Studies on the Impact of Selected Pretreatments on Protein Solubility of Arthrospira platensis Microalga

Arthrospira platensis has emerged as a novel protein feed source since it contains high protein level and quality. However, this microalga presents a recalcitrant cell wall and its main proteins form protein-pigment complexes attached to the thylakoid membrane. The objective of the present study was to evaluate the influence of mechanical/physical pretreatments (bead milling, extrusion, freeze-drying, heating, microwave and sonication) on A. platensis protein solubility. Total protein content and solubility were assessed by Bradford method and SDS-PAGE quantification. Protein degradation was assessed through quantification of protein fractions (18-26 kDa, 40-48 kDa and others) in SDS-PAGE gels. Peptide formation was evaluated using the o-phthaldialdehyde assay. The results showed a decrease in total protein content in the supernatant with extrusion (0.07 to 1.42 mg/mL) and microwave pretreatments, and in the pellet with extrusion. Therefore, extrusion, followed by microwave, was the most effective pretreatment for A. platensis proteins denaturation and solubility. It is suggested that the extrusion process cause an irreversible denaturation and aggregation of the major microalga proteins (c-phycocyanin and allophycocyanin), with a strong decrease in their solubility. Therefore, extrusion could increase the bioaccessibility of A. platensis proteins and enable the incorporation of this microalga at higher levels in monogastric diets.