The Impact of Solvent Polarity on the Phenolic and Antioxidant Capacity of Green Coffee Beans (Robusta species) extracts

Recent research generally seems to support the idea that high polar solvents are the only ones capable of extracting substantial levels of polyphenolic content and antioxidant value. Thus, the current study investigated the impact of polarity of the solvent influencing the final extraction yield, the concentration of phytochemicals, and the antioxidant activity of green coffee beans (GCB). Solvents used for extraction were n-Hexane, Dichloromethane (DCM), Chloroform, Acetone, Methanol, Ethanol, Dimethyl-sulphoxide (DMSO) and Aqueous. The findings demonstrated that the evaluated solvents were crucial to the extraction of the antioxidant capacity and overall phytochemical content. Solvents with polarity index 4.1 to 5.2 were found optimal for total extractable solids, total polyphenolic content, total flavonoid content. A positive correlation was quantified between polarity of the solvent and DPPH radical scavenging assay (r2 = 0.62), ABTS radical scavenging assay (r2 = 0.81) and ferric reducing antioxidant power (r2 = 0.65). A negative correlation was found between the polarity of solvent and total flavonoid content (r2 = -0.35) and total polyphenolic content (r2 = -0.06). The finding of this study indicates that medium polar solvent such as acetone, methanol and ethanol (polarity index 5.1, 5.12 and 5.2 respectively) were the best solvents for the extraction of polyphenolic content and antioxidant capacity in GCB. The research suggests future studies should consider variations of low, mid, and high polar solvent types for antioxidant and polyphenolic content, considering factors like plant material, phenols, methodology, temperature, and extraction duration.