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

The effects of pulsed ultrasound (PUS) (power: 240 w) with varying time (0, 3, 6, 9, 12 and 15 min) 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 (0–6 min), while had no significant effect for longer time (9–15 min). Besides, at 6 min, 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 6 min. 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 760 cm⁻¹ increased from 0 min to 6 min, and then decreased to 15 min by Raman test. Moreover, the reactive sulphur (SH) contents and disulfide bonds (S-S) of samples increased while the total SH contents decreased within 0–6 min. At 9 min 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 (T_d2) for myosin and peak temperature (T_d3) for actin were both reduced in the first 6 min, while T_d3 was not observed from 9 min following PUS treatment. Therefore, 6 min was the optimum PUS time to obtain better CMP rheological and structural properties.