Extrusion processing : effects on dry canine diets

Q.D. Tran

Research output: Thesisinternal PhD, WU


Keywords: Extrusion, Canine diet, Protein, Lysine, Starch gelatinization, Palatability, Drying.

Extrusion cooking is a useful and economical tool for processing animal feed. This high temperature, short time processing technology causes chemical and physical changes that alter the nutritional and physical quality of the product. Effects of extrusion on the feed quality for other animals than pets have been well recognized. Our studies investigated to what extent extrusion and/or drying of a complete canine diet affects lysine reactivity, amino acids, fatty acids, starch gelatinization and physical parameters.
In order to create a general view of dog food quality in practice, the physical and nutritional quality of commercial canine diets available in the Netherlands were examined. This study showed unveiled variation in lysine reactivity and starch gelatinization of commercial dry canine diets. A study was then carried out on the effects of extrusion on the physical and nutritional values of canine diets in a FIDO model. The extrusion conditions (temperatures in the range of 110 to 150ºC, 300 g/kg moisture) increased lysine reactivity, starch gelatinization and in-vitro starch digestibility. Protein digestibility and dispersibility were not affected by the extrusion conditions used. The increase in the extrusion temperature used (110 to 150ºC) decreased kibble durability but did not affect hardness. This study also concluded that optimisation of extrusion conditions during production of commercial canine diets should include the measurement of the reactive to total lysine ratio. Single ingredients of a complete canine diet did not respond in a similar way during extrusion: extrusion had no effects on animal ingredients (higher lysine contents) while extrusion could decrease (in barley) or increase (in rice) the reactive lysine content in vegetable ingredients (lower lysine content). Both reactive lysine content and ratios of reactive to total lysine of the mixture of all vegetable ingredients were hugely increased during extrusion. Finally, an additional study was carried out on the effects of drying on extruded canine diets. The results of this study showed that drying temperature (in the range of 120-160ºC) and drying time did not affect the quality of extruded canine diets in terms of amino acids and fatty acids levels while these drying temperatures reduced drying time from hours to minutes. Drying temperature only affected the reactive lysine content and, therefore, the ratio of reactive to total lysine of kibbles dried at a temperature of 200ºC. Drying temperature also affected a minority of fatty acids with fatty acid C18:3 n-3 being the most affected at a drying temperature of 200ºC.
In conclusion, extrusion at temperatures in the range of 130-150ºC and at a moisture of 300 g/kg is a mild heat treatment with respect to protein quality for pet food production. Measurement of the ratio of reactive to total lysine should be included in optimisation of extrusion conditions during pet food production. Drying temperature in the range of 120-160ºC and drying time do not affect the amino acids and fatty acids level of extruded canine diets.

Original languageEnglish
QualificationDoctor of Philosophy
Awarding Institution
  • Wageningen University
  • Verstegen, Martin, Promotor
  • Hendriks, Wouter, Promotor
  • van der Poel, Thomas, Co-promotor
Award date25 Feb 2008
Place of Publication[S.l.]
Print ISBNs9789085049036
Publication statusPublished - 2008


  • dogs
  • dog feeding
  • dry feeds
  • diets
  • extrusion
  • drying
  • protein
  • lysine
  • starch granules
  • palatability
  • feed processing


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