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.     

Application of the Chinese steamed bun starter dough (CSB-SD) in breadmaking

The application of Chinese steamed bun starter dough (CSB-SD) in breadmaking was investigated. The activation of CSB-SD to activate the growth of lactic acid bacteria (LAB) and to increase the number of yeast, prior to making bread, was conducted by mixing CSB-SD with wheat flour and water and then incubating for 24 h. Wheat flour was then substituted by this activated CSB-SD (aCSB-SD) at 10%, 30%, and 50% (w/w) to make bread. Dough and bread properties were studied comparing to the control (without aCSB-SD). From the farinograph results, a high aCSB-SD substitution level resulted in a less stability in dough with a higher degree of softening. Extensigraph results suggested that after aging, all the substituted dough yielded a greater resistance to extension with lower extensibility values than the control. Substitutions with 30% and 50% (w/w) aCSB-SD significantly increased the total CO(2) gas generation. Scanning electron microscopy SEM images of the 30% and 50% (w/w) substituted dough showed a well-developed gluten matrix. The 50% (w/w) substituted breads obtained a greater risen volume, finer crumb grain, and retained more softness after 5-d storage than the control. In addition, both the 30% and 50% (w/w) substituted breads showed a slightly increased mold stability, as compared to the 0% and 10% (w/w) substituted breads.     

The effect of Thai glutinous rice cultivars, grain length and cultivating locations on the quality of rice cracker (arare)

Physicochemical and thermal properties of two Thai glutinous rice cultivars (RD6 and Short Grain) differing in grain length (whole grain and broken rice) and cultivating locations (the upper northeastern and the middle northeastern regions) and the quality characteristics of glutinous rice cracker produced from them were studied. RD6 cultivar was different in amylose content, gel consistency, volume expansion and hardness of rice cracker with those of Short Grain cultivar. Broken rice significantly gave greater amylose content, harder cool gel texture, less swelling, lower volume expansion and harder texture of rice cracker than whole grain rice. Furthermore, structure of starch molecule of broken rice differed from that of whole rice. The physicochemical, thermal properties and the qualities of rice crackers of RD6 cultivated from the upper northeastern and the middle northeastern regions showed no significant difference. To obtain good qualities of rice cracker, the rice should have lower amylose content, softer cool paste texture, greater breakdown value and less setback of amylogram. Amylose content and alkali gel consistency (120 mg flour) were significantly correlated with several other rice properties. The analysis of both properties is useful for the industry in controlling the quality of glutinous rice being used as raw material.