VALORIZATION OF DRAGON FRUIT PEEL: EXTRACTION, STRUCTURAL ANALYSIS AND FUNCTIONAL PROPERTIES OF DIETARY FIBER

Abstract

Dragon fruit (Hylocereus undatus) peel, an abundant agricultural by-product in Vietnam, is rich in dietary fiber but often underutilized, leading to resource waste. This study aimed to optimize the extraction of soluble dietary fiber (SDF) from dragon fruit peel under acidic conditions and to characterize its structural and functional properties for potential food applications. The effects of solid-to-liquid ratio, pH, temperature, and extraction time on SDF yield were systematically investigated. Optimal extraction conditions were identified at a solid-to-liquid ratio of 1:37.5 (w/v), pH 2.5, 80 °C, and 60 minutes, resulting in an SDF yield of 14.54 ± 0.50%. Fourier-transform infrared spectroscopy (FTIR) confirmed the polysaccharide structure of both SDF and insoluble dietary fiber (IDF), while scanning electron microscopy (SEM) revealed that SDF exhibited a porous and amorphous microstructure, in contrast to the dense, fibrous morphology of IDF. X-ray diffraction (XRD) analysis further demonstrated the amorphous nature of SDF and the partial crystallinity of IDF, indicating distinct structural functionalities. Functional assessments showed that SDF had a water-holding capacity of 21.25 ± 0.34 g/g, an oil-holding capacity of 3.85 ± 0.54 g/g, and a swelling capacity of 32.36 ± 1.06 mL/g. These findings suggest that SDF extracted from dragon fruit peel possesses favorable structural and physicochemical characteristics, making it a promising candidate for incorporation as a functional ingredient in food systems. The study also supports the valorization of agro-industrial by-products, contributing to sustainable development and waste reduction in the food industry.