Energy and environmental analysis of ultrasound-assisted atmospheric freeze-drying of food.

The atmospheric freeze-drying process can be significantly accelerated using power ultrasound. This paper aims to investigate the effects of this technology on the global energy consumption of the process and its environmental impact. Apple, carrot and eggplant were chosen as representative products because of their different internal structure and water content. A mathematical model of an industrial scale plant was developed to simulate in silico the atmospheric ultrasound-assisted freeze-drying process; model parameters were tuned according to the results obtained in a pilot-scale unit. Life Cycle Assessment (LCA) was used to gain an insight into the environmental impact of the process. The results showed that, when ultrasound is applied, the total energy consumption of the whole process can be reduced by up to 70%, while the LCA analysis proved there were reductions of between 58 and 82% depending on the product for every impact category. The moisture removal unit (dehumidifier) has been highlighted as the most critical stage. The internal structure of the product dramatically affects both the energy consumption of the process and, accordingly, the environmental impact.