Effect of Sourdough Fermented by Different Lactic Acid Bacteria on Bread Quality and Flavor

In this study, the changes in the viable count of lactic acid bacteria and the contents of major organic acids in sourdough were explored during spontaneous and inoculated fermentations with the typical sourdough starter cultures Lactobacillus plantarum (Lp), Lactobacillus paralimentarius (Lpa) and Lactobacillus fermentum (Lf) separately and in combination: Lpa + Lp (1:1), Lp + Lf (1:1) and Lpa + Lf (1:1), and the effect of co-fermentation with yeast on bread quality was evaluated. The results demonstrated that Lf grew fastest in sourdough among the single cultures, while the highest number of bacterial colonies of 9.20 (lg(CFU/g)) was observed in sourdough fermented with Lpa + Lp + Lf for 10 h. From 16 h onward, the number of bacterial colonies remained stable. Furthermore, the rate of inoculated fermentation (for both single and mixed culture fermentation) was always faster than that of natural fermentation, and the sourdoughs fermented with Lf and Lpa + Lp + Lf reached the desired pH 4.0 after 16 h. Moreover, at this time, the maximum contents of lactic acid and acetic acid in sourdough were obtained (9.05 and 2.31 mg/g, respectively). Compared with ordinary dry yeast fermented bread (OFB), the specific volume of Lpa + Lp + Lf fermented sourdough bread increased by 19.43%, the hardness decreased by 38.21%, and the resilience rose by 29.17%. In the case of flavor quality, Lpa + Lp + Lf fermented sourdough bread contained the largest number (49) and amount (352.39 μg/kg) of flavor compounds including four unique esters, namely ethyl lactate, ethyl palmitate, phenethyl 2-methylpropionate and ethyl caproate. In addition, anti-aging properties of the bread were evaluated, revealing that after 7 days of storage, the quality did not remarkably deteriorate, the hardness increased by only 1.93 times, and the rate of water migration was slow during storage. In summary, Lpa + Lp + Lf fermented sourdough can significantly improve the taste of bread and extend its shelf life.