Mekelle Institute of Technology
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Item Isolation and characterization of Lactic Acid Bacteria from raw cow milk and evaluation of their probiotic potential(Mekelle University, 2025-04-28) Goiteom Senay NiguseCow milk is a rich source of lactic acid bacteria (LAB), a group of gram-positive bacteria with diverse applications in dairy, food, feed, and health. Despite this, the probiotic potential of LAB from cow milk remains under-researched. Therefore, the current study aimed to isolate and characterize LAB from raw cow milk and evaluate their probiotic potential. This study involved the isolation of LAB, followed by characterization of their morphology, various biochemical tests, and physiological properties. The LABs were evaluated for their potency and safety as probiotics, and finally, their potential use as starter cultures in yogurt formation was examined. Twenty-three (23) pure bacterial isolates were obtained from seven cow milk samples. Morphologically, eight isolates were cocci (35%), six were rods or bacilli (26%), and nine were coccobacilli (39%). Among these, nine (9) gram-positive and catalase negative isolates were selected for further investigation. These isolates were citrate-negative, non-motile, and indole- negative. All were TSIA-positive, with seven being homo-fermentative and two (M5 and M9) hetero-fermentative. Isolates M1, M2, M3, M4, M5, M6, M7, and M9 demonstrated salt tolerance at 1%, 4%, and 6% NaCl concentrations. Isolates M3 and M4 exhibited acid tolerance, growing at pH levels of 2, 4, 6, and 6.5. Isolates M1, M2, M3, M5, M6, M7, and M9 showed resistance to temperatures ranging from 15°C to 45°C. Isolates M2, M3, M5, M6, M7, M8, and M9 displayed tolerance to 0.4% and 0.6% phenol concentrations. None of the nine LAB isolates exhibited hemolytic activity. However, they showed varying degrees of antibacterial activity and displayed both susceptibility and resistance to antibiotics. Six isolates (67%) performed well as starter cultures for yogurt (riguo) production. The LAB isolates were tentatively grouped under the genera Lactobacillus, Enterococcus, and Leuconostoc. Overall, the isolated LAB from cow milk represents a potential source of probiotics. These LABs could serve as starter cultures in the dairy and food industries and may be developed into commercially viable probiotic products. Further studies, including molecular identification and characterization, are necessary to determine their specific strains.