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. [Display omitted] •The drying process of discarded onion cv. Crioula Roxa was studied.•The samples, dried at 60 and 70 °C, were subsequently rehydrated at the same temperatures.•Proteins are positively affected by the drying temperature; anthocyanins negatively.•The effective moisture diffusivities during dehydration exceeded those during rehydration.•Heat and mass transfer coefficients were determined to provide design and operation guidelines.