Assessing bioavailability of phenolic compounds in some vegetables using in vitro digestion methods

Green vegetables such as broccoli, spinach, chicory and cibes, which have a special place in our diet, are good sources of phenolic compounds and antioxidants. In this study, the effect of in vitro digestion on the phenolic compounds in fresh and cooked broccoli, spinach, chicory and cibes. Total phenolics, flavonoids and antioxidant capacities of post gastric (PG), IN (fraction that can be absorbed into small intestine) and OUT (fraction that can't be absorbed into small intestine) samples, which were provided with the in vitro gastric and intestinal digestion, were measured. Bioavailability and bioaccesiblity values were determined. After this research, it was found out that the amount of total phenolics, which belongs to raw and cooked vegetable samples, was in range of 110-143 and 63-100 mg GAE/100 g TA, respectively. Also the amount of total flavonoid was in range of 22-35 and 10-14 mg KAE/100 g TA, respectively. The antioxidant capacity of samples was measured with the method of ABTS and DPPH. The antioxidant capacities of raw and boiled vegetables were in range of 54-51% and 46-28% with the method of DPPH, 37-26% and 30-18% with the method of ABTS. These results showed that conventional cooking caused considerable decrease in the amount of total phenolics, flavonoids and antioxidants (p<0,05). As a result of in vitro digestion, the amount of phenolic compounds increased after gastric digestion despite the fact that they decreased after intestinal digestion (p<0,05). Flavonoids presented high stability in both gastric and intestinal conditions. The antioxidant capacity decreased both in stomach and intestinal digestion. Bioavailability of phenolic compounds, flavonoids and antioxidants were lower when it was compared with their initial values (p<0,05). The lowest bioavailability is determined in flavonoids. Although phenolic compounds were lost considerably as a result of cooking, it was determined that the bioavailability values of phenolic compounds in cooked vegetables except chicory are higher than raw vegetables.