Development and response surface optimization of oat-fortified dragon fruit (Hylocereus polyrhizus) roll with peel valorization for enhanced functional and nutritional properties

Abstract

The growing demand for functional foods has stimulated interest in developing value-added fruit-based products enriched with health-promoting ingredients while simultaneously reducing food-processing waste. Red dragon fruit ( Hylocereus polyrhizus ) is a rich source of phenolic compounds, anthocyanins, dietary fiber, and antioxidants, whereas its peel, often discarded during processing, contains substantial quantities of bioactive compounds. Oats are recognized for their high dietary fiber and β -glucan content, which contribute to various health benefits. Therefore, the present study aimed to develop and optimize an oat-fortified dragon fruit roll and evaluate the potential of dragon fruit peel valorization as a functional food ingredient. The physicochemical, functional, and sensory characteristics of dragon fruit pulp and peel were initially assessed. Product formulation was optimized using Response Surface Methodology (RSM) based on a Box–Behnken Design with three independent variables: sugar (20–30 g), dragon fruit peel purée (80–100 g), and oats (5–10 g). Sensory attributes including taste, aroma, flavor, appearance, and overall acceptability were used as response variables. The optimized dragon fruit–oat roll was further evaluated for physicochemical composition, color characteristics, antioxidant activity, total phenolic content, anthocyanin content, and in vitro anti-inflammatory activity using the protein denaturation inhibition assay. Dragon fruit peel exhibited considerably higher crude fiber (28.33%), total phenols (219.42 mg GAE/100 g), antioxidant activity (79.91% DPPH), anthocyanins (23.29 mg/100 g), and ascorbic acid (11.27 mg/100 g) than the pulp, demonstrating its potential as a valuable functional ingredient. Optimization identified the formulation containing 30 g sugar, 90 g dragon fruit peel purée, and 5 g oats as the most acceptable treatment, with an overall acceptability score of 8.05. The optimized dragon fruit–oat roll contained 28.40 °Brix total soluble solids, 0.832% titratable acidity, 23.50% total sugars, 14.24% reducing sugars, 5.16% crude fiber, 6.98% moisture, and 4.39% ash content. The product retained appreciable levels of total phenols (21.25 mg GAE/100 g), antioxidant activity (45.76% DPPH), and anthocyanins (7.64 mg/100 mL). Color values of L* 22.83, a* 5.79, and b* 20.72 indicated retention of the characteristic red-purple appearance of dragon fruit. The optimized roll also demonstrated concentration-dependent anti-inflammatory activity with a maximum inhibition of 60.54% at 1500 μg/mL and an IC 50 value of 1161.6 μg/mL. The results demonstrated that oat fortification enhanced the nutritional quality of dragon fruit roll, particularly dietary fiber content, while maintaining desirable sensory and functional properties. The significant antioxidant and anti-inflammatory activities observed in the optimized product highlight its potential as a health-promoting functional snack. Furthermore, the effective utilization of dragon fruit peel provides a sustainable strategy for value addition and by-product valorization. The developed dragon fruit–oat roll represents a promising functional food with enhanced nutritional and bioactive properties and potential for commercial application.