2. Types and sources of prebiotics
Non-digestible carbohydrates can be considered as prebiotic if
they achieve the following criteria (A) resistance to gastric acidity
and mammalian enzymes; (B) susceptibility to fermentation
by gut bacteria; and (C) ability to enhance the viability
and/or activity of beneficial microorganisms (Rastall & Gibson,
2006). Galactooligosaccharides (GOS), fructooligosaccharides
(FOS) and inulin are the prebiotics most commonly known.
GOS are non-digestible and are derived from lactose that occurs
naturally inmammalianmilk and consist of chains of galactose
monomers. Inulin and inulin-type fructans, are known
soluble dietary fibres (Roberfroid, 2005). Additionally, dietary fibre
containing several non-starch polysaccharides, such as
cellulose, dextrins, pectins, beta-glucans, waxes, and lignin
can adjust the transfer time through the gut, thus offering
the same useful effects as those of inulin-type fructans (Napolitano
et al., 2009). Naturally occurring prebiotic can be found in
various foods, including asparagus, chicory, tomatoes and
wheat, and it is a natural constituent of breast milk. Several
types of prebiotics and their sources aresummarised in Table 1.