Biochemistry of non-starter lactic acid bacteria isolate Lactobacillus casei GCRL163: Production of metabolites by stationary-phase cultures

Physiological and metabolic traits of Lactobacillus casei strain GCRL163 were studied in a buffered semi-defined medium supplemented with different concentrations of lactose. The extent of growth (maximum OD600 reached) was limited by concentrations of ≤1% lactose in this medium. Survival of the strain during extended incubation periods (up to 30 days) in cultures without lactose was found to be better than in cultures supplemented with lactose. Important metabolites detected in lactose-starved (0% lactose) cultures were acetate, as a major end product, as well as ethanol, diacetyl, 3-methyl-1-butanol, benzyl alcohol, 1-butanol, isopropanol, 3-(methylthio)-propanoic acid and other compounds. Viability of recovered cells declined but metabolic products continued accumulating, when the pH was kept constant at pH 5.2. It was proposed that cells entered a non-culturable state but remained metabolically active. Results indicated the potential of this strain, as a possible non-starter lactic acid bacteria adjunct, to survive and utilize alternative available substrates as energy source in cheese curd.