Abstract: To investigate the effects of different drying methods on the quality of garlic, we comprehensively analyzed the physicochemical properties (moisture ratio, drying rate, color, rehydration ratio, free amino acids, reducing sugars, total phenols, and thiosulfinates), antioxidant activity (1,1-diphenyl-2-picrylhydrazyl (DPPH) radical scavenging capacity and total reducing power) and volatile components of garlic subjected to vacuum freeze drying (VFD), hot air drying (HAD), heat pump drying (HPD), and far infrared-assisted heat pump drying (FI-HPD). The results showed that the VFD sample had good color with the highest L* and Wh values of 85.68 and 82.77, along with the highest contents of free amino acids, reducing sugars, total phenols, and thiosulfinates, and exhibited the strongest DPPH radical scavenging capacity and total reducing capacity. FI-HPD showed the shortest drying time and the fastest drying rate. A total of 80 volatile compounds were identified by gas chromatography-mass spectrometry (GC-MS). The VFD garlic had the highest content of volatile compounds (53.457 μg/g), while the FI-HPD sample had the greatest number of volatile compounds (70). Compared with fresh garlic, the VFD sample better retained the characteristic sulfur-containing flavor compounds, while higher levels of alcohols, aldehydes, ketones, and other volatile compounds were detected in the HAD, HPD and FI-HPD samples. Key aroma compounds, such as diallyl sulfide, methyl-2-propenyl disulfide, dimethyl trisulfide, diallyl disulfide, hexanal and nonanal, were identified based on their relative odor activity value (ROAV). Orthogonal partial least squares-discriminant analysis (OPLS-DA) indicated clear separations not only between the dried samples and fresh garlic, but also between the dried samples themselves. According to the variable importance in projection (VIP) scores, a total of 17 volatile compounds (VIP > 1) were selected as marker compounds. Taken together, VFD was most effective in retaining active ingredients and volatile compounds in fresh garlic, but from a practical standpoint, FI-HPD was more suitable for the energy-efficient industrial drying of garlic. This study provides a theoretical basis for selecting optimal drying method for garlic and evaluating the processing suitability of dried garlic.

Key words: garlic; drying methods; physicochemical quality; antioxidant activity; volatile components