Characterisation of wine malolactic bacteria and acetic acid from fructose metabolism : a thesis presented in partial fulfilment of the requirements for the degree of Master of Science in Microbiology, at Massey University

Abstract

Twenty-four strains of wine Lactic Acid Bacteria from the genera Leuconostoc, Lactobacillus and Pediococcus were characterised with respect to their growth responses to ethanol, temperature, pH, ability to degrade wine organic acids and utilisation of carbon sources. A novel single broth culture (HFA) was developed for the determination of heterofermentation, mannitol formation and ammonia production. Some strains of Leuconostoc oenos were found to produce ammonia from arginine. The implications of this are discussed. The production of mannitol from fructose by heterofem1entative strains indicated potential acetic acid (volatile acid) spoilage risk for wrnes.

To investigate this risk, semi-synthetic media were devised to simulate "stuck" yeast alcoholic fem1entation and the spoilage potential was evaluated under conditions of pH, substrate availability and ethanol concentration. Acetic acid production was analysed in the media by HPLC and found to occur at high levels from growth in the presence of fructose, but not glucose. The production was not affected by low pH or ethanol concentrations, or their combined effect. This indicated that acetic acid spoilage could occur under wine conditions. Other mechanisms of acetic acid production relative to this experiment are discussed. Erythritol and glycerol were detected in fermentation media but not quantified by HPLC. Their presence supported evidence of the activity of a novel glucose fem1entation pathway in Le. oenos.