Effects of MOS and IOS on the biochemical and functional traits of myofibrillar proteins of yak

Abstract: Oxidation is a potential tool to control meat quality, and the improvement of meat protein oxidation regulation theory is helpful to its application in food engineering. The protein oxidation systems in muscle are Ion Oxidizing System (IOS) and Metmyoglobin Oxidizing System (MOS). According to previous study, different oxidizing systems will lead to different oxidation phenomenon. So Elucidating the effects of different oxidation systems on biochemical and functional traits of myofibrillar proteins is helpful to improve the engineering theory and application of oxidation regulation of meat quality, which is more important for yak meat quality control because of its higher iron ion and metmyoglobin content. In order to investigate relationship between functional traits and chemical modification of myofibrillar proteins of yak under different oxidizing systems, the biochemistry traits (sulfhydryl content, disulfide bonds content, bityrosine content and surface hydrophobicity), secondary structure (α-helix percent, β-sheet percent, β-turn percent and random coil percent) and functional traits (solubility, turbidity, emulsifying activity index, emulsifying stability index, foamability and foam stability) of myofibrillar proteins of yak were analyzed under IOS and MOS with similar oxidation degree (protein carbonyl content), meanwhile the correlation coefficient between functional traits and biochemical traits of myofibrillar proteins of yak were also analyzed. It was found that there were significantly decreasing thiol group, increasing disulfide bond, increasing bityrosine and decreasing surface hydrophobicity (P<0.05) with increasing carbonyl concentration. Under IOS surface hydrophobicity insignificantly decrease when carbonyl concentration reached (1.19±0.06) nmol/mg. While the change of disulfide bond and surface hydrophobicity of MOS is more obviously than IOS when carbonyl concentration reached (1.51±0.13) nmol/mg which indicate that MOS is more sensitive to form disulfide bond. According to general liner model analysis, the interaction between oxidizing system and oxidizing degree on disulfide bonds content and surface hydrophobicity is significant which declare that the effects of oxidizing intensity on these chemical traits will be different because of different oxidizing system. When the carbonyl content increases by 1.22 nmol/mg to reach a high level, the α-helix structure will decrease by about 17%, while the proportion of the β-sheet structure significantly increases by about 13.5% (P<0.05). With the increase of the degree of oxidation, the protein solubility first increased and then decreased. The peak of the solubility appeared at the medium level (carbonyl content (1.51±0.13) nmol/mg). When the oxidation level reached the medium level, the solubility of the MOS system was significantly higher than that of the IOS system, indicating that the solubility change of the MOS system was more sensitive to the oxidation intensity. Moderate oxidation can improve the solubility and emulsification of myofibrillar proteins of yak and the optimal range of improvement depend on oxidizing system. The effect of MOS on functional traits is more sensitive to oxidation degree. Through correlation analysis, it can be found that disulfide bond is significantly correlated with solubility, turbidity, emulsification and other functional characteristics, while the most indexes secondary structure is significantly correlated with solubility and turbidity. It is shown that different oxidation systems have different effects on the biochemical and functional properties of myofibrillar, and MOS system can improve the functional properties at a lower degree of oxidation, which is related to the more significant changes in disulfide bonds and surface hydrophobicity