Heat treatment as a food-grade strategy to increase the stability of whey protein particles under food system relevant conditions

Abstract Whey proteins are well-suited for the production of protein nanoparticles (NPs). However, whey protein NPs are not stable in aqueous media unless they undergo some type of hardening. Heat pretreatment of NPs was investigated as a hardening strategy. The highest stability against redissolution in water, as evaluated by particle size distribution measurements and quantification of the soluble protein level, was achieved when NPs in 80.8 v/v% aqueous ethanol were treated for 30 min at 60 °C. Size exclusion chromatography under non-reducing and reducing conditions showed that intermolecular disulfide bridges were formed during this treatment while conformational changes of proteins, as assessed via intrinsic fluorescence and vibrational spectroscopy measurements, in the particle matrix seemed minimal. Properties of whey protein NPs were largely driven by interactions and reactions between β-lactoglobulins. Hardening also extended the stability of NPs in 8.1% v/v aqueous ethanol against disintegration, and aggregation upon thermal incubation and/or isothermal long-term storage. As untreated and heat pretreated NPs displayed distinct behavior upon resuspension in water and exposure to different environmental conditions, these insights are valuable for developing controlled release NPs displaying specific release kinetics.