Abstract
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.
Highlights
It is well established that proanthocyanidins (PAs) play an important role in both the development of grapes and the production of wine
Was noted after 120 min, while the 1000 mg/L, and 1500 mg/L PA conditions continued to show significant PA loss up to the 480-minute mark. These results further suggest a synergistic influence of PA concentration, temperature, and ethanol concentration on the kinetics of PA adsorption to cell wall material (CWM)
PA adsorption to CWM decreased as temperature and ethanol concentration increased within the system
Summary
It is well established that proanthocyanidins (PAs) play an important role in both the development of grapes and the production of wine. Localized to the vacuoles of skin and seed cells, PAs are released during the crushing process, along with other key polyphenols, as the vacuoles of the cells are ruptured. A portion of these polyphenols are immediately solubilized in the juice, but the majority are extracted into the must/wine matrix over time during the maceration process [2]. PAs have a significant impact on the taste, mouthfeel, color, and oxidative stability of red wine, high extractability is generally desired. Molecules 2020, 25, 4139 during the production process [3]. It has been shown that PA extractability is significantly hindered by adsorption interactions with solids in the fermenter [4]
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