The effect of solvent and temperature on extraction yield of phenolic compounds from soybeans, antioxidant activity and colour of extracts.

In this study the influence of solvent concentration (50, 60, 70 and 80% ethanol) and extraction temperature (25, 40, 50, 60, 70 and 80 °C) on the extraction yield of total phenolics and total flavonoids from organic soybeans were investigated. The total phenolic content (TPC) in soybean extract was determined spectrophotometrically by Folin-Ciocalteu micro method at 765 nm and results were expressed as gallic acid equivalents. The content of total flavonoids (TFC) was also measured spectrophotometrically using the aluminium chloride colorimetric assay at 510 nm with (+)-catechin as standard. Antioxidant activity (AA) of soybean extracts was evaluated using DPPH· radical scavenging method. CIE L*a*b* system was used for determination of colour parameters of extracts. The results showed statistically significant influence of solvent concentration and temperature on extraction of phenolic compounds. The best extraction yield of phenolic compounds was obtained when 50% ethanol was used at 80 °C (TPC: 4.5 mgGAE/gdb ; TFC: 2.56 mgCE/gdb). Weak correlations (r ≤ 0.298) were found between antioxidant activity of extracts and phenolic compounds. Furthermore, the phenolic content and total colour change of extracts were not correlated.