The Effect Of EPS Sourdough On The Quality Of Steamed Bread And The Optimization Of Formula

Traditional sourdough steamed bread is popular with consumers due to its unique flavor and excellent taste,and studies have showed that the metabolic activity of lactic acid bacteria(LAB)is crucial for the formation of taste and flavor.In the present study,we have collected traditional sourdough samples from Ya'an,analyzing its LAB diversity and screening for the dominant species as well as high exopoly saccharides(EPS)producing LAB isolates.EPS sourdough and steamed bread was made by using different proportion of isolates as starters,then the best proportion of isolates for EPS sourdough was selected.Afterwards,the formula of EPS sourdough was optimized and the quality difference between this steamed bread products and traditional sourdough steamed bread was compared.The main findings of the present research are listed as belows:1.Thirteen traditional sourdough samples collected from Ya'an were examined.The pH ranged from 3.98 to 4.77;the LAB counts ranged between 7.99 and 8.41 lg CFU/g,and the yeast counts ranged between 5.78 and 6.35 lg CFU/g.The average number of LAB and yeast were approximately 117.5 : 1.A total of 219 LAB isolates were obtained by traditional culture methods and the 16 S rDNA sequencing,the results showed that the genus Lactobacillus was predominant in the present study,and Lactobacillus plantarum(L.plantarum)(40.09%),L.lactis(30.88%),and Leuconostoc citreum(Leu.citreum)(15.67%)were found to be the dominant species.2.Twenty isolates capable of producing high level of EPS was obtained by observing whether they could displayed long ropy strands(>1 mm),and the EPS yield of these 20 isolates was determined,which ranged from 2.3 to 229.5 mg/g wet cell weight.Meanwhile,the EPS yield of 10 randomly picked isolates with ropy strands but a “non-ropy” colony were also determined,and a yield between 4.8 and 61.7 mg/g wet cell weight was observed.The present study showed that the strains capable of producing high level of EPS was Leu.citreum E16,the yield is 229.5 mg/g wet cell weight.3.There was no antagonistic effect between strains L.plantarum B12,L.lactis C5,Leu.citreum E16,and EPS sourdoughs using different proportions of these LAB isolates were made,which were named as spontaneous sourdough(group A sourdough),Leu.citreum E16 inoculated sourdough(group B sourdough),and L.plantarum B12,L.lactis C5,Leu.citreum E16 inoculated sourdough(group C sourdough).The basic properties of these sourdoughs were determined.In terms of the EPS yield,group B sourdough(8.1425 g/kg)>group C(5.0275 g/kg)>group A(4.4425 g/kg);in terms of fermentation activity,group B sourdough(253 mL)>group C(195 mL)>group A(170 mL);in terms of the acid producing ability,group C sourdough >group A>group B;in terms of the number of LAB,group B sourdough >group C>group A.In summary,the strain Leu.citreum E16 had better fermentation activity in the sourdough,the group C sourdough had poor fermentation activity due to excessive acidification.4.The above-mentioned sourdoughs were used to make steamed bread products,respectively,and there were significant differences in pH,texture and specific volume.In terms of the acid yield,group C steamed bread had the lowest pH and the highest total titrable tcidity(TTA);in terms of specific volume,group B steamed bread had the highest specific volume,which was significantly higher than the group A and C steamed bread;in terms of texture characteristics,group B steamed bread had better texture characteristics and compression characteristics,and the results were similar to the results of sensory evaluation.In summary,the group B sourdough was the best EPS sourdough with better proportion of inoculated LAB.5.The group B sourdough was made by using the strain Leu.citreum E16 as starter,and the effects of sourdough addition,water addition,the second proofing temperature and time on the quality of steamed bread were studied by the single factor experiment,orthogonal experiment,and the verification orthogonal experiment.The results showed that the formula of the optimized group B steamed bread were: sourdough,25%;water,46%;the second proofing temperature,35°C;the second proofing time,15 min.6.Taking group A steamed bread as the control,the quality of steamed bread after formulation optimization was tested.The results showed that the quality of optimized group A steamed bread(under the formula of optimized group B steamed bread,using spontaneous sourdough to produce the steamed bread)and optimized group B steamed bread improved.Among them,the sensory evaluation,texture characteristics and specific volume of the optimized group A steamed bread were improved obviously.The pH value of the optimized group B steamed bread was significantly reduced;the TTA value was significantly improved;the taste and flavor were better;the chewiness was reduced,and the steamed bread was chewier;the structure was dense;the specific volume is slightly improved.By measuring the volatile flavor substances,it was found that the difference in the type and content of the volatile flavor substances between optimized group A and optimized group B steamed bread was significant.The volatile flavor substances unique to the optimized group A steamed bread was mainly butyric acid,and the volatile flavor substances unique to the optimized group B was mainly hexanol.During the storage period(25 °C),the quality of the optimized group A and the optimized group B steamed bread gradually decreased,with an increasing in the hardness,a decreasing in the elasticity,and losses in characteristic flavor,but the speed of the latter declined significantly lower than the former.