Kinetics of water absorption and solute leaching during soaking of breakfast cereals

Minimization of the adverse environmental effects of discarded onions by avoiding disposal through dehydration and food-use

Onion is a commonly used vegetable in the Cuyo Region, Argentina, and important in the world global vegetable production ranking. Production levels often exceed immediate markets of fresh sale, and excesses, although still edible, are currently discarded (mostly incinerated and disposed in landfill, creating numerous environmental hazards). To minimize these adverse environmental problems, this research investigates upgrading the discarded products by dehydration, hence guaranteeing their ultimate food-use. The dehydration process of discarded onion cv. Crioula Roxa was hence studied at 60 and 70 °C, temperatures selected to maintain the main physicochemical characteristics of the onions, while also creating optimum heat and mass transfer coefficients while significantly reducing the energy consumption and CO₂ emissions. When using an electrically-heated convective dryer, the Specific Energy Consumption (SEC) values and the CO₂ emissions during dehydration at 70 °C are 738.89 kWh.kg^-1 and 264.74 kg of CO₂ kg^-1, respectively. These values are only 41.61 kWh.kg^-1 and 2-4 kg of CO₂ kg^-1 if a solar dryer is applied. The thermal diffusivities were 1.86✕10^-10 m² s^-1 (dehydration) and 1.08✕10^-10 m² s^-1 (rehydration), showing a weak effect of the dehydration process on the solid structure and properties.

Hydration kinetics of direct expanded tef flour breakfast cereals in water and milk

Hydration kinetics of tef flour breakfast cereals extruded at barrel temperatures of 110, 130, and 150°C was investigated by hydrating them in water and whole milk at 25°C (±1°C). The normalized Weibull model described the rehydration characteristics of the extrudates in water and milk adequately (R (2) = 0.98-0.99). Water absorption rate was significantly (P < 0.05) influenced by barrel temperature where extrudates processed at 150°C barrel temperature exhibited high water absorption rate followed by those extruded at 130 and 100°C, respectively. Hydration rate and equilibrium moisture content were higher for samples hydrated in water than those in milk. In view of the values of the shape parameter β, the hydration process is predominantly controlled by diffusion (β = 0.40-0.51) for samples extruded at 110°C whereas external resistance to mass transfer dominated (β = 0.60-0.73) those extruded using 150 and 130°C. Extrudates processed at 130 and 150°C exhibited better hydration characteristics. Thus, these temperature ranges could be used to produce extruded products from tef.

Uptake of tritiated liquids by individual breakfast cereal flakes

Surface liquid adhesion (SLA) and liquid absorption (LA) of tritiated liquids, including water and skim, low-fat, whole, and fat-enriched milks, by cornflakes (CF) and frosted flakes (FF) were determined by scintillation counting using water-[(3)H] at 0.5 microCi/mL. SLA or the liquid adhering to individual flakes after a short immersion period was the same for CF and FF in the case of water (approximately 0.011 microL mm(-2) of flake) but were always higher for CF than for FF and increased as the fat content in milks augmented. LA of individual flakes, followed for 300 s of soaking, increased with time and was always higher for CF than for FF (for the same liquid), however, data did not follow a regular pattern. Flakes showed quite compact outer surfaces and an internal porous matrix composed of air cells of various sizes separated by dense walls of different thicknesses. This heterogeneous microstructure of individual flakes may be the cause of the lack of a simple kinetics during the soaking process. Previous results obtained by soaking a mass of flakes overestimated the uptake of fluid by individual because they included the liquid occluded between the flakes.