Microbial profile of Tella and the role of gesho (Rhamnus prinoides) as bittering and antimicrobial agent in traditional Tella (Beer) production

Tella is widely brewed in Ethiopia. The quality may be deteriorated by microbial contaminants. Determination of profile of spoilage microorganisms in tella, bittering agents and antimicrobial activity of gesho are important. Therefore, the objective was to determine microbial dynamics of tella phases, bittering agents and the antimicrobial activity of gesho. Tella fermentation was carried out using traditional methods. Enumeration of microorganisms were carried out using Malt, MaconKey, Man Rogosa Sharpe (MRS), dextrose, nutrient and Seed Culture Medium agar. Essential oil, total, hard and soft resins as well as Minimum Inhibitory Concentration (MIC) and Minimum Bactericidal Concentration (MBC) were determined. The microbial count was significantly (P ≤ 0.05) decreased towards the end of fermentation phases. Particularly, molds and bacteria were almost disappeared at the end of fermentation phase. Yeasts were dominated at the middle of phases. This phenomenon may be due to the synergic effect of gesho antibacterial substance, alcohol concentration, reduction of pH (7.7 to 3.43) and nutrient content of tella. Total resin, soft resin, hard resin and essential oil of gesho were found to be comparable with values of varieties of hops. Therefore, gesho can substitute hops for beer production. The MIC and MBC of gesho extract against standard pathogenic and clinical bacteria were ranged from 97.5 to 780 mg/ml and 195 to 780 mg/ml, respectively. So, gesho extract during tella brewing can inhibit bacteria growth and thereby help to extend the self-life of the product. In conclusion, brewing of tella should be carried out in aseptic conditions in order to avoid risks of having pathogenic bacteria.