Efficacy of Some Chemical Preservatives in Prolonging the Shelf Life of Fermented Locust Beans ‘iru’

Abstract

In Nigeria most foods are preserved by adding salt. The efficacy of this and some other chemical preservatives in improving the storage quality of fermented locust beans was the focus of this study. Samples of fermented locust beans were separately treated with table salt (10% w/w), brine (10 and 20% solution), vinegar (4 and 6%) and lactic acid (10 and 20%). After treatment, all the samples were stored at ambient temperature and periodically analysed for sensory and microbiological properties. Samples treated with dry salt became slippery, changed in color and developed bad odor within 1, 4 and 14 days respectively. Except for the softening observed, no significant (p < 0.5) change occurred with the color and odor of the other samples during storage. A total of 29 bacterial and 6 fungal isolates were obtained. The dominant bacteria were members of the genera Bacillus, Staphylococcus, Pseudomonas, Micrococcus, Citrobacter, Microbacterium, Enterobacter, Leuconostoc, Arthrobacter, and Corynebacterium while Saccharomyces cerevisae, Aspergillus niger and other Aspergillus spp., dominated the fungal population. Other fungi were Rhizopus stolonifer, Alternaria alternata, and Candida albicans. The microbial load and diversity reduced significantly (p < 0.5) after treatment and during storage. Among the bacterial isolates, Bacillus cereus, B. pumilus, B. lentus, B. licheniformis, Staphylococcus epidermidis, S. saprophyticus Citrobacter freundii, Arthrobacter ureafaciens, Corynebacterium poinsetiae, Micrococcus denitrificans and Microbacterium sp. were inhibited by lactic acid, vinegar and brine with diameter zone of inhibition ranging from 11.0 to 24.0mm; 15.0 to 20.5mm and 12.5 to 22.5 mm respectively. This study has shown that lactic acid, vinegar and brine have some preservative effects on fermented locust beans and can therefore be used to prolong its shelf life.