Nutritional requirements of selected wine lactic acid bacteria

The vinification of most red and some white varieties involves the malolactic fermentation (MLF), which leads to acid reduction and aroma modifications. While MLF may occur spontaneously by bacteria naturally present in wines, it may be conducted more efficiently by inoculation with commercial lactic acid bacteria (LAB), generally of the species Oenococcus oeni . Development of commercial starters and nutrients has improved the control of MLF but this trend has been partly neutralized by higher alcohol concentrations, which are now encountered more frequently. Uncontrolled MLF and/or growth of indigenous bacteria can lead to wine quality depreciation. The study of pertinent metabolic activities of wine LAB is difficult due to the complex nature of the medium wine. For example, amino acids, whose metabolism may lead to the formation of biogenic amines and precursors of carcinogenic ethyl carbamate may be released from proteins by proteases during MLF, and hydrolysis of glycosides can cause liberation of sugars hindering the calculation of substrate turnover rates, metabolic kinetics and the determination of true growth requirements. Accordingly, methods to specifically support desirable bacteria, whether indigenous or selected, would be advantageous.;This work provides methods for the investigation of the metabolism and nutritional requirements of bacteria in wines. The results also have practical relevance. For example, tailored nutrient preparations could be used to favour bacterial genera, species or strains selectively, in order to offer organisms with positive qualities an ecological advantage while reducing the likelihood of bacterial spoilage and the risk of formation of compounds with potentially negative health impacts.;The nutritional requirements of selected LAB as well as the effects of specific nutrients on their growth and malolactic performance were studied. Results obtained during the development of minimal and chemically-defined media for selected bacteria suggest that, similar to dairy LAB, wine bacteria exhibit complex and strain specific nutritional requirements, especially with regards to vitamins and amino acids. Overall, the oenococcal strains displayed more amino acid auxotrophies while the lactobacilli studied were more demanding with regards to vitamins. Data obtained from this study were used to assess the relevance of individual medium compounds for bacterial growth in wine and in defined medium with a genetic algorithm.