Microencapsulation of Algae Extract Based on a Closed-loop Spray Drying System and Its Exergy Analysis

Abstract

This work is dedicated to the extraction of lutein from algae, based on a closed-loop drying system.The difference in powder recovery rate and β-carotene loading capacity between coconut husk powder, WPI, maltodextrin, cellulose, pectin, casein, and other commonly used carrier materials were compared, and the optimal temperature for spray drying was explored. Among them, maltodextrin and coconut husk powder showed excellent powder recovery rates, reaching 84%. Among the commonly used carriers, maltodextrin exhibits the highest β-carotene loading capacity, reaching 0.15 mg/g. The loading capacity of coconuit husk powder is 0.32 mg/L. The surface structure of coconut husk powder was observed by SEM, and the particles were multi-layered spheres leading to a high powder recovery rate and loading capacity. The most suitable spray drying outlet temperature was 50-55°C. A more complex heat-recovery system has been constructed to improve the exergy efficiency of the system. It consists of a condenser, a reheater, and a dryer heat-recovery unit. A “UA” product (heat-transfer coefficient×surface area) has been used to describe the heat loss in the system. Some controllable parameters, such as the cooling water flow rate, the air flow rate, and the inlet air temperature have been used to explore changes in the exergy efficiency. The study found that the cooling water rate has no obvious effect on the exergy efficiency of the system. Increasing the inlet temperature will lead to an increase in energy inflow and exergy loss in the system. However, with the increase in air flow rate, the exergy loss of the whole system decreases, and the whole system has a higher exergy efficiency. The exergy loss is mainly concentrated in the drying chamber, that is, the drying step, and the newly connected condenser and reheater have good exergy efficiencies exceeding 60%. There are further discussions on exergy loss and exergy irreversibility of the system.