Assessment of the formation of A-type proanthocyanidin by model reaction to blueberry extract and epicatechin

Blueberries are lacking in A-type proanthocyanidins, which assist in the prevention of urinary tract infections. Additive reactions to anthocyanins and a flavanol monomer promoted the formation of A-type proanthocyanidins. The four major anthocyanins of blueberry extracts are malvidin 3- O -glucoside, cyanidin 3- O -glucoside, delphinidin 3- O -glucoside and petunidin 3- O -glucoside. The model reaction of their two deglycosylation products, cyanidin and delphinidin with epicatechin, was investigated with different pH levels and under different thermal treatment conditions. At a pH 2.0–4.0, a nucleophilic addition occurred between the epicatechins and the anthocyanidins under flavylium form. Among the products, two colorless dimer adducts, A-type cyanidin-epicatechin (PAC-A2) and A-type delphinidin-epicatechin were obtained under optimal conditions (pH 2.0, at 90 °C, for 80 min, anerobic) and proved to be linked through a bicyclic bond (C4–C8, C2– O –C7) as detected in the A-type proanthocyanidins. This indicates that blueberry extract, originally rich in B-type proanthocyanidins, can produce A-type proanthocyanidins after processing.