Effect of Selected Mechanical/Physical Pre-Treatments on Chlorella vulgaris Protein Solubility

Chlorella vulgaris has been recognized as an interesting alternative feeding source since it contains a good amount of high-quality protein. However, the presence of a recalcitrant cell wall strongly affects the nutrients' digestibility, bioaccessibility, and bioavailability. The present study aimed to determine the influence of different pre-treatments (bead milling, extrusion, freeze-drying, heating, microwave, and sonication) on C. vulgaris' protein solubility. For total protein content and solubility, the Bradford method and sodium dodecyl sulphate-polyacrylamide gel electrophoresis (SDS-PAGE) quantification were used, respectively, and protein degradation was assessed by SDS-PAGE through quantification of protein fractions (26 kDa, 32-40 kDa, 66-96 kDa, and others). The o-phthaldialdehyde assay was used for peptide formation. While there were no statistically significant differences for total soluble protein measurements in the supernatant fractions, the results showed an increase in larger proteins following bead milling and microwave pre-treatments, and sonication led to higher fractions of the remaining protein (mostly of low molecular weight). Nevertheless, extrusion significantly increased the release of peptides in the soluble fractions, and, considering industrial applicability, this method may be a better choice for improving C. vulgaris protein bioaccessibility in monogastric diets.