Lactic acid bacteria and yeasts isolated from the starter doughs for Chinese steamed buns in Thailand

Isolation of lactic acid bacteria (LAB) and yeasts from the starter dough of Chinese steamed buns from four different commercial sources in Thailand was carried out. Thirty-one lactic acid bacteria and eight yeast strains were isolated. Total counts of LAB were from 1.8 × 104 to 108 colonies/g sample, whilst yeasts were very low from 10 to 2.3 × 102 colonies/g sample. The pH values of all starter doughs ranged from 3.36 to 3.52 and the Total Titratable Acidity (TTA) varied from 11.1 to 17.0 ml of 0.1 N NaOH/10 g dough. All LAB isolates were identified as Lactobacillus. The phenotypic characteristics were used to cluster all the LAB isolates into two major groups (Group A and Group B), with the B group subdivided into four groups. Phylogenetic analysis, based upon partial 16S rRNA gene sequences, showed that isolates of Group A, which all contained meso-diaminopimelic acid in their cell wall and produced dl-lactic acid, were closely related to Lactobacillus plantarum, whilst the strains of Group B that produced l-lactic acid were closely related to Lactobacillus casei. For yeasts, eight isolates based on the D1/D2 domain sequences of 26S rRNA were identified as Candida tropicalis, Pichia stipitis, Candida parapsilosis, Issatchenkia orientalis and Saccharomyces cerevisiae.