Biomedical Engineering Reference
In-Depth Information
the human alimentary tract with population numbers and species distribution characteristic of
particular regions of the gut. This allows the establishment of a complex and relatively stable
bacterial community in the large intestine. The near neutral pH and the relatively low
absorptive state of the colon further encourage extensive microbial colonisation and growth.
Through the microflora, the colon is capable of exhibiting complex hydrolytic digestive
functions. This involves the breakdown of dietary components, principally complex
carbohydrates, but also some proteins, that are not hydrolysed nor absorbed in the upper
digestive tract. The colonic microflora also derive substrates for growth from the diet (e.g.
nondigestible oligosaccharides, dietary fibre, and undigested protein reaching the colon) and
from endogenous sources such as mucin, the main glycoprotein constituent of the mucus
which lines the walls of the gastrointestinal tract. Thus, any foodstuff that reaches the colon,
e.g. nondigestible carbohydrates, some peptides and proteins, as well as certain lipids, is a
candidate prebiotic according to the above prebiotics definition.
Nowadays, many prebiotics are already used in a broad range of food applications.
However, it is still possible to identify desirable targets for enhancement of their efficacy as
prebiotics. According to the claims of the producers, these products are effective in
supporting the health of human and are also safe.
Prebiotics show both important technological characteristics and interesting nutritional
properties. Several are found in vegetables and fruits and can be industrially processed from
renewable materials. In food formulations, they can significantly improve organoleptic
characteristics, upgrading both taste and mouthfeel. For prebiotics to serve as functional food
ingredients, they must be chemically stable to food processing treatments, such as heat, low
pH, and Maillard reaction conditions. That is, a prebiotic would no longer provide selective
stimulation of beneficial microorganisms if the prebiotic was degraded to its component
mono- and disaccharides or chemically altered so that it was unavailable for bacterial
metabolism [5].
Most prebiotics are poly- and oligosaccharides [3, 4]. They are obtained either by
extraction from plants (e.g., chicory inulin), possibly followed by an enzymatic hydrolysis
(e.g., oligofructose from inulin) or by synthesis (by trans-glycosylation reactions) from mono-
or disaccharides such as sucrose (fructooligosaccharides) or lactose (trans-galactosylated
oligosaccharides or galactooligosaccharides).
Prebiotics can be used for either their nutritional advantages or technological properties,
but they are often applied to offer a double benefit: an improved organoleptic quality and a
better-balanced nutritional composition. The use of inulin and nondigestible oligosaccharides
as fiber ingredients is straightforward and often leads to improved taste and texture. These
specific forms of dietary fibre are readily fermentable by specific colonic bacteria, such as
bifidobacteria and lactobacilli species, increasing their cell population with the concomitant
production of short-chain fatty acids.
These acids, especially butyrate, acetate, and propionate, provide metabolic energy for
the host and acidification of the bowel. Lactose occurs exclusively in the milk of mammals
and one might speculate from a teleological point of view that lactose ingestion will result in
specific benefits for the suckling animal, beyond just being a source of energy. Nowadays,
more and more prebiotics are used in functional foods as ingredients which stimulate the
growth of health-promoting gut bacteria especially probiotics and offer additional health
benefits [5].
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