Conformational Changes of Tilapia Myosin during High Pressure Processing at Various pHs

Conformational changes of tilapia myosin during high pressure processing (HPP) (0.1, 300 and 600 MPa for 10 min) at various pHs (2.0, 2.5, 3.0, 4.0, 5.0, 6.0, 7.0, 11.0 and 12.0) were investigated by measuring the solubility, surface hydrophobicity, total sulphydryl content, SDS-PAGE and circular dichroism. Results showed that, at acid pH, protein molecules was partially unfolded and internal hydrophobic groups was exposed, so hydrophobicity increased (P<0.05) and solubility decreased (P<0.05), according to reducing SDS-PAGE pattern analysis, the main reason of reducing of solubility was probably the insolubility of myosin heavy chain. Therefore, the denaturation and aggregation of myosin was caused by the combination of acid regulation and high pressure treatment. The effect of high pressure treatment on the solubility was not obvious at pH 7.0 (P>0.05), and an increase in surface hydrophobicity (P<0.05) and a decrease in alpha-helix (P<0.05), suggesting that the tertiary and secondary structure of myosin were changed. At pH 11.0 and 12.0, HPP had no effect on the solubility and conformation of myosin (P>0.05). All results indicated that change of protein tertiary structure was caused by high pressure treatment in the neutral condition, and the denaturation and aggregation of protein was caused by high pressure treatment in the acidic condition.