A study on the effects of chemical modification of starch and fibre subjected to various thermo-mechanical treatments, on physical pellet quality and nutritional value of the feeds were studied. Also, effects of chemical modification of starch and proteins on physical pellet quality and nutritional value are discussed
Effect of pelleting and other feed processes on functional properties and nutritional value of starch and fibre
English language abstract In a series of experiments the effects of chemical modification of starch (Paper I-III) and fibre (Paper III) subjected to various thermo-mechanical treatments, on physical pellet quality and nutritional value of the feeds were studied. In addition, effects of chemical modification of starch and proteins on physical pellet quality and nutritional value were discussed in Paper IV.
Application of the pelleting treatment with or without conditioning resulted in limited starch gelatinisation (Paper I-III), which indicates that pelleting is of modest importance to chemical changes of starch. Data from the Paper III shows that during conventional pelleting, a majority of the gelatinisation occurs in the pellet die, and not in the conditioner. A significant increase (P<0.05) in the extent of gelatinisation was observed after expander-pelleting (Paper I) and extrusion treatment (Paper II) compared to pelleting treatment only. As a consequence of differences in structural organization of the starches among cereal sources, a higher extent of gelatinisation (P<0.05) for starches originating from oats compared to those from wheat was observed (Paper II and III). Paper I shows that formation of amylose-lipid complexes may occur during commercial feed processing when long saturated fatty acids are used. It was surprising, however, that neither expander-pelleting treatment nor use of starch varieties with high amylose content did result in any increase of amylose-lipid complex formation compared to conventional pelleting or a starch variety with normal amylose-amylopection ratio (Paper I).
Physical quality of the pellets in terms of resistance to abrasion was higher (P<0.05) for the diets based on oats compared to those based on wheat, possibly due to increased gelatinisation of oats diets (Paper II and III). In addition, data from Paper II shows a positive correlation (P<0.05) between pellet durability and addition of pre-gelatinised starch in feed rations. This indicates that starch has a potential to act as a binder if gelatinised. However, higher durability (P<0.05) of the diets composed of non starch ingredients compared to those containing either raw or pre-gelatinised starch indicates that starch has a modest effect on physical pellet quality when subjected to conventional pelleting (Paper II). Higher (P<0.05) elasticity of the pellets as a direct effect of fibre inclusion to the feeds was observed in Paper III.
Improvements (P<0.05) in starch digestibility have been observed as a consequence of increased gelatinisation (Paper I-II). This has been most notable in diets based on wheat, where improved digestibility of starch (P<0.05) was seen in all sections of the gastrointestinal tract (Paper II). With the exception of the duodenum, no such effects were observed for diets based on oats. This indicates that more severe processing (extrusion) causing more complete gelatinisation may be beneficial for diets based on wheat. Depression of the starch digestibility (P<0.05) as a consequence of amylose-lipid complex formation in diets containing long saturated fatty acids was observed in Paper I. A dramatic increase in intestinal viscosity as a consequence of conventional pelleting caused poor feed conversion and a reduction in apparent metabolisable energy and dry matter digestibility (Paper III).
