A novel rice hull - microalgal biorefinery for the production of natural phenolic compounds comprising of rice hull acid pretreatment and a two-stage Botryococcus braunii cultivation process

Recently, the rising demand of the industry for natural phenolic antioxidant compounds has turned to the study of microalgae as potential sources. Yet, more economic substrates for microalgal cultivation are sought to lower production costs. To this end, the present work deals with the utilization of rice hull hydrolysate (RHH) as substrate for microalgae Botryococcus braunii through a novel two-stage cultivation system. Initially, RHH was optimized to maximize the contained nutrients while minimizing its inhibitors content. The optimum point was reached under 121 degrees C, 60 min, 2% (v/v) H2SO4, 30% (w/v) loading. Next, B. braunii was successfully grown first heterotrophically in RHH (25%, v/v), obtaining high biomass production (6.67 g L-1) and then autotrophically to enhance phenolics accumulation. At the end, a high phenolic content of 7.44 & PLUSMN; 0.60 mg Gallic Acid Equivalents g-1 DW was achieved from the produced biomass, thus highlighting the potential of this novel biotechnological method.

Automated summary

This study utilized rice hull hydrolysate as a substrate for cultivating microalgae Botryococcus braunii in a two-stage cultivation system. The rice hull hydrolysate was optimized to maximize nutrients and minimize inhibitors content. The microalgae were successfully grown in the optimized substrate, resulting in high biomass production and high phenolic content in the produced biomass, demonstrating the potential of this novel biotechnological method.