Ultrasound-assisted extraction of polysaccharides from litchi (Litchi chinensis Sonn.) seed by response surface methodology and their structural characteristics

Litchi seed has been applied in traditional Chinese medicine since ancient time. Its polysaccharides were prepared by ultrasound-assisted extraction technique and optimized by response surface methodology. The optimal conditions to obtain the highest yield of LSP were determined as follows: 15.0 ml/g of solvent/material ratio, 45.0 min of ultrasonic time and 222 W of ultrasonic power. By structural analysis, arabinose, fructose, galactose, glucose and mannose were detected both in LSPs I and II. A small amount of fucose was only found in LSP II. The monosaccharide composition indicated that LSPs I and II were neutral polysaccharides. The glycosidic linkages between monosaccharides and their relative molar percentages were also identified. Both LSPs I and II eliminated the DPPH radical in a dose-dependent manner. Furthermore, LSP I showed a better DPPH radical scavenging activity than LSP II.Industrial relevanceThe bioactive polysaccharides, derived from plant sources, have attracted much attention by consumers and researchers due to their broad spectra of therapeutic properties and good safety. The structural characteristics of polysaccharides are highly correlated with their bioactivities. In this work, the extraction conditions of water-soluble polysaccharides from litchi seed were optimized by response surface methodology with the assistance of ultrasound. Their structural characteristics and bioactivity were investigated. The results are helpful to utilize litchi seed for food and biomedical application.

Research highlights
► Both LSPs I and II comprised Ara, Fru, Gal, Glc and Man.
► Arabinose and fructose were found to be linked as → 5)-Ara-(1 → and → 3)-Fru-(1→.
► LSP I showed a better DPPH radical scavenging activity than LSP II.
► The optimal conditions for ultrasound-assisted extraction of LSP were determined.