Study on processing stability and fermentation characteristics of donkey milk

The aim of this study was to investigate the effect of different processing treatments, including heating, ultrasonic treatment and fermentation on the stability of donkey milk. In general, the donkey milk performed stable when lower level of heat treatment and ultrasonic treatment were applied. Excessive thermal treatment ( > 85 degrees C) decreased intensity of protein bands (15, 30 and 70 kDa) as observed from Sodium dodecylsulphate polyacrylamide gel electrophoresis (SDS-PAGE). Caseins were sensitive to ultrasonic treatment, whereas the whey proteins were more stable under ultrasonic treatment. Centrifugal precipitation rate and surface hydrophobicity were increased after heating and ultrasonic treatment. In addition, an increment of particle size was detected with temperature higher than 85 degrees C was applied. No significant effects were observed on zeta potential and particle size of donkey milk after ultrasonic treatment. Fermentation allowed donkey milk to form a gel with poor textural properties but with high peptide content. The highest peptides content was obtained by using L. helveticus LZ-R-5 and Lactobacillus helveticus MB2-1.