Effect of ultrasound pretreatment on rennet-induced coagulation properties of goat's milk.

The effects of ultrasound (US) pretreatment on goat milk before rennet-induced coagulation were studied in order to improve the milk coagulation properties. Skimmed goat milk was subjected to US at 800 W for different times (0-20 min) and various parameters were evaluated. The particle sizes in US pretreated goat milk under the transmission electron microscopy were smaller than in untreated samples. For US pretreated samples, the degree of whey protein denaturation, contents of soluble calcium and phosphorus increased by 9.57%, 16.90% and 13.68%, respectively. The gel firmness, coagulum strength, final storage modulus, cohesiveness, water holding capacity and cross-linking of gels demonstrated marked increase. The turbiscan stability index (TSI) also confirmed the improvement of goat milk coagulation properties with increasing duration of US pretreatment, whereas the gelation time was prolonged.

Effect of power ultrasound pretreatment on peptidic profiles and angiotensin converting enzyme inhibition of milk protein concentrate hydrolysates.

BACKGROUND: The use of power ultrasound as a pretreatment to enhance the hydrolysis of milk protein concentrate (MPC) and subsequent angiotensin converting enzyme (ACE) inhibitory activity has been studied. Liquid chromatography was used to analyse peptide profiles of Neutrase-derived MPC hydrolysates after pretreatment at 0, 1, 3, 5 and 8 min at an ultrasound power level of 800 W. RESULTS: The peptide profiles indicated an increase in number of peptides when ultrasound pretreatment was applied. There was also an increase in the degree of hydrolysis of MPC hydrolysates. The profiles indicated that new small peptides in ultrasound pretreated samples (1-5 min) which were not present in the control samples and 8 min pretreated samples, could be responsible for increased ACE inhibitory activity. These small peptides were digested in the 8 min pretreated samples. CONCLUSION: Ultrasound pretreatment of MPC increases the ACE inhibitory activity of the hydrolysates because of the production of new small peptides. This can be used as a means to derive potent ACE inhibitory peptides at industrial scale in complex protein sources.