Lactic Acid Bacteria in an Oat-based Non-dairy Milk Substitute: Fermentation Characteristics and Exopolysaccharide Formation

Abstract

Nine strains of lactic acid bacteria were tested for fermentation characteristics in an oat- based, non-dairy milk substitute, Mill MilkTM (MM medium). Viable counts, aroma formation, lactic acid production and viscosity were the parameters investigated. In general, bacterial strains grown at 30°C yielded a better flavour and higher viable counts than those incubated at 37°C. Strains were selected for their capacity to produce exopolysaccharides in a semi-defined medium. Lactobacillus delbrueckii subsp. bulgaricus NCFB 2772 was chosen for further fermentation experiments, using yoghurt as a control. Production of exopolysaccharide and shear thinning properties were measured using a viscosimetric method. A combination of temperature stress and an increased carbon/nitrogen ratio was shown to affect the production of exopolysaccharide. Increased viscosity was found after incubation at a low temperature using glucose as a supplementary carbon source. The production of exopolysaccharides was also favoured by prolonged incubation times. The use of physical factors such as time and temperature in combination with chemical factors, i.e. media and carbon/nitrogen levels, were crucial in the course of improving exopolysaccharide production during fermentation in the MM medium.