Food antioxidant capacity determined by chemical methods may underestimate the physiological antioxidant capacity

Antioxidant capacity assays are of growing interest in the study of dietary antioxidant properties since they are able to analyse a complex mixture of antioxidants and its synergistic interactions. However, most of the antioxidant capacity assays in the literature are limited by the antioxidant extraction technique, since some antioxidants may remain associated in the extraction residues. The objective of this work was to compare an in vitro physiological procedure for antioxidant extraction with a methanol/acetone/water extraction (chemical procedure). Enzymatic digestions and in vitro colonic fermentations were used on solid plant foods daily consumed in the Spanish diet to estimate the total antioxidant capacity released during the entire digestion process. The in vitro physiological procedure yielded a higher antioxidant capacity than the chemical procedure (7000 and 900 mu mol trolox equivalents measured by ABTS, respectively). Our results suggest that determination of antioxidant capacity in food chemical extracts may underestimate the real antioxidant capacity that may be in close contact with the intestinal lumen. (c) 2006 Elsevier Ltd. All rights reserved.