Ultrasonic extraction, structural characterization, and antioxidant activity of oligosaccharides from red yeast rice

Red yeast rice is consumed as a medicinal food to lower blood lipids. Besides, it is used to color food, make wine, etc. In this study, water-soluble oligosaccharides in red yeast rice were extracted by ultrasonic-assisted extraction method. The parameters to extract oligosaccharides from red yeast rice were optimized by the Box-Behnken design under the following optimal extraction conditions: extraction temperature, 60°C; extraction time, 97 min; and liquid/material ratio, 25 ml/g. The structure and the antioxidant activity of the new oligosaccharide were preliminarily investigated. Total carbohydrates extracted from red yeast rice with 80% ethanol-water solution (v/v) were first removed from pigments using D101 macroporous adsorption resin. The total sugar contents were then purified by DE52 resins and Sephadex G-25 resins to obtain red yeast rice oligosaccharides, coded as RYRO1. Structural characterization experiments indicated that RYRO1 is an oligosaccharide with a weight average molecular weight of 874 Da and a theoretical degree of polymerization of 4.86. RYRO1 is composed of mannose, glucosamine, glucose, and galactose with a molar ratio of 0.248:0.019:1:0.026. The ABTS, DPPH, and hydroxyl free radical scavenging assays showed antioxidant nature of RYRO1.