Abstract

Despite the known impact of cooking on the food’s nutritional value, the variation in bioavailability and bioaccessibility of bioactive compounds after digestion remains inadequately understood. This study aimed to compare the effect of different cooking methods on the total phenolic content and antioxidant activity of bioaccessible and bioavailable extracts of brinjal (Solanum melongena L.), turkey berry (Solanum torvum L.), and winged bean (Psophocarpus tetragonolobus L.). Each vegetable was cooked by six methods using different combinations of coconut oil, coconut milk, and spices. The cooked vegetables were digested in vitro to evaluate their bioaccessible and bioavailable total phenolic content and antioxidant activity. The total phenolic content was determined by the Folin Ciocalteu method. Free radical scavenging activity, total antioxidant capacity, and reducing power were evaluated by the DPPH, ABTS, and FRAP assays, respectively. All the cooking methods significantly increased the total phenolic content and antioxidant activity of the extracts compared to their raw forms. The vegetables cooked with oil, milk, and spices generally showed higher total phenolics and antioxidant activity than those cooked by the other methods. We found a strong positive correlation between the total phenolic content and various antioxidant parameters. The highest bioaccessibility index for phenolic compounds was registered in the brinjal extract cooked with oil and in the turkey berry and winged bean extracts cooked with oil, milk, and spices. Different cooking methods exhibited varying effects on the antioxidant activity of bioaccessible compounds. In bioavailable extracts, variability was observed for the total phenolic content and antioxidant activity among different cooking methods for brinjal, turkey berry, and winged bean. The ABTS and FRAP assays showed the highest total phenolic content and antioxidant activity in all the vegetables cooked with coconut oil, milk, and spices.

Keywords

Solanum melongena L., Solanum torvum L., Psophocarpus tetragonolobus L., in vitro digestion, bioaccessibility, antioxidants, bioactive compounds, bioavailability, cooking methods

FUNDING

This study was funded from the research grant of Sabaragamuwa University of Sri Lanka (grant No. SUSL/RG/2016/19).

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