[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 attenuated total reflectance Fourier transfer infrared spectroscopy(ATR-FTIR)technique and automatic deconvolution, curve fitting 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 bonding interactions, which formed by the bound water O—H group and the amino acid CO 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 renaturation. Freezing could affect the stability of beef myofibrillar protein, the relative content of α-helix, β-sheet, and β-turn of beef myofibrillar protein were decreased, and the α-helix and ordered structures changed to the randon coil and disordered structures. After thawing, the increase of β-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 after thawing. That is, the lower the freezing temperature, the lower the measure of freezing denaturation of beef myofibrillar protein, 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 preservation process and a method for the quality evaluation of meat.