Optimization of Spirulina sp. Drying in Heat Pump: Effects on the Physicochemical Properties and Color Parameters

The aim of this work was to optimize the drying operation of Spirulina sp. using the heat pump to dehumidify the air. An experimental design using the drying air temperature (30, 40 and 50C) and the initial sample thickness (1, 3 and 5 mm) was performed. The responses were the physicochemical properties and the color parameters of the dried microalgae. The air temperature presented the highest effect on the phycocyanin content, while the sample thickness showed the highest influence on the other responses. The optimal operating conditions for the heat pump drying of Spirulina sp. were at air drying temperature of 50C and sample thickness of 5 mm. The phycocyanin content, total antioxidant activity and color difference were found to be 19.60 mg/g, 52.6% and 5.71, respectively. Thermograms (differential scanning calorimetry) showed that under these conditions, the product showed the highest thermal stability. Practical Applications The culture of Spirulina sp. is attractive for various commercial purposes, such as nutritional supplement for humans and animals and supply of active metabolites in the pharmaceutical and cosmetic industry. The conventional tray drying is a traditional method that is used in the microalgae drying. However, the heat pump drying enables operation in lower temperatures than the traditionally used in convective hot air drying. This operation occurs in moderate conditions of temperature and humidity due to air dehumidification, leading to retention of bioactive compounds in products that are heat sensitive. Therefore, the use of heat pump dryer for the production of dried Spirulina should be promising to preserve its phytochemicals and physical characteristics. The benefits of heat pump drying have been shown in different studies in the literature, but there are no reports about its use in Spirulina drying and its influence on the physicochemical and functional characteristics.