Effect of acidification biotechnologies on the production of volatile compounds, lactic acid and colour in red wines after the use of pulsed light pretreatment in grapes

The treatment of grapes with pulsed light is an emerging technique to reduce the populations of native microorganisms and thus implement fermentative biotechnologies in a more controlled manner with selected yeasts and bacteria. These biotechnologies can modify the profile of wines as the microbial populations thrive in different ways and produce different fermentative metabolites. The first objective of this research was to assess the use of pulsed light as a technology to reduce microbial population in grapes, and a second objective was to assess the viability of performing biological acidification in red wines with the use of Lachancea thermotolerans after the use of pulsed light. The treatment of grapes with pulsed light reduced the yeast and bacteria population 1.2 log CFU/mL and allowed the use of fermentative biotechnologies. Biological acidification with Lachancea thermotolerans produced more lactic acid than malolactic fermentation with Oenococcus oeni. Up to 4 g/L of lactic acid were reported in co-inoculations of Lachancea thermotolerans with Saccharomyces cerevisiae. On the other hand, the ester concentration, which provides floral and fruity aromas, was higher in wines that underwent malolactic fermentation. In this way, pulsed light treatment has produced wines with less aromatic volatiles and yet better perception of fruity and floral aromas as the lactic acid production was higher. Regarding colour, the wines were brighter and more intense due to the concentration of lactic acid although anthocyanins have decreased 9% and 18% in co-inoculation of Lachancea thermotolerans and Saccharomyces cerevisiae in wines with treated and untreated grapes, respectively. A deeper evaluation during large-scale winemaking is advised to assess pulsed light to reduce native microbiota before the implementation of acidification biotechnologies.