Preparation Of Bran-rich Steamed Bread By Fermentation With Lactic Acid Bacteria And Saccharomyces Cerevisiae

Steamed bread is the traditional staple food in China.The bran-rich steamed bread is rich in minerals,vitamins and dietary fiber,which is expected to play an important role in preventing chronic diseases.However,the introduction of bran ingredients can damage the internal gluten network structure of steamed bread,resulting in a smaller specific volume and a higher hardness.The higher content of insoluble dietary fiber in bran also leads to rough texture and poor taste of bran-rich steamed bread,which is unreceptive to consumers.At the same time,the peculiar smell of bran also affects the promotion of bran-rich steamed bread.The peeling method can give consideration to nutrition and food quality of the flour thereof as a better raw material of steamed bread.At present,it has been proved that the fermentation of lactic acid bacteria and yeast is beneficial to improve the texture and flavor quality of multigrain steamed bread.However,the difference in growth and metabolism of different lactic acid bacteria will lead to great difference in the final quality of dough and steamed bread.Therefore,the effects of different lactic acid bacteria and Saccharomyces cerevisiae on the physical and chemical indexes of bran-rich dough and steamed bread quality can be studied through the combination of different lactic acid bacteria and S.cerevisiae as starters,and then the best combination of strains can be screened out.Firstly,the preparation technology of dough was determined by preliminary experiment,using S.cerevisiae as fermentation strain.Then,with yeast fermentation as the control,the symbiotic relationship between the three strains of lactic acid bacteria and S.cerevisiae and their effects on the physicochemical indexes of bran-rich dough and the quality of steamed bread were investigated through the fermentation of different lactic acid bacteria and S.cerevisiae,so as to determine the best combination of strains.The results are as follows:（1）According to the water distribution and migration in dough,the preparation technology of the bran-rich dough was determined as follows.600 g of flour was weighed,adding water of ratio of flour 63%（w/w）,and then was continuously stirred at a speed of 30r/min for 14 min in a blender.（2）During fermentation,the three strains of lactic acid bacteria showed different growth rates and made the bran-rich dough undergo effective biological acidification.At the beginning of fermentation,lactic acid bacteria entered a period of rapid growth,PP proliferated fastest and LM was the slowest one within（0～5）h,and then at 6 h,the numbers of the three lactic acid bacteria tended to reach 1.2×10~8CFU/g.Compared with the growth of bacteria,acid production by fermentation showed obvious lag effect.After 3 h of fermentation,p H of dough decreased significantly,TTA increased significantly meanwhile,and this change lasted until 6 h of fermentation.Product of lactic acid surpasses at 5 h in LM-S fermented dough,with the highest content of 4.61±0.12 mg/g at 6 h.LR-S produced acetic acid with the highest content to 2.83±0.12 mg/g during fermentation.（3）The effects of different lactic acid bacteria and S.cerevisiae on the quality of dough and steamed bread were obviously different.The maximum fermentability of S,PP-S,LR-S and LM-S fermented dough was 0.41,0.83,0.60 and 0.56 at 5 h,respectively.The lactic acid bacteria significantly improved the fermentability of doughs,and the loss modulus and storage modulus of fermenting doughs were reduced,which showed that the doughs were softer and the processing performances were improved.At the same time,lactic acid bacteria fermentation significantly improved the specific volume,texture traits and compressive relaxation of bran-rich steamed bread.LR-S fermentation produced the best texture characteristics of bran-rich steamed bread,followed by PP-S.（4）The effective biological acidification in lactic acid bacteria fermented doughs increased the contents of soluble dietary fiber,although the contents of starch,protein,insoluble dietary fiber and fat where decreased by addition of those bacteria.The starch content（61.96±0.67 g/100g）and protein content（14.11±0.16 g/100g）in LM-S fermented bran-rich steamed bread were the lowest.The soluble dietary fiber content（3.95±0.77g/100g）was the highest,while the insoluble dietary fiber content（11.10±0.13g/100g）and fat content（0.248±0.01g/100g）of bran-rich steamed bread fermented with LR-S combination were the lowest.LM-S fermentation is the best method to improve the nutrition of bran-rich steamed bread.（5）The volatile components in four kinds of bran-rich steamed bread were analyzed by HS-SPME combined with GC-MS.24,25,26 and 29 flavor compounds were detected in the bran-rich steamed bread prepared by S,PP-S,LR-S and LM-S fermentation,respectively.The key flavor compounds with OAV≥1 were analyzed,and heptanal,nonyl aldehyde,decanal,octyl aldehyde,hexyl aldehyde,benzene acetaldehyde,trans-2-Nonenal,（E）-oct-2-enal,（E,E）-2,4-sebacic olefine aldehyde and hexyl acetate,2-pentylfuran were characterised.The contents of trans-2-nonenal,（E,E）-2,4-sebacal and 2-pentylfuran,which were considered to be of wheat flavor,were significantly increased by lactic acid bacteria fermentation.The contents of three aboved substances in PP-S fermented steamed bread were the highest.The organoleptic evaluation showed the same result that the wheat flavor of bran-rich steamed bread prepared by PP-S strain was the strongest,and those of LM-S and LR-S were masked by overhigh acetic acid content.