Investigation Of The Extractive Fermentation Of Monascus In Oil-water Two-phase System

Selective releasing intracellular product in Triton X-100 micelle aqueous solution to prepare whole cell biocatalyst is a novel strategy for biosynthesis of Monascus pigments,in which cell suspension culture exhibits some advantages comparing with the corresponding growing cell submerged culture.Such as non-sterilization operation,repeated utilization of mycelia,and high pigment concentration.However,the solubility of nonionic surfactant in aqueous solution is very limited.Thus,the solubilization capacity of nonionic surfactant micelle aqueous solution for releasing intracellular Monascus pigments is also limited.It is logical to replace the nonionic surfactant(Triton X-100)with an alternative solvent to intensify the extractive process.In the present work,the effect of added solvents,including ionic liquid,organic solvent,and plant oil,on releasing intracellular Monascus pigments during cell suspension culture in the nonionic surfactant Triton X-100 micelle aqueous solution was screened.Based on the screening result,the nonionic surfactant Triton X-100 was successfully replaced by edible plant oils for releasing intracellular Monascus pigments.High concentration of Monascus pigments(with absorbance nearly 710 AU at 470 nm in the oil phase,normalized to the aqueous phase volume approximately 142AU)was achieved by cell suspension culture in peanut oil–water two-phase system.Furthermore,the utilization of edible oil as extractant also fulfills the demand for application of Monascus pigments as natural food colorant.Dissolved oxygen is an important parameter during fermentation process,affecting the accumulation of the biomass and the secondary metabolite.It is reported that the increasing dissolved oxygen concentration have a positive effect of the productivity of Monascus pigment.However,the pigments will stop increasing at a very high level of dissolved oxygen while some by-products start to increase.Cell morphology will be changed and the productivity of pigments will be reduced when the dissolved oxygen concentration is low.In the present work,oxygen supply was studied in a stirred bottle bioreactor by setting cell suspension culture of Monascus sp in oil–water two-phase system for production of extracellular Monascus pigments as a model.First,the effect of dissolving oxygen concentration on secondary metabolites was examined.Then,the effect of influencing factor such as aspect ratio and stirred rate on oxygen supply was studied.Finally,the dissolving oxygen level(80%,50%,15%,and 5%)of Monascus fermentation was validated in a 5L stirred tank bioreactor.The results showed that the dissolved oxygen concentration might not be a major factor affecting pigment production using whole-cell Monascus sp as catalyst due to the relatively high pigment concentration(with absorbance nearly 400 AU at 450 nm in the oil phase)even at very low dissolved oxygen concentration.It provides experimental fact for scale-up cell suspension culture of Monascus sp in the future.