Abstract
Biofilm life-style of Lactobacillus plantarum (L. plantarum) strains was evaluated in vitro as a new and suitable biotechnological strategy to assure L-malic acid conversion in wine stress conditions. Sixty-eight L. plantarum strains isolated from diverse sources were assessed for their ability to form biofilm in acid (pH 3.5 or 3.2) or in ethanol (12% or 14%) stress conditions. The effect of incubation times (24 and 72 h) on the biofilm formation was evaluated. The study highlighted that, regardless of isolation source and stress conditions, the ability to form biofilm was strain-dependent. Specifically, two clusters, formed by high and low biofilm producer strains, were identified. Among high producer strains, L. plantarum Lpls22 was chosen as the highest producer strain and cultivated in planktonic form or in biofilm using oak supports. Model wines at 12% of ethanol and pH 3.5 or 3.2 were used to assess planktonic and biofilm cells survival and to evaluate the effect of biofilm on L-malic acid conversion. For cells in planktonic form, a strong survival decay was detected. In contrast, cells in biofilm life-style showed high resistance, assuring a prompt and complete L-malic acid conversion.
Highlights
Malolactic fermentation (MLF) consists of the decarboxylation of tricarboxylic L-malic acid to dicarboxylic L-lactic acid and CO2
Culturable cells of L. plantarum in the biofilms produced in MRS broth without stress conditions or in presence of acid or ethanol (Et12, Et14) stress were quantified using the vital count plate technique
The ability to survive and to convert L-malic acid to L-lactic acid by L. plantarum Lpls22 in planktonic or in biofilm form was evaluated in a model system at 12% of ethanol and pH 3.5 or pH 3.2
Summary
Malolactic fermentation (MLF) consists of the decarboxylation of tricarboxylic L-malic acid to dicarboxylic L-lactic acid and CO2. The failure of MLF is generally attributable to rapid cells loss vitality [23] For this reason, the capability to survive and degrade L-malic acid in acid and ethanol stress conditions represents the most important feature to be screened in the selection process of a potential malolactic strain. Cells of L. plantarum in biofilm form enhance resistance to acid and ethanol stress [31]. Most of these studies evaluated the biofilm formation of L. plantarum in relation to food spoilage or probiotic traits [32,33,34,35,36]. The survival of L. plantarum cells in biofilm life-style and the effect of high-biofilm producing strains on L-malic acid conversion were evaluated in a model wine medium
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