Effect of Physico-Chemical Factors on Growth of Starter Culture for Wine Malolactic Fermentation
Rajka Božanić, Vjera Runjić-Perić, Ivanka Pavušek and V. Marić
Faculty of Food Technology and Biotechnology, University of Zagreb, Pierottijeva 6, 4100 Zagreb, Croatia
Received June 15, 1994
Accepted September 26, 1994
The induction of the malolactic fermentation (MLF) by inoculating a wine with selected malolactic bacteria has, recently, received immense enologists' attention because of its positive influence on quality and sensory characteristics of wine. The strains of Leuconostoc oenos adapted to grow in adverse conditions of fermentation (i.e., low pH values and temperature, high concentrations of SO2 and ethanol) were the most frequently used. Since MLF of wines is performed in adverse conditions for bacterial growth in this paper the effects of temperature and pH lower than optimal, and different ethanol and SO2 concentrations on the growth of strain UR were investigated with optimal value of at least one factor of growth (T and/or pH). The simultaneous effect of these factors combined by Graeco-Latin Square method was also investigated. The optimal conditions determined for the growth of the investigated strain are: 37 °C and pH = 6.5. The growth of Leuconostoc oenos UR was good al 25 °C, while lower pH (3.0 and 4.0) and higher ethanol volume fractions (φ = 10 and 12 %) inhibited bacterial growth significantly. The investigation of SO2 concentration (30, 50 and 100 mg/l.) showed that only the highest SO2 concentration in medium slightly suppressed bacterial growth after 24 hours of cultivation. The growth of L.oenos UR in the conditions combined by Graeco-Latin Square method zvas significantly suppressed. Namely, after 24 hours of growth under such conditions, the maximal cell concentration ratio (CCR) was only 15 % of CCR value obtained at the same unfavourable pH, but in otherwise optimal conditions. The ratio between sums of squares of separate variables and total sums of squares (expressed as a percent), estimates the inhibitory influence of each variable in Greaco-Latin Square Design on the growth of L.oenos UR. It was estimated that the share of medium pH value is the most significant: 73.0 % and 8S.4 % after 24 hours and 120 hours of growth, respectively.