Novel processing methods are needed in order to manufacture heat stable egg white protein (EWP) ingredients, as native EWP is thermally liable which severely limits their application in protein beverages and other liquid food applications. This study aimed to manufacture thermally stable colloidal EWP aggregates (EWP-A) via heating of already pasteurized EWP (P-EWP) dispersion derived from commercial pasteurized EWP ingredients. EWP dispersions (4%, w/v) with different pH levels ranging from 9.5 to 12 were heated at 85 °C for 10 min to 120 min resulting in a total of 24 EWP sols; the obtained protein sols were neutralized to pH 7 for characterization. The heat treatment reduced turbidity, particle size and total free sulfhydryl group of EWP but it induced an increase of protein surface charge and formation of protein aggregates. Thirteen out of 24 EWP sols obtained from the heat treatments exhibited excellent bulk phase stability and did not form a solid gel-like material nor a precipitation after a secondary heat treatment (90 °C for 15 min). The fine emulsions (10% sunflower oil with 1% protein, w/w) made with 5 selected EWP aggregates (pH10_120min, pH10.5_60min, pH11_30min, pH11.5_30min and pH12_10min) had smaller mean droplet size (~1 µm) and higher surface charge (−40 mV), compared to the control emulsion (~40 µm, −32 mV) prepared with pasteurized EWP. The EWP-A emulsions exhibited excellent heat stability, in which bulk phase separation and change in mean particle size were not evident after heat treatment (90 °C, 30 min). However, the emulsions made from P-EWP formed a soft gel-like material after heat treatment. Interfacial property analysis showed that EWP-A adsorbed to the oil-water (o-w) interface with lower adsorption rate constants compared to P-EWP. Moreover, at the oil-water interface, the quasi-equilibrium interfacial tension induced by EWP-A adsorption was higher than that of P-EWP adsorption. The findings from this work have important implications for the production of protein-based beverages using thermally stable EWP aggregates as an ingredient.

Haotian Zheng

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