Growth studies, comparison and immobilization of selected potential sour dough lactic acid bacteria
A study was conducted to evaluate the growth of selected lactic acid bacteria in synthetic media, to compare them for sour dough production, and to study the fermentation performance of selected Lactobacillus helveticus (Lh) when immobilized in a gel matrix.^ Evaluation of the metabolites produced by each microorganism in their correspondent synthetic media indicated that Lactobacillus bulgaricus (Lb) and Lh produced a combination of lactic and acetic acids, and Lactobacillus sanfrancisco (Ls) produced a mixture of lactic and acetic acids plus ethanol. The findings also demonstrated that High Pressure Liquid Chromatography (HPLC) can be used to monitor and quantify the fermentation by-products of the mentioned lactic acid bacteria.^ Comparison of sour dough made with Lb, Lh and Ls at the optimum temperature for each bacterium indicated that Lb, Lh and Ls final breads had pH values of 4.20, 4.30 and 4.75. HPLC analysis showed that lactic acid produced by Lb and Lh was the same at 0.57% and higher than 0.37% for Ls. Acetic acid production was 0.05, 0.07 and 0.08% for Lb, Lh and Ls respectively. Ls also formed 0.14% of propionic acid. Sensory evaluation of the three sour dough breads indicated that Lh bread with pH of 4.30, and lactic/acetic and lactic/propionic acid ratios of 8:1 and 10:1 respectively, was preferred by taste panelists.^ Comparison of the results obtained from immobilization of Lh in K-carrageenan (CRG) and a combination of CRG and Locust Bean Gum (LBG) indicated that after 24 hr of fermentation, the latter performed better. The acid production by CRG/LBG immobilized Lh cells was 41% higher then CRG alone for lactic and 200% higher for acetic acid. There was 68% less cell leakage with CRG/LBG. The effect of different flow rates of 12.5, 25, and 50 ml/hr on fermentation and by-product production by CRG/LBG immobilized Lh indicated that after 24 hr of fermentation, the 50 ml/hr flow rate caused the bacterium to produce a 2.3 to 3.4 times higher volumetric productivity of acid than the 25 and 12.5 ml/hr. Comparison of immobilized and free cell fermentation of Lh indicated that entrapped bacteria showed a 23% higher glucose conversion and 8 times higher volumetric productivity of acids after 16 hr of fermentation, concluding superiority of the immobilized Lh to free cell for lactic acid production. ^
Agriculture, Food Science and Technology|Biology, Microbiology
Ahmad S Tahajod,
"Growth studies, comparison and immobilization of selected potential sour dough lactic acid bacteria"
Dissertations and Master's Theses (Campus Access).