Process optimization and ethanol use for obtaining white and red dragon fruit powder by foam mat drying

Dragon fruit shows good sensory and nutritional attributes, but it is also highly perishable. Drying is a unitary operation that promotes the reduction of moisture content, extending the useful life of the product. In this study, the elaboration of white and red dragon fruit powder by foam mat drying was studied with optimization of the proportion of foaming agent and stirring time. The use of ethanol and air temperature were evaluated on drying kinetics, effective moisture diffusivity (D_eff ), and drying rate (DR). The study was divided into two steps. In the first, density, stability, porosity and overrun foam were evaluated and the optimal condition was determined. For the white and red pulp foams, the optimal conditions were, respectively, 26.88 min and 4.12 kg 100 kg^-1 and 23.5 min and 3.44 kg 100 kg^-1 . In the second step, the foam was subjected to ethanol pretreatment and convective drying (50 or 70 °C). The best condition involved pretreatment and the highest tested temperature, with the shortest drying time and the highest D_eff and DR. PRACTICAL APPLICATION: Foam mat drying is a suitable method for drying perishable fruits, such as dragon fruit. The foam properties need to be optimized to ensure the success of the drying process. The ethanol pretreatment and the drying air temperature influence the drying kinetics. Therefore, determining the optimal process conditions is very important.