Abstract
External stimulation of the skin by ultraviolet B (UVB) radiation induces oxidative stress or inflammation, causing skin aging and skin cancer. Glycyrrhiza uralensis (licorice) has been used as a medicinal plant for its antioxidant, anti-inflammatory, antiviral, antimicrobial, anticarcinogenic, and hepatoprotective properties. The present study analyzed the effects of thermal processing on the bioactivities of licorice. Heat-treated licorice (HL) extracts had better antioxidant and anti-inflammatory activities than non-treated licorice (NL) extract. HL extracts also had higher total phenol contents than NL extract. In particular, contents of isoliquiritigenin, an antioxidant and anti-inflammatory substance of licorice, increased in proportion to the skin-protection effects of HL extracts. Heat treatment increased the contents of phenolic compounds such as isoliquiritigenin in licorice extract, which improved the UV photoprotective effect of licorice in human dermal fibroblasts.
Highlights
Ultraviolet (UV) radiation is subdivided into several main types based on wavelength, including ultraviolet A (UVA), ultraviolet B (UVB), and ultraviolet C (UVC) (100–400 nm).UVC and UVB radiation are completely or mostly absorbed, respectively, by the ozone layer in the atmosphere [1]
DPPH radical scavenging assay showed that non-treated licorice (NL) extract had the lowest antioxidant activity (IC50 value: 770.3 ± 42.3 μg/mL), while Heat-treated licorice (HL)-1 extract had significantly increased antioxidant activity and HL-2 extract had the highest antioxidant activity (IC50 value: 455.0 ± 36.5 and 299.2 ± 10.8 μg/mL, respectively)
This study confirmed the effects of thermal processes on the UV photoprotective activity of licorice in dermal fibroblasts and determined the components related to this activity
Summary
Ultraviolet (UV) radiation is subdivided into several main types based on wavelength, including ultraviolet A (UVA), ultraviolet B (UVB), and ultraviolet C (UVC) (100–400 nm). UVC and UVB radiation are completely or mostly absorbed, respectively, by the ozone layer in the atmosphere [1]. As the ozone layer is being depleted due to environmental pollution, UVB is increasingly reaching Earth’s surface [2]. Exposure to UVB leads to DNA damage, pigmentation, and inflammatory diseases, and excessive exposure can lead to skin cancer [3,4]. Exposure to UVB indirectly induces oxidative DNA damage through the generation of reactive oxygen species (ROS) [5]. Inflammation-related pathways in the skin, such as the nuclear factor kappa B (NF-κB) pathway, are activated by ROS [6]
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