Isolation, Identification And Fermentation Characteristics Of Lactic Acid Bacteria Isolated From Fermented Handmade Dairy Of Pastoral Areas In Western China

The traditional fermented handmade dairy in pastoral areas of western China is of abundant microbial resources.Beacause of the geographical features,climatic environment and living habits,they are with unique microbial resources and biodiversity.Therefore,it is of practical significance and application value to explore their characteristics.In this study,104 traditional fermented handmade-dairy(Kurut,Koumiss,Shubat and Milk dreg)were collected from pastoral areas in western China(Qinghai,Gansu,Xinjiang,Tibet and Inner Mongolia),and the lactic acid bacteria(LAB)were isolated and identified from them,the nitrite degradation ability,?-aminobutyric acid(GABA)production ability,and bile salt dissociation ability were analyzed to explore the diversity of the LAB strains from traditional fermented dairy in western China's pastoral areas and to compare the different abilities of LAB in different sources and different species.Strains with well fermented abilities and potential application values were selected.The main conclusions are as follows:(1)275 LAB strains were isolated from 104 fermented dairy in pastoral areas of western China,which were divided into 6 genera and 23 species of LAB.The dominant bacteria were judged by their abundance index.From a regional perspective: Lb.helveticus,Lb.fermentum and Lb.delbrueckii ssp.bulgaricus were the dominant LAB isolated from Qinghai;Lb.helveticus were the dominant LAB isolated from Gansu and Xinjiang;Lb.kefiranofaciens and Lb.helveticus were the dominant LAB isolated from Inner Mongolia;Lb.paracasei,Lb.plantarum,Lb.casei and Lb.breris were the dominant LAB isolated from Tibet.From the aspects of dairy: Lb.helveticus,Lb.fermentum and Lb.delbrueckii ssp.bulgaricus were the dominant LAB isolated from Kurut;Lb.kefiranofaciens and Lb.helveticus were the dominant LAB isolated from Koumiss and Shubat;Lb.breris,Lb.plantarum,Lb.casei and Lb.paracasei were the dominant LAB isolated from Milk dreg.(2)The nitrite degradation rates of 275 LAB isolates were between 4.8% and 99.9%,whose 50% of strains were over 91.3%,the strain shows well degrade-nitrite ability.The degradation rates of 44 strains were over 99.0%.There was a significant difference in nitrite degradation ability of the strains from different sources and species(P<0.05).The strain from milk dregs in Tibet were detected well degrade-nitrite ability,Among the dominant species,Lb.plantarum,Lb.paracasei,and Lb.breris showed stable and efficient nitrite degradation ability,among which Lb.plantarum has the strongest degradation ability.(3)Among the 275 strains of lactic acid bacteria,13 strains were with yielding GABA ability,Lc.lactis ssp.lactis showed the highest detection rate among all the 275 isolates.The Lc.lactis ssp.lactis with the best ability achieved a yield of(11.6±0.3)mmol/L GABA after 48 h of culture.The ability of yielding GABA was increased with the increase of culture time and peaked at 48 h after culture.The results showed that there is a significant difference in yielding GABA ability of positive strains from different sources and species within the same incubation time(P<0.05).(4)Among the 275 strains of lactic acid bacteria,83 strains with bile salt dissociation ability were detected.The detection rate of BSH-positive strains from different sources and species were different.The bile salt dissociation rates of BSH-positive isolates were between 7.0% and 98.8%,whose 50% of strains were over 49.7%,but the total bile salt dissociation rates of 4 strains were up to more than 85.0%.There were significant differences of the bile salt dissociation ability for GCA,GDCA,GCDCA,TDCA,TCA and TCDCA among all the BSH-positive strains(P<0.05).Among them,the dissociation rate of GDCA was the highest,and the TDCA was the lowest.The analysis showed that the bile salt dissociation rates of BSH-positive LAB strains from different sources and species were different(P<0.05).The BSH-positive strains from Koumiss,Shubat in Xinjiang and milk dregs in Tibet were detected well bile salt dissociation ability.Among the dominant species,Lb.breris and Lb.plantarum were detected the stronger bile salt dissociation ability.