Microwave-assisted extraction of pectin from persimmon: physicochemical properties, structural characterization and greenness assessment

In this study, the microwave-assisted extraction (MAE) of pectin from persimmon was optimized using a Box-Behnken experimental design, with pH, extraction time, and liquid-to-solid ratio as independent variables. The optimization results obtained through response surface methodology indicated optimum conditions of pH 1.78, extraction time of 8 min, and a liquid-to-solid ratio of 125 mL/g, corresponding to a predicted pectin yield of 4.28%. In the validation experiment, the actual pectin yield was determined to be 3.79 ± 0.04%, confirming a good agreement with the model predictions. The degree of esterification, methoxyl content, galacturonic acid and ash contents, water- and oil-holding capacities, antioxidant activity, rheological behavior, and structural properties (FT-IR, DSC, and 1H NMR) of the samples obtained under optimal MAE and conventional extraction conditions were compared. Based on the degree of esterification, both samples were classified as high-methoxyl, with galacturonic acid contents of 41% and 42% for the MAE and conventionally extracted samples, respectively; both values were below the ≥ 65% level specified for commercial food-grade pectin. The ash content was higher in the MAE sample (7.22%) than in the conventionally extracted sample (1.56%). MAE resulted in a pectin-rich complex with a relatively low galacturonic acid content and higher antioxidant activity than the conventionally extracted sample. Furthermore, the MAE sample exhibited higher water-holding capacity but lower oil-binding capacity than the conventionally extracted sample. Rheological analysis showed that the MAE sample exhibited higher apparent viscosity and shear stress than the conventionally extracted sample. FT-IR analysis revealed more pronounced absorption bands in the MAE sample, suggesting structural differences. DSC analysis revealed differences in the thermal behavior of the MAE and conventionally extracted samples. Additionally, 1H NMR analysis supported the presence of characteristic pectic structural features in both samples. The greenness assessment of the method was assessed using the Greenness Evaluation Metric for Analytical Methods (GEMAM), which yielded an overall score of 7.482, indicating a high level of environmental acceptability. Overall, MAE can be considered an efficient and sustainable approach for obtaining a pectin-rich complex with antioxidant activity from persimmon.