Encapsulation of labile compounds in heat- and high-pressure treated protein and lipid nanoparticles

Globular whey proteins and lipids are used in food technology for their structure-forming properties and also as matrix carriers of lipophilic bioactive compounds. Their structural properties are heat- and high-pressure sensitive, making their functional properties greatly dependant on food processing conditions. The aim of this study was to identify and quantify structural factors involved in the production of food-grade nanoparticles (100 nm to 500 nm) designed as matrix carriers of α-tocopherol (model of heat- and oxygen-sensitive lipophilic compound). Matrix carriers consisting of whey protein aggregates, alone (PV300 and PV1200) or stabilising oil-in-water hydrogenated palm oil nanoemulsions (EV300 and EV1200) were produced using a two-step hot homogenisation procedure (ultra dispersion at 65 °C followed by high-pressure homogenisation (HPH) at 300 or 1200 bar for 12 cycles). The processing treatment applied formed lower size particles accompanied by higher vitamin degradation (by 30%) in PV300 and PV1200 than in EV300 and EV1200 (less than 5% and 15%, respectively). Under storage for 8 weeks, EV1200 and PV300 presented much less vitamin protection (45% degradation) instead of around 22% and 33% for EV300 and EV1200, respectively. Physical structure characterization showed that increasing the time-intensity of HPH treatments was accompanied by i) a decreasing in the overall protein conformation stability in parallel with an increasing in protein- and vitamin molecular interactions, ii) formation of smaller size lipid droplets in oil-in-water emulsions in parallel with more protein adsorption to lipid droplets and less crystalline fat content and high energy polymorphs. These mechanisms could explain why application of increasing mechanical treatment intensity for longer physical stability against coalescence is accompanied by hindered shelf-life of resulting low size vitamin-loaded particles formed in protein-stabilised nanoemulsions.