These two wonderful articles
written by Cathy J. Saloff-Coste
grains are a complex and specific mixture of bacteria and yeasts held together
by a polysaccharide matrix. The lactic acid bacteria and yeast fermentation
of milk results in the production of numerous components, including lactic
acid, CO2, a small amount of alcohol, and an array of aromatic molecules,
all of which provide kefir with its unique organoleptic properties. Many
health benefits related to the consumption of kefir have been observed,
but rigorous research using modern scientific methods is in its early stages.
Kefir distinguishes itself from the more known fermented milk yogurt in that it is traditionally made only from kefir grains which contain a complex mixture of both bacteria and yeasts. The resulting kefir possesses unique organoleptic characteristics. Research on its health benefits is just beginning, and there remain many questions unanswered.
Two types of kefir exist: sugary, a fermented sweetened water; and milky,
a fermented milk beverage. This article addresses the milky variety, whose
norm has been established by the International Dairy Federation (2) , and
it will provide an overview of its characteristics and a discussion of
its potential health benefits.
Characteristics and consumption
kefir is just being discovered in some areas of the world, it has been
very popular in the former Soviet Union, Hungary, and Poland for many years.
In the former Soviet Union, kefir accounts for 70% of the total amount
of fermented milk consumed (4). It is also well known in Sweden, Norway,
Finland, and Germany (5) , as well as in Greece, Austria, Brazil, and Israel
(6). It is currently available in the United States, primarily as an ethnic
drink, and is growing in popularity in Japan.
The overall organization of microorganisms of grains is not completely
elucidated. More than a thousand years of consumption have demonstrated
that the microorganisms in kefir are not pathogenic. Even further, milk
inoculated with grains can suppress the growth of some pathogens such as
Salmonella or Shigella (1) . The grain matrix is composed of a complex
of 13% protein (by dry weight), 24% polysaccharide, plus cellular debris
and unknown components (6) . The principal polysaccharide is a water-soluble
substance known as kefiran. Several homofermentative Lactobacillus species
including L. kefiranofaciens and L. kefir (9-11) produce this polysaccharide.
They are an integral part of the grain, and without their presence, kefir
grains cannot be propagated. The mechanism, however, is not fully understood.
Fabrication of kefir
1. Traditional process
A second method, known as the "Russian method", permits production of kefir on a larger scale, and uses a series of two fermentations. The first step is to prepare the cultures by incubating milk with grains (2-3%), as just described. The grains are then removed by filtration and the resulting mother culture is added to milk (1-3%) which is fermented for 12 to 18 hours (6). Several problems associated with traditional kefir have led to a more modern method of production. The traditional method produces only small volumes of kefir, and requires several steps, each additional step increasing the risk of contamination.
In addition, the grains themselves are not well understood, and are not well controlled. Strong pressure from the CO2 gas content can lead to the explosion of the recipient unless appropriate containers which resist the escaping of gas are used (14). Finally, the shelf-life of traditional kefir is very short, less than three days.
2. Recent process
3. Current areas of research
Two basic procedures for manufacturing kefir have been developed using
pure cultures isolated from kefir grains. Milk can be inoculated simultaneously
with lactic acid bacteria and yeast, or it can undergo two fermentations,
the first with lactic acid bacteria and the second with yeast. Results
have been encouraging, but finding the right equilibrium of bacterial and
yeast strains to create a product with the characteristic properties of
traditional kefir including both the organoleptic qualities and the health
benefits - is a difficult task. The major difficulty is understanding the
microbiology of kefir.
