Volatile Release from Whey Protein Isolate-Pectin Multilayer Stabilized Emulsions: Effect of pH, Salt, and Artificial Salivas

Whey protein isolate (WPI) and pectin can form a multilayer at the oil-water interface when they are oppositely charged. In this study, effects of pH, salt, and artificial salivas on emulsion stability and volatile release from multilayer emulsions were investigated. Results showed that emulsions (0.5 wt % WPI, 10 wt % oil) with pectin content <= 0.1 wt % had rapid phase separation at pH 4 and 5, and emulsions with higher pectin content (>= 0.2 wt %) had good stability. Due to an electrostatic screening effect, multilayer emulsions collapsed when subjected to >= 150 mM NaCl solutions at pH 5. When diluted with artificial salivas containing salts, mucin, and/or alpha-amylase, multilayer emulsions showed rapid droplet aggregation. GC headspace analysis found that volatiles had significantly lower initial headspace concentration (C-initial) in multilayer emulsions, and the C-initial correlated negatively with pectin content in emulsions. Emulsions at pH 7 had more volatiles released to the headspace than emulsions at pH 5. However, changes in pectin content and pH did not show a significant effect on release rate of most volatile compounds. In salt-treated multilayer emulsions, C-initial and release rates of volatiles increased with NaCl content. Addition of salivas triggered higher release of hydrophobic volatiles and lower release of hydrophilic volatiles, which was mostly due to dilution effect and saliva-induced emulsion instability.