Effects of Some Physicochemical Conditions on the Growth and Histamine Production by Enterococcus Isolates from Fermented Pentaclethra macrophylla (Oil Beans) in Nsukka, Nigeria http://www.doi.org/10.26538/tjnpr/v7i12.49

Abstract

Enterococci are among the most common bacterial contaminants of fermented oil beans. Their activities result in undesired products such as histamine, the accumulation of which leads to food poisoning. This research aimed to determine the effects of physicochemical environments for growth and histamine production by Enterococcus species and ways of preventing histamine accumulation through modification of such environments. Histamine-producing Enterococcus species isolated from fermented oil beans were cultured in Niven’s broths with different pH and Sodium Chloride concentrations at different temperatures. Growth rates in each broth were determined by direct counts of bacterial cells. Histamine productions were measured indirectly by measuring pH changes with time in each broth. Statistical significances of the effects of these parameters were determined at 95% confidence interval. All the species grew at different pH used, with optimum growth observed between pH of 5 and 6. Histamine production was favoured by lower acidic pH. Different growth rates were recorded at different temperatures with optimum growth occurring at about 37oC. Growths were more rapid at Sodium Chloride concentrations of 0.5% and 1% and slowed down as concentration increased to 5% and 10%. These growth rates also had direct correlations with histamine production, with highest levels of histamine detected in the media with highest bacterial counts. The activation of histidine decarboxylase gene was a function of pH. The resulting enzyme activities were influenced by temperature and pH while bacterial biomass determined the enzyme concentration. Therefore, growth and histamine production were influenced by the interdependence of these biological factors.