Influence of curing procedures on sensory quality of vanilla beans

Introduction. During maturation, vanillin is accumulated in green vanilla beans as glucovanillin; it is hydrolyzed to free vanillin by endogenous glucosidases during curing and gives the characteristic flavor of vanilla. The objective of our study was to investigate methods of curing that could greatly reduce the time to complete the process and yield cured beans that retain high concentrations of vanillin and other flavor compounds with high sensory quality rating. Materials and methods. Mature green beans were obtained from a commercial grower (Cairns, Queensland, Australia). One batch of beans was continuously sweated at 35°C at high relative humidity (RH) for 12 d. Two further batches were blanched in water at 67°C for 3 min, and then sweated at 45°C at high RH for 4 d or at 35°C for 5 d. The beans were sweated until they turned brown. Three methods of drying were evaluated: a heat pump dryer at 40°C and RH 15%, tunnel dryer at 60°C and RH 20%, and tunnel dryer at 60°C and RH 10%. Vanillin was extracted from powdered samples of beans with n-pentane and dichloromethane (1:1 v/v) and assayed by HPLC. Glucovanillin was measured as total vanillin after acid hydrolysis of powdered samples of beans. Results and discussion. About 90% of the glucovanillin was converted to vanillin in non-blanched beans continuously sweated at 35°C, but there was only 70% conversion in beans blanched at 67°C for 3 min and sweated at 45°C for 4 d or at 35°C for 5 d. The sensory quality of cured beans was assessed by untrained panelists. Profiling showed that the beans sweated continuously at 35°C had superior aroma compared with beans blanched in hot water and sweated at 45°C or at 35°C but the appearance of non-blanched beans was less attractive. Conclusion. The study revealed that a mild hot water blanching treatment followed by sweating at 35-45°C and rapid drying is required to produce cured beans with excellent appearance and attractive aroma.