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Comparative study of polyphenols and antioxidant capacity in green coffee: the effect of extraction techniques and applied solvents

The extraction efficiency of polyphenols from green coffee beans affected by usage of two solvents (water and aqueous ethanol, 50%), and by employing three different extraction techniques, was investigated in this study. Grounded green coffee beans were subjected to conventional extraction by continuously stirring for 15 min and maintaining the temperature of solvents (80˚C) during extraction time. Bioactive profile of these extracts was compared to ones prepared by conventional extraction assisted by supercritical fluid (scCO2 as a co-solvent) and ultrasound-assisted extraction. Ultrasound-assisted extraction was performed for 30 min in a sonication bath, while extraction assisted by scCO2 was run in laboratory-scale high pressure extraction plant at following conditions: 3 hours, 100 bar and 40˚C. Spectrophotometric methods were employed to determine the content of total polyphenols and flavonoids (TPC, TFC), as well as antioxidant capacity evaluated by 2, 2-diphenyl-1-picrylhydrazyl (DPPH) and 2, 2-azinobis(3-ethylbenzthiazoline-6-sulfonic acid) (ABTS) free radical scavenging assays. Chlorogenic acid derivatives (CQADs) and caffeine content were identified and quantified by means of reversed phase high performance liquid chromatography (HPLC-PDA). According to the obtained results, water was more efficient extraction solvent in comparison to ethanol, resulting in higher overall content of bioactive compounds and antioxidant capacity. The highest extraction yield of TPC was observed in conventionally performed extraction (30.41 mg GAE/g), followed by extraction assisted with scCO2 (27.26 mg GAE/g), while extracts obtained by ultrasound-assisted extraction provided the lowest content (18.06 mg GAE/g) of polyphenols, correlating well with TFC and antioxidant capacity. HPLC analysis revealed the extraction assisted with scCO2 as more effective for CQADs and caffeine extraction, followed by conventional extraction and ultrasound-assisted extraction. Since CQADs are the predominant compounds of green coffee beans, these results could serve as a basis for the development of their efficient isolation procedures using innovative extraction approaches, with a need for further scCO2 extraction conditions optimization.

Green coffee; Extraction; Chlorogenic acids; Supercritical CO2

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