Fig.3-10 Total color values of C100, ΔMareA and OE-MareA under different nitrogen sources
3.3.3 Red, orange and yellow values of monascus rice fermented by solid state fermentation
Under the condition of rice fermentation culture without an additional nitrogen source, the color valence of pigments from the original strain C100 was highest at 475 nm. However, the knockout strain ΔMareA and overexpression strain OE-MareA exhibited a higher color value at 505 nm. After adding Gln for fermentation culture, the color values of all three strains at three wavelengths were similar to those of the original strain, indicating that Gln addition could restore red wine growth and reproduction to its original state unaffected by theAreA gene. Upon adding (NH4)2SO4, there was not much difference in color values among the three strains at three wavelengths; however, their overall color values decreased significantly. The most significant difference in color price among the three strains was observed after adding NaNO3, suggesting that NaNO3 had pronounced effects on both knockout and overexpression strains’ color prices. When Urea was used as a nitrogen source, changes in color price for all three strains were similar to those obtained with NaNO3 but less effective.
In general, knocking out the MareA gene resulted in a decrease in the color values of yellow and orange pigments, but had little effect on red pigments; overexpression of the MareA gene led to an increase in the color values of all three pigments. The addition of Gln restored the growth and reproduction of red pigment to its original state, which was unaffected by the AreA gene. When NaNO3 was added, the utilization of NaNO3 by the strain was regulated by the MareA gene, which prevented the strain from using nitrogen as a nitrogen source, resulting in significantly lower color values than the original strain. Conversely, overexpression strains exhibited significantly higher color values than the original strain with noticeable effects. As shown in Figure 3-11.