Effect of common oenological treatments on grape must vitamin content and final wine volatile composition

Abstract

Yeast nutrition is a key factor in the control of alcoholic fermentation, although the role of vitamins received limited attention for decades. Recent studies have shown that several B-group vitamins strongly influence fermentation kinetics, yeast growth and volatile compounds production [1,2]. This study focuses on the impact of oenological treatments with fining agents or nutrients on vitamins in grape must and the following fermentation process. An LC-MS method was used and demonstrates that bentonites can severely deplete the must of some vitamins: up to -92% and -72 % for vitamins B1 and B6, respectively, and -38% for B2. Carbons presented similar trends on B1 and B6, and a stronger impact on B2 and B3 compared to bentonites (up to -99% and -60%, respectively). Such reductions in vitamin content could lead to deficiencies with adverse effects on Saccharomyces cerevisiae, especially in the case of vitamin B1 (thiamine) which is deemed as essential for yeasts. On the other hand, we showed that some yeast-derived compounds can release significant amounts of B1, B2 and B3 (up to +48%, +151% and +65%, respectively), which could overcome such deficiencies. Those first results opened the possibility to adjust thiamine levels in grape must by using bentonite, to assess effects on fermentability and volatile composition directly on a real matrix instead of a synthetic medium. After fermentation monitoring, GC-FID and GC-MS were used on wine samples for the quantification of 13 higher alcohols and esters. 9 compounds were significantly impacted by initial thiamine, with an overall increase of the 5 alcohols from 356 to 386 mg/L (+8%) and the 4 esters from 307 to 423 µg/L (+38%) under normal B1 conditions compared to the deficient must. Among the most impacted compounds were 2-phenylethanol and its acetate ester (both described as floral aromas), with an increase from 35 to 53 mg/L (+51%) for the alcohol and from 217 to 323 µg/L (+49%) for the ester. Globally, B1 addition to the bentonite treated must restored the volatile profile observed in the untreated control, proving the effects on volatiles are mainly due to thiamine and not to other depleted compounds. Overall, this study provides new insights on the impact of pre-fermentative treatments on nutrient availability while confirming the importance of vitamins for wine’s volatiles. It suggests that the vitaminic status of musts could be a new parameter to consider for fermentation control.

References

1. M.S. Evers, C. Roullier-Gall, C. Morge, C. Sparrow, A. Gobert, S. Vichi, H. Alexandre (2023). Thiamine and Biotin: Relevance in the Production of Volatile and Non-Volatile Compounds during Saccharomyces cerevisiae Alcoholic Fermentation in Synthetic Grape Must, Foods, 12, 972. https://doi.org/10.3390/foods12050972

2. M.S. Evers, L. Ramousse, C. Morge, C. Sparrow, A. Gobert, C. Roullier-Gall, H. Alexandre (2023). To be or not to be required: Yeast vitaminic requirements in winemaking, Food Microbiol., 115, 104330. https://doi.org/10.1016/j.fm.2023.104330