The total viable count (TVC), pH, total volatile basic nitrogen (TVB-N) content, thiobarbituric acid (TBA) value, sensory evaluation and color of live and dead crayfish were measured during storage at 4 and 0 ℃. The results indicated that the TVC, TVB-N content, TBA value, yellowness (b* value) and total color difference (ΔE*) of both live and dead crayfish increased with storage time irrespective of storage temperature, while the pH increased after an initial decrease and the sensory evaluation score, total sulfhydryl group content and brightness (L* value) continued to decrease. Considering all above indicators together, the shelf lives of live and dead crayfish stored at 4 ℃ were 8 and 4 days, respectively, and the shelf lives of live and dead crayfish stored at 0 ℃ were 12 and 11 days, respectively. When stored at 4 ℃, the quality of live crayfish was significantly better than that of dead crayfish, whereas there was no significant difference in the quality of live and dead crayfish during storage at 0 ℃.

The protein content, pH, color, colonies number, average particle size, zeta potential, degree of proteolysis and proteinase activity of ultra-high temperature (UHT) milk with and without protein coagulation and commercial pure milk samples were determined to analyze the reasons for protein coagulation in UHT milk at the end of self-life. The results showed that the total protein content of coagulated milk samples was 2.9 g/100 g, which was not significantly different from that of milk samples without protein coagulation, but the pH decreased slightly. The total color difference (ΔE) and brightness value (L^*) decreased to 68.05 and 67.56, respectively, indicating that the color became dark, and the total bacterial count increased to 1.92 (lg(CFU/mL)). The proteinase activity was 2565.33 U/L, the degree of proteolysis was 17.07%, the average particle size was 685.8 nm, and the zeta potential increased to −19.97 mV; these data were all significantly higher than those of milk samples without protein coagulation and commercial pure milk. The trend of changes in proteinase activity was basically consistent with that of the degree of proteolysis, particle size and zeta potential for all samples tested. Protein coagulation in UHT milk at the end of shelf life may be attributed to protein hydrolysis due to increased protease activity and physical deposition caused by the enlargement of casein micelles during long-term storage at ambient temperature.

The tropomyosin (TM) fractions of crab proteins may cause allergic reactions in individuals susceptible to allergies; however, efficient and safe methods by which to reduce such allergenicity are not currently available. Therefore, in this study, the effects of three different processing methods, i.e., microwave, ultrasound, and high temperature-pressure (HTP) treatments, on the digestion stability of TM from Chinese mitten crab muscle and the allergenicity of TM digestion products were explored. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis analysis showed that microwaving had little effect on the digestion stability of TM. In contrast, ultrasound and HTP treatments facilitated the degradation of TM. Similarly, Western blotting and inhibition ELISA indicated that the IgE-binding activity of TM was significantly reduced after treatment with ultrasound or HTP. Among the three different processing methods, HTP was the most effective method for improving digestibility of TM and reducing immunoreactivity. This finding provides new insights into treatments for crab allergies.