Potential gut health benefits of synbiotics may be limited since only specific combinations enhance probiotic survival and growth, say researchers.
Three out of the five probiotics used in the research published in the Journal of Functional Foods could not utilise any of the three prebiotics used, showing growth of less than 20% compared to that seen with glucose.
Probiotic strains Lactobacillus acidophilus, Lactobacillus delbrueckii ss bulgaricus, Lactobacillus brevis, Lactobacillus acidophilus and Lactobacillus reuteri were used in the lab experiments. The UK researchers compared growth of these probiotics when coupled with prebiotics inulin, lactulose and lactobionic acid, ranking these results against a negative control of probiotics in the absence of a carbon source and a positive control of probiotics with glucose as the growth substrate.
The researchers concluded: “Ultimately synbiotic applications may offer advantages over probiotics alone; however careful consideration must be given to the synbiotic combinations if probiotic survival and growth and the associated health benefits are the desired outcomes.”
“Given the specificity of the synbiotic combinations and the relative high mutation rate of most bacteria species these combinations require constant re-evaluation to ensure efficacy of any synbiotic commercial preparation.”
They said a “key and surprising observation” was the poor utilisation of inulin as a carbon source by Lactobacilli species given the widespread commercial use of the sugar as a prebiotic.
The pros and pres
In order to colonise the colon, probiotics must survive the transition from the stomach – with the low pH of the stomach and the high concentration of bile acids in the colon being key obstacles in this process. Prebiotics have been shown to increase this survival rate – with synbiotics being the name given to the partnership of prebiotic and probiotic.
The researchers found lactulose was utilised by L. acidophilus and L. reuteri with growth comparable to glucose. Meanwhile the growth of L. reuteri in the presence of lactulose was significantly higher after 15 hours than growth in the absence of a carbon source and comparable to growth in the presence of glucose.
L. reuteri also grew well in lactobionic acid at 2.5%, however above 2.5% lactobionic acid decreased the culture medium pH below pH5, which significantly reduced the rate of cell growth. There was no growth of L. reuteri in the presence of inulin.
L. acidophilus significantly utilised lactulose in addition to glucose but minimally utilised inulin and lactobionic acid at concentrations up to 2.5% from 10 hours. Growth was not observed in 5% lactobionic acid as a carbon source again due to the pH being below five. L. acidophilus, L. delbrueckii ss bulgaricus and L. brevis could not effectively utilise inulin, lactulose and lactobionic acid as a carbon source.
The researchers noted that prebiotics have been thought to aid probiotic growth by changing the cell culture and the gastrointestinal tract pH. Yet they concluded that although lowering the colonic pH was an important growth-boosting mechanism of prebiotics, high concentrations of some prebiotics may decrease colonic pH below pH5 and this could have a negative impact on probiotic growth.
The researchers said: “In an attempt to determine the exact role of probiotics, prebiotics and synbiotics in human health, we demonstrated that prebiotics can have properties which are not dependent on their role with probiotics.”
They added: “These studies confirm that although some prebiotics may offer protection against bile acid toxicity the protection is limited and dependent on the nature of bile acids.”
Source: Journal of Functional Foods
Published online ahead of print, DOI: 10.1016/j.jff.2014.05.010
'Synbiotics: the impact of potential prebiotics inulin, lactulose and lactobionic acid on the survival and growth of lactobacilli probiotics'
Authors: O. Obasola Adebola, O. Corcoran, W. A. Morgan