ATR-FTIR分析冻结—解冻后的牛肉蛋白二级结构变化

研究了牛肉蛋白质二级结构稳定性在-18，-23及-38 ℃不同温度下的变化情况，明确了肉品工业中不同冷冻温度对肉品品质的作用机制。利用了傅里叶变换衰减全反射红外光谱(attenuated total reflectance Fourier transfer infrared spectroscopy，ATR-FTIR)技术、自动去卷积以及曲线拟合等计算方法，分析了-18，-23及-38 ℃三个温度下，牛肉肌原纤维蛋白(myofibrillar protein，MP)在冻结—解冻过程中的红外光谱图变化及蛋白质二级结构变性程度。ATR-FTIR结果显示，冻结—解冻过程中牛肉MP红外光谱图峰高、峰面积发生变化，且峰波数发生红移或者蓝移;冻结—解冻后牛肉MP红外光谱图中3 500～3 300 cm-1波段的吸收峰强度减弱甚至消失，说明解冻后牛肉MP中的结合水中O—H基团与氨基酸CO基团形成的分子内和分子间氢键断裂;冻结会影响牛肉MP二级结构的稳定性，导致牛肉蛋白质二级结构发生变化，其中除了无规则卷曲比例上升以外，α-螺旋、β-折叠、β-转角含量均下降，造成有序结构向无序结构转变;解冻后，冻结温度为-38 ℃的处理组牛肉β-折叠增加量大于-23和-18 ℃处理组，-38 ℃冻结牛肉MP二级结构的稳定性最好，解冻后蛋白质复性也最好。即蛋白质冷冻变性程度随着冻结温度的降低而减轻，蛋白质二级结构特征保持也越好。该试验研究基于肉品工业生产实际，研究结果从微观层面揭示了冻结温度对牛肉蛋白质变性的影响规律及可能的机制，为冷冻肉冻藏保鲜工艺制定提供了参考。

Effects of Freezing and Thawing Treatments on Beef Protein Secondary Structure Analyzed with ATR-FTIR

In order to further clarify the influence mechanism of different freezing temperature on meat quality in meat industry. The effects of freezing at -18,-23 and -38 ℃ on the stability of protein secondary structures of beef were studied.The at-tenuated total reflectance Fourier transfer infrared spectroscopy(ATR-FTIR)technique and automatic deconvolution,curve fit-ting and other calculation and analysis methods were used to analyze the changes of beef myofibrillar protein infrared spectra and secondary structures during -18,-23 and -38 ℃ freezing-thawing processes.ATR-FTIR results showed that the peak high and peak area of infrared spectra of beef myofibrillar protein in the freezing-thawing processes were changed,and the red shift or blue shift of wavenumbers occurred.The intensities of the absorption peak of 3 500~3 300 cm-1 in the infrared spectra of the frozen-thawed beef were reduced or even disappeared.This indicated that the intramolecular and intermolecular hydrogen bond-ing interactions,which formed by the bound water O—H group and the amino acid C—O group,in thawed beef myofibrillar protein were broken.In other words,freezing can result in the destruction of beef myofibrillar protein secondary structures and protein advanced structures unfolded.Once the beef is thawed,the unfolded protein would reaggregation,and protein renatur-ation.Freezing could affect the stability of beef myofibrillar protein,the relative content ofα-helix,β-sheet,andβ-turn of beef myofibrillar protein were decreased,and theα-helix and ordered structures changed to the randon coil and disordered structures. After thawing,the increase ofβ-sheet relative content of beef myofibrillar protein at -38 ℃ was greater than that of -23 and-18 ℃.The stability of-38 ℃ frozen beef myofibrillar protein was the best,and the protein renaturation was also the best af-ter thawing.That is,the lower the freezing temperature,the lower the measure of freezing denaturation of beef myofibrillar pro-tein,and the better the secondary structures stability of beef myofibrillar protein.The experimental study based on the actual production condition of the meat industry.And the effect of freezing temperatures on beef protein denaturation and the possible mechanism were revealed at the micro-aspect.It can be seen that the ATR-FTIR technology can reflect the changes of protein secondary structures in the process of freezing-thawing of beef,and reveal the regularity of beef protein denaturation,which can be used to identify and evaluate the quality of frozen meat.The experimental results provide a reference for the freezing preserva-tion process and a method for the quality evaluation of meat.