Optimization and characterization of physicochemical, morphological, structural, thermal, and rheological properties of microwave-assisted extracted pectin from Dillenia indica fruit.

Microwave-assisted extraction of pectin from Dillenia indica (DI) fruit was optimized using Box-Behnken design to maximize yield and quality. Parameters such as solid:solvent (1:10-1:30), microwave power (200-600 W), and extraction time (4-10 min) were varied to determine the optimal conditions. Through experimentation, the optimized extraction parameters were identified as 1:23.66 solid:solvent, 400 W microwave power, and 7 min of extraction time, under which the predicted yield and equivalent weight were 19.68 % and 915.93, respectively. The optimized conditions were validated experimentally (yield:19.4 ± 0.35 %) and equivalent weight:914.57 ± 0.62), showing close agreement with predicted values. Physicochemical properties of the extracted pectin were determined, revealing an effective pore radius of 0.263 ± 0.005 mm and a swelling index order of: water(1) > pH 6(0.7) > HCl(0.3). Moisture content was measured as 7.23 ± 0.25 %, while ash content was found to be 2.23 ± 0.25 %. Further analysis included the determination of methoxyl value, anhydrouronic acid content, degree of esterification, and protein content, which were 9.61 ± 0.31 %, 73.56 ± 1.86 %, 74.15 ± 0.28 %, and 1.16 ± 0.16 %, respectively. Monosaccharide composition revealed presence of neutral sugars, glucose, arabinose and rhamnose and molecular weight was 71,489 g/mol. Morphological characteristics, assessed using scanning electron microscopy, showed a rough, irregular surface of DI fruit pectin. Fourier-transform infrared spectroscopy (FTIR) indicated similarity to standard high methoxyl pectin, while nuclear magnetic resonance (NMR) confirmed characteristic functional groups. Thermal behaviour, determined via differential scanning calorimetry (DSC), exhibited endothermic and exothermic transitions at 83.6 °C and 260.027 °C, respectively. Rheological and functional properties revealed DI fruit pectin solution as a non-Newtonian fluid with shear thinning behaviour, forming weak gels and that its emulsion capacity increased with increase in pectin concentration. Overall, this study provides a comprehensive characterization of microwave-assisted extracted pectin from Dillenia indica fruit, offering insights into its potential applications in food industries.