Ruoqi Han

Thermal processing facilitates the transformation of major ginsenosides into rare ginsenosides, thereby enhancing the bioactive molecular profile of American ginseng. This study examined the impact of 1–4 cycles of high-temperature and high-pressure steaming (HTHPS) on ginsenoside composition, total phenolic content (TPC), total flavonoid content (TFC), and antioxidant activity in American ginseng. HTHPS significantly decreased major ginsenoside levels while increasing the content of rare ginsenosides. Following three cycles (HTHPS-3), the concentrations of Rg3, Rk1, Rg5, Rh1, F4, and Rg6 reached 8.68, 6.02, 20.07, 1.92, 3.72, and 2.57 mg/g, respectively, in contrast to their absence in the untreated control. TPC exhibited a 6.74-fold increase after HTHPS-2, whereas TFC showed a 4.27-fold increase following HTHPS-3. Pearson correlation analysis revealed strong positive correlations between rare ginsenosides, TPC, TFC, and antioxidant activity. In summary, HTHPS treatment significantly altered the bioactive profile of American ginseng. HTHPS-2 was more suitable for maximizing TPC and DPPH/ABTS⁺ radical-scavenging activities, whereas HTHPS-3 favored rare ginsenoside accumulation, particularly Rg3, Rk1, and Rg5, and exhibited a stronger ·OH radical-scavenging capacity. These findings indicate that the preferred number of HTHPS cycles depends on the target bioactive components and functional properties.

The roots, leaves, and other parts of American ginseng contain ginsenosides and polyphenols, among other bioactive components. So far, reports on exploring the changes in bioactive components within its leaves after heat treatment have been limited. In the present study, we investigated the effects of far-infrared irradiation (FIR) heat treatment from 160 to 200 ℃ on the deglycosylation and dehydration rates of the bioactive components in American ginseng leaves. As the temperature was increased, the amounts of constant ginsenosides decreased while those of rare ginsenosides increased. After FIR heat treatment of the American ginseng leaves at an optimal 190 ℃, the highest total polyphenolic content and kaempferol content were detected, the antioxidant activity was significantly enhanced, and the amounts of rare ginsenosides F4, Rg6, Rh4, Rk3, Rk1, Rg3, and Rg5 were 41, 5, 37, 64, 222, 17, and 266 times higher than those in the untreated leaves, respectively. Moreover, the radical scavenging rates for 2,2-diphenyl-1-picrylhydrazyl and 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid), and the reducing power of the treated leaf extract, were 2.17, 1.86, and 1.77 times higher, respectively. Hence, optimal FIR heat treatment at 190 ℃ is an efficient method for producing beneficial bioactive components from American ginseng leaves.