Optimization of water-soluble polysaccharides from stem lettuce by response surface methodology and study on its characterization and bioactivities

Stem lettuce is widely consumed as a vegetable in China. It is also used as a traditional Chinese medicine for a long time. Up to now, no information is available for stem lettuce polysaccharide (SLP). In this study, extraction optimization, characterization, and antioxidant activity of SLP was investigated.The maximum SLP yield of 20.89% was obtained under the optimal extraction conditions as follows: extraction temperature 95 °C, extraction time 3.3 h and ratio of water to material 25 mL/g. The sulfate content of SLP was 5.82% and the main monosaccharides were GalA, Gal, and Ara with a mole ratio of 49.2: 23.3: 22.9. FT-IR spectrum and HPGPC result further indicated that SLP is a sulfated polydisperse heterpolysaccharide. Congo-red test and AFM scan indicated that SLP might be branching and intertwining structure with triple helix conformation. Moreover, SLP exhibited potent antioxidant activity and α-amylase inhibitory activity, hence it could be used as a potential natural antioxidant and hypoglycemic agent in medicine or functional food fields.