chemical, and nutritional composition of kefir
Diacetyl is produced by Str. lactis subsp. diacetylactis and Leuconostoc
sp. (7). The pH of kefir is 4.2 to 4.6 (19). As in yogurt, the lactose
content is reduced in kefir (14), and the b-galactosidase level is increased
as a result of fermentation. Information on vitamin and mineral content
is limited and sometimes contradictory, but overall, there do not seem
to be significant variations from that of the milk used. There is also
a small increase in proteolysis, leading to an increase in free amino acids
Health properties of
Various research teams around the world have reported encouraging results, but several methodological difficulties still need to be resolved. Most studies to date have been performed in vitro or using animal models, and human studies are not available. Further, the effects of kefir grains or their isolates are often studied, rather than the product kefir, and there is no evidence that the observed effects would occur using the drink itself. Also, kefir products vary significantly according to the composition of the grains used and even according to the region in which it is made, and therefore specific effects may not be demonstrated in all kefirs. Given these caveat, a variety of health benefits are being investigated. Table 3 presents recent studies using kefir products.
Several studies have investigated the antitumor activity of kefir (20, 23, 24) and of kefir grains (25, 26) . Specific cultures isolated from kefir were also shown to bind to mutagenic substances such as indole and imidazole (27, 28). Immune system stimulation with kefir (24) and with sphingomyelin isolated from the lipids of kefir (29) have been demonstrated in both in vitro and in vivo studies.
Kefir (30) possesses antimicrobial activity in vitro against a wide variety
of gram-positive and gram-negative bacteria (20, 31), and against some
fungi (20) . In Zacconi et al.ís recent study (30), the antagonistic effects
of kefir against Salmonella kedougou were attributed to the complexity
and vitality of the kefir microflora. De Vrese et al . (32) demonstrated
that fresh, but not heat treated, disintegrated kefir grains suspended
in kefir directly enhanced intestinal lactose digestion in minipigs. This
effect was attributed to microbial b-galactosidase activity of kefir.
The above studies provide encouraging results, but much more research is
necessary in order to demonstrate similar effects using kefir in humans.
Further, a standardized, well-defined product must be used in order to
provide useful information.
Azoreductase,§-glucuronidase, glycocholic acid hydrolase, nitroreductase: colonic enzymes implicated in the conversion of procarcinogens to carcinogens. LDL/HDL: ratio between blood levels of low density lipoprotein and high density lipoprotein; level above 3 indicates increased risk of cardiovascular disease. Breath hydrogen test: measurement of hydrogen expired after oral lactose load of 12-50 g compared to base level; > 10-20 ppm indicates malabsorption.
From legend to science: Historical
Scientific interest began much later, in the early twentieth century, when Elie Metchnikoff, a Nobel-prize winning biologist at the Pasteur Institute in Paris, first suggested that lactobacilli might counteract the putrefactive effects of gastrointestinal metabolism (1). In the past twenty years, scientific research has blossomed, with an interest in topics ranging from antimicrobial effects to reduction of risk of cancer. Much valuable preliminary work has been done using animal or in vitro models, which allow for much greater control over variables than when studying humans, and which offer reproducible results. These models are also useful for studying the mechanisms involved.
Studying the effects of FM on humans presents several challenges. Fermented
milksare unctional foods, and as such, their impact on human physiology
is of a small amplitude and not easily detected. Also, early humans studies,
though numerous, were generally case reports rather than modern experimental
studies (randomized). Currently, researchers are beginning to address these
Yogurt, the ever-popular
1. Milk digestibility
2. Recovery from diarrhea
3. Immunomodulating effects
4. Reduction of risk of cancer
5. Blood cholesterol levels
Kefir, another traditional
Many health benefits have been traditionally reported. Kefir has been used for the treatment of Atherosclerosis, allergic disease, and gastrointestinal disorders, among other diseases (28). Until recently, most research has been limited to studies lacking modern statistical practices or to reports written up in Slavic languages, rendering them inaccessible to most western scientists.
