Effect of Liquid Nitrogen Quick Freezing on the Quality Characteristics of Prepared Chicken Chops during Frozen Storage

To investigate the impact of liquid nitrogen quick freezing on the quality of prepared chicken chops during frozen storage, this study compared −18 ℃ air freezing with −80 ℃ and −100 ℃ liquid nitrogen quick freezing. Then the frozen samples were stored in a −18 ℃ refrigerator for 0~180 days. The evaluation criteria included sensory scores, color, water holding capacity, texture characteristics, electronic nose analysis, pH, oxidation indicators, and total bacterial count. The results revealed a significant decrease in sensory scores for all groups with the extension of frozen time (P<0.05). However, the water holding capacity, texture characteristics, and flavor components of the samples treated with liquid nitrogen quick freezing were effectively maintained. Liquid nitrogen quick freezing also had an impact on the color of the samples. On the 180th day of frozen storage, the centrifugal loss rates for the −18 ℃ air freezing, −80 ℃, and −100 ℃ liquid nitrogen quick freezing groups were 13.47%, 8.53%, and 10.80%, respectively. The drip loss rates were 9.30%, 7.64%, and 8.35%, and the hardness values were 54.60, 60.05, and 65.17 N, respectively. The a^* value of the −100 ℃ liquid nitrogen quick freezing group was significantly higher than that of the −18 ℃ air freezing group (P<0.05). The pH of all treatment groups initially decreased and then increased. Different freezing methods did not significantly affect the total bacterial count of the prepared chicken chops (P>0.05), and the count remained below 5 lg (CFU/g) during frozen storage. Measurement of relevant oxidation indicators revealed that liquid nitrogen quick freezing effectively delayed protein and lipid oxidation. On the 180th day of frozen storage, the malondialdehyde (MDA) content in the −18 ℃ air freezing group was 21.95% and 37.43% higher than that in the −80 ℃ and −100 ℃ liquid nitrogen quick freezing groups, respectively. The total sulfhydryl group (-SH) content was reduced by 26.58% and 44.09% compared to the other two groups, respectively. In summary, the prepared chicken chops by all three freezing methods remained safe for consumption after being frozen at −18 ℃ for 180 days. But the quality characteristics of the prepared chicken chops treated with liquid nitrogen quick freezing were significantly improved during frozen storage.