Variation in Phenol and Antioxidant Bioaccessibility of Olive Oil According to Olive Maturity and Region

Many studies have investigated the effects of olive harvest time on the phenol content or antioxidant activity of olive oil. However, little research has been conducted on the bioaccessibility of these compounds in olive oil depending on maturity. The beneficial effects of components in food depend on their bioaccessibility. Therefore, this study investigated the effects of harvest time on both the bioaccessibility of olive oil phenols and antioxidant activity. The effects on orchards in different regions were also evaluated. In this study, olives were harvested at three maturation indices from 'Gemlik' variety trees at two locations. No significant difference in the amount of olive oil phenols reaching the small intestine was detected between early- and late-harvest samples. Early harvest samples had the highest bioaccessibility ratios for the copper reducing antioxidant capacity (CUPRAC) in the gastric (68.77%) and intestinal phases (308.27%). On the other hand, both the total phenol content and 2,2-diphenyl-1-picrylhydrazyl (DPPH) antioxidant activity were greater in the gastric phase of the late-harvested samples. The highest amounts of hydroxytyrosol, tyrosol, oleuropein, syringic acid and luteolin were detected in the gastric phase of the early harvest samples. According to the in vitro digestion study, early harvest can increase the bioaccessibility of hydroxytyrosol and tyrosol. However, higher oleuropein content was observed in the intestinal phase of late-harvest olive oil than in the middle-harvest olive oil. The highest CUPRAC antioxidant capacity was detected in early harvest samples for both the gastric (55.38 mu M Trolox/100 g) and intestinal (248.25 mu M Trolox/100 g) phases in the in vitro digestion system. The luteolin content in the intestinal phase and the syringic acid content in the gastric phase were statistically similar for middle- and late-harvest olive oil. In future investigations, olives may be harvested not only on the basis of their oil yield and phenol content but also on the basis of the bioaccessibility ratios of these components. Additionally, the bioaccessibility values of phenols can be used as a new marketing tool for olive oil.