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Galacto-oligosaccharides

GOS are prebiotics produced industrially. They are obtained by enzymatical transgalac- tosylation of lactose with the aid of fungal or bacterial fi-galactosidases. The amount and type of GOS produced depends on the enzyme characteristics and source, lactose concentration and source, process type, and conditions.

GOS have a safe history of use in food and in infant nutrition. They are particularly suitable for use in acid products like fruit juices, soft drinks, and heat-treated items such as bakery products. GOS are also incorporated into synbiotic formulations, which consist of both prebiotics and probiotics. In particular, GOS are used to enhance the probiotics' ability to survive, colonize, and play their beneficial functions in the GI tract.

In Europe, mainly GOS or in combination of GOS/long-chain (lc) FOS (90% GOS and 10% lcFOS) are applied in infant formulas. According to EU Directive 2006/141/EC on Infant Formulae and Follow-on Formulae, GOS can be used for infant nutrition in all EU member states. In the United States, Vivinal® GOS has a GRAS status for use in infant formulas at maximum concentration of 0.5 g/100 mL. GOS are highly resistant to digestion and absorption during transit through the small intestine. The salivary, digestive enzymes and the acidic conditions of the stomach have no effects on the acid-stable GOS. After birth, the human GIT becomes an organ in symbiosis with the intestinal microbiota, which is composed of a large number and variety of bacteria. The healthy microbiota consist of a large number of positive microorganisms, such as bifidobacteria and lactobacilli, that have an important role on stimulation of immune system activity, protection against some diseases (IBS, IBD, GI infections, obesity, etc.), and synthesis of several vitamins. GOSs have been shown to positively influence both composition and activity of the microbiota. Beneficial direct and indirect effects of GOS are shown in Table 1.2.1.2. Several clinical trials with GOS and GOS/lcFOS-supplemented infant

Table 1.2.1.2 Beneficial Direct and Indirect Effects of GOS.

Direct

Indirect (through metabolites of Microbiota)

Microbiota

Constipation’s allevation

Pathogen inhibition

Improvement of mineral absorption

Immune modulation

Nutrition of enterocytes

Adapted from Jardine, 2009.

formula for term infants have been published. The diversity and composition of the microbiota of GOS/lcFOS-supplemented infants were shown to closely be similar to breastfed infants, also at the level of the different Bifidobacterium species. In contrast, standard formula-fed groups of infants harbor a more adult-like microbiota. The supplementation of GOS/lcFOS also gives rise to stool characteristics such as pH, short chain fatty acid (SCFA) profile, that are more similar to those of breastfed infants (Bakker-Zierikzee et al., 2005; Knol et al., 2005). Also, administration of infant formulas containing GOS/lcFOS to preterm infants gave similar results with increase fecal bifidobacteria and softer stool consistency.

GOS may show a synergistic effect on the bifidogenic activity of probiotics. A study conducted on school-aged children has shown that the increase of bifidobacteria was significantly greater after the ingestion of GOS combined with Lactobacillus rhamnosus GG, compared to the ingestion of Lactobacillus rhamnosus GG alone (Piirainen et al., 2008).

GOS can also influence and support the natural defenses of human body by selectively manipulating the gut microbiota, which, in turn, may displace its less desirable members (Fooks and Gibson, 2002; Gibson et al., 2005). In addition, the metabolism of GOS by specific members of the microbiota results in the production of antagonistic agents against pathogens and SCFAs, the latter lowering the luminal pH in the colon below the values at which pathogens can multiply (Gibson and Wang, 1994; Anand et al., 1985). GOS have demonstrated a direct inhibitory action on pathogens by the prevention of bacterial adherence. They are able to act like receptor sites, coating the intestinal epithelial cells to which pathogens adhere to start the infection process (Kunz et al., 2000).

While the composition and activity of microbiota directly influence the maturation and modulation of the immune system activity, GOS indirectly influence mucosal and systemic immune activity, but their synergic action is able to produce crucial beneficial effects on the modulation of immune responses. An example is constituted by the increased production of SFCAs by GOS fermentation that contributes to maintain a noninflammatory environment in the intestine. These conditions help the microbiota, in particular some species (bifidobacteria) to proliferate and give a balanced wellbeing state.

The synbiotic effect of GOS/lcFOS and probiotic bacteria has been reported in several studies. In one of them, a supplementation of infant formula by GOS/lcFOS and Bifidobacterium longum BL999 showed a nonsignificant tendency toward fewer airway infections of the children fed compared with the control group (Puccio et al., 2007). Another study (Kukkonen et al., 2007) concerning allergic diseases in allergy-prone infants has shown that a supplementation of a combination of four probiotic strains and GOS was able to reduce eczema and IgE-associated eczema.

GOS/lcFOS have a positive effect on atopic dermatitis (AD) as well, as confirmed by several studies. AD is usually the first manifestation of an allergy during early infancy. Infant formula supplemented with GOS/lcFOS reduced the incidence of AD in high- risk infants by altering their immune development during the first six months of life. The supplementation of GOS/lcFOS was shown to induce a beneficial total serum antibody profiles (reduction of IgE levels), specifically modulating the immune response toward food allergens (Garssen et al., 2007; Van Hoffen et al., 2008). This effect lasted after the intervention period up to 2 years of age (Arsanoglu, 2008).

GOS may help the absorption of several minerals. Most studies are related to the absorption of calcium, which is very important for the bones and plays an important role in blood coagulation and muscle contraction. The bioavailability of magnesium and phosphorous is also beneficially influenced by GOS. Several studies have been conducted on mechanisms related to the stimulation of mineral absorption by GOS; and others focused the increased calcium absorption related to higher bone mineral content and better bone structure (Chonan et al., 1995).

GOS are also effective in the alleviation of constipation in people constipated or with predisposition to constipation. For example the mixture GOS/lcFOS can lead to softer feces in healthy adults with frequent or tendency for constipation, hence improving defecation (Deguchi et al., 1997). Other studies confirmed similar benefial effects in constipated elderly individuals (Shitara, 1988; Teuri and Korpela, 1998).

 
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