Biostimulants obtained after pilot-scale high-pressure homogenization of Scenedesmus sp. grown in pig manure

Microalgae are becoming an important source of high-value products such as biostimulants, biopesticides, and other low-value products such as biofertilizers or aquafeed (fatty acids and carotenoids), among others. However, extracting the biomolecules contained in the microalgae cells is difficult due to the structure and composition of the microalgal cell wall. To overcome this difficulty, mechanical cell disruption methods, such as high-pressure homogenization (HPH), can be applied to facilitate the extraction of the compounds of interest. This work focuses on optimizing the extraction of biostimulants from microalgae biomass and obtaining amino acid concentrates that can be used in several applications. The research aims to study the effect of HPH pretreatment on the production of these different bioproducts using Scenedesmus sp. biomass grown in pig sludge as the raw material. For each product, the HPH pretreatment of the wet biomass must be optimized to select the optimal conditions and the number of passes. Soft treatment of the wet biomass at 200 bar is sufficient to observe a 10% increase in the germination index (GI) of watercress seeds, while greater treatment intensities reduce the GI with respect to the untreated biomass, possibly because this increases the concentration of the molecules responsible for the bioactivity, thus causing a toxic effect on the seeds. In the case of the amino acid concentrates, better results were obtained at 600 bar, achieving a hydrolysis level of 72.9%. Lastly, the concentrations of the phenolic compounds and the salicylic acid, related with enhanced biostimulant activity, were determined using spectrophotometric methods and High-Performance Liquid Chromatography-diode array (HPLC), respectively.