41-7 |
Effect of oxygen on the metabolic and biochemical behaviour of probiotic strains of Lactobacillus acidophilus and Bifidobacterium spp. |
A. Talwalkar and K. KAILASAPATHY. Centre for Advanced Food Research, University of Western Sydney, Locked Bag 1797, South Penrith Distribution Centre, NSW 1797, Australia Currently, the poor survival of probiotic bacteria such as Lactobacillus acidophilus and Bifidobacterium spp. in yoghurts limits their ability to confer therapeutic benefits in humans. Exposure to high amounts of incorporated oxygen in yoghurt can cause oxygen toxicity in these probiotic bacteria resulting in a decrease in cell viability. Little is known however, about the various effects of oxygen on the physiology of probiotic bacteria. In this study therefore, two Lactobacillus acidophilus and four Bifidobacterium spp. were grown in different concentrations of oxygen such as 0%, 5%, 10%, 15 % and 21% in a hypoxic glove box. The metabolic response of probiotic strains in the different oxygen environments was monitored by measuring the levels of lactate and estimating the lactate to acetate ratio. Biochemical changes induced by oxygen were examined by monitoring the specific activities of NADH oxidase, NADH peroxidase and superoxide dismutase. The ability to decompose hydrogen peroxide and the sensitivity of each strain to hydrogen peroxide was also determined. As the concentration of oxygen was increased stepwise from 0% to 21%, lactate levels in L. acidophilus reduced while the lactate to acetate ratio decreased in all the Bifidobacterium spp. All strains demonstrated an increase in the concentrations of NADH oxidase and NADH peroxidase. The rise in the ability to decompose hydrogen peroxide correlated well with the increase in the specific activity of NADH peroxidase. No change was observed in the sensitivity of the strains to hydrogen peroxide. Superoxide dismutase activities failed to demonstrate any conclusive trend. The knowledge gained from this study will help in devising techniques to increase the survival of probiotic bacteria in yoghurts so that they reach consumers in sufficient numbers in order to exert therapeutic benefits.
Session 41, Dairy Foods: Dairy microbiology
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