Impact of pretreatment and different drying methods on nutritional and antioxidant properties of Turkey berry fruits (Solanum torvum)

Turkey berry ( Solanum torvum ) is a nutrient-dense indigenous fruit widely consumed in Ghana, but its high moisture content makes it highly perishable. Converting fresh turkey berries into shelf-stable powders could reduce postharvest losses and support year-round availability. This study therefore evaluated drying and pretreatment combinations that best preserve the nutritional and functional quality of turkey berry. A 2 × 4 factorial design was used, involving two pretreatment conditions (unblanched and hot-water blanched) and four drying methods (solar, freeze, convection, and vacuum). Quality attributes assessed included moisture content, proximate composition, energy value, selected minerals (iron, calcium, and phosphorus), vitamin C, total phenolic content, and antioxidant activity. Drying successfully produced shelf-stable powders, reducing moisture from 81.68% in fresh fruits to 4.19%–8.49% in dried samples, with blanched samples generally attaining lower final moisture than unblanched ones. Fresh fruits contained 3.84% protein, 65.46 kcal/100 g energy, and 2.17 mg/100 g iron, while dried powders showed higher proximate and energy values mainly due to nutrient concentration following water removal rather than absolute increases. No single drying method optimised all quality parameters, indicating that the most suitable process depends on the targeted attribute. Freeze drying and vacuum drying generally produced the best powders when nutrient retention and functional quality were prioritised. Blanched freeze-dried samples retained the highest vitamin C, while blanched vacuum-dried samples recorded the highest total phenolic content and antioxidant activity. Overall, drying offers strong potential for turkey berry value addition in Ghana when processing choices are aligned with intended nutritional or functional goals.