*2.4. Effects of FIR Treatment on Antioxidant Activities of Ginseng Leaves*

The effects of FIR treatment on the antioxidant activities of ginseng leaves are shown in Table 1. Non-FIR-processed ginseng leaves (0; IC50 = 2.33) showed relative lower DPPH free-radical-scavenging ability compared to FIR-treated leaves, especially FIR-180 (IC50 = 1.52; Table 1.) Similar to the variations in DPPH radical-scavenging ability, ABTS radical-scavenging ability initially increased from FIR-160 to FIR-180 and then decreased (Table 1). These patterns show a distinct indication that appropriate FIR treatment can significantly improve antioxidant activities of ginseng leaves. Similar results were also observed in *Oriza sativa* L. [14], *Camellia sinensis* var. sinensis [20], and *Hibiscus cannabinus* L. [21], where FIR treatment increased antioxidant activities compared to non-treated controls.


**Table 1.** Changes in antioxidant activities (DPPH/ABTS radical-scavenging ability) in ginseng leaves treated by FIR at different temperatures.

The values are expressed as the mean ± SE (*n* = 3). Different letters within the same column indicate significant differences at *p* < 0.05 on Tukey's HSD test.

In our results, extremely consistent variation patterns were exhibited between antioxidant activities and the TPC (Figure 1 and Table 1), which suggested that the antioxidant activities of ginseng leaves are most likely contributed by polyphenols rather than other compounds. The reason why stronger antioxidant activities in ginseng leaves were exhibited at FIR-160 to FIR-180 may be because FIR accelerates the release of antioxidants or leads to the transformation of certain substances to stronger-antioxidant-activity compounds, such as breakage of phenolic polymers [12,17,21]. The broken polyphenols exhibit better antioxidant activities. However, the reason why patterns of antioxidant activities decreased at higher FIR temperatures, FIR-190 to FIR-200, may be explained by the destruction of phenolic polymers and the degradation of simple formed phenolics. The degradation of phenolics may have been increasingly accelerated at temperatures higher than 180 ◦C in this study. It has been reported that ginseng leaves show stronger antioxidant activity compared to the roots [6,40]. In addition, several studies have evaluated the effects of different types of thermal processing on ginseng leaf antioxidant activities [43,44]. However, to the best of our knowledge, this is the first study to investigate the effect of FIR treatment on the antioxidant activity of ginseng leaves. Proper application of FIR can be considered a good method of improving the antioxidant activities and health benefits of herbal plants by increasing active polyphenols.
