A comparative study of Spirulina drying in heat pump dryer (HPD) and in conventional tray dryer (CTD) was performed. The effects of the methods used for the sample were evaluated in relation to the operation kinetics and the characteristics of the dehydrated microalgae. The air temperatures were 50 and 60 °C, and the absolute humidity of HPD was ten times smaller than in CTD. The values of the total drying time of HPD were 40% inferior to the found in CTD, for both air temperatures. The highest preservation of the Spirulina characteristics was found in HPD and air temperature of 50 °C, and in this condition, the values of phycocyanin, total phenolic compounds and total antioxidant activity were 14%, 60% and 10% higher than the values to the found in the same condition for CTD, respectively. These results are showing that the drying method is decisive in the product quality dehydrated.
The physicochemical, biochemical, morphologic, structural and thermal properties of the Spirulina microalgae are affected for the drying temperature. The benefits of the use of heat pump drying have been demonstrated, because in this operation is possible to use temperatures lower than the temperatures in the conventional tray drying. Besides, this operation is independent of the atmospheric meteorological conditions.