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Sorghum-Based Extruded Pet Food: Impact of Particle Size and Process Conditions on Physico-Chemical Attributes
T. Putarov (1), F. Cesar Sa (2), M. Joseph (3), A. Carciofi (2), S. ALAVI (4). (1) Sao Paulo State University (UNESP), Botucatu, Brazil; (2) São Paulo State University (UNESP), Jaboticabal, Brazil; (3) Kansas State University, Manhattan, KS, U.S.A.; (4) Kansas State Univ, Manhattan, KS, U.S.A.

Grain sorghum is rarely used in pet foods due to the lack of scientific data on the nutritional quality and acceptability of sorghum-based products. Some previous studies showed that sorghum could provide nutritional benefits related to slower digestibility of starch or lower glycemic response, which can aid in premium products targeted towards obese, diabetic and geriatric pets.  The aim of this study was to evaluate the effect of particle size on the extrusion of sorghum-based diets. Two types of sorghum (White and Red) milled at three particle sizes (0.5, 0.8 and 1.0 mm) were incorporated in a premium dog food formulation and compared to a rice-based dog food formulation. Formulas were extruded to achieve processing at two specific thermal energy: specific mechanical energy ratios (STE: SME), using different combinations of screw speed and preconditioning temperature (high STE:SME at 300RPM/ 85-90°C and low STE: SME at 400RPM/75-80°C).  Water and steam flow in the preconditioner was varied to achieve the desired pre-conditioner temperature. The mean in-barrel moisture was 26% (wb). Particle size and sorghum varieties had no effect on specific mechanical energy.  Bulk density increased with particle size. The diets extruded at 400RPM/75-80°C had higher bulk density. Starch gelatinization increased as the particle size decreased (93%, 85% and 82% of starch gelatinization for 0.5, 0.8 and 1.0 mm particle size respectively). Process conditions did not influence the starch gelatinization (85% and 87% for 300RPM/ 85-90°C and 400RPM/75-80°C respectively). White sorghum had higher percentage of starch gelatinization compared to red sorghum and rice (89%, 85% and 80%, respectively). Results indicated that sorghum can be an effective alternative to rice as a carbohydrate source in extruded pet foods.

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