As the first leavening agent in bread production, sourdough has an important role in cuisine and culture all over the world. Traditionally, sourdough was made from flour and water, allowed to ferment using the microorganisms presented naturally inside the grain and in the air. Sourdough becomes acidic when lactic acid bacteria take over the fermentation and play important role. The activities of such microorganism determine the sourdough characteristics in terms of lactic acid fermentation, proteolysis, synthesis of volatile, anti-nutrient and antifungal compounds. As the results, sourdough bread are more nutritious, tasty, coloury, fragrant and more stable during storage in comparison with breads made only by baker?s yeasts or baking powder. In general, Lactobacillus spp. are the common bacteria associated in sourdough starter. In this research, pure lactic acid bacteria were obtained from the isolation of naturally fermented sourdough samples that were collected in Can Tho City. The bacterial species giving the highest acid yields was selected and characterized. The effects of conditions during the sourdough fermentation, such as bacterial inoculation level, fermentation temperature and fermentation time, as well as the shelf life of fermented sourdough bread were also examined. As results, five strains of lactic acid bacteria were purely isolated. By morphological and biochemical tests, these five strains were identified belonging to genus Lactobacillus, family Lactobacillaceae, order Lactobacillales, class Bacilli, phylum Firmicutes. Of which, the strain of LAB-4 performed the highest activity during sourdough fermentation. This target strain was selected due to the highest total acid produced, the lowest pH and good sensory scores and it was identified as Lactobacillus plantarum, with 96% of similarity of 16S region genome by comparing the 16S-rRNA sequence. Based on statistical analysis, the results on effect of fermentation conditions showed that the favourable fermentation conditions for sourdough starter preparation were defined as follows: inoculation level at 109 cells/mL, incubation temperature at 37°C and incubation time for 4 hours. During the storage tests, based on the sensory evaluation of the ability to synthesis antifungal compounds of lactic acid bacteria, sourdough bread that was made by Lactobacillus plantarum had a longer shelf life (9 days) to compare with the treatment of bread made by baker?s yeast (6 days). Probably Lactobacillus plantarum has the ability to synthesize some compounds which have antifungal activities such as lactic, phenyl lactic acids, dipeptides cycle (L-Leu-L-Pro) and cycle (L-Phe-trans-4-OH-L-Pro), and these compounds can inhibit the outgrowth of contaminated microorganisms.
Tạp chí: The 2nd International Symposiun on Formulation of the Cooperation Hub for... & The 9th Inter-University Workshop on Education and Research..., Cantho University, Vietnam, Septemper 27, 2014
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