Benjamin Schmid

Microalgae are considered a promising resource of proteins, lipids, carbohydrates, and other functional biomolecules for food and feed markets. Competitive drying solutions are required to meet future demands for high-quality algal biomass while ensuring proper preservation at reduced costs. Since often used drying methods, such as freeze or spray drying, are energy and time consuming, more sustainable processes remain to be developed. This study tested an indirect and hybrid solar dryer as an alternative to conventional freeze drying of industrially produced Tetraselmis chui and Nannochloropsis oceanica wet paste. The effects of the drying method on biomass quality parameters, including biochemical profiles, functional properties, and microbial safety, were assessed. No significant differences were found between the applied drying technologies for total proteins, carbohydrates, lipids, and fatty acid profiles. On the other hand, some pigments showed significant differences, displaying up to 44.5% higher contents in freeze-dried samples. Minor differences were also registered in the mineral profiles (<10%). Analyses of microbial safety and functional properties of the solar-dried biomass appear adequate for food and feed products. In conclusion, industrial solar drying is a sustainable technology with a high potential to preserve high-quality microalgal biomass for various markets at expected lower costs.

Phototrophic microalgae use light to produce biomass and high-value bio-compounds for foods and feeds such as pigments and polyunsaturated fatty acids. These biomolecules can be induced by flashing light during the final growth stage. We tested different exposure times (1-6 days) of flashing light ( f = 0.5, 5, 50Hz; duty cycle = 0.05) on biomass, pigment and fatty acid productivity of Diacronema lutheri and Tetraselmis striata . Three days exposure to low-frequency flashing light of 5Hz successfully increased fucoxanthin, diatoxanthin, eicosapentaenoic (EPA) and docosahexaenoic acid (DHA) production in D. lutheri up to 4.6-fold and lutein, zeaxanthin and EPA production in T. striata up to 1.3-fold compared to continuous light. At this condition, biomass productivity declined 2-fold for D. lutheri and remained similar for T. striata compared to continuous light. Short-term treatments of flashing light as a final stage may be promising for industrial algal production to increase biomass value.

Microalgae are considered as promising source for eco-friendly antifungal agents that can potentially reduce the usage of synthetic fungicides. Hence, properties of aqueous extracts from Nannochloropsis sp., Phaeodactylum tricornutum , Scenedesmus obliquus , Chlorella vulgaris and Spirulina sp. were investigated in vitro regarding their antagonistic activity against the phytopathogenic fungi Sclerotium rolfsii , Rhizoctonia solani , Botrytis cinerea and Alternaria alternata . Scenedesmus obliquus showed the highest antifungal activity of all microalgal strains against Sclerotium rolfsii , inhibiting growth up to 32.01 ± 4.82%. Nannochloropsis sp. mitigated Sclerotium rolfsii by up to 13.96 ± 5.26%, while Phaeodactylum tricornutum suppressed the mycelial growth of Sclerotium rolfsii and Rhizoctonia solani by up to 18.35 ± 3.45%. Moreover, Phaeodactylum tricornutum and Scenedesmus obliquus inhibited Botrytis cinerea growth by up to 11.47 ± 2.06%. Microalgae with fungicidal activity could replace chemical agents in modern and sustainable agricultural food production.