Fig.3-9 Dry weight of C100, ΔMareA and OE-MareA in media with different nitrogen sources
3.3.2 Total color value of solid fermented red yeast rice
Color value is one of the main quality indicators of natural pigments, which can reflect the pigment production. In the fermentation medium of rice without an additional nitrogen source, the total color value of ΔMareA decreased compared to that of C100, while the color value of OE-MareA increased. Under the fermentation culture conditions with the addition of Gln, there was little difference in the total color values among the three strains and they were largely unaffected by theAreA gene. In rice fermentation medium with (NH4)2SO4 added, all three strains had very low total color values. When NaNO3 was added to the medium, ΔMareA strain had a lower color value than C100 while OE-MareA strain had a higher color value than that of the original strain. This effect was most pronounced. In fermentation medium with Urea added, similar but less significant results were observed compared to NaNO3addition. In summary, MareA gene affects monascus’ color value mainly through reducing MPs’ color value when MareA gene is deleted and accelerating pigment accumulation when MareA gene is overexpressed, under different nitrogen sources culture conditions adding different sources of nitrogen, overexpression of MareA gene increases MPs’ color value . Among them, the most significant effect occurred in culture medium with NaNO3. As shown in Figure 3-10.