Probiotics and Prebiotics: Concepts, Definitions and History - Aquaculture Nutrition: Gut Health, Probiotics and Prebiotics - page 175

feed handling and preparation. Additionally, there is a possibility of environmental issues as
probiotics enter into the environment. As an alternative, prebiotics have been assessed in an
attempt to overcome issues associated with probiotic applications. Instead of introducing pro-
biotic bacteria, the aim of prebiotics is to stimulate selected beneficial indigenous microbiota
populations. A prebiotic was first defined as 'a nondigestible food ingredient that beneficially
affects the host by selectively stimulating the growth and/or the activity of limited number
of bacteria in the colon, and thus improves host health' (Gibson and Roberfroid 1995). In
order for a food ingredient to be classified as a prebiotic, the authors suggested that it should
(1) be neither hydrolysed nor absorbed in the upper part of the GI tract, (2) be a selective
substrate for one or a limited number of beneficial bacteria commensal to the colon, which
are stimulated to grow and/or are metabolically activated, (3) consequently, be able to alter
the colonic flora in favour of a healthier composition, and (4) induce luminal or systemic
effects that are beneficial to host health.
The initial developmental research in prebiotics dates back to the end of the 1970s in Japan
where several carbohydrates, especially fructooligosaccharides (FOS), were selectively fer-
mented by bifidobacteria and had the capacity, upon feeding, to stimulate their growth in mam-
mals (Yazawa et al . 1978). Prebiotics mainly consist of oligosaccharides which have proved
to be able to promote beneficial bacterial growth within the GI tract (Gibson et al . 2003).
Prebiotic oligosaccharides are able to provide the necessary energy to selective species of bac-
teria which are responsible for the production of lactic, acetic and other short-chain organic
acids. Such oligosaccharides are mainly mannan oligosaccharides (MOS), FOS (including
short-chain fructooligosaccharides, scFOS) and trans -galactooligosaccharides (TOS, includ-
ing galactooligosaccharides, GOS). Inulin is a fructan polysaccharide which also has docu-
mented probiotic qualities. Not all of these glycans have been tested in aquaculture at this time.
In a more recent review for human intestinal microbiota, the prebiotic definition was
updated. Gibson etal . (2004) suggested that a prebiotic has to (1) resist gastric acidity, hydroly-
sis by (mammalian) enzymes and GI absorption, (2) be fermented by the intestinal microbiota,
and (3) stimulate selectively the growth and/or activity of intestinal bacteria associated with
health and well-being. According to Gibson et al . (2004), each one of these criteria is
important but the third criterion, concerning the selective stimulation of growth and/or activity
of beneficial bacteria, is the most important and the most difficult to achieve. This is especially
true because this step requires anaerobic sampling, and reliable quantitative microbial analysis
needs to be undertaken for a wide range of bacterial species (i.e. total aerobic and anaerobic
bacteria as well as total counts of Bifidobacteria, Enterobacteria, Lactobacillus etc.). For
this purpose it is suggested that advanced molecular techniques, such as metagenomics and
qRT-PCR, should be used. Additionally, Gibson etal . (2004) evaluated eight possible prebiotic
candidates: inulin, TOS, lactulose, isomaltooligosaccharides, lactosucrose, xylooligosac-
charides, soybean oligosaccharides and GOS. According to their criteria only three of these
glycans could be classified as prebiotics: inulin, TOS and lactulose. However, in a more recent
review, Roberfroid (2007) stated that only two fulfil the criteria for prebiotic classification:
inulin and TOS. Therefore the term prebiotic , in this chapter as is the case more broadly
across the scientific community, is generally used to describe glycans that potentially meet
the suggested criteria, rather than those that have been definitively proven to meet the criteria.
In endothermic animals, prebiotics have a long history, but in aquaculture the first
prebiotic study was reported by Hanley et al . (1995). Since then numerous papers have
been published and the most common 'prebiotics' used in fish include inulin, FOS,