J Ind Microbiol Biotechnol (2012) 39:477–494 DOI 10.1007/s10295-011-1050-4 123 FERMENTATION, CELL CULTURE AND BIOENGINEERING Comparative metabolic proWling to investigate the contribution of O. oeni MLF starter cultures to red wine composition Sulette Malherbe · Andreas G. J. Tredoux · Hélène H. Nieuwoudt · Maret du Toit Received: 20 June 2011 / Accepted: 16 October 2011 / Published online: 26 November 2011 © Society for Industrial Microbiology 2011 Abstract In this research work we investigated changes in volatile aroma composition associated with four com- mercial Oenococcus oeni malolactic fermentation (MLF) starter cultures in South African Shiraz and Pinotage red wines. A control wine in which MLF was suppressed was included. The MLF progress was monitored by use of infra- red spectroscopy. Gas chromatographic analysis and capil- lary electrophoresis were used to evaluate the volatile aroma composition and organic acid proWles, respectively. SigniWcant strain-speciWc variations were observed in the degradation of citric acid and production of lactic acid dur- ing MLF. Subsequently, compounds directly and indirectly resulting from citric acid metabolism, namely diacetyl, ace- tic acid, acetoin, and ethyl lactate, were also aVected depending on the bacterial strain used for MLF. Bacterial metabolic activity increased concentrations of the higher alcohols, fatty acids, and total esters, with a larger increase in ethyl esters than in acetate esters. Ethyl lactate, diethyl succinate, ethyl octanoate, ethyl 2-methylpropanoate, and ethyl propionate concentrations were increased by MLF. In contrast, levels of hexyl acetate, isoamyl acetate, 2-phenyl- ethyl acetate, and ethyl acetate were reduced or remained unchanged, depending on the strain and cultivar evaluated. Formation of ethyl butyrate, ethyl propionate, ethyl 2- methylbutryate, and ethyl isovalerate was related to speciWc bacterial strains used, indicating possible diVerences in esterase activity. A strain-speciWc tendency to reduce total aldehyde concentrations was found at the completion of MLF, although further investigation is needed in this regard. This study provided insight into metabolism in O. oeni starter cultures during MLF in red wine. Keywords Malolactic fermentation (MLF) · Volatile aroma composition · MLF starter cultures · Oenococcus oeni · Red wine Introduction Wine production involves a succession of biological pro- cesses including alcoholic fermentation by yeast and malo- lactic fermentation (MLF) by lactic acid bacteria (LAB). MLF in wine is performed, preferably by inoculation with Oenococcus oeni in order to reduce wine acidity by bio- transformation of the dicarboxylic L-malic acid to the monocarboxylic L-lactic acid by the malolactic enzyme [9, 15, 33, 36]. MLF improves biological stability and aVects wine organoleptic properties such as aroma, Xavour, and mouthfeel [4, 9, 29]. O. oeni is recognised as the species most tolerant to the harsh wine conditions of low pH, high sulfur dioxide (SO 2 ), and high alcohol content. For this rea- son, in addition to its favourable Xavour proWle, O. oeni is mostly selected as starter culture [33]. The complexity and diversity of the metabolic activity associated with the growth of LAB suggest that MLF may aVect wine quality both positively and negatively [15, 35]. Wine aroma and Xavour could be aVected by LAB via sev- eral mechanisms including: 1 reduction of Xavour compounds by metabolism and adsorption on the bacterial cell wall; Electronic supplementary material The online version of this article (doi:10.1007/s10295-011-1050-4) contains supplementary material, which is available to authorized users. S. Malherbe · A. G. J. Tredoux · H. H. Nieuwoudt · M. du Toit (&) Institute for Wine Biotechnology, Stellenbosch University, Private Bag X1, Matieland, Stellenbosch 7602, South Africa e-mail: mdt@sun.ac.za Downloaded from https://academic.oup.com/jimb/article/39/3/477/5994619 by guest on 12 June 2022