Comparative assessment of HTST, hydrodynamic cavitation and ultrasonication on physico-chemical properties, microstructure, microbial and enzyme inactivation of raw milk

Abstract

The effects of high-temperature short time (HTST), ultrasonication (US) and hydrodynamic cavitation (HC) on physicochemical properties, alkaline phosphatase (ALP) activity, microorganism, degree of protein hydrolysis (DPH), color, microstructure and overall particle size of raw milk were studied. The separation index (SI) was also measured during storage of treated milk at 4 ± 2 °C for 12 days. US was carried out at different intensities (200, 300, and 400 W) and time (4, 6, and 8 min) and HC at 4, 6, 8, and 10 psi for 5, 10 and 15 min. It was observed that HC showed 21% energy efficiency (η) with higher cavitational yield than US which had η <10%. Microbial log reduction of 2.30 ± 0.17 TPC and 2.26 ± 0.17 (YM) was obtained by HTST treatment. And about 0.9 and 0.7 microbial log reduction were observed in HC and US treatment respectively. Initially in non-thermal treatment, ALP activity increases slightly by 1–2% at 4 psi (HC) and 200 W (US), but with further increase in time and intensity, ALP activity decreases. In addition to that, there was an increase in the DPH from 0.716 ± 0.09% to about 3.608 ± 0.52 and 3.77 ± 0.15% in US and HC treated samples respectively. Also, with an increase in time and intensity, number of fat globules increased with a decreased diameter and overall particle size. In non-thermal treatment, except for samples treated at 200 W (US) and 4 psi (HC), no separation was observed during the storage which could be due to reduced size of fat globules (from 6.3 μm to 3–2.2 μm).