Mandacaru is a cactus native to the semiarid region of Brazil, of which the fruits are edible, highly perishable and rich in bioactive compounds, present mainly in the peel. The aim of this study was to determine the drying kinetics of the processed peels of the mandacaru fruit at three different temperatures, fit mathematical models to the experimental data, determine the effective diffusivity and the thermodynamic properties and evaluate the influence of the drying conditions on the bioactive compound concentrations. The residues from the mandacaru fruits, composed of the peels, were ground with a 3% ascorbic acid solution to transform them into a homogeneous paste. The peel paste was placed in stainless steel trays, spread out to give an approximately 0.5 cm layer and dried in a convective drying oven with forced air circulation at a velocity of 1.0 m/s at temperatures of 50, 60 and 70°C. Mathematical models found in the literature were fitted to the drying kinetics of the mandacaru fruit peel paste, and of these the Midilli model fitted the experimental data best. The effective diffusivity of the water increased with drying temperature, as also the Gibbs free energy. The activation energy was to the order of 39.15 kJ/mol. The enthalpy presented positive values, decreasing with increase in drying temperature, but the entropy presented negative values, progressively lower with increase in temperature. Important betalain concentrations were determined in the mandacaru fruit peels, especially betaxanthins, an active principal of interest to the food industry as a natural pigment. Despite the decrease in concentration of the bioactive compounds with convective drying, the powders still presented significant amounts, the temperature of 70°C resulting in the highest bioactive compound concentrations in the powder samples.

Practical applications

The use of the data presented here for the thermodynamic properties and bioactive compounds provides support for the use of the dried Mandacaru residues (previously discarded) in the production of new foods, due to knowledge of the processing time and composition of the sample. The Mandacaru peel powder, rich in bioactive compounds, could be incorporated into various food formulations in the bakery and yogurt segments, amongst others.