Thermal Control Using Far-Infrared Irradiation for Producing Deglycosylated Bioactive Compounds from Korean Ginseng Leaves

Abstract

Although ginseng leaf is a good source of health-beneficial phytochemicals, such as polyphenols and ginsenosides, few studies have focused on the variation in compounds and bioactivities during leaf thermal processing. The efficiency of far-infrared irradiation (FIR) between 160 °C and 200 °C on the deglycosylation of bioactive compounds in ginseng leaves was analyzed. FIR treatment significantly increased the total polyphenol content (TPC) and kaempferol production from panasenoside conversion. The highest content or conversion ratio was observed at 180 °C (FIR-180). Major ginsenoside contents gradually decreased as the FIR temperature increased, while minor ginsenoside contents significantly increased. FIR exhibited high efficiency to produce dehydrated minor ginsenosides, of which F4, Rg6, Rh4, Rk3, Rk1, and Rg5 increased to their highest levels at FIR-190, by 278-, 149-, 176-, 275-, 64-, and 81-fold, respectively. Moreover, significantly increased antioxidant activities were also observed in FIR-treated leaves, particularly FIR-180, mainly due to the breakage of phenolic polymers to release antioxidants. These results suggest that FIR treatment is a rapid and efficient processing method for producing various health-beneficial bioactive compounds from ginseng leaves. After 30 min of treatment without leaf burning, FIR-190 was the optimum temperature for producing minor ginsenosides, whereas FIR-180 was the optimum temperature for producing polyphenols and kaempferol. In addition, the results suggested that the antioxidant benefits of ginseng leaves are mainly due to polyphenols rather than ginsenosides.

Accumulation of Antioxidative Phenolics and Carotenoids Using Thermal Processing in Different Stages of Momordica charantia Fruit

“…The polyphenols are important antioxidant contributors [ 10 , 11 , 12 , 13 ] and the significantly increased total phenolic content in the thermally treated M. charantia can support the increased antioxidant activities, which were evaluated using three different assays ( Figure 2 and Figure 3 ). A chromatogram at 280 nm is widely used to study the polyphenols because the absorption at this wavelength is suitable for detecting a large number of such compounds [ 32 ]. Based on the lambda max of the peaks at 280 nm in our data and the phenolic acid profiling of M. charantia from a previous report [ 24 ], the peaks we detected are considered to be phenolic compounds.…”

Increasing the Amounts of Bioactive Components in American Ginseng (Panax quinquefolium L.) Leaves Using Far-Infrared Irradiation

“…However, it is important to acknowledge that FIR drying also has its drawbacks, including the generation of high heat, which can potentially lead to burns upon exposure [18]. In our previous research, we showed that FIR can significantly increase the TPC in ginseng leaves and promote ginsenoside transformations [12]. Geng et al [19] found in their research that after infrared drying, the content of TPC in carrot slices increased, and the antioxidant activity also increased significantly.…”

“…The deglycosylation of panasenoside is concurrent with kaempferol degradation; increasing the FIR temperature gradually caused the panasenoside deglycosylation rate to become lower than the kaempferol degradation rate. This explains why the panasenoside content in American ginseng leaves decreased rapidly while the kaempferol content increased relatively slowly, reaching the highest value after FIR treatment at 190 • C [12]. Although the kaempferol content in American ginseng leaves reached the highest value after FIR treatment at 190 • C, its content in ginseng leaves was different, and it stopped increasing after FIR treatment at 180 • C. This could have been caused by the different compositions and amounts of panasenoside in the raw material used.…”

“…It has been proven that the ginsenoside content in American ginseng leaves is significantly higher than that in the roots [11]. In our previous research, we showed that heat treatment transforms the constant ginsenosides in ginseng leaves into rare ginsenosides with a higher physiological activity and significantly increases the total polyphenolic content (TPC) [12]. Moreover, American ginseng leaves are a high-quality source of ginsenosides, polyphenols, and other bioactive ingredients that are not only underused but also often discarded.…”

Tissue-Specific Antioxidant Activities of Germinated Seeds in Lentil Cultivars during Thermal Processing

“…Both the 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical scavenging ability and the 2,2′-azino-bis (3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) radical scavenging ability were used to assess the antioxidant activities of the samples. These assays were performed as described by Lim et al [ 26 ] and Duan et al [ 27 ], respectively. The radical scavenging activity of the samples was expressed as mg of vitamin C equivalent (VCE)/g dry weight.…”