dc.description.abstract |
Food quality, safety, flavor, and aroma are improved by metabolites produced by lactic acid bacteria
(LAB) that include organic acids, bacteriocins, and hydrogen peroxides. The metabolites could inhibit
the growth of food borne pathogens and spoilage microorganisms in foods. Furthermore, LAB play a
crucial role in the fermentation process by giving unique flavors and textures to food products,
prolonging its shelf life, emhancing safety and quality. LAB also have probiotic roles that effectively
combat foodborne pathogens. LAB have gained attention for bacteriocin production and their
biopreservative properties. Thus, the objective of this study was to isolate and characterize LAB
retrieved from Ethiopian traditional fermented foods and beverages for their probiotic, bacteriocin
production, and preservative activities. In addition, the study was conducted to assess the bio
preservative potential of LAB in milk, fruits, and vegetables. Traditional fermented foods and
beverages were collected from East Wollega Zone and Jimma Town. About, 180 samples, 30 each
(kotcho, bulla, borde, shamita, bukuri, and ergo) were collected and transported to Jimma University's
Microbiology Laboratory for isolation of LAB following standard methods. LAB isolates were
characterized using morphological, biochemical, physiological, and MALDI ToF/Ms techniques.
Concurrently, the effects of acid, temperature, enzymes, and food preservatives on the antagonistic
activities of LAB strains were evaluated. The study further evaluated potential probiotic LAB based on
their tolerance to bile salt and acid, gastrointestinal simulation, auto- and co-aggregation,
hydrophobicity, antibiotic resistance, bacteriocin production, and bio-preservation activity. The
bacteriocin assay was evaluated at various temperatures, incubation times, and growth medium to
determine the optimal conditions for bacteriocin production. Solvent extraction methods for
concentrating of bacteriocins were developed, and various extraction procedures were tested for
successful bacteriocin recovery. The ability of the LAB isolates to prolong the shelf life of test foods
was evaluated. About, 956 LAB isolates were recovered from 180 traditional fermented food and
beverage samples. As revealed from phenotypic and morphological characteristics, Lactobacillus,
Lactococcus, Streptococcus, Pediococcus, and Enterococcus species dominated all the six traditional
fermented foods and beverages. Lactobacillus was the most abundant genus with even distribution in
all the traditional fermented foods and beverages. Bulla harbored the highest number of LAB
communities, followed by Ergo. Over 580 of the 956 isolates showed strong inhibitory activity against
selected food borne pathogens. Furthermore, 340 LAB had antagonistic effects against all the selected
food borne pathogens. Using MALDI-ToF/MS analysis, the majority of the isolates were identified as
Pediococcus species (P. acidilactici and P. pentosaceus) followed by Enterococcus species mainly E.
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faecium (n = 6), Lactococcus lactis (n = 2), Bacillus species (B. infantis), and Rothia dentocariosa
(n=1)). Pediococcus pentosaceus (23.33%) dominated the microbial ecology of all the selected
Ethiopian traditional fermented foods and beverages followed by Enterococcus faecium (20%), and
the least common species was Lactococcus lactis (6.67%). All of the isolates, 17 of them showed
potential capacity to produce antimicrobial activity, putative bacteriocins, survive in simulated
gastrointestinal tracts, and inhibitor substances were all studied in vitro and in artificially simulated
environments. Out of 340 that demonstrated potential antagonistic effects, 44 (13%) of isolates
survived at pH 2 and 3 for 3 and 6 h, respectively, with survival rates ranging from 33.825% to 100%.
Because they were acid- and bile-tolerant isolates, 125 of the 340 LAB isolates were screened as
potential probiotic candidates. Among 125 isolates, 39 (31.20 %) were identified as the best acid and
bile salt-tolerant, with the potential capacity to produce bacteriocin. All the thirty-nine promising
bacteriocin producers were susceptible to tetracycline (30 g/ml) and chloramphenicol (15 g/ml), but
highly resistant to kanamycin (20 g/ml), with some being resistant or susceptible to streptomycin (10
g/ml) and ampicillin (10 g/ml). Additionally, the isolates showed nearly 75%–95% survival rates at
low pH (2, 2.5, and 3), bile salt (0.3%), intestinal inhibitor substances, and simulated gastro-intestinal
conditions, respectively. The potent isolates also showed strong potency for aggregation (50-120 %)
and cell surface hydrophobicity (70-116%). P. pentosaceus JULABB16 was identified as the most
effective isolate in controlling the spoilage microorganisms and extended the shelf life of tested fruits
and vegetables by at least thee weeks. Likewise, Lactococcus lactis was found to be the potential isolate
to maintain the quality of milk. The entire potent and selected LAB demonstrated potential preservative
efficiency because they did not cause browning or off-odor on fruits and vegetables for thee to four
weeks. In conclusion, this study demonstrates the significant potential of lactic acid bacteria (LAB) to
extend the shelf life of fruits, milk, and vegetables. The research has established a foundation for the
selection of specific antimicrobial peptides and the further development and application of LAB for
antibacterial and probiotic activities. The findings underscore the efficacy of certain LAB isolates in
enhancing the longevity and safety of various food products. Moving forward, further research should
focus on the practical applications of these LAB isolates in food preservation strategies and probiotic
formulations, aiming to leverage their full potential in extending shelf life and promoting health
benefits. |
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