Changes Of The Intermolecular Forces And Secondary Structure Of Myosin From Litopenaeus Vannamei Induced By Dense Phase Carbon Dioxide And Their Correlation With Gel Strength

Dense phase carbon dioxide（DPCD） is a promising non-thermal food processing technology, which has many advantages, for example, mild treatment and minimal food quality loss. Literatures and our previous researches demonstrated that DPCD can induce proteins to form gel, whose gel network structure was compacter and gel strength was stronger than those induced by heat. In order to illuminate the mechanism of protein forming gel induced by DPCD, using myosin from Litopenaeus vannamei as model protein, we investigated the critical concentration of myosin forming gel, the chemical interaction and secondary structure changes of myosin forming gel and the correlation of the chemical interaction and secondary structure with gel strength. The research contents and conclusions were shown as follows:（1） Effects of the pressure（5-30 MPa）、temperature（30-40 ℃） and exposure time（5-30 min） on the critical concentration of myosin gel formation and the gel strength were investigated. The results showed that the pressure and temperature had the significant effect on the critical concentration of myosin forming gel. Although the exposure time has no significant effect on the critical concentration of myosin forming gel, the gel became tighter with the increase of pressure. The critical concentration of myosin forming gel was higher at lower pressure and temperature, and decreased with the pressure or temperature rising. When DPCD induced myosin to form gel, heating effect was mainly acting at lower pressure（5¹0 MPa）, while heating effect and carbon dioxide molecular effect were acting together at high pressure（>10 MPa）. The gel strength was the highest and 14.28±0.57 N·mm when the shrimp surimi was treated by DPCD at the pressure of 25 MPa, the temperature of 50 ℃ and the exposure time of 20 min.（2） The chemical interaction changes of myosin forming gel induced by DPCD and their correlations with gel strength were analyzed. The results showed as follows: Compared with untreated myosin, the content of hydrogen bond and ionic bond of the myosin treated by DPCD was decreased, while the content of hydrophobic bond, disulfide bond and non-disulfide covalent bond was increased. At the same temperature, the pressure of DPCD had no significant effect on chemical interaction of myosin forming gel. At the same pressure, when the temperature（40-60 ℃） of DPCD treatment was rising, the content of hydrogen bond and disulfide bond had no significant change, the content of non-disulfide covalent bond increased, the content of hydrophobic bond decreased, and the content of ionic bond was first decreased and then increased. Under the same temperature, the content of ionic bond and hydrogen bond was the negative correlation with gel strength, while the content of hydrophobic bond, disulfide bond and non-disulfide covalent bond was the positive correlation with gel strength. In other words, the lower was the content of ionic bond and hydrogen bond, the higher was the content of hydrophobic bond, disulfide bond and non-disulfide covalent bond, the greater was myosin gel strength induced by DPCD. Therefore, hydrophobic bond, disulfide bond and non-disulfide were the main chemical reaction during the myosin forming gel.（3） The second structure changes of myosin forming gel induced by DPCD and their correlations with gel strength were analyzed. The results showed as follows: Compared with the untreated, heat treated and atmospheric pressure CO₂ treated myosin, the content of α-helix of myosin treated by DPCD decreased significantly, while the content of β-sheets, β-turns and random coil increased significantly. At the same temperature, with the pressure of DPCD increasing, the content of α-helix decreased, the content of β-sheets increased, the content of β-turns and random coil had no significant change. At the same pressure, with the temperature of DPCD increasing, the content of α-helix decreased, the content of β-sheets, β-turns and random coil increased little. The secondary structure of myosin showed good correlation with the gel strength during the myosin forming gel induced by DPCD. The content of α-helix was the negative correlation with the gel strength, while the content of β-sheets、β-turns and random coil was the positive correlation with the gel strength. Therefore, when DPCD induced myosin to form gel, the α-helix structure of the myosin could transfer to the β-sheets, β-turns and random coil structure, especially β-sheets structure.The above results preliminary revealed the mechanism of myosin forming gel induced by DPCD. It provides the theoretical foundation for further optimizing and designing the process of myosin forming gel induced by DPCD. DPCD as a non thermal food processing technology has many advantages and the researches are reported more and more in recent years. If the technology would be applied to industrial production, the related basic theory and practical application will need to be researched further.