The effect of roasting on boron isotope ratio in coffee beans: Implications for provenance studies of roasted coffee.

• Roasting resulted in a small negative shift of δ11B values in coffee beans. • Mechanism of boron isotope fractionation during roasting was studied. • Boron isotope fractionation occurs in capillary water of coffee beans. • δ11B values of roasted coffee can be used as a marker of coffee origin. We determined δ11B values of green and roasted coffee beans from 20 locations worldwide and conducted laboratory experiments with the aim to investigate boron isotope fractionation during roasting. Authentic single origin roasted coffees were found to be isotopically lighter than their green bean counterparts, with an average difference of 1.5‰. This isotope fractionation can be explained as arising from partial dissociation of boric acid in capillary water of green beans, where 11B isotopes are preferentially partitioned into molecules of undissociated boric acid and are then volatised during roasting. However, boron isotope fractionation induced by roasting was significantly smaller than between-origin variations in δ11B values of green coffee beans that had the range of ∼54‰. This implies that δ11B isotopic composition of roasted coffee retains the geographical origin information within δ11B values of green beans when regional differences in boron isotopic composition of coffee are considered. [ABSTRACT FROM AUTHOR]