Ultrasound-Assisted Emulsification of Roasted Coffee Oil in Complex Coacervates and Real-time Coffee Aroma Release by PTR-ToF–MS

Roasted coffee oil (RCO) is rich in volatile organic compounds (VOCs), but the VOCs’ volatility and the presence of unsaturated fatty acids make RCO unstable. The microencapsulation process can extend RCO properties by transforming the liquid RCO into stable powders for further application in coffee brews to better result in-cup. In this work, a central composite rotational design was used to study the effect of the emulsification process and discuss the effect of added microcapsules to instant coffees on the time-resolved release of VOCs upon reconstitutions. Capsules were produced by complex coacervation loaded with RCO, and ultrasound-assisted (US) emulsification was used to obtain stable coffee oil–loaded emulsions. VOC release was monitored by proton-transfer reaction time-of-flight mass spectrometry (PTR-ToF–MS). High encapsulation efficiency (EE) (> 80%) was obtained even at a high load (100%) of RCO. EE was only affected by US power while particle mean size (D43) was strongly affected by US power and the RCO concentration. The presence of microcapsules affected the VOC release from the moment of reconstitution. The microcapsules accelerated the VOC release in soluble coffee, while in instant cappuccino, an opposite effect was observed. A zero-order model described well the mechanism of VOC release during the first 300 s. The diffusional exponent values of the Korsmeyer–Peppas equation explained a zero-order transport during the first seconds of release (burst effect) and a non-Fickian release mechanism when the release slowed down. Such findings shed new light on the development of instant coffees in order to improve their sensorial properties.