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Lactobacillus acidophilus

by Faro Jones

Tuesday, July 27, 1999

Lactobacillus acidophilus and other lactic acid bacteria are important in the fermentation of many foods from dairy products to fruits and vegetables. Fermentation occurs when bacteria break down sugars and carbohydrates to produce alcohol, carbon dioxide and lactic acid (Vela, 1997). These by-products are responsible for the unique taste of fermented foods and help preserve and increase palatability.

Currently new research suggests that there are alternative ways of using lactic acid bacteria, most notably the species L.acidophilus . The research shows that L. acidophilus can also be used as a probiotic or living organism, which upon ingestion in certain numbers, exert health benefits beyond inherent basic nutrition (Wood, 1992). There is still need for more research in this area, but L. acidophilus is linked to decreased instances of vaginal yeast infection, gastrointestinal dysfunction and even boosting immune function.

In this paper I will go over some general facts about lactic acid bacteria. I will then show how L. acidophilus is used in the dairy industry and finally I will go over some of the new health claims and research associated with L. acidophilus.

Family: Lactic Acid Bacteria

L. acidophilus is a member of one of the eight main genera of lactic acid bacteria. The genera, Lactobacillus, Streptococcus, Lactococcus, Leuconostot, Bifidobacterium, Carnobacterium, Enterococcus and Sporolactobacillus can then be divided into species, subspecies, variants and strains. Each genus and species have different characteristics but they are generally chained cocci or rod shaped gram (+), nonmotile, nonsporulating bacteria that produce lactic acid as a major or sole product of fermentative metabolism (Salminen & Wright, 1993).

Lactic acid bacteria use lactose as their main source of carbon to produce energy. Lactic acid bacteria use energy to transfer lactose (main sugar of milk) through their cell membrane. The lactose is metabolized to lactic acid and in some species also acetic acid, ethanol and carbon dioxide. Lactic acid bacteria that only produce lactic acid as an end product are called homofermentative; those that also produce acetic acid, ethanol and carbon dioxide are termed heterofermentive. The by-product of this reaction is energy that the bacteria use for growth. The end products of fermentation ultimately change taste and texture of food.

Genus: Lactobacillus

There are many species of Lactobacillus bacteria that are found in a variety of environments, from dairy products to the human gastrointestinal tract (GI). Species of Lactobacillus that have been isolated from the GI tract are, L. acidophilus, L. fermentum, L. plantarunm, L. brevis, L. caesi, L. leichmanii, and L. mintus.

Lactobacillus are able to live in highly acidic environments of pH 4-5 or lower. This pH is well below the pH other lactic acid bacteria can live in and because of this, Lactobacillus is responsible for the final stages of fermentation in products.

Species: L. acidophilus

L. acidophilus is probably the best well-known species of Lactobacillus . L. acidophilus is naturally found in the human and animal GI tract, mouth and vagina. It can also be found in certain dairy products and freeze dried in capsule and tablet form in grocery and health food stores.

L. acidophilus is characterized as being a rod shaped motile bacteria grows in or without the presence of oxygen. L. acidophilus is also characterized as a homofermentative that only produces lactic acid as its sole product.

Dairy Industry

There are many types of fermented dairy products that use L. acidophilus . The most familiar to Americans are sweet acidophilus milk and yogurt. Sweet acidophilus milk is consumed by individuals who suffer from lactose maldigestion and intolerance, a condition that effect approximately 75% of the worlds population (Wardlow, 1999). Maldigestion and intolerance occurs when enzymes (lactase) cannot break down lactose or milk sugar in the intestine. Failure to digest lactose results in discomfort, cramps and diarrhea.

Sweet acidophilus milk is made by inoculating milk with the L. acidophilus bacteria. After inoculation, the milk sets for 24 hrs. and yields a type of buttermilk that has a low content of lactose (Vela, 1997). L. acidophilus is also used in the preparation of yogurt. L. acidophilus along with other lactic acid bacteria are added to milk to decrease the pH. When milk becomes acidic, proteins in the milk break down and coagulate to form a gel (Vela, 1997).

Nutritional Supplementation

L. acidophilus can be found in many natural health stores and grocery stores around the country. It is primarily found in 470-1000mg capsules, 2.5 billion-14 billion live cells of bacteria. The natural health industry claims that L. acidophilus is a probiotic or 'friendly' organism that helps the body fight disease and restore health. There are an enormous amount of health claims associated with taking L. acidophilus , these claims vary from relieving constipation to killing deadly strains of E.coli and Salmonella (Wood, 1992). I will focus on L. acidophilus effect on vaginal yeast infections, the immune system and GI system.

Many health food stores and manufacturers claim that taking regular doses of acidophilus or eating yogurt high in L. acidophilus will decrease the presence of vaginal yeast infections in women. Research findings are inconsistent and few in numbers. It is known that L. acidophilus is already present in the vagina of healthy women and important in maintaining pH. However, it is not known if eating products high in L. acidophilus or taking acidophilus tablets have an effect on microflora of the vaginal tract.

Another health claim is that L. acidophilus can help maintain a healthy balance of intestinal flora by increasing acidity of the intestine, killing off harmful bacteria. Research suggests that there may be some validity to this claim. In one of the many research reports on L. acidophilus and gastrointestinal tract health, L. acidophilus was demonstrated to have anti-microbial effects against pathogens and fungal microorganisms (Buttris, 1997). Also since L. acidophilus is able to survive in environments of pH 4-5 or below, it is able to survive the harsh conditions of the stomach and pass through to the small intestine.

Lastly manufactures claim that eating foods high in L. acidophilus , or taking supplements, boost your immune system. Again research is inconsistent in this area. Some research claims that L. acidophilus enhances acrophage and lymphatic activity, in other words, boosting your immune system (Takahashi et al., 1993). Other research gives inconclusive data (Tejuda et al., 1999).


You may be wondering why manufactures are making these claims about L. acidophilus supplements when the research on it so varied. According to the Food and Drug Administration (FDA), unlike health claims, nutritional support statements need not be approved by FDA before manufactures market a product. Also these health claims are generally very vague, usually only linking intake to a possible decrease in disease. H3>Conclusion

L. acidophilus is one of the more popular species of lactic acid bacteria. It is used in the preparation of fermented dairy products like acidophilus milk and yogurt. Currently, new research is underway to test the health benefits associated with taking L. acidophilus supplements. Many manufactures of this supplement link intake of L.acidophilus with a decrease in certain diseases, like yeast infections, gastrointestinal distress and low immune activity. However, there needs to be more research in this area before their claims are substantiated.

References cited

Buttris, J. 1997. Nutritional properties of fermented milk products. International Journal of Dairy Technology 50(1):21-27

Salminen, S. and Von Wrigh, A., ed.1993. Lactic Acid Bacteria. Marcel Dekker Inc, NY

Takahashi et al. 1993. BioScience-Biotechnology and Biochemistry. 57(9):1557-1560 Tejuda et al. 1999. Effects of Lactobacillus spp. On cytokinan production of RAW 264.7 macrophage and El-4 thynoma cell lines. Journal of Food Protection.62(2);162-169

Vela, G. 1997. Applied Food Microbiology. Star, CA

Wardlow, G.M. 1999. Perspectives in Nutrition. Mcbraw-Hill, Boston

Wood, B.J, ed. 1992. The lactic acid bacteria in health and disease. El Sevier Appied Science, London

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