Utilizing surplus bread as an ingredient in dog food: Evaluating baking and extrusion processing on physicochemical properties and in vitro digestibility performance

This study probed the effects of integrating surplus bread crumbs (BC) into dog food formulations, examining the resulting influence on the rheological, physicochemical, and in vitro digestibility properties of the products processed using baking and extrusion methods. Increasing BC concentration led to increased mean cold viscosity values, decreased peak and paste viscosity, higher expansion indices, and lower bulk density. Lightness of the samples (L* values) increased significantly with higher BC ratios, resulting in lighter-colored products. The hardness of the extrudates ranged between 23.1 N and 49.4 N, and decreased with increasing BC ratios. This suggested changes in structural properties due to the addition of BC. Microstructural analysis using scanning electron microscopy demonstrated a more homogeneous matrix in BC containing samples, possibly due to in-teractions between the gelatinized starch and denatured gluten proteins from the BC. The in vitro apparent di-gestibility coefficients showed no significant variation in dry matter digestibility across BC ratios, while crude protein digestibility decreased and nitrogen-free extract digestibility increased with higher BC ratios. Specific Mechanical Energy (SME) values were found to be lower in BC-containing samples (p<0.05), indicating potential energy-saving benefits during the production process.