Effects of pulsed ultrasound on rheological and structural properties of chicken myofibrillar protein

The effects of pulsed ultrasound (PUS) (power: 240w) with varying time (0, 3, 6, 9, 12 and 15min) on rheological and structural properties of chicken myofibrillar protein (CMP) were examined. PUS treatment significantly caused a decrease in the viscosity coefficients (k) but an increase in the flow index (n) value of CMP solutions within short time (0-6min), while had no significant effect for longer time (9-15min). Besides, at 6min, the solubility and microstructure of CMP samples were optimum. The primary structure of CMP was not altered by PUS treatment. However, Raman spectroscopy revealed a decrease in the α-helix and β-sheets proportion and an increase in the β-turn of CMP following PUS treatment. Random coil reached a maximum at 6min. The changes in tertiary and quaternary structure of CMP by PUS treatment also occurred. As PUS time extended, S0-ANS for CMP increased measured by ANS fluorescence probe method. However, the normalized intensity of 760cm-1 increased from 0min to 6min, and then decreased to 15min by Raman test. Moreover, the reactive sulphur (SH) contents and disulfide bonds (S-S) of samples increased while the total SH contents decreased within 0-6min. At 9min and above, the contents of reactive SH groups were almost equal to the contents of total SH groups. Differential scanning calorimetry (DSC) of CMP showed that peak temperature (Td2) for myosin and peak temperature (Td3) for actin were both reduced in the first 6min, while Td3 was not observed from 9min following PUS treatment. Therefore, 6min was the optimum PUS time to obtain better CMP rheological and structural properties.