The Effects of Temperature and Ethanol on Proanthocyanidin Adsorption to Grape Cell Wall Material in the Presence of Anthocyanins
Department of Viticulture and Enology, University of California, One Shields Avenue, Davis, CA 95616, USA
Department of Chemistry and Biochemistry, University of Texas at Tyler, 3900 University Blvd, Tyler, TX 75707, USA
E&J Gallo Winery, 600 Yosemite Blvd, Modesto, CA 95354, USA
Authors to whom correspondence should be addressed.
Academic Editors: Rocio Gil-Muñoz and Encarna Gómez-Plaza
Molecules 2020, 25(18), 4139; https://doi.org/10.3390/molecules25184139
Received: 8 August 2020 / Revised: 30 August 2020 / Accepted: 7 September 2020 / Published: 10 September 2020
(This article belongs to the Special Issue Wine Chemistry: The Key behind Wine Quality)
The quantitative and qualitative impacts of anthocyanins on proanthocyanidin adsorption to grape-derived cell wall material were investigated in fifteen unique systems of varying temperatures, ethanol concentrations, and proanthocyanidin concentrations. Proanthocyanidin solutions were exposed to cell wall material and monitored for changes in concentration over 24 h. Increases in both temperature and ethanol resulted in a larger retention of proanthocyanidins in solution and typically faster adsorption kinetics. Analysis of the solution after exposure to cell wall revealed a significant reduction in the molecular weight of proanthocyanidins present in solution, suggesting that anthocyanins do not alter a previously described mechanism of preferentially binding large molecular weight molecules. Additionally, a reduction in polymeric pigment abundance was noted in most conditions, suggesting rapid formation of polymeric pigment in the model solution and preferential adsorption of the polymeric pigment to cell wall material. Compared to a previous study of proanthocyanidin adsorption in the absence of anthocyanins, a significantly larger percentage of proanthocyanidin material was lost via adsorption—up to 70% of available material. In a winemaking context, this may suggest a preferential loss of polymeric pigment via adsorption to cap cell wall material compared to non-pigmented proanthocyanidins and free anthocyanins.