Mathematical modeling of proanthocyanidin bioactivity using a protein precipitation assay and dose-response models

Christopher William Beaver

Proanthocyanidin (PA) induced bovine serum albumin (BSA) aggregation was modeled using traditional dose-response models. BSA was stained with Remazol Brilliant Blue-R (RBB) so that BSA could be measured spectrophotometrically. The chosen dose-response model can describe both stimulatory and inhibitory functions of PA induced RBB-BSA aggregation. The molecular weight of active RBB-BSA monomers (RBB-BSAactive) was estimated, and the change in both molecular weight of RBB-BSAactive and precipitation of RBB-BSAactive was modeled. The dose-response model was used to conceptually derive a constant called the tannin activity ratio (TAR). Mathematically, the TAR was defined as the molar ratio of maximum precipitated PA in catechin equivalents (CE) to maximum precipitated RBB-BSA. PA derived from Vitis vinifera L. fruit and wine and purified PA oligomers from Theobroma cacao were compared using the TAR. The comparison of T. cacao oligomers revealed that the TAR is only reliable if PA of homogeneous molecular weight are used so that the true moles of PA can be used in the TAR calculation rather than CE. A sensory study of Columbia Valley Cabernet Sauvignon was conducted using descriptive analysis to determine the effect of deficit irrigation on perceived color and astringency. The sensory study was also meant to relate the TAR constant and astringency, however the TAR constants of the wines were not significantly different. Four different irrigation treatments were applied to the same vineyard block: a full season water deficit, an early season water deficit, a post-veraison water deficit, and a control. The full and early deficit wines were more saturated in color, more purple, and more astringent than the control. The post veraison deficit had little effect on color and astringency as compared to the control. Chemical analysis of the wines revealed that while astringency was correlated with PA concentration, the relationship may not be linear. This study successfully modeled PA induced BSA aggregation using traditional dose response models, and the TAR was clearly defined and explored. Unfortunately, the analysis of purified T. cacao PA oligomers revealed that the TAR constant can be misleading unless PA of homogeneous polymer length are used in the analysis.

Mathematical modeling of proanthocyanidin bioactivity using a protein precipitation assay and dose-response models

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