Study On The Edible Nutritional Yeast

In the paper, screening of nutritional yeast parent strains, mutation of rich riboflavin strain, shake-flashing culture conditions as well as fermentation technology of nutritional yeast were studied.Baker yeast(Saccharomyces cerevisiae) BY-1-8, Candida yeast(Candida utilis) CY-1-11, beer yeast( Saccharomyces carlsbergensis) SY-1-10 and milk brewer yeast (Saccharomyces uvarum) MY-1 were used for a group of tests. Through the tests, the yeast strain (MY-1), which had the maximum riboflavin and extraction, was selected. Through three-step continual EMS mutation, the adenine autotrophy strain(Ml-3) and the adenine-requiring revertant strain(M2-8) were screened successively, and the resistant strain(M3-20) to ammonium ion variant was further screened. Then the strain (M3-20), which has 245. 56mg/kg riboflavin, was got. Compared with parent strain, the riboflavin content of the mutation strain was increased by 150%.Shake-flash culture conditions of nutritional yeast were studied with mutant M3-20.Two-lever-factor tests and climb-quickly methods were used to design experiment. At the same time, according to factor analysis and the response surface analysis, data were analyzed with statistical software, such as SAS, Origin. In the end we got an optimal culture conditions as follows.(1) Seed medium: yeastponder10g/L, glucose 40g/L, (NH4)2SO4 0.86g/L, KH2PO40.6g/L,MgSO4.7H2O0.5g/L ,pH spontaneous combustion.(2) Fermentation medium: glucose 35.6g/L, yeastponder 67g/L, bean oil 10g/L, glycine 6g/L,(NH4)2SO4lg/L,KH2PO40.2g/L,MgSO4.7H2O0.5g/L, NaCl lg/L,ZnSO40.4mg/L,FeSO44mg/L,CoSO411.5mg/L,pH6.0.(3)Fermentation conditions: breed cultivation time 7h,loading size (80/500ml A ),inoculation size10%,cultivation temperature 30 C ,200r/min,the optimum culture time was 16h.The high-riboflavin containing strain was used to study the fermentation process, including the experiment of Crabtree effect and the technology of feeding culture, etc. The results showed that during the batch fermentation, when the glucose concentration was 5%, yeast cell concentration is sovereign, and the glucose concentration has no remarkable inhibition to the initial stage of fermentation. During the flow-plus culture of 16 hour, the results showed that effects of feeding oil and glycine were good, the biomass and content of riboflavinwas 33.2g/L and 237mg/kg respectively. The feet laid solid foundation for production of nutritional yeast full of riboflavin.