People around the world want their coffee to be both satisfying and inexpensive. To meet these standards, roasters usually use a mix of two types of beans, arabica and robusta. However, some use more of the cheaper Robusta than they acknowledge because the composition of the beans is difficult to determine after roasting. Now researchers in ACS report & # 39; Journal of Agricultural and Food Chemistry have developed a new way of judging exactly what is in this cup of Joe.
Coffee blends can be of good quality and taste. However, Arabica beans are more desirable than other varieties, resulting in higher market value for mixes containing a higher proportion of this variety. In some cases, manufacturers dilute their blends with the less expensive Robusta beans, but this is difficult for consumers to see. Recently, methods of chromatography or spectroscopy have been developed to authenticate coffee, but most of them are labor and time consuming or use chloroform for extraction, which limits the types of compounds that can be detected. In some studies, the researchers used nuclear magnetic resonance spectroscopy (NMR) to monitor the amount of 16-.Ö-Methylcafestol (16-OMC) in coffee, but its concentrations vary depending on geographic location and variety. Therefore, Fabrice Berrué and colleagues wanted to build on their previous work with NMR to assess the chemical composition of each coffee bean variety and confirm the blends of real samples.
The researchers extracted compounds from a test kit of pure coffee and known mixtures with methanol and identified the compounds using NMR. The team found 12 compounds with measurable concentrations and two had significantly different amounts between coffees. Elevated levels of 16-OMC were only seen in Robusta, while high levels of kahewol – a compound previously found in coffee beans by other researchers – were different in Arabica. There was a direct, reproducible relationship between 16-OMC and Kahewol concentrations found in the mixtures of the two varieties. The team then measured 16-OMC and Kahewol levels in 292 samples from manufacturers around the world, along with other taste molecules. They were able to successfully authenticate pure coffee even with relatively low concentrations of the two indicator compounds. For samples where the composition of the mixtures was known, the team's predictions were within 15% of the true ratio. The new method leads to a more robust and reliable method for verifying unadulterated coffee and predicting blends than approaches previously described, the researchers say.