| Due to the safety and health advantages of natural pigments and the potential harm of synthetic pigments,the trend of replacing synthetic pigments with natural pigments is increasing worldwide.Monascus pigments,which were synthesized by Monascus sp.through the polyketone pathway,have been widely used for more than two thousand years and still play an important role in the food industry.Monascus yellow pigments is one of the important pigments.However,the problem that hinders its industrial production is the low production of yellow pigments.At present,extraction fermentation is the most effective strategy to increase the production of Monascus yellow pigments,however,there are still many problems in extraction fermentation,such as the use of extractant greatly increases the production cost,how to recycle,and the fermentation process also exists emulsification phenomenon.Therefore,it is necessary to find another fermentation regulation method that can promote the production of Monascus yellow pigments and is relatively simple.Through literature review,it was found that alcohols or sugar alcohols could improve the production of secondary metabolites during fungal fermentation process Therefore,based on Monascus purpureus ZH106-E,a strain with high yellow pigments production kept in our laboratory,alcohol or sugar alcohol was added in the submerged fermentation of Monascus purpureus to investigate their effects on the production of yellow pigments,and its underlying mechanism was explored.First,the effects of alcohol addition on the production of yellow pigments by submerged fermentation of M.purpureus ZH106-E were studied.The type,amount and time of alcohol addition was optimized.The results showed that when 3%(v/v)ethanol was added at the beginning of Monascus fermentation,the yellow pigments production could reach 394 U·m L-1,which was increased by 71%compared with the control group.Then,the mechanism of ethanol addition was explored through a series of experiments such as growth curve,ATP measurement and RT-q PCR.The results showed that the addition of ethanol decreased acetyl-Co A in secondary metabolism(pigments synthesis)and thus more acetyl-Co A flow to the primary metabolism(tricarboxylic acid cycle)in the early fermentation stage,and accumulate more hyphae.In the late fermentation period,due to the volatilization of ethanol,the secondary metabolism(pigments synthesis)returned to normal level,and the addition of ethanol significantly increased the production of yellow pigments due to more biomass accumulated in the early period.Second,the effects of sugar alcohol addition on the production of yellow pigments by submerged fermentation of M.purpureus ZH106-E were studied.The type,amount and time of sugar alcohols addition was optimized.The results showed that when 4%(v/v)mannitol was added at the beginning of Monascus fermentation,the yellow pigments could reach 427 U·m L-1,which was increased by 102%compared with the control group.Then,the mechanism of mannitol addition was preliminarily explored through a series of experiments,including growth curve,scanning electron microscope and RT-q PCR.The results showed that the addition of mannitol accelerated the growth of hyphae,increased the expression of pigments synthesis genes,stimulated the synthesis of Monascus pigments earlier.Finally,the extraction experiment of Monascus yellow pigments was conducted.The pigments produced by Monascus fermentation was determined mainly within the cell.Hence,the intracellular yellow pigments extraction method was optimized by a series of experiments.By comprehensive consideration on the extraction effect,cost,and safety,etc,the extraction method of Monascus yellow pigment was determined as follows:using ethanol as the extraction solvent,the ratio of material to solvent was 1:4.The extraction rate of yellow pigments could reach 99%by extracting at 35?for 5min,which provided a useful reference for the industrial production and extraction of Monascus yellow pigments. |
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