Effect of drying technology on the physical, rehydration, flavor, and allicin content of single-clove garlic

This study aimed to investigate the effect of vacuum-freeze drying (VFD), hot-air drying (HAD), heat-pump drying (HPD), far-infrared combined-heat-pump drying (FI-HPD), medium- and short-infrared radiation (IR) drying (MSIRD) on drying characteristics, rehydration, color, microstructure, flavor, and texture of single-clove garlic slices. Herein, MSIRD presented the shortest drying time, the fastest decrease in moisture content, and a markedly higher drying rate than those of other treatment groups. Furthermore, the nuclear magnetic resonance (NMR) results showed that MSIRD could quickly and effectively remove moisture from garlic slices, especially free-flowing water. The scanning electron microscopy (SEM) results showed the uniformly distributed porous structure on the surface of HPD and MSIRD tissues and their good rehydration ability. Compared with fresh garlic slices, the brightness of dried garlic slices considerably increased; however, medium- and short-infrared waves caused the garlic slices to turn brown, resulting in a noticeable yellowing of the surface. In total, 51 volatile compounds (including 9 alcohols, 6 aldehydes, 9 ketones, 2 acids, 7 esters, and 18 other types) were identified in garlic slices through gas chromatography-ion mobility spectrometry (GC-IMS) analysis. Among them, 28 substances were common components of five drying treatments. Butyl acetate and ethyl valerate were characteristic flavor compounds of garlic after high-temperature treatment. Furan and other substances with caramel and sweetness were found in the VFD group, which formed the characteristic aroma components of freeze-dried garlic slices. Principal component analysis (PCA) showed that drying temperature considerably affected the flavor of garlic. Altogether, this study provides a new approach to using infrared technology for garlic drying.