Shehabi Murtaza, Jangala Krishna Pallavi
Sweet lime peel is a significant, underutilized agro-industrial byproduct with high dietary fiber content and untapped prebiotic potential. This study investigated the impact of ultrasonication on the structural and functional evolution of SLP dietary fibers extracted via 1% HCl. The modified soluble dietary fiber (SDF) and insoluble dietary fiber (IDF) fractions were characterized using Fourier-transform infrared spectroscopy, X-ray diffraction, field emission scanning electron microscopy, and differential scanning calorimetry. Ultrasonication markedly augmented the hydration and lipophilic properties of the SDF; specifically, swelling capacity, water-holding capacity, and oil-holding capacity increased to 7.04 ± 0.54 mL/g, 3.13 ± 0.39 g/g, and 4.16 ± 0.51 g/g, respectively, compared to untreated controls (4.00 ± 0.31 mL/g, 2.57 ± 0.21 g/g, and 2.30 ± 0.29 g/g). XRD analysis showed that ultrasonication reduced the degree of crystallinity from 31.6% to 28.7% in SDF and from 44.9% to 37.8% in IDF, indicating disruption of the ordered cellulose structure while FTIR spectra exhibited intensified and broadened peaks in the 3000-3300 cm-1 and 1000-1050 cm-1 regions, suggesting enhanced hydroxyl group exposure. In vitro fermentation trials revealed that the structural reorganization of sonicated SDF significantly enhanced its prebiotic efficacy. Lactobacillus plantarum counts increased from 8.23 ± 0.57 to 9.51 ± 0.26 log CFU/mL over 16 h, yielding a positive Prebiotic Activity Score of 1.36 and maintaining up to 71% recoverability following simulated gastrointestinal digestion. These results demonstrate that ultrasonication is an effective strategy for upcycling citrus waste into high-value functional ingredients for the food industry.