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Scientific
Publications - Work Done by Microbiology Reader
K. Hallamaa, M. Saarela, J. Mättö, and T. Mattila-Sandholm, The Effect of Lactose Derivatives o n the Technological and Probiotic Properties of Selected Lactobacilli, ASM 2002 Poster, 1p, VTT Biotechnology, Finland
INTRODUCTION Probiotic bacteria are defined as live microorganisms that are beneficial to human health. Lactulose, lactitol and lactobionic acid are compounds that can be produced from lactose (or whey) and which, unlike lactose, are not absorbed in the small intestine of lactose-absorbing subjects. Thus, all these compounds have a potential to function as prebiotics, substrates that promote the growth of beneficial microbes in the large intestine. The aim of the present study was to investigate the ability of lactobacillar strains to utilize lactose derivatives in different growth conditions and to determine how lactose derivatives effect the stability and different characteristics of the potentially probiotic strains.
METHODS To study the ability of lactobacillar (Table 1) strains to utilize lactose derivatives, carbohydrate-free MRS was used as a basal growth medium and it was supplemented with 0.5, 1, or 2 % of lactulose, lactitol, lactobionic acid, glucose, galactose, or lactose. Carbohydrate utilization was studied by measuring the turbidity and pH of the cultures after 2 days incubation and by automated turbidometry (Bioscreen C system). The strain properties investigated were acid and bile tolerance, antimicrobial activity against selected pathogens (studied by automated turbidometry), stability in milk as fresh / freeze-dried cells during storage at 4ºC, and growth during yogurt fermentation.
Table 1. The bacterial strains used in this study Table 2. The carbohydrate utilization of studied strains Figure 1. Bile and acid tolerance of the strains after growth with glucose, lactulose, or lactitol.
RESULTS The results of kinetic experiments (Table 2) showed that lactulose was the best-utilized lactose derivative and it was chosen as a substrate for further studies where different probiotic and technological properties were investigated. No significant differences were observed in antimicrobial activity of the strains against Escherichia coli, Staphylococcus aureus, Salmonella typhimurium, Candida albicans, and Candida krusei when the lactic acid bacteria were grown with glucose or lactulose as a main fermentable carbohydrate. In both cases the growth of E. coli, S. aureus, and S. typhimurium was inhibited and the growth of C. albicans and C. krusei was enhanced by the growth medium filtrates of lactic acid bacteria. Lactic acid control sample had similar effects to the indicator strains than LAB growth medium filtrates, so the observed effects were probably caused by organic acids produced during bacterial growth. Lactulose did not have an effect on the stability of fresh or freeze-dried cells in milk during storage at 4ºC or during yogurt fermentation as compared with the results obtained without lactulose supplementation.
CONCLUSIONS * Lactulose proved to be the best utilized lactose derivative for the strains in
growth studies and fermentation end-product analysis when lactitol, lactulose,
or lactobionic acid were used as fermentable carbohydrates.
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