Near and mid Infrared spectroscopy to detect malolactic biotransformation of oenococcus oeni in a wine-model

The aim of this work was to verify the potential of Infrared (IR) spectroscopy in near and mid regions to detect the beginning of the malolactic fermentation (MLF) occurring in a model-wine and the further cells autolysis. MLF in wine is a secondary biotransformation due to Lactic Acid Bacteria that usually occurs spontaneously or after starter inoculation at the end of alcoholic fermentation. Nowadays, it is desirable to supply winemakers with a new rapid and non-destructive approach to monitor MLF progress and IR spectroscopy technology appears to be suitable for this purpose. The transformation of L-malic acid into L-lactic acid was carried out by inoculating a synthetic wine with an Oenococcus oeni culture and it was monitored through microbiological and chemical methods. At the same time FT-NIR spectral data, in diffusive transflection mode using an optic probe, and FT-IR spectra, using a ATR cell, were collected. Principal Component Analysis of the spectra was able to identify absorption bands related to the key molecular modifications that took place during the L-malic acid transformation. Thus, to discriminate samples according to the fermentation phase. Although this study is a preliminary approach, results confirm that NIR and MIR spectroscopy could be successfully applied to detect the start of MLF and the autolysis of the LAB cells.