Thesis (Ph.D.)--Chulalongkorn University, 2009

Lactic acid bacteria (LAB) and yeasts were isolated from the Chinese steamed bun starter doughs (CSB-SD) from four different commercial sources. Thirty-one LAB and eight yeast strains were isolated. Total counts of LAB were from 1.8 x 104 to 108 cfu/g sample, whilst yeasts were very low from 10 to 2.3 x 10[superscript 2] cfu/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. Based on the phenotypic characteristics, they were divided into two major groups (Group A and Group B), with the B group subdivided into four groups. Genotypic 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 (61.3%), whilst the strains of Group B that produced L-lactic acid were closely related to L. casei (38.7%). For yeasts, based on the D1/D2 domain sequences of 26S rRNA, eight yeast isolates were identified as Candida tropicalis (12.5%), Pichia stipitis (12.5%), C. parapsilosis (12.5%), Issatchenkia orientalis (12.5%) and Saccharomyces cerevisiae (50%). Application of Chinese steamed bun starter dough (CSB-SD) in breadmaking was studied. Prior to substituting CSB-SD in wheat flour for making bread, CSB-SD was activated (aCSB-SD) to increase the microbial growth and number, especially yeasts. The effects of the amount of CSB-SD and activation time during preparation of the aCSB-SD on dough and bread properties were studied. The aCSB-SD was prepared by using 2 different amounts (100 and 200 g) of CSB-SD and 3 different activation times (12, 24 and 36 h). Results indicated that the aCSB-SD improved aged dough rheology and white bread properties on volume, softness and shelf life when compared to the control (without aCSB-SD). However, too long activation time (36 h) combined with higher amount of CSB-SD (200 g) led to a weakened and damaged gluten structure, and subsequently contributed to poor bread properties. Furthermore, the effects of the amount (10, 30 and 50%) of aCSB-SD for partial substitution in wheat flour to breadmaking on dough and white bread properties were also studied. From farinograph, more substitution amount contributed to less stability and more weakness in dough. Results from extensigraph suggested that after aging, all substituted doughs yielded greater resistance to extension and less extensibility values than the control. The 30 and 50%-substituted doughs significantly produced total CO2 gas more than that from the control and 10%- substituted doughs. The 50% substituted breads obtained greater volume, finer crumb grain cells and retained more softness after 5-days storage than the control and the other substituted bread (10 and 30%). SEM images of the 30 and 50% substituted doughs showed well-developed gluten matrix. Application of Loog-Pang (Thai traditional starter) in breadmaking was also studied. The isolation and identification of LAB and yeasts in two types of Loog-Pang (Loog-Pang-Lao and Loog-Pang-Kaw- Mag) from twelve different sources were conducted by phenotypic and genotypic methods, prior to studying on the application of Loog-Pang in breadmaking. It was found that the number of LAB ranged from < 10 to 8.8 x 10[superscript 10] cfu/g sample, whilst that of yeasts ranged from < 100 to 2.0 x 10[superscript 9] cfu/g sample. Total forty-five LAB isolates were identified as Pediococcus pentosaceus (89%), L. plantarum (6.6%), L. fermentum (4.4%). Regarding yeasts, fifteen isolates were identified as Saccharomycopsis fibuligera (53.3%), S. cereviseae (26.7%), C. krusei (13.3%) and C. fermentati (6.7%). Loog-Pang from nine sources was used to study on their effects on dough and white bread properties. First, it was prepared as Loog-Pang starter dough (LP-SD) and the LP-SD was used to substitute in wheat flour of 20%. The results showed that all LP-SDs produced total CO2 gas more than that from the control dough (without LP-SD). Loog-Pang of R8 and R11 attained significantly the better white bread volume than that of the control, however, their firmness of fresh and 3-day stored bread was comparable to those of the control. As for the bread quality of the other LP-SD-substituted breads, they were poorer than those of the control and R8 and R11- substituted breads. The dough rheology of the poorer breads exhibited more weakness and lower elasticity than those of the control and R8 and R11 doughs. However, all LP-SD substituted breads showed the positive effect on anti-mold growth