Influence of high-intensity ultrasound and heat treatment in continuous flow on fat, proteins, and native enzymes of milk

The effect of continuous flow high-intensity ultrasound (with and without heat generation) on alkaline phosphatase, gamma-glutamyltranspeptidase, lactoperoxidase, whey proteins (alpha-lactalbumin and beta-lactoglobulin), casein, and fat was studied in milk. Results were compared with those obtained using a conventional heating system having similar processing conditions. Hardly any effect on enzymes was observed when ultrasound was applied without heat generation. The highest denaturation of enzyme and whey proteins was found in samples subjected to ultrasound and heat. At 61, 70, and 75.5 degrees C a synergistic effect between ultrasound and heat was observed for the inactivation of alkaline phosphatase, gamma-glutamyltranspeptidase, and lactoperoxidase, respectively. A noticeable synergism between ultrasound and heat was detected for alpha-lactalbumin and beta-lactoglobulin denaturation. No changes in the casein were observed after any of the conditions assayed. As a consequence of ultrasound effects, a substantial reduction (up to 81.5%) in the size of the fat globule was observed. When 70 and 75.5 degrees C were achieved during high-intensity ultrasonic homogenization, a better particle distribution was observed as compared to that obtained at lower temperatures. This work describes the influence of continuous flow high-intensity ultrasound on important milk components as a first step for future processing applications.