Microwaving expansion kinetics of corn third-generation extruded pellets under different moisture content

The third-generation extruded pellets are formed via extrusion at high moisture content and moderate temperature. The combination of nonexpanding extrusion and microwave expansion is referred to as the production of third-generation snacks allowing the preservation of thermally sensitive ingredients. In this study, a Brabender Kompakt extruder KE 19/25 was used to get corn third-generation pellets with three moisture content mixtures (25, 30, and 35 %). These pellets were subjected to microwave expansion at eight microwave application times (between 10 and 90 s). The drying curves were fitted to three mathematical models (Page, Logarithmic, and Midilli and Kucuk). The model's coefficients were determined by non-linear regression analysis, and the models were compared based on their coefficient of determination (R²). Root means square error (RMSE) was calculated between experimental and predicted moisture ratios. The Page model best fits the experimental data, closely followed by the Midilli and Kucuk model. The constant drying k showed an inversely proportional trend to the moisture content of the mixtures for the Page model, which could be related to the diffusion coefficient. Due to microwaves' high heating velocity, the constants were higher than the unit. The variables evaluated at extruded pellets were appearance, sectional expansion index (SEI), and volumetric expansion index (VEI). The evolution of expansion indexes during the microwave process strongly depends on moisture content. Pellets with 35 % water content showed the lower SEI and VEI values, and pellets with 30% water content followed this behavior closely. In contrast, pellets with 25 % water content exhibited a higher expansion index in all the application times evaluated. According to the results of drying curves, expansion indexes, and appearance, the recommended expansion time with 25, 30, and 35 % moisture content for mixtures is 50, 60, and 60-75 s, respectively.