Effects of different extraction methods on the structural, antioxidant and hypoglycemic properties of red pitaya stem polysaccharide

Processing conditions can change the compositions and microstructures of polysaccharides, resulting in favorable and unfavorable effects on their chemical characteristics and bioactivites. Here, this study comparatively evaluated the effects of the commonly used hot water, alkaline, acidic, enzymatic, ultrasonic and hot water-alkaline extractions on the structural features and antioxidant and hypoglycemic properties of pitaya stem polysaccharides. Nuclear magnetic resonance spectroscopy showed six polysaccharides had similar glycosyl types. Scanning electron microscopy exhibited the surface morphology of the extracted six polysaccharides differed significantly. Polysaccharide obtained by hot water showed better antioxidant and hypoglycemic properties than that of the other polysaccharides. These data suggested that alkaline, acidic, enzymatic, ultrasonic and hot water-alkaline extractions have various influences on the degradation of polysaccharides without varying the major structure in comparison with hot water extraction. Additionally, monosaccharide composition and molecular weight of polysaccharides are two chief factors affecting the bioactivity of pitaya stem polysaccharides.