Innovative vs. classical methods for drying heterotrophic Chlorella vulgaris: Impact on the nutritional properties, safety, sustainability and costs

The microalgae Chlorella vulgaris is an interesting emerging food source, but to compete with other alternative protein sources, production costs must be reduced. The drying process plays a critical role in production as it ensures product stabilization and quality preservation. However, drying is a cost-intensive process and different drying methods and drying parameters can significantly affect the composition and quality of the final product. This study analyzed the effects of the conventional drying methods freeze drying (FD) and spray drying (SprD) as well as the innovative drying methods solar drying (SolD), pulse combustion drying (PCD) and agitated thin film drying (ATFD) on the nutrient composition, the content of polycyclic aromatic hydrocarbons, the microbial count (total bacterial count, yeasts, molds, E. coli) as well as the environmental impact and production cost. Except for ATFD, showing changes in the carbohydrate and fiber content, the effects of drying methods on nutrient composition were minor. SprD was identified as having the greatest environmental impact and being the most cost-intensive, whereas SolD performed best, with only a slight reduction in vitamin B6 and some mineral elements compared to FD. PCD performed second best but needs improvement in terms of drying yield to reduce production costs.