Abstract
Three lactic acid bacteria (LAB) isolates designated AS1, AS2 and KN4 isolated from kunun-zaki (a sorghum based non-alcoholic beverage widely consumed in Northern Nigeria) and identified as Lactobacillus plantarum, Lactobacillus brevis and Lactobacillus delbruckii, respectively, produced significant inhibitory compounds in broth. The partially purified inhibitory compounds were screened by agar spot assay method for antagonistic activity against target Gram positive and negative bacteria as well as yeasts associated with food spoilage. The partially purified compounds exhibited strong activity against Staphylococcus aureus ATCC 12600, Bacillus cereus and Escherichia coli ATCC 11775. The inhibitory compound produced by AS1 and KN4 inhibited Bacillus subtilis. Only the inhibitory compound produced by AS1 affected Candida albicans and Candida krusei. Analysis of variance indicated that there was a significant difference (P<0.05) in the susceptibility of the different target organisms to partially purified inhibitory compounds. Gram positive bacteria were affected more than yeasts. Proteolytic enzymes, trypsin and pepsin, but not catalase and α-amylase, completely inactivated antagonistic activity of the compounds demonstrating their proteinacious nature. The inhibitory compounds were fairly heat stable and also stable over broad pH ranges. The use of these or related GRAS isolates in the production of this and related beverage may increase the safety, shelf life and marketing appeal of such beverages Key words: Bacteriocins, lactic acid bacteria (LAB), target organisms, antimicrobial activity.
Highlights
Lactic acid bacteria (LAB) play essential roles in the fermentative production of many traditional foods
Spoilage and food-borne microorganisms used in this study were Staphylococcus aureus, ATCC 12600, Escherichia coli, ATCC 11775 obtained from Bioresources Development and Conservation Programme (BDCP) Centre, Nsukka
Agar) was incubated with approximately 5 × 107 cells/ml of target organism to be tested for sensitivity to LAB culture and overlaid on MRS agar plates on which LAB isolates were grown in triplicate
Summary
Lactic acid bacteria (LAB) play essential roles in the fermentative production of many traditional foods. In some parts of Africa, they play important parts in the production of alcoholic beverages and cereal based weaning formulae. Undesirable contaminants in some food products, LAB, through their fermentative activities exert a positive effect, imparting desirable flavours and inhibiting a variety of food spoilage and pathogenic organisms (Strom et al., 2002; Buddle et al, 2003). This study is designed to screen Akamu and Kununzaki (cereal based non-alcoholic beverages) widely consumed in Nigeria for bacteriocin-producing LAB and to examine the partially purified bacteriocins for their capacity to inhibit the growth of selected spoilage and food-borne pathogens
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