Scrrening And Identification Of Lactic Acid Bacteria From SuanTangZi Dough And Its Application In Bread

Suan Tang Zi is a national traditional fermented food in northern China,which is rich in lactic acid bacteria(LAB),and has great potential for the development and utilization.Although LAB used in bread fermentation can effectively increase the nutritional value,improve the texture characteristics,and delay the aging of bread,it has higher requirements on the quality of LAB.In this study,lactic acid bacteria strains for bread fermentation were screened and identified from Suan Tang Zi dough,and the effect of LAB on the baking quality,free amino acid content and the quality of bread during storage were studied.The aim is to enrich the special strain library for bread fermentation,and provide theoretical guidance for the development of new bread products.The main research contents and results are as follows:(1)57 LAB were scrrened from 5 Suan Tang Zi sample according to traditional separation technology.18 strains of LAB were obtained through the preliminary screening of acid production capacity,and 5 strains of LAB were re-screened according to the ability of flavor formation and growth capacity.Molecular biology identification results showed that the five lactic acid bacteria were L.paracasei(SA6),L.pentosus(SB7),L.plantarum(SC1),L.curvatus(SD2)and L.paracasei(SE4).(2)The selected strains were made into a sourdough starter,and the dough fermentation characteristics,stretching characteristics,molecular weight distribution of gluten,free thiol(SH)content,reducing sugar(RS)content and starch gelatinization enthalpy(ΔΗ)were used as indicators to investigate the effects of the addition of sourdough on the properties of gluten and starch.Results showed that sourdough can enhance the gas production capacity of the yeast in the dough,reduce the strength of the dough,and significantly increase the ductility and viscosity of the dough.Molecular weight distribution of gluten analysis showed that the addition of sourdough destroys the disulfide bonds in the gluten protein and increases the content of low molecular weight polymer protein(PP),monomer protein(MP)and free thiol in the dough.RS content analysis results showed that the addition of sourdough increases the RS content in the dough by breaking the glycosidic bonds between starch molecules.WDSB7 has the highest RS content in all breads,135.88mg/g.DSC analysis results indicated that the addition of sourdough reduces ΔΗ value of the dough,and the ΔΗ value s of WDSB7 and WDSE4 were significantly lower than other doughs,which were 4.39J/g and 4.38J/g,respectively.(3)The physical and chemical properties of bread,baking quality,storage quality and free amino acid content of bread were used as indexes to analyze the effects of the addition of sourdough on bread quality.Sourdough makes bread p H drop significantly,and TTA rises significantly.Bread specific volume and texture analysis results showed that WBSE4 has the largest specific volume(6.13 m L/g)and the smallest hardness(145.83g).The internal texture structure analysis showed that,except for WBSC1,the cells density(CD)and pore area fraction(AF)of other breads were higher than those of the control bread.The addition of sourdough increases the flavor,overall acceptability and free amino acid content of bread,and WBSB7 has the highest free amino acid content.Bread storage quality results show that sourdough fermentation can delay the hardening rate of bread and the moisture migration rate in bread,and reduce the increase rate of ΔΗ.Except the sourdough starter made by SA6,other sourdough can significantly reduce the water migration rate in bread and delay the redistribution of water in bread.Comprehensive analysis of the hardness,ΔΗ and moisture migration rate of bread during storage,SB7 and SE4 participate in fermentation to improve the aging quality of bread better than other strains.In summary,the LAB selected from the Suan Tang Zi dough can significantly improve the quality of bread and delay the aging of bread.Among them,SB7 and SE4 have better effects on improving bread quality than other strains,and have good application prospects.