Estudo sobre a desidratação de microalgas em secador rotatório

Abstract

Microalgae are microscopic organisms used to obtain relevant compounds for the pharmaceutical, chemical and food industries, among others. They also have their applicability extended to several important areas such as effluent treatment, energy production or animal and human nutrition. Spirulina is a term used to denominate diverse species of microalgae that have been used as food for hundreds of years and its importance in the fight against hunger has already been agenda of the UN. Spirulina platensis is a blue-green micro-organism that has in its biochemical composition significant amount of nutrients such as proteins, carbohydrates, lipids, minerals and bioactive nutraceutical compounds, such as phycocyanin. This microalgae also has a high amount of moisture, which makes it susceptible to bacterial growth and degradation. Therefore, the aim of the work was to dehydrate the microalgae using a rotary drier with inert bed. The equipment has the possibility of drying paste materials and has a post-drying product ready for commercialization, requiring only packaging. In order to determinate the experimental conditions, a complete factorial design with three variables in two levels were used: drying air temperature (50oC and 90oC), inert filling factor (15% and 27%) and speed of rotation (40 RPM and 60RPM). A productivity estimative for each experiment as well as analysis of final moisture (UF), water activity (Aw) and bioactive compounds (total phenolic content, flavonoid content, total acidity and phycocyanin content) were performed for the microalgae in natura and after the dehydration process to evaluate the efficiency of moisture removal and the impacts of the technique on the bioactive compounds. The experiment that obtained the best value of productivity was the one that used temperature of 50oC, 27% of filling factor and 60RPM rotation, reaching the value of 60,12%. All the experiments reached satisfactory values of final moisture and water activity. Regarding the bioactive compounds, it was not possible to verify a better global condition for all compounds, however, in all conditions their amount stayed close to those in the in natura microalgae or even higher, under specific conditions. It was observed that the phenolics and phycocyanin had their best results with a 15% filling factor and 60 RPM rotation, but differed in the temperature (90oC for phenolics and 50oC for phycocyanin). Flavonoids and acidity also had their optimal condition in the same filing factor (27%) and rotation (40RPM), but at different temperatures (90oC for phenolics and 50oC for acidity).