Screening, Identification and Fermentation Property of a Yeast Strain R6 Accumulating Alpha-ketoglutaric Acid

A yeast strain R6 was obtained by the method of thiamine（VB1） auxotrophic negative selection from the edible oil-polluted soil in Zibo, China. Physiological and biochemical experiments revealed that strain R6 shared common feature with Rhodotorula mucilaginosa according to the API 20 C AUX yeast identification system which has been tested previously. Furthermore, the 18 S r DNA gene of strain R6 was amplified and sequenced. Phylogenetic analysis based on the 18 S r DNA sequence and the relatives indicated that R6 shared 99% homologies with the members of R. mucilaginosa, suggesting that strain R6 belonged to R. mucilaginosa.Investigation showed that strain R6 possessed the capacity of accumulating exocellular alpha-ketoglutaric acid（alpha-KG）. Finally, the fermentation conditions of R6 to accumulate alpha-KG was optimized by controlling each single fermenting variable and detected through high performance liquid chromatography（HPLC）. Results showed that both VB1 and Ca CO3 in fermentation medium were the key factors influencing the cumulant of alpha-KG. The discovery of natural auxotrophic strain R6 not only broadened the microbial resource which can achieve lots of alpha-KG production through fermentation, but also laid a foundation for further fermentation regulation to achieve excessive alpha-KG accumulation.

Study on the safety and excellent probiotic properties of fermentation strains isolated from traditional dry-cured duck for starter development

The indigenous starter cultures isolated from fermented food can compete with spoilage and pathogenic bacteria and improve the flavor and organoleptic properties of products.The purposes of this work were to screen and assess the safety,potential probiotic,and fermentation properties of indigenous starter cultures isolated from dry-cured ducks.The properties of indigenous starter cultures were investigated by antibiotic resistance,virulence genes,in vivo toxicity,simulated gastrointestinal,adhesion capacity to Caco-2 cells,inoculation fermentation,etc.Overall,six strains were isolated and identified,including Lactobacillus sakei D15,Weissella hellenica D20,Lactobacillus curvatus D2,Staphylococcus simulans D12,Staphylococcus equorum D19,and Staphylococcus edaphicus D17.The obtained strains showed high safety.Additionally,most strains displayed excellent probiotic properties,including tolerance to lower pH,lysozyme,bile salt,and a high survival rate of the simulated gastrointestinal phase.The adhesion ability of strain cells to Caco-2 cells was 9.22%-14.21%.And the probiotic properties of strains can be strengthened by the expression of specific enzymes.The inoculation with the isolated strains(LS-D15,LC-D2 and SS-D12)could contribute to the formation of volatile flavor compounds in samples.Overall,results demonstrated that strains possessed excellent safety and probiotic properties,and can be used as starter cultures to enhance the quality and flavor of the dry-cured duck.