Bitter cola (Garcinia kola) powder and its ethanolic extract were assessed for their ability to inhibit the growth of a wild strain of Saccharomyces cerevisiae isolated from a brewery environment. The iso-alpha acid contents of the G. kola powder, G. kola extract and hop extract were determined as 5.85 mg/l, 6.34 mg/l and 7.65 mg/l, respectively, showing that the iso-alpha acid contents of G. kola extract and G. kola powder compared relatively well with that of hop extract. The antimicrobial activity of both agents, using Humulus lupulus ethanolic extract as control, showed a high dependence on the temperature of assay. At most of the temperatures evaluated (30 – 45 oC), the rates of antimicrobial activity differed. Garcinia kola ethanolic extract and hops extract displayed total inhibition of the wild yeast growth at temperature of 40 oC at concentrations of about 0.039 mg/ml and 0.078 mg/ml respectively. Humulus lupulus extract (hops) had the highest generation time at 450C at a concentration of 0.078 mg/ml. The complete inhibition of the yeast growth by G. kola extract at 40 oC indicated that it had higher antimicrobial activity against this yeast than hops extract. In all the temperatures evaluated both G. kola ethanolic extract and powder compared favourably with hops extract with respect to antimicrobial activity against a wild strain of Saccharomyces cerevisiae at various concentrations. These results revealed that the antimicrobial activity of these hopping agents were temperature and concentration dependent.
A Moneke, B Okolo, C Asogwa, F Ire
