Coffee is considered as the most popular beverage in the world for its unique sensory properties and physiological effects. From a chemical composition point of view, lipids are major coffee components and may contribute to loss of sensory quality. The roasting process is responsible for the flavour development and is a time-temperature-dependent highly complex process, whereby hundreds of chemical reactions and changes occur simultaneously. These modifications may involve not only triacylglycerols fraction, but also tocopherols, which are important lipophilic constituents present in the coffee oil with antioxidant properties. Furthermore, in addition to the important technological aspects, triacylglycerols and tocopherols profiles could also be useful in the discrimination of Arabica and Robusta coffees (either green or roasted). In this research, we have focused our attention on the modification of triacylglycerols and tocopherols from different Arabica and Robusta coffee beans subjected to different degrees of roasting.
In the present study, 5 pure coffee samples for each species have been analyzed. Coffee samples were obtained from several countries: India, Vietnam, Colombia, Guatemala, Brazil, Nicaragua and Uganda. Furthermore, the effect of the roasting temperature and time have been also assessed by using 5 different roasting levels (green, light, medium, dark, very dark). For triacylglycerols analysis, a novel LC method based on charged aerosol detection (CAD) has been developed for improving the separation of TAGs. Regarding TAGs profiles, no significant changes were observed depending on the roasting degrees even if some differences have been observed between Arabica and Robusta. Tocopherols were monitored by NP-HPLC- FL analysis. In this case, tocopherols composition has been proven to be useful in the discrimination of Arabica and Robusta coffees. On the other hand, the Arabica and Robusta coffees behaviour at the 5 different roasting levels was similar without significant decreases in tocopherols content in both varieties. This study showed that the roasting level has no significant impact on TAGs and tocopherols composition on both Arabica and Robusta coffee, even if tocopherols profile has been confirmed as a valuable marker of coffee variety. Furthermore, a novel ultrahigh pressure liquid chromatography coupled with CAD detection has been developed and applied to the analysis of coffee oil triglycerides.