Abstract
Chicken breasts were frozen using 3 methods: the super slow freezing method (approximately -0.30°C/min), the slow freezing method (approximately -1.4°C/min), and the liquid nitrogen-freezing method (approximately -250°C/min). They were stored at -20°C for 3 weeks. After thawing, each chicken breast was heated at 75°C for 15 min by vacuum cooking. The chicken breast frozen using the slow freezing method became tenderer than those frozen using the other methods. Cryo-scanning electron microscopy observations (×200) indicated that the liquid nitrogen-freezing method did not cause extensive damage to the muscle fiber structure. However, scanning electron microscopy observations (×20,000) revealed that the myofibril structure of the chicken breast frozen using the slow freezing method was the most similar to that before freezing. These results suggest that the hardness of the frozen chicken breast after vacuum cooking mainly depends on the state of the myofibril structure.
