Application of thermo-cylindrical type focused-ultrasound as novel milk pasteurization: microbial inactivation, immunoglobulin G retention, and physicochemical characteristics

This study aimed to investigate the efficacy of focused ultrasound as a novel milk pasteurisation technology to replace conventional low-temperature long-time (LTLT) method. The microbial inactivation, immunoglobulin G (IgG) retention, and physicochemical properties of milk treated with focused ultrasound were evaluated. Thermo-cylindrical type (55 °C) focused ultrasound was used for all experiments. Milk was subjected to focused ultrasound at 30 W and 100 W for 0, 10, 20, and 30 min to investigate the antimicrobial effects of this method. The total aerobic bacteria, coliforms, Escherichia coli O157:H7, and Listeria monocytogenes counts decreased (p < 0.05) with increasing focused-ultrasound power and treatment time. Thus, focused ultrasound treatments were applied at 30 W and 100 W for 30 min in subsequent milk quality evaluation and compared with LTLT-treated milk. The IgG retention value of milk treated with focused ultrasound at 30 W and 100 W was higher than that of LTLT-treated milk (p < 0.05). The alkaline phosphatase activity, pH, and whiteness index of milk treated with focused ultrasound at 100 W did not differ from LTLT-treated milk (p > 0.05). Moreover, milk treated with focused ultrasound at 100 W exhibited the smallest particle size and fat globules (p < 0.05). In conclusion, focused-ultrasound treatment at 55 °C and 100 W for 30 min improves milk microbial safety. Additionally, it preserves IgG activity and improves milk quality and stability by reducing fat globule size. Thus, focused ultrasound has the potential to become a novel milk pasteurisation technology for excellent antimicrobial effects and milk quality.