Abstract
Monascus species can produce secondary metabolites that have a polyketide structure. In this study, four types of extracellular water-soluble yellow pigments (Y1–Y4) were generated by submerged fermentation with Monascus ruber CGMCC 10910, of which Y3 and Y4 had strong yellow fluorescence. The composition of the pigment mixtures was closely related to the fermentation temperature. The dominating pigments changed from Y1 to Y3 and Y4 when fermentation temperature increased from 30 to 35 °C. Increasing the temperature to 35 °C changed the metabolic pathways of the pigments, which inhibited the biosynthesis of Y1 and enhanced the biosynthesis of Y3 and Y4. Moreover, the yield of Y1 reduced insignificantly, while the yields of Y3 and Y4 increased by 98.21 and 79.31% respectively under two-stage temperature fermentation condition. The expression levels of the relative pigment biosynthetic genes, such as MpFasA2, MpFasB2, MpPKS5, mppR1, mppB, and mppE, were up-regulated at 35 °C. The two-stage temperature strategy is a potential method for producing water-soluble Monascus yellow pigments with strong yellow fluorescence.
Highlights
Monascus spp. has been widely used in the production of Monascus pigments for colouring traditional foods in Asian centuries (Juzlova et al 1996)
Pigment biosysthesis in M. ruber CGMCC 10910 under different temperatures Fermentation temperature of 30 and 35 °C were suitable for both cell growth and glucose consumption; a low temperature of 25 °C was not suitable (Fig. 1a)
The UV–Visible spectra absorption peak of the extracellular pigment compositions was at 350 nm at 25 and 30 °C, and 388 nm at 35 °C (Fig. 1c)
Summary
Monascus spp. has been widely used in the production of Monascus pigments for colouring traditional foods in Asian centuries (Juzlova et al 1996). Many of the identified Monascus pigments are fungal metabolites called azaphilones with a polyketide structure, including the six well-known Monascus pigments red (monascorubramine and rubropunctamine), orange (monascorubrin and rubropunctatin), and yellow (monascin and ankaflavin) (Patakova 2013). Some azaphilone metabolites from Monascus spp. are known to have fluorescent characteristics (Table 1). The medium composition in submerged fermentation has a significant influence on the yield and quality of the Monascus yellow pigments (Chen and Johns 1994; Yongsmith et al 1993). Cultivation conditions affect the production of Monascus yellow pigments, for example, low pH facilitates the production of yellow pigments (Shi et al 2015). Low temperatures (24 or 25 °C) yield higher amounts of the pigment during the submerged fermentation of
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