HOW 'PROBIOTICS' FIGHT FOOD-BORNE ILLNESS
By Beatrice Trum Hunter
From Consumers' Research Magazine. Issue : Dec.1993
Photo By Peter Beard
Food-borne illness caused by infectious pathogens has developed into an important health problem in our time. However, there are beneficial bacteria that can help prevent or mitigate the effects. In recent years there is growing awareness of beneficial bacteria, termed "probiotics" (from the Greek, "for life"). Interest is developing to utilize them for disease prevention and control.
Use of probiotic bacteria is not new, but long employed with dairy foods. In ancient times, the Roman historian, Pliny, recommended fermented milks to treat gastrointestinal infections. Early in this century, bifobacteria (the predominant intestinal organisms of breast-fed infants) were given to infants suffering from gastric upset in the belief that these beneficial bacteria would displace putrefactive ones which would displace putrefactive ones responsible for infantile diarrhea. During that same period, the Russian scientist, Metchnikoff, reported that consumption of large amounts of yogurt replaced toxin-producing intestinal bacteria, and would result in better health and extended longevity. All of these uses of probiotics in dairy foods depend on the action of live microorganisms, especially lactic acid bacteria.
Gradually, as probiotics have been examined, additional findings have been made about their beneficial effects in the digestive system. They help maintain the normal intestinal and urogenital microflora and help prevent infections.
Probiotics help prevent some food-borne illnesses. Both bifobacteria and lactobacilli inhibit common microbial pathogens, such as salmonella, campylobacters, escherichia, and shigella. The lactobacilli especially seem to inhibit pathogens in the urogenital tract, including prevalent Candida albicans.
In test tube experiments, L. acidophilus inhibited the growth of 27 different types of bacteria in lactic acid-free preparations. Ten of the bacteria were common pathogens.
In other studies, Salmonella typhi died within 30 to 48 hours in yogurt. Escherichia coli were unable to develop, Salmonella paratyphi and Corynebacteriae diphtheriae lost their pathogenic properties, and Neisseria meningitides and Vibrio comma lost their virulence.
Pathogenic bacteria are seldom recovered after being kept for two to four days in yogurt that contains from 1.65% to 2% lactic acid.
Probiotics help protect against infantile, traveler's and antibiotic-induced forms of diarrhea. A report from Canada noted that diarrhea developed in all newborn babies fed on regular cow's milk; none, on fermented milk.
Probiotics can help individuals who have too little or too much hydrochloric acid secretion in the stomach to normalize the level.
Probiotics in dairy products alleviate lactose intolerance. Lactose malabsorbers may tolerate fermented milk products, which contain less lactose than regular milk. Also some fermented milk products contain a form of lactic acid that is more easily metabolized than others.
L.acidophilus supplementation relieves chronic constipation. Although weeks, or even months, may be needed, ultimately beneficial results are achieved.
In supplement form, L.acidophilus has been reported to mitigate herpes simplex (an oral ulceration) within 48 hours.
Probiotics in fermented milk products boost the nutritional value of foods. For example, yogurt that contains live lactobacilli and bifidobacteria have increased biological value of protein, and increased levels of most B vitamins (folic acid, niacin, thiamine, riboflavin, and pyridoxine), and vitamin K. Fermented dairy products also may also increase the bioavailability of important mineral nutrients, such as calcium, zinc, iron, manganese, copper, and phosphorus. This improvement might be due to the lowering of the gastric pH by fermented foods.
Probiotic bacteria-containing dairy food products, including infant foods, are available commercially. Fermented milk products containing live L. acidophilus and Bifidobacterium bifidus are sold in many countries. Yogurts containing probiotic bacteria such as live S. thermophilius, L. bulgaricus and L. acidophilus are widely available. Some European countries, notably Germany, France, Switzerland, Denmark, Finland, Czech, and Slovakia, as well as Japan, sell numerous dairy products that contain strains of other probiotic bacteria. Some of these same European countries also sell pharmaceutical preparations that contain probiotics. Unfortunately, the United States lags far behind. However, some interest is developing.
In the Future
Researchers at Utah State University have been experimenting with starter cultures of L.acidophilus and B. bifidus to produce ice cream mixes. The researchers found that these bacteria survived freezing for as long as five months, thus ensuring that enough of the bacteria would survive passage to the digestive tract to bestow their helpful benefits. This product, if developed successfully, would differ from many commercial frozen yogurts now being sold, which do not have these bacteria to provide the benefits of yogurt. Some of the presently available frozen yogurts have not been fermented, and are more like soft-serve ice cream, with only 5% to 10% yogurt added to the ice cream mix.
Several studies have shown that B. bifidus helped rid the intestinal tract of harmful bacteria. As people age, the number of B bifidus naturally present in the intestinal tract decreases, and the number of harmful bacteria, such as clostridia, streptococci and coliform increases.
Apart from the long recognized benefits bestowed by probiotics in the digestive system, more recent investigations may hurtle probiotics into a wave of the future. A host of other health benefits may be offered by consuming fermented dairy foods.
