Proanthocyanidin content in foods is largely underestimated in the literature data: An approach to quantification of the missing proanthocyanidins

The content of proanthocyanidins (PA) in foods is usually determined by HPLC analysis of aqueous-organic extracts. However, the appreciable amounts of PA that remain in the residues of extraction usually are not considered for analysis. Attempts to determine these non-extractable proanthocyanidins (NEPA) by enzymatic-chemical methods have obtained partial results. The general aim of this work was the estimation of the total content of PA, including both extractable PA (EPA) and NEPA in some foods included in the USDA database. A specific procedure based on depolymerization by HCl/BuOH treatment was used to quantify NEPA. The content of NEPA in analyzed samples ranged from 11 mg/100 g for pear to 6.7 g/100 g dry weight for red grape pomace. The results showed that literature data underestimate the actual content of PA in foods. NEPA may have a significant contribution to the healthy effects associated to PA-rich foods and diets.