Effect of different drying methods on the phenolic, flavonoid and volatile compounds of Stevia rebaudiana leaves

Different drying methods (hot air drying, freeze drying and shade drying) were evaluated to discern the optimal conditions for the preservation of flavonoid, phenolic and volatile compounds in stevia leaves. All the methods applied affected the antioxidant and volatile compounds in dried stevia leaves differently. 2‐Hexenal, hexanal and α‐pinene were the most abundant volatile compounds produced by freeze drying and shade drying (21.1‐19.7; 14.2‐10 and 19.4‐5.04 µg/g, respectively); and furan tetrahydro and α‐pinene (3.2 and 3.1 µg/g, respectively) by air drying. While chlorogenic acid, coumaric acid and sinapic acid were the most abundant phenolic compounds produced by all the drying treatments (with values that ranged between 88.6‐191.8; 41.7‐91.3 and 33.2‐178.5 mg/100g dry weight of stevia, respectively). The content of volatile compounds was higher with shade drying, whereas most flavonoids and phenolic acids had higher concentrations following freeze drying, although some flavonoids and phenolic acids exhibited a higher increment with air drying. There is no best drying treatment, however, freeze drying results in an extract with satisfactory antioxidant properties and good aromatic characteristics. Copyright © 2015 John Wiley & Sons, Ltd.