Apparent matrix effect of commercial mannoprotein on the wine fruity esters during wine aging

The long-term storage of wine affects its volatile compound profile, leading to alterations in the overall aroma1,2. Fruity esters are volatile compounds that contribute to the aroma of wine and play an important role in maintaining aroma stability3. Building on evidence that spent yeast polysaccharides could impact the stability of wine esters2, this study aims to further investigate the role of mannoproteins (MPs) in maintaining the stability of these esters. Commercial MPs and MPs purified from the alcoholic fermentation of synthetic grape juice were used in the study. Their composition and molecular weight distribution were analyzed using UV spectrophotometry, electrophoresis, and high-performance liquid chromatography. The analysis revealed a total protein content of approximately 25% for the commercial MPs, with their molecular weights primarily distributed between 40-180 kDa and 7.5-40 kDa. To examine the influence of MPs on the stability of fruity esters, concentrations of 200 and 400 mg/L of MPs were added into a model wine system containing 12% ethanol, 5 g/L tartaric acid, and pH 3.0. This model wine was then spiked with various esters (ethyl isobutyrate, ethyl butyrate, isoamyl acetate, ethyl hexanoate, ethyl octanoate, ethyl decanoate, and ethyl phenylacetate) added at concentrations naturally found in wine. Through accelerated aging at 50°C for two and a half months, the concentration of these esters was determined by liquid-liquid extraction and gas chromatography-mass spectrometry. The findings show a hydrolysis rate of 92% for isoamyl acetate and between 64% and 82% for other ethyl esters after 1 month, with continued hydrolysis observed until the end of the period. The addition of MPs was found to slightly retard this hydrolysis, with the 400 mg/L concentration proving more effective than 200 mg/L. Further investigation in a real wine system, as well as the analysis of the sensory impact, is necessary to ascertain the role of MPs on wine aroma. References 1. 2. 3. Dias, D. A.; Clark, A. C.; Smith, T. A.; Ghiggino, K. P.; Scollary, G. R. Wine bottle colour and oxidative spoilage: Whole bottle light exposure experiments under controlled and uncontrolled temperature conditions. Food Chem. 2013, 138 (4), 2451-2459. DOI: https://doi.org/10.1016/j.foodchem.2012.12.024. Kong, C.-L.; Zhu, D.-Y.; Zhao, Y.; Zhao, T.-Y.; Tao, Y.-S. Spent yeast polysaccharides in mixed alcoholic fermentation between Pichia kluyveri, Pichia fermentans and Saccharomyces cerevisiae retarded wine fruity ester hydrolysis. Journal of Food Composition and Analysis 2022, 105, 104200. DOI: https://doi.org/10.1016/j.jfca.2021.104200. Jackson, R. 11 - Shelf Life of Wine. In The Stability and Shelf Life of Food (Second Edition), Subramaniam, P. Ed.; Woodhead Publishing, 2016; pp 311-346.