Effects of HHAIC pretreatment on enzymatic activity kinetics and quality of Litopenaeus vannamei

This study aims to investigate the effects of high-temperature high-humidity air impingement cooking (HHAIC) on enzyme inactivation characteristics and quality of Litopenaeus vannamei (L. vannamei). The activities of catalase (CAT), trypsin (TRY), polyphenol oxidase (PPO), and superoxide dismutase (SOD) in L. vannamei were determined under different temperatures (70, 90, 110 ℃) and HHAIC pretreatment durations (0, 45, 90, 135, 180, 225, 270, 315, 360 s). Kinetic models for enzyme inactivation were established using first-order kinetics model, Weibull distribution model, and Logistic model. The cooking process parameters were predicted through the kinetic models and a systematic investigation was made on the impacts of the color, texture, and antioxidant activity. The results showed that higher temperatures accelerated heat transfer rate at the early stage of HHAIC pretreatment. Under different temperatures, the changing trends of the internal temperature of L. vannamei were basically consistent, which could be generally divided into three stages. They were rapid-rate temperature rise stage, reduced-rate temperature rise stage, and constant-rate temperature rise stage, respectively. The relative activities of CAT, TRY, PPO, and SOD all showed a downward trend with the extension of HHAIC durations and the increase of temperature. The Logistic model could better fit the inactivation process of CAT and TRY at lower temperatures. At the same temperature, the coefficient of determination of the first-order kinetic model was the lowest compared with the Weibull distribution model and Logistic model, indicating that the PPO inactivation process did not conform to the simple unimolecule reaction mechanism. The relative activity of SOD (50.28%) was relatively high after 360 s of cooking at 70 ℃, which was related to the high thermal stability of SOD. The performance of the Weibull distribution model indicated a strong fit by the high coefficient of determination and low prediction error. Therefore, the Weibull distribution model exhibited higher accuracy for the inactivation of CAT, TRY, PPO and SOD by HHAIC pretreatment than the first-order kinetic model and Logistic model. The L*, a*, b*, ∆E and chromaticity values all exhibited a tendency to increase initially and then decrease. After four minutes of cooking at 90 ℃, the hue angle of L. vannamei was the smallest (62.51°), indicating that the color of the L. vannamei was most inclined to red under such condition. The hardness, gumminess and chewiness of L. vannamei first increased and then decreased during HHAIC pretreatmen, while the elasticity showed varying degrees of increasing and decreasing trends. After four minutes of cooking at 90 ℃, the hardness (18.56 N) and chewiness (31.70 mJ) of L. vannamei were relatively high, showing that the L. vannamei had better palatability under such condition. The astaxanthin from L. vannamei had a high scavenging capacity for ABTS free radical, while its scavenging capacity for OH free radical was generally weaker than that for ABTS and DPPH free radicals. The DPPH free radical and OH free radical scavenging rates reached the maximum values of 95.61% and 70.80% when cooked for four minutes at 90 ℃, respectively. Overall, the L. vannamei cooked at 90 ℃ for four minutes exhibited better quality, and this condition was determined as the optimal cooking condition after comprehensive consideration. The relative activities of CAT, TRY, PPO, and SOD showed extremely significant negative correlations (P < 0.01) with elasticity, L*, a*, and b* value, DPPH free radical scavenging rate, and OH free radical scavenging rate. The relative activities of CAT and TRY showed a significant negative correlations with chewiness (P < 0.05). However, the relative activities of CAT, TRY, PPO, and SOD showed no significant correlations with ABTS free radical scavenging rate (P > 0.05), while showed a negative correlation overall. In conclusion, this study can provide certain theoretical references and technical bases for the pretreatment and deep processing of L. vannamei products.