The effects of temperature and ethanol on the kinetics of proanthocyanidin adsorption in model wine systems.

Abstract

The kinetics, quantitative and qualitative effects of grape proanthocyanidin (PA) adsorption to grape skin-derived cell wall material (CWM) were investigated in five different temperature-ethanol conditions. Progress curves for each condition were constructed by monitoring the decrease in concentration of PA solutions after exposure to CWM over 720 minutes. Adsorption isotherms were constructed for each condition, and a Langmuir equation model was applied to each via regression analysis. Compositional changes in the PA solutions after exposure to CWM were determined using phloroglucinolysis and gel permeation chromatography (GPC). A negative correlation between PA adsorption and both temperature and ethanol concentration was found. Progress curves suggested that both temperature and ethanol affect the equilibration rate of the adsorption reactions. Additionally, equilibration rates for lower temperature and ethanol concentration conditions were found to be much longer than previously reported, taking up to 720 minutes. Phloroglucinolysis results showed no discernable correlation between temperature or ethanol concentration and %galloylation or %gallo units of adsorbed compounds. Analyses by phloroglucinolysis and GPC indicate a preferential adsorption of larger molecular weight PA s under all conditions, though no discernable impact on PA composition was detected. Additionally, findings suggest that both temperature and ethanol concentration impact the percent reduction in molar mass of the PA solution. Data from this study was ultimately utilized to develop a computational model for predicting phenolic extraction during red wine fermentations.