Fundamental Food Microbiology, Third Edition - Fuad Fathir

INTESTINAL BENEFICIAL BACTERIA 217
Figure 15.1 (A) Cells of an adherent strain of Lab. acidophilus are associated with the calf
intestinal epithelial cells. (B) Cells of a nonadherent strain of Lab. acidophilus
remain uniformly distributed and do not show adherence to epithelial cells from
the same source.
stomach acid and bile salts and lysozyme in the intestine. In studies, it may be better
to use cells grown for 16 to 18 h and maintained before feeding under conditions
that retain their maximum viability.
D. Dose Level and Duration
Consumption of large numbers of live cells (10 9 per day), that are not stressed, over
a period of time (ca. 14 d) is advocated to obtain benefit. Use of preparations that
have low levels of viable cells, many of which could be stressed, cannot provide
expected results. Many products that are currently marketed do not have the needed
level of viable cells to produce beneficial effects (Table 15.1). Some products also
have bacteria that are associated with improper sanitary practices.
E. Induced Lactase Trait
In Lab. acidophilus, lactase is an induced enzyme. To study the lactase effect, strains
should be grown in lactose-containing media. In commercial preparations, a strain
may be grown in glucose and thus not have lactase when consumed.
F. Antibacterial Substances
Many studies have reported that strains of beneficial intestinal bacteria produce
metabolites that are active against many Gram-positive and Gram-negative bacteria.
Some of these were identified, such as several bacteriocins, organic acid, and reuterine.
Other substances need to be identified and examined in purified form for
their antibacterial effectiveness.
G. True Species and Strains
Many species and strains used by many probiotic food producers do not have either
proper identity or information of original sources. Also, many species that were
previously regarded as Lab. acidophilus have been found to be different species,
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