Effect of microoxygenation applied before and after malolactic fermentation on monomeric phenolics and tannin composition of Pinot Noir wine

Abstract

Background and Aims: This study examines the effect of microoxygenation (MOX) applied before and after malolactic fermentation (MLF) on monomeric phenolic compounds and the tannin composition of a young Pinot Noir wine. It provides a complementary study to an earlier report on the effect of MOX on Pinot Noir colour and pigment development. Methods and Results: Two oxygen doses [10.8 and 52.4 mg O₂/(L month)] were applied either before or after MLF for 30 days. The wines were analysed by a series of HPLC-based methods for phenolic compounds, with sources including both the Pinot Noir grape and a minor contribution from commercial tannin and oak additives. Post-MLF MOX led to the near complete hydrolysis of cis-and trans-coutaric acids and to the conversion of trans-caftaric acid to caffeic acid, which has been associated with MLF. An increase of syringic acid was also found with post-MLF MOX. For tannin composition, MOX decreased the proportion of trihydroxylation (%Tri-OH) but increased galloylation (%Galloyl). Between MOX treatments, the effect of MOX dosage was much stronger than MOX timing on phenolic measures. Conclusions: Post-MLF MOX greatly affected the enzymatic hydrolysis of hydroxycinnamic acids. With MOX, the decrease in %Tri-OH and the increase in %Galloyl could increase astringency perception. The higher oxygen dosage had a greater impact on tannin composition than shown previously with colour-related parameters. Significance of the Study: The influence of MOX on Pinot Noir phenolic composition has not been reported previously in such detail. Applying MOX to a young Pinot Noir wine altered the phenolic units responsible for astringency.