Analysis and properties of polysaccharides extracted from Brassica oleracea L. var. capitata L. by hot water extraction/ultrasonic-synergistic enzymatic method

In this study, the polysaccharides (BOLP) of Brassica oleracea L. var. capitata L. were extracted by ultrasound-assisted pectinase (UAEE) and hot water extraction (HAE), and the extraction conditions of the two methods were optimized by establishing response surface methodology (RSM), and the HAE-BOLP and UAEE-BOLP obtained under the optimal extraction conditions were analyzed for their chemical compositions, preliminary structural characterization and in vitro antioxidant activity tests. The findings demonstrated that, in the ideal circumstances investigated by RSM, the BOLP extracted by UAEE was superior to that of HAW, both in terms of sugar content and extraction rate, in which the extraction rate was 1.51 times higher than that of HAE, and the amount of solvent used for extraction was greatly reduced. As far as the antioxidant activity test is concerned, UAEE-extracted BOLP showed more reducing power and ABTS⁺ radical scavenging ability than HAE, reaching about 97.61 % scavenging of ABTS⁺ at 4 mg/mL. In addition, structural characterization showed that UAEE-BOLP is an acidic polysaccharide containing glucuronic acid with α- and β-glycosidic bonds, whereas HAE-BOLP contains only β-glycosidic bonds, and both polysaccharides contain furanose and pyranose ring structures. In this study, the ultrasound-assisted pectinase extraction method for BOLP was reported for the first time. Additionally, the in-vitro antioxidant activity of BOLP was measured for the first time. This work fills the gap regarding the antioxidant activity of BOLP, and it can provide a theoretical basis for the future development and utilization of BOLP in fields such as biopharmaceuticals and food additives.