Coffee adulteration has become widespread and has diversified into many forms along the commercial chain. Adulterated coffee beans cause significant roasting and brewing inconsistencies resulting in poor product quality and sensory characteristics. Tainted coffee products are also labelled as high-quality products and marketed at a premium cost. The deliberate mixing or trading of high-quality green coffee beans with lower grade varieties is recognized as the most difficult form of adulteration to identify. As the US coffee market continues to grow, reaching a retail value of $88B USD in 2018 and approximately $5.84 B USD of total coffee imports in 2019, economically motivated adulteration (EMA) continues to threaten the coffee industry. Therefore, safeguarding the coffee industry from such EMAs has significant economic impact not just globally, but also on national and local levels.
Effective analytical tools for detecting adulterated coffee are critically essential for the coffee industry. To address this challenge, a high-throughput and on-line selected ion flow tube-mass spectrometry (SIFT-MS)-based analytical system was developed for the authentication and adulteration analysis of coffee beans from single geographical origins.
Single-origin green coffee beans (pure and pre-mixed) from Coffee arabica and Coffee canephora (Robusta) cultivars were roasted at an optimized time and temperature. Off-gas volatile compounds were measured in real-time during the entire roasting duration using an online SIFT-MS. Volatile compounds were monitored within the instruments mass spectral range. Data evaluation was performed using time-series data analysis and classification model schemes. Comparison of volatile intensities was performed using chemometric techniques through principal component analysis and ANOVA.
Emission profiles revealed that volatile compounds form and decay at different times during roasting. Characterization of these compounds showed that their occurrences and intensities were specific for each coffee variety. Unique ion identifiers were determined and used as key volatile markers in authenticating single-origin coffee beans. Coffee bean adulteration was also detected and identified successfully through on-line SIFT-MS analysis of key volatile compounds during roasting. Thus, online SIFT-MS is an effective analytical tool for the real-time analysis of volatile compounds during coffee roasting.