Agriculture Reference
In-Depth Information
In animal production, dietary fibres are usually described as a combination of components
of the edible parts of plants or their extracts, or synthetic analogues (Bach Knudsen,
2001). They include four major components issued from the plant cell wall: cellulose,
hemi-cellulose, pectin and lignin, and some polysaccharide cytoplasmic components
such as resistant starch (amylose and amylopectin), guar gum and mucilage (alginate) .
The analysis of dietary fibres according to Van Soest et al. (1991), together with more
recent analytical methods describe the different fibre components, corresponding to
resistant starch, non-digestible oligosaccharides, lignin and non-starch polysaccharides
(NSP), with further subdivisions into the fraction insoluble in neutral detergents (NDF:
neutral detergent fibre) and insoluble in acid detergents (ADF: acid detergent fibre;
Champ et al. , 2003; see Figure 5.1 for an overview) .
The sources of dietary fibres are plant foods, fruits, vegetables, nuts and grains (Table 5.1).
The key characteristics of dietary fibres are their resistance to digestion and absorption in
the small intestine, usually with complete or partial fermentation predominantly in the
large intestine. Dietary fibres can be characterized by their physicochemical properties,
including their solubility in water, leading to classification as either soluble or insoluble,
viscosity, gel formation, water-binding capacity, swelling and fermentability (Blackwood
et al. , 2000). Although the bulkiness of fibres varies and may depend on their structure
(volume) and water-binding capacity, all fibres have bulking properties, because their
inclusion in isocaloric diets reduces dietary energy density (Wanders et al. , 2011).
5.3
Dietary fibres and satiety process: metabolism and
physiological effects
Depending on the sources of dietary fibres and their physicochemical properties, their
inclusion has been shown to affect the available energy content of the feed (Noblet and
Le Goff, 2001) and to influence satiety processes, including the three main phases of
the satiety cascade: the sensory and cognitive, the post-ingestive and post-absorptive
phases (Benelam, 2009; Blundell and Burley, 1987). Many studies have addressed the
energy value of dietary fibres and estimated the range of their contribution to energy
Dietary carbohydrates
Lignin
Digestible carbohydrates
Dietary bre (non-digestible carbohydrates and lignin)
Starch and sugars
Resistant
starch
Non-digestible
oligosaccharides
Non-starch polysaccharides
Lignin
Pectins
Fructans
Neutral dergent bre
Hemi-cellulose
Acid detergent bre
Acid detergent
lignin
Cellulose
Lignin
Figure 5.1. Schematic representation of dietary fibres (De Leeuw et al ., 2008, adapted from Van Soest analysis,
1991).
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