Abstract
The study was conducted to evaluate in vitro probiotic properties of lactic acid bacteria (LAB) isolated from fermented Shamita and Kocho. Sixteen samples, 8 each of Shamita and Kocho, were collected from Arat-Kilo and Merkato sites in Addis Ababa, respectively. The average pH values of Shamita and Kocho samples were 3.52 and 3.44, respectively. A total of 140 LAB were isolated, of which 101 isolates (72%) were found to inhibit one or more of the sensitive test organisms Shigella boydii and Salmonella typhimurium but none of them had antimicrobial activity against Staphylococcus aureus. The inhibition diameters on agar medium ranged from 8.5 to 17.5 mm. The 101 isolates having antagonistic effects against the test organisms were evaluated for their bile tolerance. Thirty six isolates (36%) tolerated 0.3% bile salts for 48 h with 55 to 93% survival. The 36 bile tolerant isolates were evaluated for their acid tolerance and 25 (69%), 30 (83%) and 34 (94%) tolerated pH 2, pH 2.5 and pH 3 for 3 h, respectively. Further extension of the incubation period for 6 h reduced the number of isolates to 21 (58%) and 33 (92%) at pH 2 and pH 3. Thirty of the bile tolerant isolates (83%) showed 80 to 94% survival at pH 2.5 for 6 h. These isolates were selected as LAB candidates with probiotic potential. Based on their phenotypic characteristics, the 30 isolates were identified as Lactobacillus (17 isolates), Leuconostoc (6 isolates) and Pediococcus (4 isolates) and Lactococcus (3 isolates). Antibiotic resistance patterns of the 30 isolates showed 100% resistance against oxacillin but lower resistance to levofloxacin; 57% of the isolates were resistant to penicillin. However, all the isolates were sensitive to erythromycin and gentamicin. Multiple drug resistance patterns were observed in two isolates one each from Shamita Lactobacillus (S9) and Kocho Lactobacillus (K64) having multiple resistances to penicillin, levofloxacin and oxacillin. Nine isolates (30%) were selected as probiotic candidates for further test on different fermented foods. Key words: Lactic acid bacteria; Lactobacillus, Leuconostoc, Pediococcus, Lactococcus spp., acid tolerance, antimicrobial activity, bile tolerance.
Highlights
Fermentation is an ancient widely practiced technology and fermented foods are an essential part of diets in all parts of the world
A total of 160 different colonies were selected and purified, of which 140 colonies were confirmed as lactic acid bacteria (LAB) isolates
The results revealed that 30 isolates had 80 to 94% survival rate at pH 2.5 for 6 h and these isolates were selected as LAB candidates with probiotic potential (Table 8)
Summary
Fermentation is an ancient widely practiced technology and fermented foods are an essential part of diets in all parts of the world. Traditional fermented foods are indigenous to a particular area and have been developed by the local people using age-old techniques and locally available raw materials (Rose, 1977). Traditional fermentation processes are increasingly attracting the attention of scientists and policy makers as a vital part of food security strategies and for their commercial value (Van de Sande, 1997). Fermentation is a process in which raw substrates are converted into fermented food products by the action of microorganisms or their enzymes to desirable compounds that result in new aroma, flavor, taste and texture. Fermentation helps to increase the sensory quality, palatability and acceptability of the products (Campbell-Platt, 1987). Some of these processes involve ethanol production by yeasts or organic acids by lactic acid bacteria (LAB). It helps to extend the shelf-life of foods by preventing the outgrowth of spoilage microorganisms and foodborne pathogens (Motarjemi, 2002)
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