| Steamed bread is a traditional table delicacy of the Chinese nation,and fermentation is extremely important in steamed bread making.Sourdough is a traditional starter for flour food,which has a positive impact on the sensory,flavor and shelf life of products,and has become a popular research again in recent years.There are many researches on sourdough abroad,which focus mainly on the isolation and identification of microorganisms and the improvement of product(bread)quality.The starch and gluten are the main components of wheat flour,which play an important role on depengding the quality of dough and steamed bread.However,study of sourdough steamed bread also for the lack of complete scientific theoretical support and there is still a lot of research space for sourdough steamed bread in China.At present,the research on improving the rheological properties and product quality of gluten-free dough by sourdough fermentation is mainly focused.However,researches on the properties of starch and gluten,dough rheology and steamed bread quality are not rich enough in sourdough fermentation,especially in sourdough fermentation with different strains.Therefore,the dominant yeast Saccharomyces cerevisiae,the dominant homofermentation lactic acid bacteria Lactobacillus delbrueckii subsp.bulgaricus and the dominant heterofermentation lactic acid bacteria Lactobacillus brevis in the traditional sourdough were selected for sourdough fermentation.They are Saccharomyces cerevisiae fermentation(Sce)?Saccharomyces cerevisiae mixed with Lactobacillus delbrueckii subsp.bulgaricus fermentation(Sce-Lb)?Saccharomyces cerevisiae mixed with Lactobacillus brevis fermentation(Sce-Lbr).The differences of starch and gluten properties in the fermentation process were studied and compared.In addition,their effects on dough rheology and steamed bread quality were also compared.The changes of dough basic components during sourdough fermentation with different strains were analyzed.The results showed:the p H value of dough gradually decreased and TTA gradually increased during sourdough fermentation,and the change degree was Sce-Lbr>Sce-Lb>Sce;There was no obvious change of total starch content during sourdough fermentation;The amylase activity first increased slightly with the increase of fermentation time,but it decreased significantly during12h-24h fermentation,and the reduction degree from was consistent with that of p H value;Similarly,the water-soluble total sugar content also showed a significant decrease trend from 12h to 24h,which was consistent with the reduction degree of amylase activity;The content of water-soluble substances increased significantly with the increase of fermentation time,but it decreased significantly during 12h-24h fermentation,and the content of water-soluble substances in the same fermentation time was Sce-Lbr>Sce-Lb>Sce;The total pentosan content changed little during Sce and Sce-Lb fermentation,but it decreased significantly during Sce-Lbr fermentation and water-soluble pentosan content increased during the fermentation of three strains.The changes of structure and physicochemical properties of wheat starch granules during sourdough fermentation with different strains were analyzed.The results showed:In terms of basic components,the content of damaged starch decreased significantly during sourdough fermentation;The amylose content of Sce?Sce-Lb and Sce-Lbr decreased significantly from 0-3h,0-6h,and 0-3h fermentation,respectively,and they remained stable with the increase of fermentation time.In terms of granule structure,the apparent morphology of starch granulees changed obviously during sourdough fermentation,but there was no obvious difference among different strains;The molecular structure and crystalline structure of starch granules did not change during fermentation,but the changes of absorbance ratio at 1047 and1022 as well as relative crystallinity showed the same trend.That is,they gradually increased during Sce and Sce-Lb fermentation,but increased fast then decreased slightly during Sce-Lbr fermentation.In terms of physicochemical properties,The solubility of wheat starch decreased obviously in the fermentation of three strains;The peak viscosity and retrogradation value of starch increased first and then decreased during Sce and Sce-Lb fermentation,while they showed such a trend in the early stage of Sce-Lbr fermentation but increased significantly with the continuous fermentation;The gelatinization enthalpy of wheat starch increased during the the fermentation of three strains;The gel hardness decreased by Sce-Lb and Sce-Lbr fermentation,and it decreased more in Sce-Lbr fermentation.The changes of dough rheological properties and gluten properties during sourdough fermentation with different strains were analyzed.The results showed:In terms of the dynamic rheological properties of dough,the storage modulus(G')and loss modulus(G”)of dough decreased significantly with the increase of fermentation time while tan?increased gradually,and the change degree was Sce-Lbr>Sce-Lb>Sce.In terms of the change of gluten,the content of gluten and GMP as well as gluten index decreased significantly,while the content of free sulfhydryl increased significantly,and the change degree was Sce-Lbr>Sce-Lb>Sce.In terms of the microstructure of dough,the gluten network gradually became loose and the large A-starch granules gradually exposed during Sce and Sce-Lb fermentation,while obvious holes and cracks have been observed in the gluten matrix after 3h fermentation in Sce-Lbr.The effects of adding sourdough with different strains on the rheological properties of dough and the quality of steamed bread were analyzed.The results showed:In terms of the basic rheological properties of dough,sourdough addition significantly reduced the development time,stability time,farinograph quality number(FQN),and increased the degree of softening;The tensile curve area and extensibility(E)were decreased while the resistance to extension(R)of dough increased;The change degree was Sce-Lbr>Sce-Lb>Sce,and the greater the addition ratio,the more obvious the change was.In terms of the dynamic rheological properties of dough,the addition of sourdough significantly reduced G'and G”but increased tan?,and the change degree was also Sce-Lbr>Sce-Lb>Sce,which was consistent with the weakening degree of gluten.In terms of the Rheofermentometre evaluation,the addition of sourdough increased the Hm significantly,but there was no significant difference among different strains;TX and R value were also increased and the V loss was decreased,among which mixed strain sourdough changed more greatly.In terms of the quality of steamed bread,the addition of Sce-Lb and Sce-Lbr sourdough significantly reduced the hardness and chewiness of steamed bread,and Sce-Lbr of sourdough steamed bread changed more;The addition of Sce-Lb and Sce-Lbr sourdough increased the resilience of steamed bread;The addition of sourdough also delayed the hardening speed of steamed bread during storage,and the adiditon of sourdough with mixed strains had the most significant improvement effect on aging.The results of correlation analysis showed that the properties of starch and gluten protein and water soluble matter after sourdough fermentation were significantly correlated with the rheological properties and texture properties of steamed bread. |
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