Bio-accessibility of nutritional and antioxidant contents of naturally fermented Sphenostylis stenocarpa (African yam bean) during gastrointestinal digestion

Background: Sphenostylis stenocarpa (African yam bean, commonly called Otili) is an underutilized legume valued for its protein, carbohydrate, mineral, and phytochemical richness, but limited information exists on its digestibility and antioxidant bio accessibility. Objective: This study examined the nutritional and antioxidant properties of fermented flour (DF) and shaft fractions (NDF) of S. stenocarpa under simulated gastrointestinal digestion. Materials and Methods: All reagents used in this study were of analytical grade and suitable for biochemical and physiological experiments. Bean shaft and flour samples underwent in vitro digestion, the release and stability of both nutritional and anti-nutritional factors were assessed across the oral, gastric, and intestinal phases. Results: Findings revealed that fermented flour exhibited greater digestibility and higher bio accessible levels of phenolics (546.65 ± 0.02 mg/g) and flavonoids (332.33 ± 0.03 mg/g) compared with the shaft fraction, which retained many compounds bound to fiber. Sugar composition differed between fractions: reducing sugars were most abundant in digestible fractions at the colon (7.29 ± 0.03 mg/g) and intestine (6.88 ± 0.02 mg/g), whereas glucose (1.15 ± 0.02 mg/g) and fructose (1.40 ± 0.02 mg/g) dominated in non-digestible fractions at the intestine. Sucrose appeared mainly in non-digestible fractions at the colon (0.04 ± 0.02 mg/g) and intestine (0.01 ± 0.01 mg/g). The shaft fraction contributed higher ciceritol content (3.98 ± 0.03 mg/g) compared with the flour fraction. Conclusion: In conclusion, fermentation enhanced the release of soluble antioxidants and sugars in flour fractions, while shafts served as a reservoir of bound polyphenols and oligosaccharides that may provide delayed colonic benefits. These findings establish S. stenocarpa as a valuable functional food and demonstrate that fermentation improves its nutritional and health-promoting potential.