Binding of retinyl acetate to whey proteins or phosphocasein micelles: Impact of pressure-processing on protein structural changes and ligand embedding

- Retinyl acetate (RAC) was embedded into pressure-processed whey proteins or phosphocaseins.
- Dynamic (UHPH) or isostatic (HP) high pressure is proposed as tools to improve RAC embedding.
- 2.3-3.7 nmol RAC was retained per mg of pressure-denatured whey proteins, less than after STTT.
- 3.8-5.4 nmol RAC was carried per mg of PC through pressure-induced PC structural changes.
- Combined pressure and mild temperature increased RAC embedding in PC assemblies.

A whey protein isolate (WPI) and native phosphocaseins (PC) at pH 6.5-6.6 were processed with retinyl acetate (RAC) using pressure-assisted technological tools to improve RAC embedding through processing-induced protein structural changes. To this end, protein-RAC dispersions were submitted to ultra-high pressure homogenisation (UHPH) at 300 MPa and an initial fluid temperature (Tin) of 14 °C or 24 °C, or isostatic high-pressure at 300 MPa and 14 °C or 34 °C for 15 min. A short-time thermal treatment (STTT, 73 °C for 4 s) able to generate WPI aggregates was assessed for comparison. Processing effects were investigated in terms of protein particle sizes and molecular weights (Mw). Mw calculated using protein size determination obtained from light scattering measurements were in agreement with the known values. The amounts of RAC retained in WPI particles (unfolded and/or aggregated proteins) or in PC assemblies were quantitated after protein precipitation by ammonium sulphate. A 2.3-3.7 nmol RAC was carried per mg of pressure-denatured whey proteins, significantly less than after STTT (6.3 nmol RAC per mg of heat-denatured whey proteins) indicating that RAC embedding varied according to the technological tool, pressure or temperature. A 3.8-5.4 nmol RAC was carried per mg of PC assemblies through pressure-induced dissociation/reassociation of PC micelles. Combined pressure and mild temperature increased RAC embedding in PC assemblies.