VALORIZATION OF RICE HUSK BY HYDROTHERMAL PROCESSING TO OBTAIN VALUABLE BIOPRODUCTS: XYLOOLIGOSACCHARIDES AND MONASCUS BIOPIGMENT

Rice husk is a readily available residue which can be used for producing bioproducts in a biorefinery context. In this study, the hemicellulose fraction was hydrolyzed in a hydrothermal process to produce xylooligosaccharides (XOS), whereas the cellulosic hydrolysate was used for red pigment production by Monascus ruber Tieghem IOC 2225. The highest XOS (X2-X4) production (2.26 g per 100 g of rice husk) was achieved at 180°C for 68 minutes in a non-stirred Parr reactor (50 mL). Subsequently, using a stirred parr reactor (1 L) at 180°C for 60 minutes, 3.6 g of XOS (42% of xylobiose, 35% of xylobiose, 13% of xylotriose, 7% of xylotetraose, and 3% of xylopentaose) per 100 g of rice husk were obtained. The XOS was then purified by using ultrafiltration (UF) with two diafiltration membranes at 6.5 pH, resulting in the recovery of approximately 95% of total XOS. Further purification was conducted with nanofiltration (NF) at 3.8 pH, recovering approximately 85.4% of XOS in the retentate. This process yielded XOS with a purity of 75% based on the total sugar content. Additionally, the enzymatic process yielded 132 g of total sugar per kg of pretreated biomass, and the hydrolysate was used to produce 2.1 UA490nm of red pigment by M. ruber after 7 days. These results highlight the potential of rice husk as an interesting biomass for the development of a multiproduct biorefinery.