Investigation Of Biosynthesis And Biodegradation Of Extracellular Monascus Pigments

Red Yeast Rice is produced by solid-fermentation of Monascus on rice,which has been utilized as food additive and traditional Chinese medicine for more than a thousand year.As one of the important secondary metabolites,Monascus pigments,the natural food colorant,are generally accepted to be predominantly cell-bound,including both intracellular and surface-bound pigments.The processing of fermentation broth and the determination of pigment concentration are based on this theory.Due to the cell-bound nature and intracellular accumulation of Monascus pigments which is a barrier to pigment production,many strategies like high cell density culture,solid culture and in situ extraction are managed to solve this problem.However,these strategies are proved to be complicated with low efficiency.In contrast,resting cell culture using mycelia after extractive fermentation is a valid way for high pigment production.In the present study,production of extracellular crystal pigments by submerged culture was confirmed by microscopic observation and two-step filtration,correcting the long-term misconception as well as the pigment concentration analysis method.By determining pigments in various sections,the past method using filtration is confirmed to cause neglect of crystal pigments and underestimation of the pigment concentration.Thus,whole fermentation broth should be vigorously mixed with ethanol(70 %,V/V,p H=2)for further determination.According to mycelia morphology,the lumps of pigments on the mycelia surfaces could be washed by the nonionic surfactant micelle aqueous solution which actually dissolved extracellular crystal pigments instead of releasing intracellular or cell-bound pigments to extracellular broth.As a result,mycelia can be directly utilized for resting cell culture without extractive fermentation.The bioactivity of mycelia as whole cell biocatalyst for biosynthesis and biodegradation of Monascus pigments was examined in both an aqueous solution and a nonionic surfactant micelle aqueous solution.Following up the new fact,a new strategy had been developed for preparation of pigment-free starved mycelia,making the check of Monascus pigments biodegradation possible.The effect of nonionic surfactant Triton X-100 under all concentration conditions on biodegradation of OMP(orange Monascus pigments)was investigated quantitatively.It showed that surfactant can accelerate the OMP biodegradation,whose speed depended on the surfactant concentration.The nonionic surfactant at 5g/100 m L exhibited the strongest influence and the inter-conversion between OMP and YMP(yellow Monascus pigments)had been observed during OMP or YMP biodegradation process.More interestingly,mycelia preferred to biodegrade OMP than YMP.Based on the absence or presence of Triton X-100 during growing cell culture and resting cell culture,cell suspension cultures were conducted by 4 different ways.High mycelia bioactivity for biosynthesis of OMP was maintained under all conditions which finally declined with the increase of culture period.The nonionic surfactant could accelerate OMP biodegradation and the decline rate of mycelia bioactivity during growing cell culture,while having nearly no influence during resting cell culture.In conclusion,cell suspension culture in the aqueous solution provided an effective way for accumulating Monascus pigments.High OMP concentration of near 4 g/L was achieved after glucose fed-batch.In summary,the investigation of biosynthesis and biodegradation of extracellular Monascus pigments achieves to increase the production yield of OMP and simplify the pigment extraction process,which is of great significance for producing food colorant,water-soluble red pigment derivative.Meanwhile,the study lays the foundation for the interconversion between OMP and YMP as well as its mechanism.