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In-barrel moisture on extrusion parameters and kibble macrostructure in cat foods

Francine Mendes Peres ; Mayara Aline Baller ; Peterson Dante Gavasso Pacheco ; Thaila Cristina Putarov ; Mariana Monti ; Bruna Agy Loureiro ; Aulus Cavalieri Carciofi
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Water addition is required for proper extrusion of pet food; it favors dough flow, starch hydration and cell structure formation. However, the effects of different in-barrel moisture are not completely known for cat foods. The aim of this study was to evaluate the implications of six different additions of water in the extruder barrel on processing traits and kibble formation. A diet for cat maintenance was formulated following the requirements of FEDIAF guide (2013). Six amounts of processing moisture were tested by modulation of water addition in a single-screw extruder barrel, in a completely randomized design. After stabilization (45min), extrusion parameters was recorded at each 10 min, with four samplings per treatment (considered the experimental unit, n = 4). The raw material and extruded diets were analyzed for chemical composition. The specific mechanical energy (SME) and macrostructure of the kibbles was calculated according Riaz (2003). Results were submitted to variance analysis and compared by polynomial contrasts using the GLM procedure of SAS (P<0.05). The in-barrel moisture (IBM) increased from 21.6% to 32.6% with water addition. The greater fluidization of the dough reduced SME input (SME = 0.039 x IBM? - 3.27 x IBM + 79.90; P<0.001; R? = 0.8499), and the mass temperature (Temperature = 0.1286 x IBM? - 9.95 x IBM+ 303.12; P<0.001; R? = 0.9041) and pressure (Pressure = 0.0085 x IBM? - 2.84 x IBM+ 138.43; P<0.001; R? = 0.8757) during extrusion. It resulted in quadratic reduction on kibble apparent density (dens) (dens = 2.28 x IBM? - 130.69 x IBM+ 2208.23; P<0.001; R? = 0.9281), whose values was lowest for moistures from 25% to 29%, and increased after that. The kibble expansion ratio (ER) showed an opposite results, with higher expansion on moistures between 25% and 29% (ER = -0.0765 x IBM? + 4.43 x IBM- 51.36; P<0.001; R? = 0.6436). This study showed that high moisture increases dough fluidity and reduces the shear, explaining the reduction on SME, and worse kibble formation. The low moisture in the barrel reduced the kibble expansion, explained by reduced water vaporization (flash off) and internal cell formation.