Isolation and kinetics and bio-molecular characterization of malolactic bacterial strains by musts and wines from different zones for the high quality wine production

Abstract

Malolactic fermentation (EML) is regarded as an important metabolic process for the production of quality wines, particularly in cool climate winegrowing areas, improving their sensory characteristics (reduction of acidity, increase of aromatic complexity) and microbiological stability. This bioconversion is called secondary fermentation because it occurs in wine after the alcoholic fermentation (primary fermentation) when yeast lees release nutrients (amino acids, vitamins) for bacterial growth. Different malolactic bacteria genera (Pediococcus, Oenococcus, Leuconostoc, Lactobacillus) are present in low concentrations on grapes and grape leaves and some of these remain at low cell density during alcoholic fermentation as a function of SO2 concentration and operative parameters used (wine cellar temperature, kind of container, maceration). On the contrary of how it happens for the alcoholic fermentation, malolactic starters cultures aren't widely used because of their reduced effectiveness. This can be due to the modalities of selection of the bacterial strains that often come from enological regions very different from those of employment. In order to obtain selected strains able to metabolize malic acid even at low temperatures (10degC), several natural isolates of lactic acid bacteria were obtained from different high quality Italian musts and wines. The ability of microrganisms to metabolize malic acid at lower temperatures obviates the necessity of warming cellar (a practise which increases the possibility of undesiderable microbial activity) and could have a significant impact on wine quality and energetic consumes of winemaking process. Moreover, the availability of bacterial strains which are autocthonous and, at the same time, technologically efficient, in agreement with the tendencies of wine market, could represent a valid instrument for producing typical wine. As the kinectics of malolactic fermentation are related to the number of viable bacteria, the evolution of microbial strains isolated was evaluated at two different temperatures (10degCC and 25degC) and the related kinetics constants (ko) calculated. Among the natural isolates of lactic acid bacteria, two bacterial strains (strains b and K), both belonging to Lactobacillus genus, show a good growth rate even at low temperature (criophylic strains) and will be screened for further enological characteristics (tolerance to SO2 , ethanol, and fumaric acid) to verify if they could be viable microorganisms for economic commercial scale control of malolactic fermentation process.