Japan was the first country to recognize the value of fermentable oligosaccharides (i.e., in the 1980s the identification of human milk oligosaccharides). But it was only in 1995 when the concept of prebiotics as useful substances in the modulation of the gut microbiota was introduced. Currently, there is not full agreement on a unique definition. Recently, the International Scientific Association of Probiotics and Prebiotics (ISAPP) gave the following definition: “A dietary prebiotic is a selectively fermented ingredient that results in specific changes, in the composition and/or activity of gastrointestinal microbiota, thus conferring benefits upon host health” (Gibson et al., 2011). Prebiotics are nondigestible foods that make their way through our digestive system and help keep beneficial bacteria healthy. Prebiotics are specific nutrients, usually nonabsorbable carbohydrates like fructo- and galacto-oligosaccharides, which are naturally present in whole grains, fruits and legumes, and milk. These oligosaccharides are able to interact with host and bacterial surfaces, contributing to a better host protection from pathogenic infection. For instance, human milk oligosaccharides (HMO) have been demonstrated to bind directly to invading pathogens, preventing host cell attachment and subsequent colonization of the gastrointestinal epithelial cells (Manthey et al. 2014). They may be present in concentrations of up to 12 g/L, making them the third largest component of breast milk. Their presence in relatively large amounts in breast milk suggests that these components may play an important role in early infant microbiota development. Although it is not yet fully clear, feeding infants with breast milk of healthy mothers lowers the incidence of infectious and allergic diseases. In addition to their prebiotic effects, HMO can work as receptor-analogs to inhibit the adhesion of pathogens on the gut epithelial surface and interact directly with the immune cells. There are probably considerably more than 130 different saccharides in human milk (Boehm and Stahl, 2003), and their complexity is the main reason why oligosaccharides with structures identical to HMOs are not yet commercially available as dietary ingredients (Gunther Boehm et al., 2007).
In some animal models of obesity, highly fermentable carbohydrates such as fructans, arabinoxylans, or glucans are able to counteract several metabolic alterations linked to obesity, including hyperglycemia or systemic inflammation (Neyrinck et al., 2012). Several human intervention studies with prebiotics support their interest in the control of glycemia, adiposity, and endotoxemia, which are related to an increase in the gut content of specific bacteria, such as Bifidobacteria, Akkermansia municiphila, or Faecalibacterium prausniztii (Salzar et al., 2014). Most studies have been carried out on fructans (inulin and fructo-oligosaccharides (FOS) derived from different crops or from sucrose) and on galacto-oligosaccharides (GOS). For these ingredients, selective fermentation studies have been carried out, covering their effect on human gut microbiota to verify the positive and potential health benefits for host. Prebiotics, however, include the disaccharide lactulose, other oligosaccharides and resistant dextrins, polysaccharides such as polydextrose, arabinoxylans, and resistant starches, as well as some polyols such as lactitol and isomalt. Some prebiotics occur naturally in foods like chicory, cereals, agave, and milk. Today, many prebiotics and some potential prebiotics fall into the nutritional and regulatory definition of dietary fibers and are labeled as nutrients of that category. But the mono and disaccharide are not considered as dietary fibers according to EU and CODEX definitions.