Effects Of Lactic Acid Bacteria Fermentation Types On The Flavor Characteristics Of Sourdough Steamed Bread

Steamed bread has been considered a kind of representative traditional staple food in China where it is widely consumed. As an ancient biotechnology, sourdough steamed bread was made from sourdough starter containing lactic acid bacteria. Currently, the production of the domestic market steamed bread took the single highly active yeast as the starter. Although fermented wih a fast speed, commercial yeast fermentation products lack in flavor and odor, compared with sourdough steamed bread. The present domestic study on the flavor of steamed bread is limited, and little information about flavor characteristics of the sourdough steamed bread produced with different fermentation categories of lactic acid bacteria has been reported.This study was aimed to assess the flavor characteristics of sourdough steamed bread, identify the characteritic odor compounds and screen strains for odor-producing in steamed bread.The main contents and results were as follows:1. In order to evaluate the flavor of steamed bread prepared with different fermentation types of lactic acid bacteria, and investigate the differnences of three fermentation types. Electronic sensory analyzers(electronic nose and electronic tongue) were used to collect data of odor and taste characteristics of steamed bread. Multivariate statistical analysis showed that principal component analysis can distinguish steamed bread samples fermented wih differnet types on the smell and taste. Obligately heterofermentative samples were more approximate to facultatively heterofermentative samples on flavor, but difffered greatly from obligately homofermentative samples on flavor.2. In order to further clarify the influences of different fermentation types on steamed bread’s flavor, on the basis of descriptive analysis, this study established flavor models for the samples fermented with different fermentation-type lactic acid bacterias. Doughy flavor was a feature of obligately homofermentative samples. The characteristic odors of obligately heterofermentative samples were malt, fruit, yogurt and frankincense flavor, while facultatively heterofermentative samples featured a vinegar flavor. The taste model showed that obligately homofermentative samples presented a strong sweet taste and facultatively heterofermentative samples presented sour and bitter taste, with a weak sweet taste. Obligately heterofermentative samples showed a strong fruit, salty and bitter taste. The consumer preference test showed that Lactobacillus fermentum. 381 and Lactobacillus brevis. 135, stand for obligately heterofermentative strains, got the highest scores, 9.2 and 8.6 respectively in sensory evaluation.3. Through SPME-GC-MS method to detect volatile compounds in steamed bread, it showed 143 flavor compounds were detected in 24 steamed bread samples fermented with different lactic acid bacteria. There existed differences in the contents of flavor substances, especially alcohols. Obligately heterofermentative samples contained higher alcohol contents than obligately homofermentative samples, and the average concentration is 98.68 μg/100 g sample. The characteristic odor compounds of obligately heterofermentative samples mainly included 3-Methylbutanal, 1-Octene-3-ol, Ethyl acetate, Hexanal, Benzaldehyde, Phenylethyl alcohol, 2,3-Butanedione, 2-Pentylfuran, Isobutyl acetate, Acetic acid, 3-Methylbutanoic acid and so on, which brought milk-like, flowery and fruity odors to the final products.4. Through the determination of p H, TTA, and the contents of organic acid and free amino acids, it showed that heterofermentative dough contained significantly higher acetic acid, with a higher titratable acidity, than homofermentative dough. The contents of sweet-taste amino acids, such as alanine and proline, produced in obligately homofermentative dough, were significantly higher than the other two types of heterofermentative dough samples. Obligately heterofermentative dough contained more bitter-taste amino acid, such as phenylalanine, arginine, tyrosine and and isoleucine, and higher contents of acidic amino acids, such as glutamic acid and aspartic acid.