Ultrasound improves the rheological properties and microstructure of rennet-induced gel from goat milk

Abstract

Goat milk was treated by ultrasound (US) at 20 kHz and 12.1 ± 0.89 W from 15 to 30 min. The influence of the treatments on the rheological properties and microstructure of the rennet-induced gel was measured. The particle size, zeta potential, hydrophobicity, and secondary structures affected by the treatments were also measured. Sonication time >20 min resulted in a significant (p ≤ 0.05) increase in the storage modulus (G′) compared with that of the controls (raw goat milk and pasteurised goat milk), while the rennet coagulation time was significantly decreased. Scanning electron microscopy showed the gel microstructures of the sonicated samples were more interconnected. US treatments reduced the particle size and changed the secondary structures of the protein which were significantly increased in β-sheets and random coils. However, there was significant decrease in α-helix and β-turn. The β-sheet increase showed a positive correlation (r = 0.74) with hydrophobicity.