Comparing the Drying Characteristics, Phytochemicals, and Antioxidant Characterization of Panax quinquefolium L. Treated by Different Processing Techniques

American ginseng (AG) has long been used as an ingredient in the food and pharmaceutical industries because of its nutritional and economic value. AG is rich in nutrients, and its quality is greatly affected by how it is processed. However, there is a relative paucity of research on the comprehensive evaluation of different processing techniques of AG. This study evaluated the differences in quality formation and properties of low-temperature softened, blanched, steamed followed by hot air drying, and vacuum freeze-dried AG (LTS-HAD, BL-HAD, ST-HAD, and VFD, respectively). The results demonstrated that AGs treated with VFD had the fastest drying time (85 h) and succeeded in preserving the color and microstructure of fresh ginseng. The contents of ginsenoside Rg1 and Rb1 in LTS-HAD samples were 2.81 ± 0.01 mg/g and 10.68 ± 0.66 mg/g, respectively, which were significantly higher than those in VFD samples (p < 0.05). Moreover, ST-HAD samples had an attractive reddish-brown appearance and higher antioxidant activity. Simultaneously, the formation of the ginsenosides Rg6, (S) Rg3, (R) Rg3, Rk1, and Rg5 was discovered. BL-HAD samples had an intermediate quality among the above samples. A total of 58 volatile compounds were identified, including aldehydes (14), alcohols (13), ketones (10), esters (6), terpenes (6), acids (5), and heterocyclic compounds (4). PCA of ginsenosides and volatile components, as well as correlation analysis with color and antioxidant activity, resulted in the identification of different processed products and potential bioactive components.