Professor Bob Rastall, head of the department of food biosciences at the University of Reading, UK, was speaking at Pre-& Probiotics 2012, a virtual conference and expo organized by NutraIngredients-USA and NutraIngredients last week.
Pectin-derived oligosaccharides: ‘We have quite a lot of scope here’
He said: “We are looking at novel candidate prebiotics from biomass and I think this is a potentially attractive thing to do particularly in the context of sustainable production.
“We are quite interested in seeing whether we can turn this concept into reality of bio-refining functional food ingredients.
“We have been doing some work evaluating polysaccharides you might find in biomass sources… We’ve been dissecting pectins using enzymes and chemical approaches and testing out the different fractions [oligosaccharides].
“We see a much more selective type of fermentation with these than with the parent pectins.”
Some of the most encouraging results were from oligoarabinosidesand oligogalactosides – which both generated significant increases in bifidobacteria and bacteroides prevotella in recent tests conducted at the University of Reading - he said.
“So maybe what we need to do is look for sources of pectins that are rich in arabinans and galactans and consider those as candidate prebiotics... Think of the different biomass sources available to use and we have quite a lot of scope here.”
Resistant starch and polydextrose
Right now, he said, there was good quality human data behind four classes of prebiotics: inulin, FOS (fructo-oliggosaccharides), GOS (galacto-oliggosaccharides), and lactulose.
A second tier of potential candidates with “varying degrees of evidence behind them” included polydextrose, lactosucrose, resistant starch, gentio-oligosaccharides, xylo-oligosaccharides, isomalto-oligosaccharides, soybean oligosaccharides, he said.
Of these, xylo-oligosaccharides could “probably be considered” to be genuine prebiotics, he said, while the jury was still out on resistant starch and polydextrose.
“There is accumulating data around resistant starches, but I don’t think we have enough consistent data from good quality human trials with molecular-based microbiology. There is data in animals and gut model systems that is promising, but I don’t think it comes together to form a convincing argument.
“However, I wouldn’t be at all surprised if we were to consider certain resistant starches as prebiotics in the future. We’re doing work on this at Reading at the moment.”
As for polydextrose, he said: “Polydextrose is an excellent dietary fiber, but I am not personally convinced it is a prebiotic”.
Rastall said he was “quite excited” about oligodextrans, with recent in batch culture tests showing lower molecular weight varieties had good bifidogenic effects, while higher molecular weight varieties had positive effects on the ratio of propionate to acetate (short-chain fatty acids), a factor believed to be important in lipid metabolism in the liver.
He added: “Maybe these will be promising prebiotics when they are tested in humans?”
Molecular decoys: Prebiotics and anti-adhesive activity
Meanwhile, novel prebiotics that could act as “molecular decoys” also had great potential, he said.
“It is well-known that lots of pathogenic bacteria bind to oligosaccharide structures on cell surfaces, so the idea is maybe we could perhaps manufacture oligosaccharides and use them as molecular decoys such that pathogens will bind to the oligosaccharides in the food ingredients rather than to the ones on your cell surfaces.
“This is another aspect of prebiotic functionality that we can consider when asking the question, is something a prebiotic or not?”
Can we extend prebiotic concept outside of the gut?
More generally, he said: “I think the future is good for prebiotics but we need to understand the fermentation properties of carbohydrates in much more detail.
“We need to acquire a structure/function understanding in my view and we need to understand why some carbohydrates seem to stimulate bifidobacteria and lactobacilli and others don’t. Then we need to go beyond that and look at effects on metabolism.
“We also need more data on the health consequences of prebiotics and more good quality human studies with clear health outcomes and I think these need to be coupled with mechanistic studies if we are going to try and address the question of whether we can have a cause and effect relationship.”
Meanwhile, there was “no reason in principle” why we shouldn’t extend the prebiotic concept outside of the gut, he added.