The effect of bentonite fining on the volatile and non-volatile profile of Italian white wines

Bentonite is used in white winemaking to remove the heat unstable wine proteins responsible for haze formation [1], but being an non-specific adsorbent, it removes some other wines compounds linked to wine quality including volatiles [2]. This study was designed to provide information on the potential impact of bentonite fining on non-volatiles and volatiles in some Italian monovarietal white wines in order to investigate whether their depletion differs according to the variety, when the right amount of bentonite is used to reach full stability. Thirteen unfined white wines from 5 Italian varieties (Fiano, Falanghina, Greco di Tufo, Vernaccia di San Gimignano, Vermentino di Gallura), sampled within those of the D-Wines program, were treated with the minimum bentonite (Na-Ca Bentonite) dose required to reach protein stability as determined by fining trials, and compared with the untread wines for chemical composition (by HPLC-SEC), protein profiles (by RP-HPLC), polysaccharide (by HR-SEC) and phenolic concentration (by colorimetric method), particles’ size (by nanoparticles tracking analysis) and 107 volatile profiles (by GC-MS/MS [3,4]). Wines heat instability ranged from 10 to 177 NTU, but these values did not correlate well with their bentonite requirements (R2 = 0.6138) that was between 200 to 800 mg/L. The impact of bentonite fining led to several wine modifications including a decrease in titratable acidity and an increase in Na and Ca concentrations. Besides the obvious decrease in protein content (on average -83%), fined wines contained significantly less phenolics (on average – 35%). Total polysaccharides and the mean particle sizes were slightly reduced. When looking at the volatile compounds, a general slight decrease was observed, particularly for the ethyl esters, with some wines seeing a lower decrease that was not in line with the dose of bentonite used. In general, the results confirm that bentonite is a non-specific adsorbent that can affect the wine quality, but the observed variations could not be related to the dose of bentonite used, indicating that the detrimental effects may occur starting from minimal bentonite additions. References (max 5) 1. Van Sluyter, S.C.; McRae, J.M.; Falconer, R.J.; Smith, P.A.; Bacic, A.; Waters, E.J.; Marangon, M. Wine Protein Haze: Mechanisms of Formation and Advances in Prevention. J. Agric. Food Chem. 2015, 63, 4020–4030, doi:10.1021/acs.jafc.5b00047. 2. Lambri, M.; Dordoni, R.; Silva, A.; Faveri, D.M.D. Effect of Bentonite Fining on Odor-Active Compounds in Two Different White Wine Styles. Am. J. Enol. Vitic. 2010, 61:2, 225–233. 3. Carlin, S.; Lotti, C.; Correggi, L.; Mattivi, F.; Arapitsas, P.; Vrhovšek, U. Measurement of the Effect of Accelerated Aging on the Aromatic Compounds of Gewürztraminer and Teroldego Wines, Using a SPE-GC-MS/MS Protocol. Metabolites 2022, 12, 180, doi:10.3390/metabo12020180. 4. Piergiovanni, M.; Carlin, S.; Lotti, C.; Vrhovsek, U.; Mattivi, F. Development of a Fully Automated Method HS-SPME-GC-MS/MS for the Determination of Odor-Active Carbonyls in Wines: A “Green” Approach to Improve Robustness and Productivity in the Oenological Analytical Chemistry. J. Agric. Food Chem. 2023, doi:10.1021/acs.jafc.2c07083.