二维红外相关光谱研究熟度对肌原纤维蛋白构象的影响

熟度是指牛排烹煮到可食用的程度，是影响牛排的适口性和消费者满意度的重要因素。肌原纤维蛋白是肌肉中一类重要的盐溶性结构蛋白群，其热凝胶特性与肉品品质密切相关。加热是使生肉变熟的关键工艺，近年来，国内外在加热过程对肌原纤维蛋白凝胶特性及其结构变化影响方面开展了广泛的研究，但在熟度对牛肉蛋白结构影响研究方面却鲜有报道。为了探究熟度对肌原纤维蛋白结构影响及其变化机理，在现代红外光谱分析的基础上，将ATR-FTIR技术与二维相关光谱相结合，利用红外光谱、二阶导数光谱和二维相关光谱动态跟踪熟制过程蛋白结构变化规律，说明蛋白在烹饪过程的主要变化，为揭示熟度引起的蛋白构象变化机理和西餐牛排烹饪工艺优化提供理论依据。结果表明，在1 700～1 500 cm-1波数范围内，熟度对肌原纤维蛋白特征吸收峰强度影响显著，从特征峰强度变化趋势可见，肌原纤维蛋白特征峰强度呈阶段性变化：第一阶段，从对照组到一分熟，特征峰强度下降，属于加热初期；第二阶段，从一分熟到五分熟，特征峰强度无显著变化，属于加热中期；第三阶段，从五分熟到过熟，特征峰强度继续减弱，属于加热后期；同步谱分析结果表明，在1 650，1 640，1 556和1 540 cm-1附近出现自相关峰，且自相关峰两两之间的交叉峰均为正交叉峰，说明这些自相关峰对于熟度变化较为敏感，且峰强度与蛋白烹饪熟度之间呈正相关；由自相关峰光谱强度顺序可以看出，五分熟是蛋白温度敏感区变化的转折点，在从对照组到五分熟的烹饪过程中，肌原纤维蛋白的温度敏感重点区域位于酰胺Ⅱ带，而在从五分熟到过熟的烹饪过程中，蛋白的温度敏感重点区域位于酰胺Ⅰ带的α-螺旋结构。得到的这些由熟度变化引起的肌原纤维蛋白分子结构动态变化的微观信息，可为西餐牛排烹饪工艺过程控制和优化提供理论依据。

Effect of Degree of Doneness on Conformation of Myofibrillar Proteins by Two-Dimensional Infrared Correlation Spectroscopy

Degree of doneness（DOD）is an important factor affecting the palatability and consumer satisfaction of steak. Myofibrillar proteins are important structural proteins, which are closely related to meat quality. Heating is the key technology of meat processing. In recent years, there were lots of articles that reported the effects of thermal treatment on the structural properties of myofibrillar proteins, but few reports on the effects of DOD on its structure. Based on modern infrared spectroscopy, the attenuated total reflectance Fourier transform infrared spectroscopy （ATR-FTIR）was combined with two-dimensional correlation spectroscopy, using infrared spectroscopy, second derivative spectroscopy and two-dimensional correlation spectroscopy to track the cooking process of myofibrillar proteins dynamically. The main changes in the protein cooking process were explained by analyzing the trend and regularity of characteristic peaks. The results showed that in the range of 1 700~1 500 cm-1, DOD had a significant effect on myofibrillar proteins’ characteristic absorption peak. As the DOD increased, the intensity change of myofibrillar proteins characteristic peak was divided into three stages: the first stage was the initial stage of heating, and the intensity decreased from control to rare; the second stage was the middle stage of heating, from rare to medium. There was no significant change in peak intensity; the third stage was the late stage, from medium to over-cooked, and the peak intensity decreased significantly. The synchronous spectrum analysis results showed four autopeaks near 1 650, 1 640, 1 556, 1 540 cm-1, and the cross peaks between the two autopeaks were all positive. The autopeaks intensity analysis results showed that the medium was the turning point of the change of the protein’s temperature sensitive region. When proteins were cooked from control to medium, the amide II band was the sensitive region of myofibrillar proteins, while the sensitive region was the α-helix of amide I banded when proteins were cooked from medium to over-cooked. The information of the dynamic changes of myofibrillar proteins molecular structure caused by cooking provided a theoretical basis for the control and optimization of Western steak cooking.