Probiotics and Prebiotics: Concepts, Definitions and History - Aquaculture Nutrition: Gut Health, Probiotics and Prebiotics - page 177

catalase expression in the distal gut. The latter are important enzymes of the primary antioxi-
dant enzyme system of the animal and help prevent oxidative stress and free radical generation.
Butyrate is also closely linked with the osmoregulation processes of the gut and the absorption
of sodium (Hamer et al . 2008).

7.3.2 Trans -galactooligosaccharides (TOS) and
galactooligosaccharides (GOS)
TOS are produced from lactose by enzymatic transgalactosylation. The oligomers are linear
and consist of lactose and several galactose molecules with β-1,6 or β-1,4 linkages; they are
not hydrolysed by human small-intestinal β-galactosidase and will pass undigested into the
colon (Burvall et al . 1980). The effect of TOS on gut microbiota is conflicting. Leforestier
et al . (2007) reported that TOS modified the gut microbiota in mice, while Alles et al . (1999)
reported that TOS had no effect on human gut microbiota even though TOS were completely
fermented in the colon. GOS consist of 2-20 molecules of galactose and glucose (Figure 7.1)
and can be produced through enzymatic treatments of lactose by enzymatic reactions using
β-galactosidases from Lb. reuteri , Aspergillus oryzae or Kluveromyces lactis (Yang and Silva
1995; Patel and Goyal 2011). The compounds are viscous with good moisture retention; they
are a third of the sweetness of sucrose and are stable at high temperatures and in acidic envi-
ronments (Macfarlane et al . 2008). GOS have been extensively tested in endothermic animals
(Sako et al . 1999; Vos et al . 2007; Macfarlane et al . 2008; Roberfroid et al . 2010). Knowledge
about the use of GOS as a food ingredient has shown that they can enhance health-related
physiological activities (production of SCFAs, energy transduction in colonocytes, growth and
cellular differentiation of colonic epithelial cells, lipid and carbohydrate metabolism) and con-
tribute to a significant increase in faecal LAB and bifidobacteria. These activities can provide
protection against enteric pathogens, reduce the numbers of potentially pathogenic bacteria ( E.
coli and Campylobacter ), facilitate the normal function of the gut, improve mineral bioavail-
ability including magnesium, iron or zinc, and decrease blood lipid content (Newburg 1997;
van den Broek et al . 2008; Macfarlane et al . 2008; Roberfroid et al . 2010). In human studies
GOS, in combination with FOS, have been extensively investigated (Roberfroid et al . 2010).

7.3.3 Mannan oligosaccharides (MOS)
According to Spring (2003), the initial interest in using MOS (Figure 7.2) as feed additives
for animal nutrition was adapted from studies at the end of the 1980s by Oyofo et al . (1989a;
1989b). These studies evaluated the ability of mannose to inhibit the adherence/colonization
of microbial pathogens, such as Salmonella Typhimurium, to GI epithelial cells of broiler
chickens. Many studies in terrestrial animals have shown that MOS are able to reduce the

CH 2 OH CH 2 OH CH 2 OH

O

O O O

Gal 1 B 4 Gal 1 B O 4 Glc 1 H-OH

Fig. 7.1 Chemical structure of galactooligosaccharides.