Probiotics may help reduce high serum cholesterol levels. Organic acids (such as uric, orotic, and hydroxymethylglutaric) present in fermented milk, have been found to inhibit cholesterol synthesis. Also, some strains of lactobacillus and bifidobacteria deconjugate bile acids, which results in less absorption of cholesterol from the intestine.
In epidemiologic studies, the Masai people, who traditionally consume large amounts of saturated fat but also consume large quantities of fermented milk in their daily diet, were found to have normal cholesterol levels, and showed few signs of cardiovascular problems. (Another contributing factor to their good health may be their physical activity.)
Probiotics in dairy foods are credited with helping to prevent osteoporosis.
Probiotics can help reduce the side effects of hepatic encephalopathy, an advanced liver disease that also involves degeneration of brain function.
The immune system may be strengthened by lactic acid bacteria. By increasing the body's specific and non-specific immune mechanisms, lactic acid bacteria were found to offer protection against infections by enteric pathogens, such as the prevalent Listeria monocytogenes. ( See "Food for Thought," CR, November 1991.)
Live lactobacilli have been suggested for AIDS patients, to help inactivate the HIV virus.
Gamma-interferon is a substance that modulates immune function and helps prevent infections. Test-tube experiments showed that small amounts of live lactobacillus-containing yogurt produced three to four times as much gamma- interferon in humans' blood as heat-treated yogurt ( in which these valuable probiotic bacteria are killed.)
In human studies, individuals fed a diet supplemented with lactobacillus-lacking skim milk showed no increase of these immune system enhancers.. It was suggested that individuals who suffer from allergies might benefit from lactobacillus containing yogurt as a means of increasing anti-allergenic responses.
Probiotics exhibit anti-cancer activity, and they may help prevent cancers in the colon and bladder. In animal tests, lactic acid bacteria were found capable of suppressing tumor formation. It is difficult to extrapolate from animal tests to human experience, but cases have been reported in which prolonged therapy with L. acidophilus has made human colon tumors disappear.
Colon cancer has been related to the consumption of large amounts of red meat and saturated fats. However, the Finnish population appears to be an exception. Although Finns consume high levels of both red meats and saturated fats, they also consume large quantities of fermented dairy products such as yogurt, and other strains of probiotics in fermented milk, such as "ropa," "pimma," and "filla bima". These products may protect the Finns from colon cancer.
It has been reported that lactic acid bacteria can inactivate potent mutagenic compounds in food products, such as azo dyes used in some food colors, and nitrosamines which can form from nitrite preservatives. Also, lactic acid bacteria may reduce the activity of certain fecal enzymes in the colon that are capable of converting potential carcinogens into active ones.
Recently, a practical application of probiotics was suggested for restaurant use. By adding lactobacilli to Waldorf-type salad, and allowing the salad to ferment, its shelf -life was extended to five weeks. Untreated, such salad soon becomes contaminated with microorganisms and becomes unfit for consumption. The process, devised in the Netherlands at the University of Wageningen, made use of a naturally-occurring lactobacillus isolated from the water in which soy curd had been soaked. The bacteria were mixed with the salad dressing, allowed to incubate and then the salad with dressing was refrigerated. The lactic acid produced by the bacteria during the incubation period prevented the growth of other bacteria when the salad was held at refrigerated temperature. The fermentation delayed oxidation of the saturated fatty acids in the dressing's oil because the added bacteria consumed all of the oxygen. It is thought that the process would be suitable for salads in which thick dressings comprise at least 30% of the total bulk. The addition of cumin or oregano was found to be undesirable because they inhibit lactic acid bacteria growth.
Doubtless, additional benefits and practical applications will be discovered as probiotics are investigated more fully. Those in fermented dairy foods have been explored to some extent. The healthy benefits of probiotics in many non-dairy foods are largely unexplored. Traditionally, many non-dairy foods were fermented to improve their keeping quality, wholesomeness, and flavor. Along the way, it was discovered that fermentation also improved nutritional values by producing desirable enzymes, and by synthesizing some vitamins. Also, fermentation may result in a more favorable amino acid balance in some foods. Examples of beneficial, fermented, nondairy foods are sauerkraut and numerous soybean products.
Probiotics are but one group of naturally occurring substances that can be utilized for health benefits. Other groups include bacteriocins, antioxidants, and phytochemicals. All await further elucidation and applications for maintenance or improvement of human health.
The author, Beatrice Trum Hunter, MA, has written more than 30 books on food and environmental issues, frequently before widespread public awareness. She was food editor of Consumer's Research Magazine for more than two decades. She is an honorary member of The Price Pottenger Nutrition Foundation, as well as an honorary fellow of The International Academy of Preventative Medicine and an honorary member of The American Academy of Environmental Medicine. She has been the recipient of many awards, including The Jonathan Forman Award of The Society for Clinical Ecology, The New Hampshire Society for Preventative Dentistry, and The Donnon Pepper Humanitarian Award. She can be reached at 243 Falls Road, Deering, N.H. 03244