Evaluation of pretreatments used to obtain hydrolysates from microalgae biomass, and their effects on the recovery of carotenoids and fatty acids intended for agriculture applications

Microalgae are considered a promising raw material for a variety of applications thanks to their nutritional profile. However, the rigid cell walls of certain species require pretreatments to facilitate the release of bioactive compounds. This study evaluated the impact of different pretreatments, including high-pressure homogenization (HPH), milling with alumina (M-AL), ultrasound (US), and microwave (MW), on protein hydrolysis and the recovery of fatty acids and carotenoids from the biomass of Nannochloropsis gaditana , Isochrysis galbana and Arthrospira platensis . All pretreatments significantly influenced protein hydrolysis. US at 80 % intensity resulted in the highest degree of hydrolysis (DH) for I. galbana (77 %), followed by N. gaditana (62 %). However, A. platensis showed no improvement compared to the control. Carotenoid recovery varied among species: the highest yield was achieved by N. gaditana (195 %) with US at 80 %, followed by I. galbana (180 %) with MW at 360 W, while the lowest recovery was observed in A. platensis (133 %) with HPH at 800 bar. Fatty acid yields also increased, with N. gaditana reaching 113 % (HPH at 800 bar) and 116 % (US at 80 %), and I. galbana reaching 112 % and 124 % under the same conditions. The highest recoveries in A. platensis were obtained with HPH at 400 and 800 bar (139 % and 135 %, respectively), compared to the untreated control. The bioactivity of the hydrolysates was assessed through the germination index of garden cress seeds. Only I. galbana hydrolysates enhanced germination, suggesting that specific pretreatments can improve the recovery of functional compounds from microalgae. • Ultrasound is a highly effective method for increasing protein hydrolysis. • Carotenoids recovery is species-dependent and improves with targeted treatments. • Mechanical disruption and ultrasound boost fatty acids release and reduce oxidation. • Isochrysis galbana hydrolysates stimulated Lepidium sativum seeds germination.