Optimization of selenylation conditions for lycium barbarum polysaccharide based on antioxidant activity

Lycium barbarum polysaccharide (LBP) was modified by HNO3–Na2SeO3 method according to L9(34) orthogonal design to obtain nine selenizing LBPs (sLBPs), sLBP1–sLBP9. Their antioxidant activities in vitro were compared by free radical-scavenging test. sLBP6, sLBP8 and sLBP9 presented stronger activity. In vivo test, 14-day-old chickens were injected respectively with sLBP6, sLBP8 and sLBP9 taking LBP as control, and serum GSH-Px and SOD activities and MDA content were determined. The results showed that three sLBPs could significantly enhance GSH-Px and SOD activities and decrease MDA content. The actions of sLBPs were significantly stronger than that of unmodified LBP. These results indicated that selenylation modification could significantly enhance the antioxidant activities of LBP, sLBP6 possessed the best efficacy and could be exploited into an antioxidant. The optimal modification conditions were 400 mg of sodium selenite for 500 mg of LBP, reaction temperature of 70 °C and reaction time of 6 h.