铵盐对紫色红曲霉合成代谢红曲色素及桔霉素的影响

研究紫色红曲霉(Monascus purpureus)Y20液态发酵过程中不同铵盐对目的产物红曲色素及有害物质桔霉素的合成代谢的影响。在发酵培养基中添加不同铵盐,检测M.purpureus Y20发酵液中红曲红色素、红曲黄色素及桔霉素含量,分析其变化及原因。结果表明:M.purpureus Y20发酵过程中发酵液pH值相对较稳定,未添加铵盐的对照组发酵液基本维持在pH4.8;添加CH_3COONH_4、NH_4H_2PO_4、C_6H_5O_7(NH_4)_3的发酵液pH6;添加NH_4NO_3、(NH_4)_2SO_4、NH_4Cl的发酵液初始pH5.5,发酵过程中持续降低至pH2.5左右;含有0.3 mol/L NH_4~+的(NH_4)_2SO_4的发酵液中桔霉素含量降为0.05 mg/L,较对照组降低88.6%;含有0.1~0.3 mol/L NH_4~+的NH_4Cl发酵液中桔霉素含量降为0.05 mg/L;含有0.3 mol/L NH_4~+的NH_4NO_3发酵液未检出桔霉素,红曲黄色素含量较对照组升高31.0%、红曲红色素含量降低11.6%;添加CH_3COONH_4、NH_4H_2PO_4、C_6H_5O_7(NH_4)_3的发酵液无桔霉素检出,但菌体干质量较小,色价较低。因此,添加铵盐可影响发酵液pH值,影响M.purpureus Y20对营养物质吸收和代谢,改变红曲色素的组成比例和抑制桔霉素的生成;添加适量(NH_4)_2SO_4、NH_4Cl、NH_4NO_3有利于促进红曲黄色素的生物合成,阻碍桔霉素的生成。

Effect of Addition of Ammonium Salts to Culture Medium on the Biosynthesis and Metabolism of Pigments and Citrinin in Monascus purpureus

The effects of adding different kinds of ammonium salts to the culture medium on the biosynthesis and
metabolism of pigments and citrinin in M. purpureus Y20 during liquid-state fermentation were studied by examining
changes in the contents of monascus red pigment, monascus yellow pigment and citrinin. Also, we elaborated the underlying
causes for the changes. The results showed that pH values of the fermentation broth of M. purpureus Y20 without added
ammonium salt remained stable at 4.8 during fermentation, while those obtained with the addition of CH3COONH4,
NH4H2PO4 or C6H5O7(NH4)3 were maintained at greater than 6. The initial pH of the culture medium with the addition of
NH4NO3, (NH4)2SO4 or NH4Cl was below 5.5, and then decreased to around 2.5 during fermentation. The final citrinin
content of the groups with 0.15 mol/L (NH4)2SO4 and 0.1-0.3 mol/L NH4Cl, respectively, during fermentation dropped to
0.05 mg/L, indicating an 88.6% reduction when compared with the control group with no added ammonium salt. No citrinin
was detected in the fermentation broth with 0.3 mol/L NH4NO3 added, and a 31.0% increase of yellow pigment content
and an 11.6% decrease of red pigment content were observed compared with the control group. Similarly, no citrinin was
detected in the fermentation broth with the addition of CH3COONH4, NH4H2PO4, or C6H5O7(NH4)3, but color value and
biomass were lower, suggesting that the addition of ammonium salts could affect the pH environment of the fermentation,
and plays an important role in reducing citrinin and changing the proportions of monascus pigments. The addition of
NH4NO3, NH4Cl and (NH4)2SO4 can contribute to the biosynthesis of monascus yellow pigment and the inhibition of citrinin.