Study On Production Of Monascus Yellow Pigents In Liquid-state Fermentation

Monascus pigments are natural pigments produced by fermentation of Monascus.Among this, monascus red pigment has been widely used in a lot of food, while yellow element is not enough research. However, citrinin, a human toxic substance, is also synthesized in this fungus. Therefore, how to improve the production of yellow pigments and reduce the content of citrinin are the main purpose of this paper.Fristly, strain M2 with higher yield of pigments and lower production of citrinin was selected as the research strain, which was identified as Monascus purpureus. Then we used the single factor experiments to optimize the culture conditions. When the revolution was 150 r/min, temperature was 30? and fermentation time was 4 days, the production of yellow pigments was obtained 66.0 U/mL. The yellow tone was 1.09 and the citrinin content was 10.36 mg/L.The effects of initial pH on pigments and citrinin were researched. It revealed that the pH could significantly influence the production of pigments and citrinin .When the initial pH of medium was below 4.5, the orange pigments were the main products. When the pH above 4.5, the yellow pigments were the main pigment. When the pH below or equal to 6.5 or the final pH below or equal to 3.5, citrinin content decreased with the decreasing pH.Based on the synthetic pathway of monascus pigments, five different fatty acids were added to the culture medium, respectively. It was found that decanoic acid and palmitic acid were of great advantage for yellow pigments. When decanoic acid and palmitic acid concentration were 0.05 mL/L and 0.025 g/L, respectively, the yellow pigment production increased by 42.9% and 17.9% compared with the control. As far as citrinin was concerned,five fatty acids all showed inhibitory effect.According to the structural transformation of monascus pigments, antioxidants were added to the culture medium to promote the synthesis of yellow pigments. It was found that the effect of adding 0.2 g/L potassium pyrosulfite was the most obvious. In this condition,the production of yellow pigments was 80.0 U/L,being 1.35 times of the control group;yellow tone was 1.28, being 1.25 times of the control group.Response surface method was applied to search for optimum conditions of metal ions.Resultly,the optimum conditions were that calcium ion was 0.40 mmol/L,ferrous ion was 0.30 mmol/L and sodium ion was 0.15 mmol/L, respectively. The final production of yellow pigments were 94.8 U/mL, being 1.50 times of the control, but citrinin content was not affected.We evaluated the most significant variables for Monascus yellow pigment,yellow tone and citrinin in the above experiments.Then an orthogonal test was further investigated the optimum level.The maximum production of yellow pigment of 106.1 U/mL were achieved in the medium containing 0.1 g/L potassium pyrosulfite, 0.3 g/L diammonium hydrogen phosphate, 0.3 mL/L decanoic acid and 0.2 mmol/L sodium ions. Meanwhile, yellow tone was 1.20 and citrinin content was 2.09 mg/L. Yellow pigment increased by 1.60 times, yellow tone increased by 1.14 times and citrinin had a reduction of 77.2% compared with the control.