Effect of culturing lactic acid bacteria with varying skim milk concentration on bacteria survival during heat treatment

Abstract Four lactic acid bacteria (LAB) strains were cultured in reconstituted skim milk with different solids contents to compare the thermotolerance of resulting cultures. As milk concentration was increased from 5 to 30 wt%, the population of non-lactose-fermenting strains increased by around 1 log at stationary growth phase. High solids milk maintained relative stable pH (ΔpH  108 CFU/mL) and growth capability after heat treatment at 65 °C for 10 min, indicating a general thermoprotective effect irrespective of metabolic pathways. Besides cellular response to high osmolality during bacterial growth, we proposed that the increased concentration of protective dairy components and the increased viscosity and thermal resistance of culture medium also contributed to the excellent thermotolerance.