Optimization of the ultrasound-assisted fermentation process of Buffalo's milk (Bubalus bubalis)

Abstract

Previous studies have demonstrated that the application of sub-lethal levels of ultrasound (US) can enhance fermentation efficiency and introduce novel characteristics to the resulting dairy products. However, exposing the lactic acid bacteria to US changed their metabolic activities. Therefore the optimum growth conditions of US-treated bacteria may vary from their native counterparts which is not reported to-date. In this work, the US was applied to a mixed culture of Lactobacillus bulgaricus, Streptococcus thermophiles, S. lactis, S. diacitilactic and S. cremoris as a pre-treatment for the fermentation of buffalo's milk. This study aimed to optimize the physicochemical and textural properties of buffalo's milk set-yoghurts using Response Surface Methodology. The experiments were conducted using the central composite design with three independent variables: sonication time (0–5 min), fermentation temperature (38–42 °C) and inoculum level (0.07–0.11 mL/100 mL). A control experiment was prepared according to the commercial conditions (0.1 mL/100 mL inoculum fermented at 42 °C without sonication). The inoculum concentration of 0.09 g/100 g. incubation temperature of 42 °C and sonication for 4.6 min were found optimum for the production of buffalo's milk set-yoghurt with 54.5 % desirability using ultrasound-assisted fermentation. The resulted processing conditions shortened the time to reach the maximum acidification rate (T_m) by 40 % and reduced the syneresis by 14.4 % (w/w) while improving the springiness of the gel by 36 % compared to the control set-yoghurt. Hence, it can be concluded that the optimized parameters for US-assisted fermentation offer a novel approach to enhance the efficiency of the fermentation process of buffalo milk set-yoghurt while improving the product quality and processing efficiency.