Potential Probiotic Properties of Lactic Acid Bacteria Isolated from Malted and Spontaneously Fermented Acha (Digitaria exilis) Flour

Abstract

Aim: To isolate, characterise and identify Lactic Acid Bacteria (LAB) with potential probiotic properties from malted and fermented Acha (Digitaria exilis). Place and Duration of Study: The study was carried out at the Department of Microbiology, University of Ibadan, between May 2017 and October, 2017. Methodology: Collected acha grains was sorted, malted for 48 hours, dried milled and sieved. The flour was reconstituted, fermented spontaneously for 72 hours and sampled every 24 hours for isolation of LAB. Results: The probiotic properties of 40 LAB strains isolated were evaluated in vitro. Based on their antimicrobial activity against some common foodborne pathogen and antibiotic susceptibility pattern to standard antibiotics, 14 LAB strains were selected for further screening. They all exhibited strong antimicrobial activity against Staphylococcus aureus, Salmonella sp., Escherichia coli, Bacillus sp. and Pseudomonas aeruginosa. All selected strains were investigated for acidic pH and bile salt tolerance, tolerance to NaCl and simulated gastric juice, cell surface characteristics which includes hydrophobicity and auto-aggregation assay. Production of DNAase, gelatinase, Exopolysaccharide and haemolytic ability were investigated for safety assessment. Five strains (L12, L15, L118, L213, L214) exhibited tolerance to 10% NaCl concentration and pH 2. All the selected 14 LAB strains resisted the bile salt up to 1.0% except L15 and tolerated simulated gastric juice with a sharp decrease by 90min followed by an increase in the count after 180 min except for isolates L12 and L17. Auto-aggregation value ranged from 0.88% to 93.71% with the highest value recorded for L17 (93.71%). LAB117 had the highest (43.39%) microbial adherence to hydrocarbon (MATH) value and least in L19 (2.08%). All the 14 LAB strains were negative to safety tests but all produced exopolysaccharide except LAB L13 and L19. Based on the morphological, biochemical and physiological characteristics, the 14 LAB isolates were identified as Lactobacillus plantarum (L15, L17, L117, L214), Lactobacillus casei (L113, L116, L213), Lactobacillus sp. (L13, L19, L22, L211), Enterococcus sp. (L12, L115) and Pediococcus sp. (L118). Conclusion: The selected 14 isolates have the probiotic properties required for use as a potential probiotic in weaning food supplements with the best probiotic properties recorded with Lactobacillus plantarum L117 strain.