Improvement of Robusta coffee aroma with l‐leucine powder

BACKGROUND l‐Leucine powder (LP) was added to green Robusta coffee beans in order to reduce the difference in flavour between Robusta and Arabica coffee. l‐Leucine was selected as an additive based on the Maillard reaction. The pre‐treatment method conducted in this study was a short soaking (M1) or spraying procedure (M2), then LP was added at varying levels up to 3% (w/w, 30 g kg−1). All samples were roasted (240 °C for 15 min) and extracted using an espresso machine. Volatile compounds were analysed by solid‐phase microextraction‐gas chromatography‐mass selective detection. RESULTS Thirty volatile compounds (six pyrroles, eight pyrazines, three phenols, nine furans, two ketones, two aldehydes) were analysed. In 15 coffee samples, the levels of total volatile compounds (based on peak area ratios) ranged from 8.9 (M1‐1) to 15. Non‐treated Robusta had higher levels of bitter aroma compounds than Arabica coffee, and Robusta coffee had lower levels of bitter aroma compounds when pre‐treated with LP. The sum of bitter volatiles (phenols, pyrroles, pyrazines) was lowest in M1‐5 (3% LP), M2‐1 (1% LP; both dried at 50 °C for 15 min) and M2‐7 (3% LP, dried at 70 °C for 15 min) compared with non‐treated Robusta (P