Fundamental Food Microbiology, Third Edition - Fuad Fathir

214 FUNDAMENTAL FOOD MICROBIOLOGY
reduced amounts of lactose in yogurt, as compared to milk, and to the supply of
lactase from the dead cells. In contrast, the intestinal bacteria, especially some
Lactobacillus species, could, under proper conditions, colonize the small intestine
and subsequently supply lactase. Different studies, however, did not unequivocally
prove the desired benefits, probably because of differences in study methods, including
the use of strains that lack b-galactosidase, use of strains that are not host specific,
use of species that are not of the intestinal type or unable to adhere to the intestine,
use of preparations with low viable cells, and lack of expertise in microbiology and
gastroenterology research.
B. Reducing Serum Cholesterol Level 1,4–6
Consumption of fermented dairy products (some containing unknown microorganisms)
and high numbers of live cells of beneficial intestinal bacteria has been
associated with low levels of serum cholesterol in humans. This is attributed to
two possible factors. One is the ability of some intestinal lactobacilli to metabolize
dietary cholesterol, thereby reducing amounts absorbed in blood. The other possibility
is that some lactobacilli can deconjugate bile salts and prevent their
reabsorption in the liver. The liver, in turn, uses more serum cholesterol to synthesize
bile salts and indirectly helps reduce cholesterol level in serum. However,
results of several studies by different researchers do not always favor this hypothesis.
Again, this can be due to differences in experimental design, such as use of
strains that do not metabolize cholesterol or deconjugate bile acid, and other
reasons described before.
C. Reducing Colon Cancer 1,4–6
Many of the undesirable bacteria in the colon have enzymes that can activate
procarcinogens, either present in food or produced through metabolism of undesirable
bacteria, to active carcinogens that, in turn, can cause colon cancer.
Beneficial intestinal bacteria, both Lactobacillus and Bifidobacterium species, by
their ability to control growth of undesirable bacteria in the colon, can reduce
the production of these enzymes. Also, beneficial bacteria, by increasing intestinal
peristaltic activity, aid in regular removal of fecal materials. This, in turn, lowers
the concentrations of the enzymes and carcinogens in the colon and reduces the
incidence of colon cancer. Several studies have shown that oral consumption of
large numbers of live cells of the beneficial bacteria reduces fecal concentrations
of enzymes such as b-glucuronidase, azoreductase, and nitroreductase of undesirable
colon bacteria. However, the relationship between reduction of these
enzymes and reduction in colon cancer from the consumption of beneficial intestinal
bacteria has not been studied, and thus contributions of these bacteria in
controlling colon cancer are not clearly known. Animal studies have shown that
formation of aberrant crypts, considered to be putative precancerous lesions, is
reduced by consuming live cells of beneficial GI tract bacteria, especially bifodobacteria.
Again, the results are not consistent, which could be due to the factors
listed before.