Differentiation of degrees of ripeness of catuai and tipica green coffee by chromatographical and statistical techniques

The quality of green coffee is influenced by the degree of ripeness of the fruit at harvest. The aim of this study was to identify chemical markers differentiating between degrees of ripeness. Two coffee varieties, Catuai and Tipica, from the same farm were analysed using the following parameters and methods: caffeine and chlorogenic acid content using high-performance liquid chromatography (HPLC), sucrose content using hydrophilic interaction chromatography, high-molecular weight fraction (HMW) using high-performance size-exclusion chromatography (HPSEC) and volatile compounds using headspace solid phase micro extraction gas chromatography/mass spectrometry. The best method for differentiating between degrees of ripeness was found to be principal component analysis (PCA) based on HPLC data. HPSEC showed differences in the HMW fraction for different degrees of ripeness and both coffee varieties. Volatile profiles allowed separation of both varieties; yet, except for ripe Catuai, no separation was achieved for the degree of ripeness

Real-time mass spectrometry monitoring of oak wood toasting: elucidating aroma development relevant to oak-aged wine quality

We introduce a real-time method to monitor the evolution of oak aromas during the oak toasting process. French and American oak wood boards were toasted in an oven at three different temperatures, while the process-gas was continuously transferred to the inlet of a proton-transfer-reaction time-of-flight mass spectrometer for online monitoring. Oak wood aroma compounds important for their sensory contribution to oak-aged wine were tentatively identified based on soft ionization and molecular mass. The time-intensity profiles revealed toasting process dynamics illustrating in real-time how different compounds evolve from the oak wood during toasting. Sufficient sensitivity was achieved to observe spikes in volatile concentrations related to cracking phenomena on the oak wood surface. The polysaccharide-derived compounds exhibited similar profiles; whilst for lignin-derived compounds eugenol formation differed from that of vanillin and guaiacol at lower toasting temperatures. Significant generation of oak lactone from precursors was evident at 225 (o)C. Statistical processing of the real-time aroma data showed similarities and differences between individual oak boards and oak wood sourced from the different origins. This study enriches our understanding of the oak toasting process and demonstrates a new analytical approach for research on wood volatiles

Measuring partition coefficients of VOC's and their temperature dependence by dynamic stripping and Proton-Transfer Reaction Time-of-Flight Mass Spectrometry (PTR-ToF_MS)

Air-water partition coefficients play a significant role in understanding processes like aroma release from food, for many environmental phenomena or in medical analysis (breath analysis). The equilibrium of gas dissolved in a liquid (e.g. water) can be described via Henry`s Law constant (HLC). We have developed and validated a dynamic approach using a stripping cell configuration coupled on-line to a PTR-ToF-MS to measure with high accuracy the HLC of VOCs. This methodology allows the rapid determination of water-air partition coefficients, even for molecules with low volatility, and over an extended temperature range (25-90°C)

Applications of PTR-ToF-MS on coffee

Over the last decade, PTR-MS has made major contributions to the progress in coffee research. The research group Analytic and Analytical Technologies at the Zurich University of Applied Sciences in Wädenswil, has established over the last two years a strong research focus on the science of coffee. In this frame, PTR-ToF-MS is used in concert with complementary analytical technologies, to address applied research projects. Here we report on a series of on-going projects, where PTR-ToF-MS plays a significant role. We outline how PTR-ToF-MS data are being integrated into extensive analytical studies, to achieve a more comprehensive understanding of the subject under study. This includes (i) fundamental investigations on the temperature dependence of partition coefficients of volatile flavor compounds (ii) on-line process monitoring and (iii) the development of a predictive model for coffee sensory profiles

Analysis of the structure of condensed tannins in water extracts from bark tissues of Norway spruce (Picea abies [Karst.]) and Silver fir (Abies alba [Mill.]) using MALDI-TOF mass spectrometry

Condensed tannins extracted from the bark of softwoods have been proven to be suitable compounds in the formulation of environmentally friendly adhesives and resins. Their chemical structure has been shown to significantly influence their properties and possible applications. Condensed tannins extracted from the bark of Norway spruce (Picea abies [Karst.]) and Silver fir (Abies alba [Mill.]) still lack a detail characterization of their chemical structure. In an effort to address this deficiency, barks from these species were collected and extracted in water at 60°C. The dried extracts were analyzed by MALDI-TOF mass spectrometry to identify the building blocks and to determine the degree of polymerization of the tannin oligomers. The condensed tannins extracted from spruce bark at the used conditions were mainly composed of procyanidins with a polymerization degree up to 13. Silver fir extracts revealed a predominance of prodelphinidins with a polymerization degree up to 9. The presence of less common building blocks such as stilbene glucosides and flavan-3-ols gallates was also hinted. Different curing times and viscosities in resin formulations are expected between the two studied species, as well as in comparison to the most known and available tannins from tropical species

On-line analysis of the coffee roasting process with PTR-ToF-MS : evidence of different flavor formation dynamics for different coffee varieties

Proton transfer reaction time of flight mass spectrometry is a powerful tool to analyse on-line processes with a high mass resolution. Here, the formation of volatile organic compounds (VOCs) during the coffee roasting process was monitored. A variation of not only the time-temperature roasting parameters (roast degree and length of roasting process) but also the variation of the coffee origin revealed changes in the coffee flavor formation: (i) different VOCs were formed differently during roasting the same type of coffee along the same time-temperature roasting profile, (ii) these formation pathways changed when changing the time-temperature roasting profile, and (iii) roasting different coffee origins led to different flavor formation pathways for the same VOCs. Roasting Colombian and Guatemalan coffee (both coffea arabica) led to similar formation pathways, whereas the Ethiopian coffees (Djimmah and Yirga Cheffe, both coffea arabica) showed different time-intensity profiles of the VOCs, as did the Indonesian coffea canephora var. robusta (Malangsari)

Online monitoring of coffee roasting by proton transfer reaction time-of-flight mass spectrometry (PTR-ToF-MS) : towards a real-time process control for a consistent roast profile

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 (1 Hz) and mass resolution (5,500 m/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