Abstract
Chardonnay wine malolactic fermentations were carried out to evaluate the chemical transfers occurring at the wood/wine interface in the presence of two different bacterial lifestyles. To do this, Oenococcus oeni was inoculated into must and wine in its planktonic and biofilm lifestyles, whether adhering or not to oak chips, leading to three distinct enological conditions: (i) post-alcoholic fermentation inoculation in wine in the absence of oak chips, (ii) post-alcoholic fermentation inoculation in wine in the presence of oak chips, and (iii) co-inoculation of both Saccharomyces cerevisiae and O. oeni directly in Chardonnay musts in the presence of oak chips. Classical microbiological and physico-chemical parameters analyzed during the fermentation processes confirmed that alcoholic fermentation was completed identically regardless of the enological conditions, and that once O. oeni had acquired a biofilm lifestyle in the presence or absence of oak, malolactic fermentation occurred faster and with better reproducibility compared to planktonic lifestyles. Analyses of volatile components (higher alcohols and wood aromas) and non-volatile components (Chardonnay grape polyphenols) carried out in the resulting wines revealed chemical differences, particularly when bacterial biofilms were present at the wood interface. This study revealed the non-specific trapping activity of biofilm networks in the presence of wood and grape compounds regardless of the enological conditions. Changes of concentrations in higher alcohols reflected the fermentation bioactivity of bacterial biofilms on wood surfaces. These chemical transfers were statistically validated by an untargeted approach using Excitation Emission Matrices of Fluorescence combined with multivariate analysis to discriminate innovative enological practices during winemaking and to provide winemakers with an optical tool for validating the biological and chemical differentiations occurring in wine that result from their decisions.
Highlights
Microbial biofilms are three dimensional complex and dynamic systems composed of one or several species of microorganisms attached to a surface and surrounded by a self-produced extracellular matrix
This quantification and the support effect were consistent with the data of Bastard et al [6], which demonstrated the presence of microcolonies after 3 days of culture, and bacteria developed in biofilm at 6 days
This work highlighted that regardless of the enological conditions applied to winemaking practices in the presence or absence of wood, O. oeni biofilm lifestyles preserve their malolactic activity in wines and confer technological properties to wine associated with the chemical transfers occurring at the wood/wine interface
Summary
Microbial biofilms are three dimensional complex and dynamic systems composed of one or several species of microorganisms attached to a surface and surrounded by a self-produced extracellular matrix. They regulate biogeochemical transformations in environmental substrates and are involved in biotechnological applications in medical and industrial fields [1, 2]. In the agro-food industry Clean-in-Place procedures are used to maintain satisfactory sanitary conditions. Despite these procedures, undesirable spoilage microorganisms may persist, especially when they have developed biofilm structures [3,4,5]. Microbial biofilms are of primary concern in the food industry since they can develop on any kind of surface in contact with food products (rubber, stainless steel, polyvinylchloride, polyurethane, and wood) [9, 10]
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