Valorization of red dragon fruit peel (Hylocereus polyrhizus) as a functional ingredient for fortified biscuits: physicochemical, nutritional, and sensory implications

This study valorizes red dragon fruit peel (an agro-industrial byproduct) as a useful ingredient in biscuits. Proximate analysis of the Red dragon fruit peel powder (RDFPP) revealed a high crude fiber (23.68%), ash (10.60%), and carbohydrates (43.32%), along with bioactive components such as total phenolic content (0.34 mg GAE/g), flavonoids (53.32 mg QE/g) and antioxidant activity: 43.22%). Fourier transform infrared spectroscopy identified functional groups associated with polysaccharides, phenolic content, flavonoids, and lipids in both peel and biscuits. Biscuits containing 0-9% RDFPP were evaluated for physicochemical, bioactive, sensory, and microbiological qualities. Increasing RDFPP substitution increased ash (0.71% to 2.27%) and fiber (0.08% to 0.74%), while decreasing moisture (5.58% to 4.21%) and pH (5.34 to 5.03), enhancing shelf stability. Antioxidant activity and bioactive compounds increased proportionally, with 9% RDFPP showing the highest values (total phenolic content: 0.50 mg GAE/g; total flavonoids: 1.99 ± 0.02 mg QE/g; DPPH: 38.79%). Sensory evaluation indicated that 6% RDFPP was the ideal acceptability level, after which color (darker, L*: 36.61) and taste declined due to betacyanin pigments and acidic significance. Scanning electron microscopy analysis revealed structural porosity at higher RDFPP levels, correlating with texture changes. Microbial shelf-life studies showed that RDFPP has antimicrobial properties, reducing bacterial growth in 9% RDFPP biscuits (8.09 log 10 CFU/g) compared to the control (8.45 log 10 CFU/g) after 15 days. These findings highlighted the ability of RDFPP to enhance nutritional and functional properties of baked products. A 6% RDFPP substitution optimized antioxidant enrichment, fiber fortification, and consumer acceptance, providing a sustainable solution for repurposing agricultural waste into value-added foods.