Antimicrobial phenolic extracts able to inhibit lactic acid bacteria growth and wine malolactic fermentation

The purpose of this study was to determine whether phenolic extracts with antimicrobial activity may be considered as an alternative to the use of sulfur dioxide (SO2) for controlling malolactic fermentation (MLF) in winemaking. Inhibition of the growth of six enological strains (Lactobacillus hilgardii CIAL-49, Lactobacillus casei CIAL-52, Lactobacillus plantarum CIAL-92, Pediococcus pentosaceus CIAL-85, Oenococcus oeni CIAL-91 and O. oeni CIAL-96) by phenolic extracts (n = 54) from different origins (spices, flowers, leaves, fruits, legumes, seeds, skins, agricultural by-products and others) was evaluated, being the survival parameter IC50 calculated. A total of 24 extracts were found to significantly inhibit the growth of at least two of the LAB strains studied. Some of these extracts were also active against two acetic acid bacteria (Acetobacter aceti CIAL-106 and Gluconobacter oxydans CIAL-107). Transmission electron microscopy of the bacteria cells after incubation with the phenolic extract confirmed damage of the integrity of the cell membrane. Finally, to test the technological applicability of the extracts, the eucalyptus extract was added (2 g/L) to an industrially elaborated red wine, and the progress of the MLF was evaluated by means of residual content of malic acid. Addition of the extract significantly delayed the progress of both inoculated and spontaneous MLF, in comparison to the control wine (no antimicrobial agent added), although not as effective as K2S2O5 (30 mg/L). These results demonstrated the potential applicability of phenolic extracts as antimicrobial agents in winemaking.