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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.

This work evaluated the use of roasted coffee oil (RCO) and the effects of ultrasound (US)-assisted emulsification on RCO-in-water emulsion properties, the changes in the composition of volatile organic compounds (VOCs) of roasted coffee aroma during US and microencapsulation by spray drying, and VOCs release profile upon instant coffee reconstitution. VOCs were determined by gas chromatography-mass spectrometry, and the release profile was monitored in real-time by Proton Transfer Reaction Time-of-Flight Mass Spectrometry (PTR-ToF–MS). US was found to be effective in producing stable submicron emulsions (≤ 2.0 µm) that resulted in high encapsulation efficiency (> 90%) of the microparticles. Significant changes were detected in VOC composition throughout the microencapsulation process. The addition of microparticles loaded with RCO in instant coffee did not change the VOCs release profile during the brew preparation but was effective in increasing coffee aroma.

A real-time automated process control tool for coffee roasting is presented to consistently and accurately achieve a targeted roast degree. It is based on the online monitoring of volatile organic compounds (VOC) in the off-gas of a drum roaster by proton transfer reaction time-of-flight mass spectrometry at a high time (1Hz) and mass resolution (5,500m/Δm at full width at half-maximum) and high sensitivity (better than parts per billion by volume). Forty-two roasting experiments were performed with the drum roaster being operated either on a low, medium or high hot-air inlet temperature (= energy input) and the coffee (Arabica from Antigua, Guatemala) being roasted to low, medium or dark roast degrees. A principal component analysis (PCA) discriminated, for each one of the three hot-air inlet temperatures, the roast degree with a resolution of better than ±1 Colorette. The 3D space of the three first principal components was defined based on 23 mass spectral profiles of VOCs and their roast degree at the end point of roasting. This provided a very detailed picture of the evolution of the roasting process and allowed establishment of a predictive model that projects the online-monitored VOC profile of the roaster off-gas in real time onto the PCA space defined by the calibration process and, ultimately, to control the coffee roasting process so as to achieve a target roast degree and a consistent roasting. Figure Online monitoring of coffee roasting by real-time analysis of the roaster off-gas using PTR-ToF-MS. In a first phase, 42 calibration experiments were conducted at three different roasting temperatures and to three final roast degrees, to generate the 3D space defined by the three first principle components PC1, PC2 and PC3. Inverted triangles mark the dark roast degree, square medium and circle light, respectively. The hot-air inlet temperature is marked as follows: high (black), medium (grey), low (white). The different hot-air inlet temperatures and roast degrees are clearly separated. In a second phase, an online monitored PTR-ToF-MS spectrum of a roasting process was projected onto the 3D space, allowing following in real-time the roasting process and halting the roasting with a precision better that ± 1 Colorette roast degree

The yield of C60+ ions reflected from the surface of graphite is found to be a bimodal function of the energy of impact. Below 140 eV (6 km/s), the yield decreases with energy and the scattering time-of-flight peak is sharp. Above 170 eV, the yield increases, but the peak is broad and asymmetric, corresponding to delayed electron emission from an impact-heated, neutralized cluster. There is also evidence for fragmentation to C58 and C56. The emission process may be analogous to that reported for scattered C60-. Application of statistical rate theory to either observation (C60± ) gives an estimated 25-30 percent transfer of impact energy into cluster internal modes. The decreasing yield at highest energies (>400 eV) may result from adhesion processes (C60-surface bonding) that could also account for the absence of delayed electron emission in C60-silicon collisions.