Friday, October 29, 2010
NMR and Food Chemistry - Coffee
Many of us enjoy a hot delicious cup of coffee. Many (not including myself) will even spend a great deal of money and a great deal of their time in a long queue to get it! The coffee snobs will preach about the differences between a freshly brewed cup of java and the lowly cup of instant coffee. Is there really a difference? Spectrum A in the figure below shows the 13C CPMAS NMR spectrum of ground coffee. Among other things, the spectrum consists of resonances from the woody fibers, polysaccharide gums, tannins, alkaloids and aromatic oils. Spectrum B is the spectrum of used coffee grounds which were subsequently dried. The spectrum is due to the woody fibers and other insoluble material. Spectrum C is the difference between spectrum A and B and represents all the "goodness" of a fresh brewed cup of coffee. Among other things, it represents all of the alkaloids, tannins and aromatic oils. Spectrum D is the 13C CPMAS NMR spectrum of instant coffee which is manufactured by freeze drying brewed coffee. The spectrum is very similar to the difference spectrum, C. This indicates either that the difference between a freshly brewed cup of coffee and a cup of instant coffee lies in very low concentration constituents or that the coffee snobs are wasting their money and time in long queues. I think both are true.