What’s in a cup? Researchers develop novel way to determine coffee purity
14 Jan 2021 --- Researchers from the American Chemical Society are exploring new ways to access exactly what is in coffee. The bean composition of coffee can be difficult to determine after roasting, and roasters typically blend two types of beans, arabica and robusta.
Arabica beans are more desirable than other types, resulting in a higher market value for blends containing a higher proportion of this variety.
In some cases, producers dilute their blends with the less expensive robusta beans, yet that is hard for consumers to discern.
Global consumers opt for coffee that is both satisfying and reasonably priced. Some use more of the cheaper robusta to meet these standards than they acknowledge, and the bean composition is often unknown.
The researchers have published their findings in ACS’ Journal of Agricultural and Food Chemistry touting the new method to verify that the coffee has not been adulterated.
Arabica beans are more desirable than other types.
The perfect blend
Recently, methods involving chromatography or spectroscopy were developed for coffee authentication. Still, most of these are labor- and time-intensive or use chloroform for the extraction, limiting the types of compounds that can be detected.
In some studies, researchers used nuclear magnetic resonance (NMR) spectroscopy to monitor the amount of 16-O-methylcafestol (16-OMC) in coffee, but its concentrations vary depending on geographic location and cultivar.
So, Fabrice Berrué, lead researcher and colleagues wanted to build on their previous work with NMR to assess each coffee bean's chemical makeup and confirm the blends of real samples.
Identifying coffee compounds
The researchers extracted compounds from a test set of pure coffee and known blends with methanol and identified the compounds with NMR.
The team found 12 compounds with measurable concentrations, and two had significantly different amounts between the coffee varieties.
Elevated concentrations of 16-OMC were unique to robusta, while high concentrations of kahewol – a compound previously found in coffee beans by other researchers – were distinct in arabica.
There was a direct, reproducible relationship between 16-OMC and kahewol concentrations found in the two varieties' blends. The team then measured 16-OMC and kahewol levels, in addition to other flavor molecules, in 292 samples from producers around the world.
They could successfully authenticate pure coffee, even with relatively low concentrations of the two indicator compounds. For samples in which the composition of blends was known, the team's predictions were within 15 percent of the actual ratio.
The new method more robustly and reliably verifies unadulterated coffee and predicts blends better than previously reported approaches, the researchers say.
Edited by Elizabeth Green
