Thin layer chromatographic profiling and antioxidant activity of extracts from a muscadine grape skin commercial preparation Sian Ramdass 1,2 , Milena Mechkarska 1 1 Department of Life Sciences, Faculty of Science and Technology, The UWI, Trinidad and Tobago, 2 Department of Chemical Engineering, Faculty of Engineering, The UWI, Trinidad and Tobago The muscadine grape Vitis rotundifolia has gained increasing attention due to its rich source of bioactive secondary metabolites which have the potential for development into anticancer therapeutic agents. Moreover, many of these compounds are natural antioxidants with the ability to reduce/prevent free radical-mediated oxidative damage. Our preliminary research revealed that the dichloromethane extract from a commercially available muscadine grape skin exhibits the highest cytotoxic potency against PC-3 prostate cancer cells (the concentration that inhibits cell growth by 50% (IC 50 ) = 0.714µg/mL). This study was undertaken to determine the phenolic content and the in vitro antioxidant activity of various extracts from a muscadine cultivar and the subsequent correlation to their cytotoxic activities. The major phytochemical constituents of specific extracts were assessed as well. The grape skin powder was repeatedly macerated in ethanol yielding the total ethanolic extract (TEE). Liquid- liquid extraction of the TEE using solvents of increasing polarity resulted in four (4) additional extracts; hexanes (HXE), dichloromethane (DCME), ethyl acetate (EAE), and n-butanol (NBE). Total phenolic content (TPC) of all extracts was determined by the Folin-Ciocalteau colorimetric method, using gallic acid as a standard. The antioxidant activity (AOA) was measured using the 2,2-diphenyl-1-picylhydrazyl (DPPH) free radical scavenging assay. Thin Layer Chromatography (TLC) of two selected extracts with desired potencies was carried out using reverse and normal phase silica plates respectively, and the resultant TLC fingerprint profiles were visualized under both visible and UV light. Subsequently, the plates were individually treated with ten (10) visualization stains. The EAE revealed the highest TPC of 325.82 ± 0.07 mg gallic acid equivalents (GAE) /g. The EAE also had the greatest AOA (IC 50 = 0.116mg/mL), followed by DCME > NBE > TEE > HXE. For all extracts, TPC was positively and significantly correlated with AOA (r = 0.9744; P < 0.05), while there was a weak and negative association of the TPC (r =-0.119; P > 0.05) and AOA (r =-0.268; P > 0.05) with the cytotoxicity against PC-3 cells. The TLC fingerprint profiles of the extracts with the highest AOA (EAE) and the greatest cytotoxic activity (DCME) revealed bands with varying retention factor (Rf) values in the ranges of 0.05 - 0.94 and 0.07 - 0.97 respectively. Qualitative phytochemical screening of both extracts verified the presence/absence of bioactive components, together with additional secondary metabolites. The findings from our study can be summarized as follows: i) the phenolic compounds contribute to the AOA of V. rotundifolia extracts; ii) the in vitro cytotoxic activity of the DCME is not due to the TPC and AOA; iii) alkaloids and carboxylic acids are present in the DCME (the highest potency against the PC-3 cells) but absent from the EAE (the highest AOA). In conclusion, this study confirms the presence of medicinally relevant phytochemicals in
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© The Author(s), 2023
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