Supercritical-anti solvent precipitation for obtaining high polyphenols powders from yarrow plant

Abstract

In recent years the interest in using supercritical fluids for particle formation processes and for encapsulation of interesting compounds into polymeric matrices has increased. Unlike conventional particle formation processes, such as coacervation, crystallization by evaporation and spray drying, the use of supercritical fluids, namely supercritical CO2, allows for employing low processing temperatures, avoiding the use of toxic organic solvents and achieving a solvent-free product. Moreover, owing to their physico-chemical properties, supercritical fluids allow for reaching lower particle sizes and in a more controlled morphology than conventional processes that could promote a better bioaccessibility and bioavility of the compounds. Regarding the application of supercritical fluids for particle formation in the food field, the studies are mainly focused in the micronization and/or encapsulation of pure food compounds, such as β-carotene, quercetin, transresveratrol and lycopene, among others. Nevertheless, this technique has recently been studied for fractionating vegetable extracts with the aim of obtaining a fraction enriched in certain compounds of interest. In this sense, the selective precipitation of curcuminoids from a turmeric ethanolic extract, the concentration of antioxidants from Eucalyptus leaves extract and partition of catechins and caffeine from a green tea extract have been satisfactorily carried out. In this work, the selective fractionation of an Achillea millefolium (yarrow) liquid extract was accomplished using Supercritical Anti-solvent (SAS) technology to produce a powdered precipitate with high content of phenolic compounds. Yarrow plant has traditionally been used in folk medicine for treatment of asthma, bronchitis, skin inflammation and hepatobiliary diseases. This plant has awoken interest due to it has been recognized to have beneficial properties, such as antioxidant, antiinflammatory, antimicrobial and antimutagenic activity. In this case, polyphenols constitute a group of compounds that could contribute to the potential properties of yarrow, especially flavonoids. For obtaining the precipitates concentrated in phenolic compounds, firstly an ultrasound-assisted extraction (UAE) with ethanol was carried out. Once the yarrow extract was obtained, the SAS precipitation of the extract was performed. In this case, the precipitations were carried out at 40 ºC, three different pressures (10, 15 and 20 MPa) and CO2/extract ratio of 31. The total phenolic compounds content was measured by Folin-Ciocalteu method and additionally, the morphology and particle size was determined by Scanning Electron Microscopy (SEM) and laser diffraction, respectively. By means of SAS precipitation, dry precipitates, with a concentration of total phenolic compounds from 2.3 to 2.9-fold higher than the contained in the UAE extract and a precipitation yield up to 41%, were obtained. Regarding the size analysis, the pressure increasing, in particular from 10 to 15 MPa, resulted in a smaller size particle (250 μm at 20 MPa) and size range (0.5-600 μm at 20 MPa). Therefore, the selective fractionation of the phenolic compounds from a UAE yarrow extract was achieved, obtaining precipitates with high content of phenolic compounds with potential use as a natural antioxidant food ingredient.