from indigenous fermented foods and human gut ... - Thapar University

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Chapter II Review of Literature
2000). The consumption of yogurt and fermented milk containing lactic acid bacteria has
been proven to alleviate lactose indigestion symptoms because of the lower lactose content,
and its hydrolysis by microbial β-galactosidase (Gilliland and Kim, 1984; Mustapha et al.,
1997). This enzyme is sensitive to low pH and, therefore, bacteria surviving low pH protect
the enzyme from activity loss until it reaches its site of action, which is the small intestine
(Zarate et al., 2000).
On the other hand, bacteria sensitive to bile salts present a membrane with increased
permeability, which allows two events which may or may not be exclusive: one is the
transport of the substrate at higher rates into the bacterial cell, and the other one is the
increased release of the bacterial enzyme into the lumen. Probiotic bacteria, with higher
resistance to bile salts, release less amounts of enzyme into the lumen. Therefore, yogurt
starter cultures which do not survive the effect of bile, seem to be more effective in
alleviation of lactose intolerance (de Vrese et al., 2000).
Another desirable property of some probiotic strains is their ability to reduce
cholesterol levels (De Smet et al., 1998; du Toit et al., 1998). This property has been partly
related to bile salt hydrolase (BSH), which deconjugates bile salts by releasing the amino acid
(taurine or glycine) bound to the side chain of the steroid core. Deconjugated bile salts are
less soluble, and thus easily excreted via faeces, resulting in decreased reabsorption and
recirculation of bile salts into the liver. Consequently, more cholesterol is needed for de novo
synthesis of bile salts (Usman and Hosono, 1999). BSH activity has also been related to the
ability of some bacteria to survive bile and colonize the intestine (De Smet et al., 1995;
Klaenhammer and Kullen, 1999), but this hypothesis is controversial because others have
found that deconjugated salts are more toxic than their conjugated counterparts (Grill et al.,