Percorrer por autor "Cruz, Victoria Franco"
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- Supercritical extraction of polyphenols from different vegetable matrices and their retention and recovery using molecularly imprinted polymersPublication . Cruz, Victoria Franco; Dias, Rolando; Brioude, Michel de MeirelesDifferent kinds of vegetable residues abundant in Trás-os-Montes region, namely walnut leaf, walnut shell, almond shell, grape marc, olive leaf and onion shell (a worldwide available biomass) were considered as possible sources of polyphenols. Extraction with supercritical carbon dioxide (at T=40 °C, P=160 bar and ethanol as co-solvent), ultrasound extraction and Soxhlet extraction were alternatively used to obtain mixtures containing these bioactive compounds. Aiming at the subsequent separation and concentration of the polyphenols from the complex extracts obtained, molecularly imprinted polymers (MIPs) were used as a kind of engineered adsorbents. MIP particles synthesized by precipitation polymerization with 4-vinylpyridine (4-VP) as functional monomer and quercetin as template were applied in the retention and recovery of the polyphenols. Comparative studies with commercial polymeric adsorbents (namely with the resin DAX8) were also performed. Batch adsorption, solid phase extraction (SPE) and operation in HPLC columns packed with the adsorbents were considered in these uptake/release studies. The identification and quantification of polyphenols was performed using Liquid Chromatography with Mass Spectroscopy and Diode Array Detector (LC-MS-DAD) and also with the more straightforward HPLC-DAD technique. With the supercritical CO2 (SCCO2) extraction conditions used, the richest phenolic profiles were obtained with onion shell and almond shell. Indeed, quercetin and many quercetin analogues (e.g. quercetin-O-glucoside, quercetin-O-diglycoside, quercetin dimer-O-hexoside, etc) were identified in these onion shell extracts, while quercetin, isorhamnetin-3-O-rutinoside or catechin (e.g.) were identified in the almond shell extracts. However, in spite of a similar composition, a higher phenolic content was measured for extracts obtained with the ultrasounds (US) or Soxhlet (SHOX) extraction, comparatively to supercritical CO2 extraction (e.g. around 10 mg/g of total phenolic compounds with US and SHOX extraction and 1 mg/g with SCCO2 for onion shell extracts, in a dry basis of plant residue). Benefits of molecular imprinting in the designing of tailored adsorbents to be used with downstream processing of polyphenols were evidenced in this research. Indeed, a very high polyphenol retention was here shown to be possible with MIPs, even when solvents with low water content are used (e.g. ethanol/water 80/20). Thus, the hydrophobic interactions, that usually is the main driving force for adsorption with common synthetic resins, is not the unique mechanism allowing the retention of these bioactive compounds in the synthesized molecularly imprinted polymer networks. The functionalization of the materials (here with pyridyl functional groups) and the creation of imprinted tailor-made cavities (promoting analogue mechanisms to antigen/antibody or substrate/enzyme binding) were congenial for the improved performance of the MIPs. Additionally, the manipulation of the particles morphology (through precipitation polymerization), allowing a facile binding accessibility (e.g. due to surface imprinting) should also contribute for the observed superior performance of the MIPs in polyphenols retention. The distinctive features of the MIP adsorbents were here demonstrated through the direct processing of plant extracts without water addition (e.g. using an ethanol/water 80/20 onion shell extract). A polyphenol-enriched fraction, containing quercetin and analogue molecules, was recovered at the end with the minimization of thermal treatments (only alcohol evaporation is needed if a dry residue is wanted). Thus, the simplification of the adsorption/desorption process was achieved and energetic costs can also be cut down (besides the minimization of the possible thermal degradation of the bioactive compounds). Summing up, this research demonstrate that MIP adsorbents can be helpful in the design of new and more flexible adsorption processes (e.g. working with a wider range of water content), aiming at the valorization of polyphenols present in plant extracts. Food industry, pharmaceutics and cosmetics are examples of applications fields for the principles here outlined.