Effect of gamma-radiation on major aroma compounds and vanillin glucoside of cured vanilla beans (Vanilla planifolia)

Cured vanilla beans were irradiated (5, 10, 15, 20 and 30 kGy) for a possible enhancement of vanillin content by radiolysis of vanillin glucoside. The vanillin content of control and irradiated (30 kGy) samples were 26.6 ± 0.85 and 26.9 ± 0.70 mg/g (dw), respectively, while vanillin glucoside were 7.74 ± 0.2 and 7.35 ± 0.35 mg/g (dw). Radiation caused no significant changes (p ⩽ 0.05) in aroma constituents. In a pulse radiolysis experiment, vanillin glucoside on reacting with OH radical gave transients with absorption peaks at 360 nm and 410 nm. The species absorbing at 410 nm has been interpreted to be a hydroxyl radical adduct. It decayed at the same rate in the presence of oxygen, while the absorption at 360 nm did not. Results obtained revealed that the more stable one absorbing at 360 nm is aldehydic radical. Hence the highly stable oxygen–carbon linkage between vanillin and glucose limits the possible enhancement of aroma quality of irradiated beans.