Recent studies have investigated antibacterial (29), immunological (30), antitumoral (31), and hypocholesterolemic(32) effects of kefir consumption on animals. Results suggest potential benefits. Fresh, but not heat-treated grains in kefir enhanced intestinal lactose digestion in minipigs (33). While awaiting more research, it is important to remember that kefir, like yogurt, has been and continues to be a part of the regular diet in central and eastern Europe for centuries. Bifidobacterium: a natural inhabitant of the intestines Bifidobacteria were first described in 1900 by Tissier (34) . Since that time, their classification has evolved continually, and currently includes around thirty species (35, 36) . In general, they are strictly anaerobic, Gram-positive rods which often have special nutritional needs and grow slowly in milk. Very few strains are adapted well enough to milk that they both grow in sufficient numbers and survive well throughout the shelf-life of the FM.
Although bifidobacteria produce both lactic acid and acetic acid as major end-products of metabolism (heterofermentative), many microbiologists consider them to be lactic acid bacteria, albeit a special case. Tissierís hypothesis almost 100 years ago that bifidobacteria might have health benefits(37) was based on the following observations. Bifidobacteria are normal inhabitants of the human intestinal tract throughout the life cycle, beginning just days after birth. Further, they are often the predominant microorganism in the gut of breast-fed infants. It has since been shown that breast-fed babies are less at risk for diarrheal disease than formula-fed infants (38). In addition to the above inherent characteristics of bifidobacteria, some strains of the micro-organism survive intestinal transit in sufficient numbers to exert a metabolic effect in the gut (39,40).
1. Effects on the intestinal microflora
2. Effect on mild constipation
3. Prevention of diarrhea
4. Immunomodulating effects
Lactobacillus casei: new interest in an old bacteria
The group L. casei consists of several species of facultatively anaerobic and hetero-fermentative, mesophilic lactic acid bacteria(48). Their metabolism provides organoleptic qualities to several traditional FM and cheeses, and more recently, to new fermented milks. L. casei have been detected in the feces of both infants (49) and adults (50). Their ability to survive transit through the intestinal tract in adequate numbers to have a physiological effect (50) , coupled with their potential health benefits make L. casei an ideal candidate for a probiotic.
1. Treatment of diarrhea
2. Effects on the intestinal microflora
3. Immunomodulating effects
In addition, consumption of L. acidophilus has led to modifications of various parameters of the immune system (46), and to a decrease in several fecal enzymes associated with colon cancer (66). Less well-known bacteria include Lb. helveticus (67), L. plantarum(68) , and L. reuteri (69). These lactic acid bacteria have different microbiological and metabolic characteristics than the ones listed above, but may also exhibit health effects, such as stabilizing the intestinal microflora or reducing the duration of diarrhea.
Probiotic effects of lactic acid bacteria and FM can be categorized in the following way: effects on the small intestine and digestion, direct modification of the colonic microflora and its metabolism, and general effects initiated in the colon. Thus, yogurtís main health benefit is related to improved lactose digestion; while bifidobacteria primarily affects the balance of the colonic microflora; and kefir and L. casei provide more global benefits, the first in relation to its antimicrobial effects and the second to diarrhea. In all cases, the lactic acid bacteria must be present in the FM in very large numbers, and must be live and active. Not all effects have received as yet adequate scientific attention. Few studies have compared various types of FM. As more research is performed using human subjects and with rigorous methodology and statistically valid conditions, the variety of health benefits of FM will become more well-defined.
Amidst the plethora of sometimes contradictory evidence, it is important to remember the nutritional and organoleptic qualities of yogurt and kefir that make them both healthful and pleasant choices in a balanced, varied diet, regardless of probiotic effects. The probiotics discussed in this report are incorporated in FM because of health benefits beyond inherent nutrition, and are appropriate for individuals with specific health goals. Taken together, they represent the best of both tradition and modern science; FM and probiotics have journeyed from nutrition practice to nutrition science and back again.
These two wonderful articles were written by Cathy J. Saloff-Coste from Dannone at their website www.dannone.com
**Copyrights 2000 Raw Health & Kris A. Pletschke **
Permission required to reduplicate content on rawhealth.net