Chemistry Reference
In-Depth Information
utilized for food preservation. Currently, there is a greater consumption of processed
foods in addition to a sterile food supply, and the ingestion of food-based pre- and
probiotics has become more limited.
13.2 DEFINITIoNs
Prebiotics are defined as “a nondigestible food ingredient that beneficially affects
the host by selectively stimulating the growth and/or modifying the metabolic activ-
ity of one or a limited number of bacterial species in the colon that have the potential
to improve host health.”
2
Prebiotics are found naturally in many foods, are present
in breast milk, and can also be isolated from plants (e.g., inulin from chicory root)
or synthesized (e.g., enzymatically from sucrose). The major prebiotics for bacterial
growth in humans are dietary carbohydrates that have not been digested in the upper
gastrointestinal tract. These most often include resistant starch, nonstarch polysac-
charides, and nondigestible oligosaccharides.
3
It is primarily the nondigestible oligo-
saccharides, such as human milk oligosaccharides, fructo-oligosaccharides (FOS),
and galacto-oligosaccharides (GOS) that have been found to selectively stimulate
beneficial bacteria to the point of providing a quantifiable benefit. Although some
proteins and lipids are partially nondigestible, their prebiotic benefits are not as well
characterized.
Several definitions of probiotics exist. For example, a probiotic has been defined
as “a live microbial food ingredient that, when ingested in sufficient quantities,
exerts health benefits.”4
4
Similarly, the Joint FAO/WHO (Food and Agriculture
Organization / World Health Organization) Working Group on drafting “Guidelines
for the Evaluation of Probiotics in Food” has recommended more specifically that
probiotics be defined as “live microorganisms which when administered in adequate
amounts confer a health benefit on the host.”
5
Therefore, the focus becomes micro-
organisms that are not just safe, but also must have a demonstrable benefit to the
host. Probiotic microorganisms can be found both in supplement form and as com-
ponents of foods. Examples of probiotics include certain strains of
Lactobacillus,
Bifidobacterium, Streptococcus, Enterococcus,
and
Saccharomyces.
Many are con-
sumed in foods such as yogurts and other cultured dairy products.
13.3 ColoNIZATIoN
Normally individuals receive their first exposure to bacteria during the birthing
process. Prior to that time, the gastrointestinal tract is sterile. During childbirth, an
infant swallows bacteria present in the birth canal; these bacteria rapidly colonize
the small and large intestine, and the intestinal immune system learns to recognize
these bacteria as desired residents of the gastrointestinal tract. Besides extrinsic fac-
tors, such as mother's dietary intake or use of probiotics, type of birth (vaginal or sur-
gical), gestational age, and primary source of nutrition (bottle or breastfed); intrinsic
factors including underlying neonatal health, immunologic status, gastrointestinal
