Effect of High-Pressure Homogenization on the Functional and Emulsifying Properties of Proteins Recovered from Auxenochlorella pyrenoidosa

Auxenochlorella pyrenoidosa is a microalga that stands out due to its high protein content. The objective of this work was to study the effect of high-pressure homogenization (HPH) on the recovery of proteins from A. pyrenoidosa and their application as functional emulsifiers. Untreated and HPH-treated (400–800 bar, 1 and 4 passes) aqueous cellular suspensions were incubated at 40 °C for 6 h. The aqueous extracts were collected, the proteins were precipitated at pH 3, and the Auxenochlorella pyrenoidosa protein concentrates (APPC) were lyophilized. Increasing HPH pressure and number of passes (400–800 bar, 1 and 4 passes) improved protein recovery yield up to 57%. Higher HPH pressures also reduced α-helix and β-sheet structures, exposing the hydrophobic protein core. This protein modification led to APPCs with increased oil-holding capacity (2.83 g oil/g APPC). The surface tension of APPC solutions reached a minimum value of 28.6 mN/m at an APPC concentration of 2% w/w. The APPCs from untreated and HPH-treated biomass were used to stabilize nanoemulsions (2–6% sunflower oil), comparing one-step homogenization (high-speed homogenization) with the two-step homogenization method (combining high-speed and high-pressure homogenization). The two-step method led to significantly smaller oil droplets with narrow size distribution, leading to stable nanoemulsions with improved resistance to centrifugation and heating–cooling cycles. Due to APPC’s great emulsifying properties, A. pyrenoidosa proteins have a promising potential for various applications such as delivery systems stabilization. Additionally, the low energy requirements, continuous processing capability, and scalability of HPH make it a suitable process for industrial applications.