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Photostability and photoprotective effects of brown macroalgae Halopteris scoparia influenced by seasonal changes

Brown macroalgae have recently been the focus of many research due to their composition and the accumulation of specific metabolites with several health benefits and biological activities. Additionally, the extracts of Halopteris scoparia (HASC) have shown to have protective and preventive activity against human cancer cells. In this study, the evaluation of HASC against harmful ultra-violet (UV) light was done in regard to different activities, namely pigment determination by HPLC analysis, the transmission of erythema (Te) and pigmentation (Tp), along with the calculation of sun protective factor (SPF), antityrosinase and antioxidant activities. Antioxidant activity was also analysed before and after irradiation using UV-B light (8 W, 2000 μW cm−2) for different time periods (30, 60, and 120 minutes). Analysis was performed on two different fractions obtained with the solid-phase extraction (SPE) method, methanolic F3 and dichloromethane F4 fractions, from three different harvesting seasons (February, April, and June 2021). HPLC analysis revealed several pigments in HASC samples. The most abundant were fucoxanthin, lutein, and β-carotene. The highest concentrations were found in the sample from February. Interestingly, the less lipophilic pigments such as fucoxanthin, lutein, astaxanthin, and canthaxanthin, were observed in the F3 fraction, while the F4 fraction contained more lipophilic pigments chlorophyll a and β-carotene. The highest antioxidant activity using DPPH and ABTS assays was also observed for the February sample which could be explained by the presence of pigments such as β-carotene with known activity against free radicals. SPF was high for all HASC samples when compared to a known UV filter Benzophenone-3 (BP-3). % Te and % Tp showed a high protective effect for all samples, with the lowest transmission for HASC from February, especially the F4 fraction which can be attributed to the presence of β- carotene. No significant difference was observed in antioxidant activity after UV-B irradiation for all tested time periods and samples. Only the HASC June samples have shown a slight decrease in antioxidant activity after 120 minutes. Additional chemical characterization of obtained extracts is in progress to further evaluate additional bioactive compounds present in samples that could influence the photostability of these samples and could have applications as natural sun-protective agents.

Seaweeds ; UV-light ; pigments ; antioxidants

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