| A acetic acid bacteria（AAB）strain A3 was isolated from the traditional steamed bread starter Jiaozi,and it has been identified as Acetobacter tropicalis based on its physiological and biochemical characteristics and 16S rRNA gene sequences.The optimized fermentation conditions for acetic acid of strain Acetobacter tropicalis A3were achieved by single factor experiments,which are as follows:ethanol content 3.0%（v/v）,temperature 37°C,rotation speed 180r/min,pH 5.5±1.Under these conditions,the yield of acetic acid of this bacterium can reach 29.7g/L.When strain Acetobacter tropicalis A3 was applied to make Chinese steamed bread sourdough,the results showed that with the extension of fermentation time,the sourdough added AAB A3 produced more total acid.The content of reducing sugars in the sourdough was shown downward trend at first and then increased.The content of lactic acid and acetic acid in the dough added with different bacterial starters was analyzed by high performance liquid chromatography（HPLC）method,and the content of acetic acid in the sourdough added with AAB A3 was found to be 7.3%higher than the sourdough added with LAB.The total content of essential amino acids in the sourdough added with AAB A3 increased by25%,especially for leucine（Leu）,phenylalanine（Phe）and valine（Val）.The effect of AAB A3on the quality of Chinese steamed bread was also investigated.The aspect of the index of height to diameter ratio,specific volume and whiteness of Chinese steamed bread were determined.The results showed that the ratio of height to diameter of Chinese steamed bread was adjusted by adding AAB A3 and Angle’s yeast after fermentation for 8 hours.The maximum of the ratio of height to diameter is 0.76,the maximum specific volume is 2.5,and the maximum whiteness is 54.06.The evaluation score of steamed bread started by AAB A3was up to 92.The hardness of steamed bread added with AAB A3 was relatively small and the elasticity when the sourdough was fermented for 8 hours.Chinese steamed bread often become mildewed when it was stored at room temperature for a week.After 15 days of storing,the amount of mold on the steamed bread was counted by plate counting method.The number of mold in the steamed breads added with AAB A3 was1.74(calculated as Log100 cfu/g),which was less than that of steamed bread without AAB.So the addition of AAB in Chinese steamed bread might could help to inhibit the growth of mold,improve the product’s storage time,and extend the shelf life. |
