Metabolomics-based Analysis of the Effects of a Compound Phosphorus-free Water-retaining Agent on the Quality of Bullfrog Meat in Frozen Storage

The aim of this study was to determine the effect of the compound phosphorus-free water-retaining agent on the quality of bullfrog meat during frozen storage with a focus on addressing protein denaturation and reduced water-holding capacity. The effects of phosphorus-free water-retaining agent on the quality of bullfrog meat stored at −20 ℃ were investigated using non-targeted metabolomics and by determining thawing loss rate, texture, sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) analysis of myofibrillar protein, and Ca2+-ATPase activity. Results showed that the compound phosphorus-free water-retaining agent significantly reduced the thawing loss rate (P<0.05) and improved the water holding capacity of bullfrog meat during frozen storage. In addition, the rate of decrease in elasticity and stiffness was significantly lower in the treatment group than in the control group (P<0.05). SDS-PAGE showed that the water-retaining agent inhibited protein degradation and maintained myofibrillar protein stability. Furthermore, the Ca2+-ATPase activity was significantly higher in the treatment group (compared to the control group, P<0.05), indicating delayed protein denaturation. Microscopic sections of muscle tissue indicated that the compound phosphorus-free water-retaining agent maintained the integrity of muscle fibers by alleviating mechanical damage to muscle fibers due to ice crystal formation. Pairwise comparisons using OPLS-DA revealed 55 common differential metabolites. The major metabolic pathways involved were protein digestion and absorption, ABC transporter proteins, D-amino acid metabolism, aminoacyl-tRNA biosynthesis, and mineral absorption. In summary, the phosphorus-free water-retaining agent composed of sorbitol, sodium citrate, and dried honey powder could effectively improve the quality of bullfrog meat in frozen storage and significantly inhibit water loss, protein denaturation, and microstructural deterioration. The results of this study provide a scientific basis for the frozen storage of bullfrog meat.