Optimizing Nutrient and Antioxidant Retention in Solanecio biafrae Leaves: Comparative Impact of Common Cooking Methods

Abstract

Background: Solanecio biafrae (Bologi) is a nutrient-rich leafy vegetable widely consumed in Nigeria for its dietary and therapeutic benefits. However, domestic cooking methods may alter its nutritional and functional properties. Methods: Fresh S. biafrae leaves were collected in June 2024 from local farms in Osun State, Nigeria. Leaves were subjected to direct steaming, indirect steaming, pressure cooking, and microwave cooking for 5 min. All treatments were analyzed in triplicate (n = 3 per cooking method). Proximate parameters were evaluated using analytical standard protocols. Vitamin contents were assessed through appropriate spectrophotometric and chromatographic procedures. Mineral concentrations were measured by atomic absorption spectrophotometry, while phytochemical constituents were estimated using established colorimetric methods. Antioxidant capacity was examined through DPPH (2,2-diphenyl-1-picrylhydrazyl) radical scavenging activity, Ferric Reducing Antioxidant Power (FRAP), and ferrous ion (Fe²+) chelation assays. Statistical evaluation of the data was performed using one-way ANOVA, and mean separation was carried out with Duncan’s multiple range test using SPSS software (version 25.0). At p<0.05, statistical significance was determined. Results: Pressure cooking yielded the highest protein (3.23±0.78%) and vitamin C (190.25 ± 0.05 mg/100g), while microwave cooking retained the most fibre (2.68±0.08%), folate (659.92±0.16 µg/100g), and phenols (1157.89±0.28 mg (Gallic Acid Equivalents [GAE])/100g). Raw leaves had the greatest carbohydrate (13.81±0.80%) and Fe²+ chelation (73.79±0.63%). Indirect steaming showed the strongest DPPH (47.73±2.16%) and Ferric Reducing Antioxidant Power (FRAP: 416.80±0.10 mg Ascorbic Acid Equivalents [AAE] /100 g). Conclusion: Cooking methods significantly influenced nutrient and antioxidant retention in S. biafrae. Pressure cooking and microwave cooking best preserved nutrients, while indirect steaming maximized antioxidant activity.