Rice straw hydrolysis and cultivation of Xanthophyllomyces dendrorhous for astaxanthin production and antioxidant properties

Abstract

Astaxanthin is a natural pigment with strong antioxidant activity and is widely supplied as dietary supplement. The red yeast Xanthophyllomyces dendrorhous is one of the potential sources for astaxanthin production. Rice straw was considered for utilization on cultivation and astaxanthin production. Rice straw was treated by autoclave-assisted alkaline pretreatment. and hydrolyzed by cellulase hydrolysis. X. dendrorhous TISTR5730 was cultured and accumulated as the astaxanthin on rice straw hydrolysate. The highest reducing sugar concentration of rice straw hydrolysate was 89.82±0.39g/L (0.71±0.01g/g) when using rice straw (3.3%) and cellulase loading (3 mL). High cell density X. dendrohous TISTR5730 cultivation on rice straw hydrolysate with 20 and 40 g/L of initial reducing sugar was investigated. 40 g/L was appropriate for biomass production while 20 g/L was suitable for astaxanthin accumulation. The highest astaxanthin content was 417.28±50.89 µg/g cell basis at 192 h. Astaxanthin productivity and yield coefficient were 0.01±0.00 mg/L/h and 0.11±0.01 mg/g sugar consumed. The antioxidant activities of astaxanthin were determined by DPPH and ABTS scavenging and FRAP reducing power. The produced astaxanthin represented the high antioxidant activities with IC50 of 9.30 and 1.67 µg/mL of DPPH and ABTS scavenging respectively and FRAP reducing power of 5.31±0.07 µg TEAC/mL. This research indicated that rice straw hydrolysate could be an alternative medium for astaxanthin production. Antioxidant activity of astaxanthin was proved and was feasible for further applications.