Fructooligosaccharides
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.