Cold gelation of whey protein isolate with sugars in an ultrasound environment

Dispersions of whey protein isolate (9.5% protein) with 1.5% of sugar (glucose, mannose or xylose) were preheated, and ions-induced gelation was performed in an ultrasound environment at room temperature. Depending on the used sugar, sonication increased, decreased or did not change the rheological properties of gels (storage modulus, hardness and ultrasound viscosity). That was contrary to the formation of Maillard reaction compounds, which probably by occupation of active sides of proteins, induced the formation of a weaker three-dimensional gel network. For most samples, sonication increased the value of the contact angle, switching their surface character from hydrophilic to hydrophobic one. The surface free energy of the obtained gels decreased after sonication, and such surfaces were less susceptible to wetting. The increase in the value of the contact angles corresponded to the increase in the roughness of the gels after sonication. The relationship between the surface roughness and the wettability can be attributed to the surface wetting state (Wenzel state, Cassie-Baxter state, and transition state). For the gels surfaces with lower roughness, the liquid was more susceptible to penetration to the surface due to large adhesive forces (Wenzel model) and for higher roughness, the liquid was more susceptible to resting on the “air micro cushions” (Cassie-Baxter model). The ultrasound-induced cold-gelation for the preparation of natural protein/sugar gels can offer a potential approach to develop new functional products with tailor-made attributes.