Effects of extrusion processing on nutrients in dry pet food

Extrusion cooking is commonly used to produce dry pet foods. As a process involving heat treatment, extrusion cooking can have both beneficial and detrimental effects on the nutritional quality of the product. Desirable effects of extrusion comprise increase in palatability, destruction of undesirable nutritionally active factors and improvement in digestibility and utilisation of proteins and starch. Undesirable effects of extrusion include reduction of protein quality due to e.g. the Maillard reaction, decrease in palatability and loss of heat-labile vitamins. Effects of extrusion processing on the nutritional values of feeds for livestock have been well documented. Literature results concerning effects of extrusion on dry pet foods, however, are scarce. The present review discusses the results of studies investigating the impact of extrusion cooking on the nutritional quality of dry pet foods.