Monascus-fermented sorghum: pigments and monacolin K produced by Monascus purpureus on whole grain, dehulled grain and bran substrates

Monascus-fermented products are widely consumed in Asian countries as food colorant, preservative, supplements and in traditional medicine. Whole sorghum grain, dehulled sorghum grain and sorghum bran are potential substrates for solid state fermentation with Monascus purpureus. The objective of this research was to study pigments and monacolin K production by Monascus purpureus using whole sorghum grain, dehulled sorghum grain and sorghum bran as substrates. Monascus purpureus, isolated from commercial Monascus-fermented rice was used in the fermentation of the whole sorghum grain, dehulled sorghum grain and sorghum bran treated with or without soaking. After sterilization, the substrate was inoculated with Monascus purpureus culture containing 5 x 105 spores/mL, then incubated at 30oC with 70% relative humidity for 14 days. The Monascus-fermented sorghum was dried and analyzed for the colour, biomass, pigments and monacolin K contents.The Monascus purpureus grew on all types of substrate with biomass content of 7.41 to 44.69 mg/g. During fermentation, the mold produced yellow, orange and red pigments; and monacolin K on all types of the substrate. Ethanol soluble pigments were in a range of 12-96.4 AU/g; 3.7-47.7 AU/g and 2.8-59.7 AU/g respectively for yellow, orange and red pigments, while water soluble pigments were in a range of 3.9-32.4 AU/g; 1.6-20.8 AU/g; and 1.3-21.5 AU/g. Sorghum bran treated by soaking were found to yield more water soluble pigments, whereas sorghum grain substrate was found to be the best substrate for ethanol soluble pigments and monacolin K production. The results of this study shows that Monascus-fermented sorghum is a promising source of pigments and monacolin K and that further studies on the process optimization, effect of drying method on the pigments stability, separation of the pigments and the bioactivities evaluation are being carried out.