Innovazioni tecnologiche in mangimistica per la valorizzazione delle biomasse residuali nel settore del petfood. Analisi delle caratteristiche macrostrutturali indotte dai processi di estrusione nella produzione di diete per cani con differenti livelli di inclusione di Pastazzo d’Arancia.

Aim of the study was to evaluate the effect of inclusions of orange pulp (OP) at different dosages and of two different die diameter (Dd) during the extrusion of dog foods, on processing parameters, starch gelatinization (SG), in vitro digestibility of organic matter and kibble macrostructure. The experiment followed a 5x2 factorial arrangements, with 5 diets (4 experimental and 1 control) and 2 Dd, with a total of 10 diets. Five normal maintenance diets were formulated: four diets with different inclusions of OP (5%, 10%, 15% and 20%) in substitution of the corn meal and one diet without OP. The diet was manufactured in a single screw extruder with two die diameters (Dd) (5 and 7 mm), resulting in two die open areas of 19.6 mm2 and 39,5 mm2. The other extruder parameters were unchanged. Data were analyzed via ANOVA (SAS), considering the variables OP inclusion and Dd and their in-teractions and compared by polynomial contrasts (P<0.05). The increase of the OP concentration in the diets determined, during the extrusion, a reduction in radial expansion and piece volume and an increase in the longitudinal expansion and piece density. The best longitudinal expansion, obtained with OP, was associated with fiber structures consisting in a higher number of small cells with shapes closer to spheres. The changes in the parameters driving expansion could be due to the differences in the rheological properties between the continuous starch matrix and the OP particles, their interac-tion and their low physicochemical compatibility. Die diameter of 7 mm determined a reduction in radial expansion and piece volume and an increase in cutting force and in piece density. The specific mechanical energy - SME was significantly reduced by the increased Dd and OP inclusion. The die with diameter of 5 mm should be used for greater radial expansion and starch gelatinization. Further studies on the OP inclusion may clarify the influence of different fibers on palatability, sensory properties and acceptance by dogs. In the same way, it would be advantageous to regulate the water absorption/retention properties of these fibers, for their use as filling components in diets characterized by low energy content.