Synergy of in-situ formation of carbonic acid and supercritical CO2-expanded liquids: Application to extraction of andrographolide from Andrographis paniculata

Abstract

The environmental impact of excessive solvent usage in the pharmaceutical industry has generated research interests in the area of green and sustainable extraction processes. In this study, solvent minimization was done by exploiting the synergistic effect of pH lowering (via in-situ H2CO3 formation) and solvent’s volume expansion (via CO2-expanded solvent) in the extraction of andrographolide from Andrographis paniculata. Conventional solid-liquid extraction (CSLE) and CO2-expanded liquid extraction (CXLE) were conducted using different solvents at a pressure range of 0.1–10 MPa and 40 °C in a batch-type extraction vessel to verify both the independent and combined effect of pH and the solvent’s volume expansion coefficient (V/V0) in the extraction recovery. Also, fresh and spent biomass were analyzed using X-ray Diffraction (XRD), Fourier Transform Infrared Spectroscopy (FTIR) and Scanning Electron Microscopy (SEM) in order to assess the physical impact of the extraction scheme. The highest andrographolide recovery of 65% was obtained using CXLE with ethanol and water at pH = 3.02 and V/V0 = 4.8, owing to the synergistic effects of the two variables. Furthermore, an increase in extraction recovery with decreasing pH and increasing V/V0 was observed. Moreover, a significant morphological difference between the fresh and spent samples was observed from the results of characterizations, indicating a disruption in the cell wall associated to the expansion of the solvent as it penetrated the plant matrix. The proposed novel extraction strategy allowed a high extraction recovery of andrographolide while complying with sustainable and green practices.