Optimization of microwave-assisted extraction and structural characterization of pectin from sweet lemon peel

The microwave-assisted extraction of pectin from sweet lemon peel (SLP) was optimized using Box-Behnken design. The highest pectin yield (25.31%) was observed under optimal condition (microwave power of 700 W, irradiation time of 3 min and pH of 1.5). The physicochemical, structural and some bioactivity of the SLP pectin isolated at optimum condition was evaluated. The SLP pectin was rich in galacturonic acid and galactose (87.2 mol%), high in molecular weight (615.836 kDa) and low in degree of esterification (1.2-35.1%). Furthermore, the SLP pectin was composed of 55.7% linear region (homogalacturonan) and 42.2% hairy region (rhamnogalacturonan-I). Also, the FT-IR and H-NMR results confirm the major presence of low methylated galacturonic acid rich structure in the isolated samples. In addition, SLP pectin showed good emulsifying and antioxidant properties. A pseudoplastic flow behavior was observed for SLP pectin solution at higher concentrations (1% w/v <). These results represent an inexpensive source for pectin extraction with high pectin yield and good properties.