Effect of Drying Methods on the Drying Kinetics and Volatile Components of Vanilla Beans

Abstract

This study evaluated the effects of hot air drying (HAD), infrared drying (IRD), and vacuum freeze drying (VFD) on the drying characteristics and volatile components of vanilla. The results indicated that both IRD and VFD were effective in preserving the original color of the samples. Compared to HAD and VFD, IRD significantly shortened the drying time by 21.05% and 42.11%, respectively. The Page model was identified as the best mathematical model for simulating the drying characteristics of vanilla beans. The drying method exhibited a significant impact on the types and contents of volatile components in vanilla. Compared to the original vanilla (ORI), the volatile component content increased by 38.00% and 35.00% for the samples treated with IRD and HAD, respectively. Notably, IRD retained a greater variety of original volatile substances and exhibited the highest contents of ketones and esters at 10.35 and 0.83 mg/g, respectively. In contrast, the HAD sample resulted in the highest contents of acids and hydrocarbons at 2.96 and 0.87 mg/g, respectively, while VFD led to a reduction in the content of all volatile components. The comprehensive scoring results from principal component analysis ranked the samples as follows: IRD > ORI > HAD > VFD. Partial least squares discriminant analysis (PLS-DA) and cluster analysis confirmed that 27 characteristic volatile compounds played an important role in distinguishing the four samples. These results suggested that IRD was the optimal drying method for vanilla, which would provide a theoretical basis for the selection of drying processing for vanilla.