Utilization of low-cost agricultural by-product rice husk for Monascus pigments production via submerged...

Monascus pigments (MPs) produced by the genus Monascus, have been utilized for more than 2000 years in the food industry. In the present study, by submerged batch-fermentation (SBF), we were able to obtain a mutant strain with a high tolerance of inhibitory compounds generated from rice husk hydrolysate, allowing the production of MPs.

The mutant strain, M. Purpureus M523 with high rice husk hydrolysate tolerance was obtained using the atmospheric and room temperature plasma (ARTP) screening system, producing 39.48 U mL^-1 extracellular total MPs (yellow and orange MPs), using non-detoxified rice husk diluted sulfuric acid hydrolysate (RHSAH) as the carbon source in SBF. Extracellular MPs (exMPs) production was enhanced to 72.1 and 80.7 U mL^-1 in supplemented SBF (SSBF) and immobilized fermentation (IF) using non-detoxified RHSAH, with productivities of 0.16 and 0.37 U mL^-1  h^-1 , respectively. In addition, our findings revealed that despite having a high RHSAH tolerance, the mutant strain was unable to degrade phenolic compounds. Furthermore, we discovered that inhibitory compounds, including furfural (Fur) and 5'-hydroxymethyl furfural (5'-HMF), not only inhibit MP biosynthesis, but also regulate the conversion of pigment components.

The low-cost agricultural by-product, rice husk, can serve as an efficient substitute for MP production with high productivity via IF by Monascus spp. © 2021 Society of Chemical Industry.