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Fructooligosaccharides
or FOS are chain polymers of the sugar fructose that are found
in a variety of foods. The sugar units can be linked in a
single straight chain or can be a chain with side branches.
In many cases small amounts of glucose are also contained
in the chain. Chemically, FOS is difficult to define, because
the length of the fructose chains can vary from source to
source. Therefore a FOS analysis of a food may report the
total of several closely related compounds. Inulin is an example
of a longer chained compound that is considered a FOS. The
shorter (lower molecular weight) compounds tend to have a
sweet taste.
The size and complexity of the FOS molecule gives it desirable
characteristics. Although the simple sugars fructose and glucose
are quickly absorbed into the body by the intestines, FOS
for the most part is indigestible and therefore acts as a
non-digestible fiber in the diet. This is because the human
does not have the enzymes to break down the FOS as it travels
down the digestive tract. When the FOS reaches the large intestine
and the colon, the bacteria that are found there start to
break down the FOS. These bacteria have the enzymes needed
to break down FOS. Bifido bacteria have been reported to use
FOS. It is believed that foods that promote bifido bacteria
growth are good for the health.
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