Breeding And Culture Environment Of Yeast Strains With High Production Of 2, 5-Dimethyl-4-Hydroxyl-3(2H)-Furanone

2,5-Dimethyl-4-hydroxy-3(2H)-furanone (DMHF) is one of a high-grade hydroxyl-furan- one aroma compounds. DMHF exhibits strawberry-like flavor in dilute solutions and caramel-like flavor in concentrates. DMHF is extensively used as food flavoring due to its low odor thresholds and flavor-enhancing properties. DMHF production by microbial fermentation has good prospect because of its expensive price. Accomplishing breed yeast strains with high production of DMHF and study on related factors in the process of DMHF biosynthesis in the dissertation. The main contents of this dissertation can be summarized as follows:(1) Screeing a fine yeast strain producing 36.2mg/L DMHF, named as SX-21. The SX-21 yeast strain was identified as Pichia guilliermondii by 18S rDNA.(2) Treated with ultraviolet ray and nitrosoguanidine (NTG), screeing a high production mutant of DMHF, named as NTG-SX-103. In the culture containing 100g/L D-fructose- 1,6-diphosphate (FDP), the concentration of DMHF can reach 92.5mg/L, which was 1.5 time higher than SX-21's.(3) Study on factors of DMHF biosynthesis by NTG-SX-103 through single factor experiment, FDP as precursor, NaCl, initial pH and rotational speed were key factors in the procees of DMHF biosynthesis. In the condition of initial pH 5.8 and 250r/min and in the wort containing 100g/L FDP and 120g/L NaCl., the concentration of DMHF can reach 205.2mg/L, which was 4.5 time higher than in the intial culture. In the culture containing 400g/L FDP, the concentration of DMHF can reach 704.7mg/L, above 100mg/L reported in published literature.(4) High concentration NaCl can greatly promote production of DMHF.The concentration of DMHF in the culture containing 120g/L NaCl was 2.6 time higher than without NaCl. Exogenous sorbitol insteading of NaCl can also promote production of DMHF greatly. Exogenous Ca2+ as an essential messenger in salt stress condition promoted increasion of DMHF by 50%.(5) In high salt stress condition, membrane permeability increased by determination of extracellular nucleic acid in 260nm and 2-nitropehenyl in 420nm. In the process of fermentation, FDP almost wasn't utilized by NTG-SX-103 strain presenting in fermentation broth during the fermentation. The increase of membrane permeability in high concentration of NaCl, promoted FDP, its metabolite combining with related enzymes of biosynthetic DMHF, and DMHF yield increase. Increasing membrane permeability by addition of surfactants and organic solvents can also promote production of DMHF. Membrane permeability was a key factor during the process of DMHF biosynthesis.(6) Adding exogenous FDP and NADPH into extractions of enzyme solution in extra cell, cell and cell membrane. DMHF was only formed in the cell membrane extraction. The key enzymes of biosynthetic DMHF localed in the cell membrane.