Food-grade strategies to increase stability of whey protein particles: Particle hardening through aldehyde treatment

Protein particles are promising systems for encapsulation purposes and structure building and stabilization in a food context (Arroyo-Maya & McClements, 2015; Oduse, Campbell, Lonchamp, & Euston, 2017). Whey protein isolate (WPI) nanoparticles can be easily produced using liquid antisolvent precipitation. An additional particle hardening step is however often required, since WPI particles tend to disintegrate in aqueous environment. In this study, the potential of different food-grade aldehydes (i.e., cinnamaldehyde, salicylaldehyde, syringaldehyde, vanillin and p-anisaldehyde) to stabilize the protein particle matrix was explored. In general, the largest increase in stability against disintegration was observed for vanillin-treated particles. Incubation with vanillin did not only improve particle stability in aqueous environment, but also during isothermal storage (T=6, 23 or 37 °C for 3 weeks) and thermal treatment (T≤80 °C for 30 min). Although less pronounced, an increased particle stability in aqueous environment was also observed after salicylaldehyde or syringaldehyde treatment. All particles however disintegrated at pH values far removed from their isoelectric point (IEP≈pH 4.9), while extensive aggregation was observed near the IEP and under variable salt concentrations (0–250mM NaCl). Vanillin treatment did not induce conformational changes or covalent bond formation within the particle matrix. Therefore, the observed hardening effect presumably results from non-covalent interactions between vanillin and protein molecules. The provided insights will serve as a basis to further optimize the stabilization of protein-based systems, with the eventual goal of increasing their application potential in the food industry.status: publishe