as protein, crude fat, and glycogen, did not change differentially. On the other hand, each group of live oysters (4 individuals) spat out an average of about 690–695 ± 0.4 mg of impurities and dirt. These are new achievements and discoveries. When the depurated oyster meat was stored at a low temperature, the freshness period could be extended to 21 days, which is much longer than the 5 days of the un-depurated oyster meat, and this is a significant difference. If coupled with vacuum packaging, the effect will be even better.