In vitro gastrointestinal digestion, bioaccessibility, and cellular antioxidant activity of indigenous leafy vegetables

Indigenous leafy vegetables (ILVs) are recognized for their nutritional value and potential health-promoting properties, yet limited data are available on the bioaccessibility and cellular uptake of their antioxidant compounds following digestion. This study systematically investigated the total phenolic content (TPC), total flavonoid content (TFC), antioxidant activities, and cellular antioxidant activity (CAA) of five ILVs from Ga-Molepo, Limpopo Province, before and after simulated gastrointestinal digestion. Results showed that free phenolic and flavonoid fractions in raw ILVs were significantly higher than those in the digested samples, with Bidens pilosa showing the greatest raw free TPC (4719.34 µg GAE/g) and TFC (184.89 µg QE/g). Following digestion, free TPC and TFC declined markedly across species, particularly during the intestinal phase, whereas bound fractions exhibited variable patterns, including transient increases during both the gastric and intestinal phases in some species. Antioxidant capacities (DPPH, ABTS, FRAP) closely mirrored TPC and TFC trends, with free fractions showing a progressive linear decrease through gastric and intestinal phases, while bound fractions displayed fluctuating but occasionally elevated activity. Among the five ILVs, B. pilosa and Cleome gynandra exhibited the highest phenolic content and antioxidant stability, as further supported by strong CAA in Caco-2 cells, indicating their potential as bioaccessible sources of dietary antioxidants. These findings demonstrate that while ILVs possess strong antioxidant potential, their bioaccessibility and cellular antioxidant effects differ across species. This study provides novel insights that support the potential of B. pilosa and C. gynandra as candidates for functional food applications.