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Extraction of anthocyanins from grape pomace Syrah (Vitis vinifera L.) with pressurized liquids and concentration of the extracts by nanofiltration

Author: Débora Tamires Vitor Pereira

Abstract. The use of agro-industrial by-products is important to reduce environmental impacts and generate value-added products, especially when performed through clean technologies. Grape marc obtained from wine production has a high concentration of bioactive compounds, mainly anthocyanins with functional properties even after vinification, thus representing a potential by-product for applications in pharmaceutical, food and cosmetic industries. Pressurized Liquid Extraction (PLE) integrated to Membrane Separation Process (PSM) is an efficient alternative to extract and concentrate compounds of interest from plant matrices using green technologies. Given this context, the objective of this work was to obtain extracts rich in monomeric anthocyanins (AM) and phenolic compounds (FT) by PLE from grape marc and concentrate the anthocyanins through PSM. The PLE solvents were: acidified water pH 2.0, water and ethanol pH 2.0 (50%, w/w), 100% ethanol and water and ethanol (50%, w/w) at different temperatures (40 - 100 °C), at a fixed pressure of 10 MPa. The effect of temperature (40 - 85 °C) on anthocyanin extraction was also studied, using the solvent that achieved the highest AM yield. The PLE kinetics was investigated through extraction curves obtained by measuring the AM and FT yields along time. Two mathematical models were fitted to the experimental curves. The three-line Spline model was fitted to the experimental data using the SAS 8.02 PROREG system, followed by the NLIN procedure of the same program. The Two sites desorption kinetics model was fitted to the experimental data using the Microsoft EXCEL Solver. The extracts obtained from PLE were evaluated in terms of yield of AM, FT and antioxidant capacity (CA) by the ORAC and FRAP methods. The best PLE condition for AM was water and ethanol 50/50 (pH 2.0, w/w) at 40 °C. For phenolic compounds, water and ethanol 50/50% (w/w) at 100 °C achieved the highest yield. The best extract with in terms of anthocyanins was submitted to PSM in frontal mode using microfiltration (MF), ultrafiltration (UF) and nanofiltration (NF) processes, in order to select the best membranes for AM concentration. The membranes MV020, NP010, NP030 and NF270 were thus chosen to the tangential filtration process, based on the anthocyanin retention index (R%) and permeate mass flow (J_p). The MV020-NP010 sequential process was the most effective for AM concentration, based on R%, J_p and concentration factor (FC). The extracts obtained at the best PLE conditions of AM and FT, as well as the concentrates from tangential filtration, presented high antioxidant capacities by the ORAC method. Extraction with pressurized liquids combined with the membrane separation process showed high efficiency to recover and concentrate compounds of high nutraceutical and commercial value, such as anthocyanins.

Keywords: Pressurized Liquid Extraction, grape marc, anthocyanins, phenolic compounds, antioxidant capacity, nanofiltration.