Put simply, probiotics are good bugs in the battle against bad bugs. When they are around in the human gut, for example, they have a knack of keeping harmful microbes at bay.
Probiotics have existed for thousands of years, notably in fermented foods, but biotechnology has facilitated their generation in greater numbers and provided some key insights into how they work.
It has opened up an exciting new front in preventive medicine and nutrition, even if the science and potential benefits have yet to be fully evaluated. A research initiative between scientists at Teagasc's Dairy Research Centre at Moorepark in Co Cork and NUI Cork has, however, shown that cheese is a highly effective probiotic food.
The majority of probiotic food products already on the market are generally consumed within days or weeks of manufacture, such as fermented milks and yoghurt. "When considering cheddar cheese as a probiotic food, however, the relatively long ripening time of six months to two years means the probiotic organism must be able to survive and/or grow long after the time of manufacture," explained Teagasc's research officer in dairy quality, Dr Catherine Stanton.
Using a Lactobacillus strain, they have shown that the probiotic can survive to a level of 100 million cells per gram, which suggests that cheese is as good a vector as other traditional probiotic foods, if not better, she added. The effectiveness of probiotic cheeses using lactobacillus and enterococcus strains was evaluated in feeding trials using pigs which have a digestive system similar to humans.
Prof Gerald Fitzgerald of the Department of Microbiology and National Food Biotechnology Centre in NUI Cork has been investigating the suitability of particular strains in dairy products and how probiotics work, research begun by his colleague, Prof Kevin Collins. Teagasc has then used these strains in specific products, with Ms Gillian Gardiner carrying out significant work on the potential of cheese as a carrier of the good bugs.
Probiotics have an ability to get to the intestinal tract and overcome the body's protective hurdles, such as the acid environment of the stomach and bile secreted by the liver which breaks down fats. The microbes have demonstrated ability to adhere to epithelial cells lining the intestinal wall.
Once there, they colonise the gut and display antibiosis activity, i.e. they inhibit harmful bacteria by a process of "competitive exclusion".
This happens through their production of waste by-products such as lactic acid, acetic acid and inhibitory peptides. Strains are tested for immunological effect, such as an inflammatory response. Those used in the probiotic cheese do not cause any such problem.
The main benefits that have been claimed for probiotics include antitumour properties; reduction in blood cholesterol; improved lactose digestion; relief from constipation; stimulation of immune function; improved resistance to gastrointestinal infections; vitamin production; and reduction of undesirable antibiotic effects.
Prof Fitzgerald stressed that probiotics are only as good as the science-supported claims which can be proved for them. In the case of cholesterol, for instance, some scientists are sceptical. Based on the amount of published evidence he believes that case is "not proven yet". Unfortunately, some of the early scientific evidence on these "novel foods" was quite shoddy, he added.
Dr Paul Ross, head of dairy quality at Moorepark, said that marketing was just as important as health claims that are endorsed by clinical medical research of high standard. A low-fat probiotic cheese was produced in Britain but is believed to have failed because of poor marketing.
The Teagasc-NUI Cork research shows probiotics can be introduced in standard cheese-making with little extra cost. A small inoculation leads to growth at high levels over the maturation process. The organism is kept "in suspended animation" until eaten.
The work has advanced to the point of commercial trials, probably later this year. While the home market for probiotics is in its infancy, it is a huge multi-million-pound business in Germany, Japan and the US.