Microwave Extraction of Antioxidant Polysaccharides from Plantago depressa and Their Effects on SOD and GSH-Px in Drosophila melanogaster Model

A microwave extraction method was developed to isolate antioxidant polysaccharides from Plantago depressa (psyllium), and the structure, free radical-scavenging ability, as well as in vivo antioxidant activity of psyllium polysaccharides were analyzed. The optimal condition for microwave extraction was as follows: duration of microwave radiation of 35 min, extraction temperature of 80 °C, and ratio of liquid to solid of 80:1 (mL/g). The yield of psyllium polysaccharides by microwave extraction was significantly higher than that by heating extraction (p < 0.05). The volumes of P. depressa samples notably increased after microwave extraction, which implied that microwave radiation might loosen the structure of cells and tissues of psyllium leaves and facilitate the exudation of target polysaccharides from leaf samples. The structure of polysaccharides was analyzed by infrared spectroscopy. The effective concentrations of psyllium polysaccharides scavenging DPPH• and ABTS•+ radicals by 50% (EC50) were 0.20 and 0.10 mg/mL, respectively. Moreover, P. depressa polysaccharides increased activities of superoxide dismutase (SOD) and glutathione peroxidase (GSH-Px) in Drosophila melanogaster. In conclusion, microwave extraction seems to be an efficient method to isolate bioactive polysaccharides from P. depressa, which were a potential source of natural antioxidants.