Study On The Effect Of Different Lactic Acid Bacteria Fermented Sourdough On Bread Quality And Flavor Characteristics

Sourdough is a kind of dough obtained by fermentation of grains(wheat flour,etc.),water and active microorganisms,such as lactic acid bacteria and/or yeasts for a period of time.Studies have shown that compared with bread made by ordinary dry yeast fermentation,sourdough fermentation technology can help improve the texture of bread,enhance bread flavor,extend bread shelf life,and increase the nutritional value of bread.However,at present,it is not very clear about the changes of flavor substances in the process of compounding lactic acid bacteria fermented sourdough and the influence of compound lactic acid bacteria fermented sourdough on bread quality.In this thesis,the typical strains of sourdough,Lactobacillus plantarum(LP),Lactobacillus paralimentarius(LPA)and Lactobacillus fermentum(LF)are used as fermentation bacteria to discuss natural fermentation of sourdough(Control group),3 single lactic acid bacteria(LPA,LP,LF)and 4 compound lactic acid bacteria,namely LPA+LP(1:1),LP+LF(1:1),LPA+LF(1:1)and LPA+LP+LF(1:1:1),changes in the main organic acids and flavor substances in the process of fermenting sourdough,and their effects on bread quality when co-fermented with yeast.On this basis,we will further study the technology of sourdough to improve bread,in order to provide theoretical and technical reference for the quality control of my country's industrialized sourdough bread production.The main research contents and results are as follows:(1)Through the determination of the growth status of lactic acid bacteria,the acidification rate,the content of organic acids(acetic acid and lactic acid)and the content of volatile flavor substances during the fermentation of sourdough by lactic acid bacteria,the analysis of each of the eight groups of sourdough during the fermentation process Changes in indicators.The experimental results showed that the Lactobacillus fermentum LF group grew the fastest in the single strain fermented sourdough,while the compound lactic acid bacteria LPA+LP+LF group sourdough had the highest number of lactic acid bacteria colonies when it was fermented for 10 hours,reaching 9.20 Log CFU/g sourdough.And the number of colonies reached a stable at 16 h.At the same time,the rate of lactic acid bacteria(single,compound)fermented sourdough was always faster than that of naturally fermented sourdough,and the sourdough of Lactobacillus fermentum LF group and LPA+LP+LF group reached p H 4.0 at16 h of fermentation.At 16 h,the contents of lactic acid and acetic acid in sourdough reached the maximum(9.05 mg/g sourdough and 2.31 mg/g sourdough).At the same time,when fermented for 16 hours,the types and contents of flavor substances in the sourdough dough reached the maximum.Among them,the LPA+LP+LF group sourdough had the highest flavor substance content(259.34 ?g/kg)and the most types(40 kinds).Moreover,the content of floral and fruity flavors such as 2,4-decadienal,octyl formate and hexyl acetate in this group of sourdough all reached the maximum.Based on the above analysis,the acidity and p H of the LPA+LP+LF group compound lactic acid bacteria fermented sourdough reached a stable level,and the content of organic acid and flavor substances reached the maximum,and the quality of sourdough was better than other groups.(2)The 8 groups of sourdough fermented for 16 h were further applied to the making of sourdough bread,using physical property analyzer,GC-MS gas chromatography mass spectrometry and other analysis and detection methods,and the specific volume and quality of bread Structural properties,sensory scores,anti-aging properties,and volatile flavor substances are evaluation indicators.By comparing the quality of 8 groups of sourdough bread and Ordinary dry yeast fermented bread(OFB),it can be seen that lactic acid bacteria(single,complex)With)the quality of fermented sourdough bread is better,especially the LPA+LP+LF group fermented sourdough bread has the lowest p H(4.64),and the specific volume of the bread has increased by 19.43%,the hardness has been reduced by 38.21%,and the recovery has increased by 29.17%.In addition,in terms of flavor quality,the LPA+LP+LF group fermented sourdough bread has a higher content of flavor substances(310.59 ?g/kg)and the most types(49 kinds),including four unique ester substances(lactate ethyl ester).Ester,ethyl palmitate,phenethyl 2-methylpropionate and ethyl caproate).At the same time,in terms of the anti-aging properties of bread,the hardness of LPA+LP+LF group bread only increased by 192.93% after storage for 7 days,and the rate of water migration during storage was slow.In summary,the compound lactic acid bacteria(LPA+LP+LF)fermented sourdough can significantly improve the taste quality of bread and extend its shelf life.(3)Finally,using single factor and response surface experimental design,the specific volume,texture and sensory scores of the bread were used as evaluation indicators to study the effects of the addition of LPA+LP+LF fermented sourdough,the addition of dry yeast and the proofing time on the bread.The quality of LPA+LP+LF compound lactic acid bacteria fermented sourdough bread is determined as follows: LPA+LP+LF compound lactic acid bacteria fermented sourdough add amount 30%,dry yeast add amount 1.0%,proofing time 90 min.The specific volume of product bread(6.08 mL/g)and hardness(208.214 g).