Changing oxidoreduction potential to improve water-soluble yellow pigment production with Monascus ruber CGMCC 10910

Background: Monascus pigments are widely used in the food and pharmaceutical industries due to their safety to human health. Our previous study found that glucose concentration induced extracellular oxidoreduction potential (ORP) changes could influence extracellular water-soluble yellow pigment production by Monascus ruber CGMCC 10910 in submerged fermentation. In this study, H₂O₂ and dithiothreitol (DTT) were used to change the oxidoreduction potential for investigating the effects of oxidative or reductive substances on Monascus yellow pigment production by Monascus ruber CGMCC 10910.

Results: The extracellular ORP could be controlled by H₂O₂ and DTT. Both cell growth and extracellular water-soluble yellow pigment production were enhanced under H₂O₂-induced oxidative (HIO) conditions and were inhibited under dithiothreitol-induced reductive conditions. By optimizing the amount of H₂O₂ added and the timing of the addition, the yield of extracellular water-soluble yellow pigments significantly increased and reached a maximum of 209 AU, when 10 mM H₂O₂ was added on the 3rd day of fermentation with M. ruber CGMCC 10910. Under HIO conditions, the ratio of NADH/NAD+ was much lower than that in the control group, and the expression levels of relative pigment biosynthesis genes were up-regulated; moreover, the activity of glucose-6-phosphate dehydrogenase (G6PDH) was increased while 6-phosphofructokinase (PFK) activity was inhibited.

Conclusions: Oxidative conditions induced by H₂O₂ increased water-soluble yellow pigment accumulation via up-regulation of the expression levels of relative genes and by increasing the precursors of pigment biosynthesis through redirection of metabolic flux. In contrast, reductive conditions induced by dithiothreitol inhibited yellow pigment accumulation. This experiment provides a potential strategy for improving the production of Monascus yellow pigments.