In order to study the effect of superchilling storage on the sensory quality and postmortem lactic acid metabolism in pork, pork tenderloin was stored at superchilling (−1 ℃) or chilling (4 ℃) temperature immediately after slaughter. At 0.5, 2, 6, 12, 24, 72, 120 and 168 h, quality indicators including drip loss, color and pH, as well as the activities of major enzymes involved in glycolysis and related metabolic pathways were determined. The results showed that superchilling storage effectively reduced the quality deterioration of pork and slowed down the rate of glycolysis and lactic acid metabolism. During 0.5–12 h postmortem, some of the nine enzymes tested including hexokinase, phosphofructokinase and lactate dehydrogenase were significantly inhibited (P < 0.05). From the perspective of post-mortem metabolism, superchilling temperature can effectively inhibit the activity of glycolytic enzymes, delay the accumulation of lactic acid and the reduction in meat pH, and improve the quality deterioration of pork during storage.

An extraction and purification method for soluble polyphenol oxidase (sPPO) and membrane-bound polyphenol oxidases (mPPO) from Agaricus bisporus was developed involving temperature-induced phase partitioning, fractional precipitation with ammonium sulfate, and DEAE anion exchange chromatography. The purity, molecular mass and enzymatic reaction kinetics of purified PPO were investigated by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE), Native-PAGE and Michaelis-Menten equation. The specific activities of sPPO and mPPO toward catechol were 6912.88 and 19092.94 U/mg, and increased by 12.20 and 10.86 times, respectively, compared with that of crude PPO. The results of enzymatic reaction kinetics showed that the catalytic activities of sPPO and mPPO toward different substrates were greatly different and were higher toward catechol. mPPO had a stronger affinity to the substrate catechol and a higher reaction rate than sPPO. The optimum pH and temperature for both PPO enzymes were 6.8 and 30 ℃, respectively. This study may lay a foundation for future research on mass spectrometry identification and enzymatic properties two forms of PPOs from A. bisporu and inhibition of enzymatic browning caused by PPO.