Graphene oxide-assisted ethanol reflux extraction of total flavonoids from Ginkgo biloba leaves: study of kinetics and mechanism

Abstract

Ginkgo biloba leaves (GBL) contain many biologically active compounds such as flavonoids and terpene trilactones. In this study, graphene oxide (GO)-assisted ethanol reflux extraction (GERE) was adopted to extract the Ginkgo flavonoids (GF) from GBL, and the kinetics and mechanism of GF extraction were studied. SEM, XRD and FT-IR results all showed that GO could disrupt the cellulose structure and reduce the crystallinity of GBL. Through the obtained experimental data, it can be seen that So–Macdonald model was suitable to describe the extraction kinetics with high values of the coefficient of determination (R2 ≥ 0.994) and low values of the residual sum of squares (RSS ≤ 0.00022). The optimum leaching conditions of GERE were 70% (v/v) of ethanol concentration, 16 mL/g of liquid to solid ratio, 1.5 mg/g of GO dosage and 140 rpm of stirring speed at 70°C for 4 h by the single factor experiments. Under these conditions, the equilibrium yield of GF by GERE reached 82.63%, about 5.60% higher than the conventional ethanol reflux extraction (ERE). The value of the apparent activation energy obtained was 3.69 kJ/mol for GERE, 6.35% lower than that for ERE at a temperature within the range of 40–70 °C. HPLC results indicated that GO could not decompose flavonoids. The higher yield of GF can be attributed to the catalytic hydrolysis to the cell wall by GO, which can decrease the apparent activation energy and accelerate the leaching of GF at the fast diffusion stage. GERE method is an efficient and green extraction technology and So–Macdonald model satisfactorily described the extraction kinetics of Ginkgo flavonoids.