Identification And Biodiversity Of Yeasts Isolated From Traditional Fermented Milk Products In Xinjiang And Qinghai Of China

The yeast flora of traditional fermented milk products, such as koumiss, kurut and fermented goat milk in Xinjiang and Qinghai of China, were analyzed. The identification and biodiversity of the yeast involved in traditional fermented milk products were investigated. It forms an essential step towards the preservation and exploitation of the hidden potential of the wealth of yeast biodiversity. The results also provide the basic data for systematically understanding the characteristics of koumiss, kurut and fermented goat milk, give useful information for further utilization of yeast in traditional fermented milk products.The counts of yeast in koumiss samples collected from Xinjiang were ranged from 3.12×104 CFU/mL to 2.23×106 CFU/mL. Generally, in koumiss samples, the counts of the yeasts were lower than those of lactic acid bacteria by one or two logarithm. A total of eighty-seven yeast strains were isolated from twenty-eight home-made koumiss samples. They were identified using standard conventional identification methods. And the results were combined with analysis of the large-subunit (26S) rDNA gene D1/D2 domain region sequences of them. The predominant strains proved to be mainly Kazachstania unisporus (49.4% of the total isolates) and Kluyveromyces marxianus (26.4%). Others were identified as Saccharomyces cerevisiae for eight strains, Pichia membranaefaciens for two strains, Pichia fermentans for six strains, Pichia manshurica (synonym Pichia galeiformis)for two strains and Pichia kudriavzevii (synonym Issatchenkia orientalis)for three strains. The combination of K. unisporus and Kl. marxianus was predominant group in koumiss samples in Xinjiang. And the strains of S. cerevisiae and Pichia sp. were never present alone.Variation on the lengths of the ribosomal ITS region (ITS1, 5.8S rRNA and ITS2) of the different yeast strains in koumiss was observed. Three isolates and a type yeast strain were selected for analysis of ITS region sequences. The results confirmed that the ITS region sequencing was a reliable and useful method for yeast taxology.The counts of yeast in kurut samples collected from Qinghai were ranged from 2.60×106 CFU/mL to 2.00×109 CFU/mL. They were lower than those of lactic acid bacteria by one or two logarithm in the samples of Haibei, but were slightly more than those of lactic acid bacteria in the samples of Hainan. A total of seventy-four yeast strains were isolated from twenty-five samples. The predominant strains proved to be mainly P. fermentans (43.2%), S. cerevisiae(27.0%) and Kl. marxianus (24.3%). Others were identified as K. unisporus for one strain, P. kudriavzevii for one strain, Rhodotorula mucilaginosa for one strain and Candida zeylanoides for two strains. P. fermentans - Kl. marxianus, P. fermentans - S. cerevisiae and Kl. marxianus - S. cerevisiae were the predominant groups in kurut samples collected from Qinghai.The counts of yeast in fermented goat milk samples collected from Qinghai were ranged from 2.07×105 CFU/mL to 1.63×108 CFU/mL. They were lower than those of lactic acid bacteria by two or three logarithm in the same sample. A total of thirty-five yeast strains were isolated from eleven samples. The predominant strains proved to be mainly Kl. marxianus (45.7%) and P. fermentans (34.3%). Others were identified as S. cerevisiae for six strains and Rh. mucilaginosa for one strain. Kl. marxianus - S. cerevisiae and P. fermentans - S. cerevisiae were the predominant groups in fermented goat milk samples collected from Qinghai.