High Performance Screening And Functional Optimization Of Compound Bread Starter

Compound starter is a baking starter composed of yeast and lactic acid bacteria,which is favored for the improvement of the taste,flavor,shelf life of baked goods.In order to obtain a fast-waking compound starter,in this study,high-throughput screening was performed on 6kinds of food sources such as grape broth,kefir grains,kombucha,kefir,kimchi and buckwheat flour.Two strains of yeasts which have high gas production have been selected,and seven strains of lactic acid bacteria that inhibit the growth of the main mold in the dough.The two yeast strains were named Saccharomyces cerevisiae LBBE-1 and Kluyveromyces marxianus LBBE-2.The waking time of LBBE-1 in European bread was less than 120 min,which was selected as the main gas-producing strain;LBBE-2was selected as the main flavor strain.After tolerant domestication,the concentration of LBBE-1 domesticated strain has increase to 8.5 times than the original strain in 300 g·L^-1 glucose and 20 g·L^-1 NaCl.According to the baking test,the yeast can achieve less than 140 min waking time in the sweet bread.The evaluation showed that the sweet bread made by the domesticated strain LBBE-1 has3.5%,7.7%,7.4%and 5.3%higher tissue morphology,smell,taste and storage than commercial yeast.Also,LBBE-1 was 44.2%shorter than the original strain on waking time;the waking time of the European bread is 1.4%higher than that of the original strain,and the tissue morphology score is increased by 3.6%.In order to obtain the production process of two strains of yeasts,these two strains were optimized on shake flask level and fermentor culture conditions.In a 15 L fermentator,after 22 h culture,the maximum cell concentration of LBBE-1reached92.9,which number of viable cell was 6.3×10⁹ cfu·mL^-1.OD₆₀₀ of LBBE-2 was 82.4,and the number of viable cell was determined to be 4.8×10⁹ cfu·mL^-1.Seven strains of lactic acid bacteria that were selected from the preliminary screening can inhibit the growth of mold.Six strains of lactic acid bacteria were included in the list of bacteria that can be used in food issued by the Ministry of Health in 2010,which were named Pediococcus lactis B0110,Lactobacillus helveticus LAB2,Lactobacillus rhamnosus BBE2,Lactobacillus paracasei Y-3,Lactobacillus acidophilus Y-4,Lactobacillus plantarum BEE8.The inhibitory zone size of 6 strains against bread mold was over 20 mm;each strain can produce different volatile flavor substances and present different compound aromas.At the same time,LAB2 can produce milky,rose,and peach aromas and has the highest yield of flavor substances;B0110 can produce higher free amino acids.In order to further obtain the culture process of 6 strains of lactic acid bacteria,single-factor optimization,Plackett-Burman test,orthogonal experiment under shake flask conditions and fermentor culture were carried out.Finally,in a 15 L fermentor,the maximum cell concentration and live bacteria of each lactic acid bacteria were achieved.To facilitate the use and store of the cell,the lyophilization conditions of 2 strains yeast of and 6 strains of lactic acid bacteria were optimized,and finally the viable count of LBBE-1,LBBE-2,B0110,LAB2,BBE2,Y-3,Y-4 and BBE8 was greater than 1.00×10¹⁰ cfu·g^-1.By optimizing the ratio of 2 yeasts and 6 lactic acid bacteria,LBBE-1,LBBE-2,B0110,LAB2,BBE2,Y-3,Y-4,BEE8 in mass ratio of 10:1:3.66:3.66:3.66:3.66:3.66:3.70,bread specific volume was 4.15 mL·g^-1,and it is not easy to lose water during storage.The amount of this compound stater added in flour is 5%,which can rapidly waking achieved within 120 minutes.Finally,this paper obtained a compound starter with natural origin,rapid waking and good flavor and process of preparation.