An overview is given of effects of the diet ingredients and their composition (e.g., starch,
protein, sugar, fat and fibre content) on production characteristics of pellets and on their physical
quality (pellet hardness and pellet durability) as compound animal feeds.Large differences exist in
the effect on pellet physical quality within and between groups of diet ingredients when
incorporated in pelleted animal diets. Differences in pellet quality between groups of diet
ingredients, e.g., grains or legume seeds, can be attributed to differences in their physico-chemical
properties which, in turn, are primarily affected by processing history, geographical and climatic
origin and cultivar. Differences in physico-chemical properties due to the latter factors are also the
main causative contributors to differences in pelleting quality (e.g., throughput, energy consumption
of the pellet press) within groups (e.g., cereals or legume seeds); thus, in the resulting pellet
quality. Raw materials within one group are much more the same than between groups with
respect to pelleting properties and pellet quality, since their composition varies only within a
relative narrow range. Because of the inherent variability of the raw materials, the effects of its
constituents were investigated with respect to pellet quality. Effects of raw material constituents,
both their level and physico-chemical properties, may provide more information on pelleting
characteristics and pellet quality than the diet ingredient inclusion level of the raw material per se.
The effects of starch (native versus gelatinized), sugar, protein (raw versus denatured), and
solubility and resiliency of fibre are discussed with respect to pellet quality. When pellet hardness
or durability is lacking, pellet binders may be used to improve pellet quality. The effects of pellet
binders and their mode of action are discussed. It is concluded that more research effort should be
directed towards the effects of individual constituents and their respective properties, since the
latter seems to affect, to a large extent, the final hardness and durability of pelleted compound
* Corresponding author.
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