Extraction technology optimization and antioxidant activity of polysaccharides from pumpkin seeds

Abstract: Pumpkin seeds are rich in lipids, proteins, phytosterols, vitamins, minerals and other valuable components. In recent years, many researches have showed pumpkin seeds can significantly reduce serum cholesterol and triglycerides, and play a role in the prevention and mitigation of cardiovascular disease as well as in preventing prostate disease. It has been found that natural polysaccharides extracted from plant seeds possess various important biological activities, such as anti-cancer, antioxidant, immunization and hypolipidemic activities. However, there is not much published information on polysaccharides in pumpkin seeds. For the development and utilization of polysaccharides in pumpkin seeds, at present, degreased pumpkin seed powder was used as raw material, and the extraction of polysaccharides was mainly performed by hot-water extraction. The optimum extraction technology was studied and the preliminary structure of polysaccharides was analyzed by using infrared spectrum scanning (IR) and gas chromatography (GC). Taking polysaccharide yield as an index, the effects of extraction time, extraction temperature, liquid-solid ratio were studied through the single-factor experiment. And then on the basis of single-factor experiment, the optimum extraction condition was investigated with the response surface methodology (RSM) according to the Box-Behnken center combination design principle by the Design-Expert 8.0 software. The results showed that the optimum parameters were: extraction time 2.5 h, extraction temperature 60 °C, liquid-solid ratio 40:1 mL/g, and the extraction yield of pumpkin seed polysaccharides was 2.25%. Under this condition, the actual value was 2.18%, which was closely matched with the predicted yield. The result showed that, the developed model was adequate and precise when compared with experimental data. The monosaccharide composition of polysaccharide was analyzed through comparing the retention time against the standards by GC. Composition analysis indicated that the polysaccharides were composed of rhamnose, arabinose, xylose, mannose, glucose and galactose with a mole ratio of 0.52 : 0.88 : 0.73 : 0.14 : 1.00 : 1.12. The IR spectrum showed that pumpkin seed polysaccharide exhibited the typical absorption peaks of a polysaccharide within the wave number of 4000-500 cm-1. Three strong absorption peaks of polysaccharide within the range of 1072-996 cm-1 indicated the possible presence of pyranose ring in polysaccharides. There was no peak at 1730 cm-1 of COOH, which showed that polysaccharides were neutral heteropolysaccharide with the absence of uronic acid. The antioxidative assays in vitro showed that polysaccharides presented certain scavenging activity toward DPPH·, HO·, and O2-·. The scavenging activity was increased with the increasing of the sample concentration within the test dosage range. At the same test concentration, the scavenging effects of polysaccharide against these 3 radicals were slightly lower than ascorbic acid. The scavenging rate of polysaccharide was respectively 21.3%±0.14%, 57.14%±0.28% and 40.50%±0.64% at the mass concentration of 1.0 mg/mL. In the future, pumpkin seed polysaccharides might be expected to play a promising role as dietary free radical scavengers for oxidative damage prevention. The experimental results provide the basis for the further preparation of pure polysaccharide product, the structure characterization and the biological activity determination. At the same time, this study provides the theoretical basis for the further development of the pumpkin seed function and the improvement of the added value of nonfat pumpkin seed cake.