Effect of Variable Temperature Liquid Nitrogen Quick-Freezing Combined with Composite Cryoprotectant on the Quality of Frozen Prepared Monopterus albus

To enhance the liquid nitrogen freezing efficiency and improve the quality of frozen prepared Monopterus albus, the effect of variable temperature liquid nitrogen quick-freezing combined with composite cryoprotectant treatment on the quality of prepared M. albus was investigated. Deep-fried cured M. albus was treated with a novel composite cryoprotectant consisting of 4% xylooligosaccharides, 4% sorbitol and 0.3% sodium bicarbonate before precooling followed by liquid nitrogen freezing at variable temperatures (from -80 to -50 ℃). Internal temperature, moisture content, thawing loss, centrifugal loss, moisture state, thiobarbituric reactive substances (TBARS) value, acid value (AV), fluorescent compound content, and total volatile basic nitrogen (TVB-N) content were measured, and ice crystal morphology and microstructure were observed. The results indicated significantly lower thawing loss (3.80%), centrifugal loss (11.6%) and free water percentage (24.4%) under variable temperature liquid nitrogen quick-freezing compared with freezer freezing (P < 0.05), and significantly lower thawing loss under variable temperature liquid nitrogen quick-freezing compared with constant temperature liquid nitrogen quick-freezing (P < 0.05). After freezing for 24 weeks, prepared M. albus treated with the cryoprotectant exhibited significantly lower ice crystal size, thawing loss, centrifugal loss, TBARS value, AV, fluorescent compound content, and TVB-N content as well as more complete microstructure of muscle fibers, and its quality did not significantly differ from that of M. albus treated with a commercial cryoprotectant (P > 0.05). These findings suggested that pre-cooling followed by variable temperature liquid nitrogen quick-freezing combined with the novel composite cryoprotectant could enhance the quality of prepared M. albus during frozen storage, which will offer theoretical support for the development of highly efficient freezing and preservation technology for prepared M. albus products.