Extraction_of_proanthocyanidins_from_gra

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suggest 8 MPa was the most suitable pressure for supercritical carbon dioxide extraction of grapemarc.3.1 Effect of solvent flow rateIn Figure 3 the overall extraction curves (OECs) (phenols content vs. time) obtained for grape marcextracted at 8 MPa/ 313.15 K, 6CO 2 -15%EtW and 4CO 2 -15% EtW solvent flow rate for 300 minare plotted to evaluate the effect of solvent flow rate on the extraction of total phenols.Both OECs exhibit a constant-extraction rate period (CER) of 150 min, and a diffusion-controlledperiod (DC) follows. An intermediary falling extraction rate (FER) period cannot be observed [24]The initial linear period (CER) corresponds about the 84 and 65% of the final extracted phenols at6CO 2 -15%EtW and 4CO 2 -15%EtW flow rate, respectively. It is worth noting that the OECsoverlapping up to 150 min. This indicates that the extraction velocity is independent of solventflow rates and corresponds to the extract solubility. The slopes of these lines, as they are related tothe extract solubility, only depend on pressure and temperature. After 150 min, the OECs diverge,exhibiting a diffusion-controlled period (DC) and here the slopes depend on particle size andsolvent flow rate. Such trends corroborates the hypothesis of the broken plus intact cells modelproposed by Sovová [25] . The kinetic parameters calculated from the adjustment of the OECs at6CO 2 -15%EtW and 4CO 2 -15%EtW flow rate for the diffusion controlled period (DC) are reportedin Table 1. The results indicate that as the flow rate decreases the mass transfer increases. Thiscould be attributed to the fact that 4CO 2 -15%EtW flow rate is slower than 6CO 2 -15%EtW andthus the contact time between the solvent and the compounds to be extracted is increased. Thismay have positively affected the extraction efficiency.3.2 Effect of co-solvent percentagesIn Figure 4 the OECs are plotted to evaluate the effect on the extraction of total phenols at 8 MPa/Accepted Manuscript13.15 K, of 7.5 and 15% EtW at 4 kg/h CO 2 flow rate, and 10 and 15% EtW at 6kg/h CO 2 flowrate. By the comparison of the OECs, it is possible to observe that the highest values of phenolsextraction are obtained at 4CO 2 -7.5%EtW flow rate (2600 mg GAE 100 g DM -1 ) and 6CO2-10%EtW-flow rate (2527 mg GAE 100 g -1 DM ).Carbon dioxide, ethanol and water are solvents with different polarities that, when mixed indifferent proportions allow to obtain homogeneous solvent mixtures, depending on the particulartemperature and pressure and the individual solvents molar fractions. Table 2 reports the individualsolvent molar fractions calculated at 4 and 6 kg/h CO 2 flow rate with different percentage of theethanol-water mixture at 57% (v/v) ethanol as co-solvent. It is worth to note that the highest7Page 7 of 22
extraction of phenols are obtained at lowest co-solvent percentages used, 4CO 2 -7.5%EtW and6CO2-10%EtW flow rates, when the molar fractions of water and ethanol are the lowest and thoseof carbon dioxide the highest. This could be due to two main factors: a) the increase of co-solventpercentage to 15% may induce the saturation of CO 2 with ethanol-water, with consequent formationof two or three phases for the specific conditions of temperature and pressure of the system [26, 27]; b) solvent-solvent interactions in competition for the solvation of solutes occur at 15 % cosolvent,reducing extraction and decreasing the process yield.3.3 Yield, fractionation of proanthocyanidins and antioxidant activityChemical composition of grape marc extracts obtained by conventional methanol extraction andSC-CO 2 at 4CO 2 -7.5%EtW and 6CO2-10%EtW flow rate is reported in Table 3. The processefficiency is quantitatively related to extraction yield. The global yields of SC-CO 2 at 4CO 2 -7.5%EtW and 6CO2-10%EtW flow rates are 13.1 and 14.6 % w/w, respectively, lower thanclassical extraction with methanol, which was 15.6% w/w. The results obtained indicate that bothSC-CO 2 modified with EtW and methanol extract a large number of soluble compounds.-The highest value of phenols concentration is found for methanol extraction (2813 mg GAE 100 g DM 1 ). Pinelo et al. [18] reported methanol as the most selective organic solvent for extracting phenoliccompounds from grape marc. However, it is interesting to note that phenols extracted by SC-CO 2 ,both at 6CO2-10%EtW (2527 mg GAE 100 g -1 DM ) and 4CO 2 -7.5%EtW (2600 mg GAE 100 g -1 DM )flow rate give yields, ranging about 90-92% of methanol extraction yield.Phenolic yields resulted similar to that (3169 mg GAE 100 g -1 DM ) reported by Aliakbarian et al. [28]using subcritical water, and much higher (198.4 and 173.1 g kg -1 of extract, respectively at4CO 2 -7.5%EtW and 6CO2-10%EtW flow rate) than 23 g kg -1 of extract reported by Farìas-Campomoneset al [16] .The highest total antioxidant activity for grape marc extracts is obtained at 6CO2-10%EtW flowrate (8703 mg α–tocopherol 100 g DM -1 ). Under these operating conditions, total antioxidant activityAccepted Manuscriptincreased by 20% compared to 4CO 2 -7.5%EtW flow rate (7187 mg α–tocopherol 100 g DM -1 ) andit is about 13- folds that of methanol extract (678 mg α–tocopherol 100 g DM -1 ). This suggests thatdifferent CO 2 flow rate and percentage of co-solvent affect the SC-CO 2 extraction of phenolsresponsible for the antioxidant activity of the extracts, as well as the extraction methods.Both the extracts obtained at 6CO2-10%EtW (703.7 mg catechin 100 g -1 DM ) and 4CO 2 -7.5%EtW(630.2 mg catechin 100 g -1 DM ) flow rate, compared to methanol extract (159.0 mg catechin 100 g -1 DM )present high level of total proanthocyanidins (PAs).8Page 8 of 22
Page 1 and 2: Accepted ManuscriptTitle: Extractio
Page 3 and 4: The extraction of phenolic compound
Page 5 and 6: where m i is the mass of particles
Page 7: R210, Buchi, Flawil, Switzerland),
Page 11 and 12: [2] J.M. Souquet, V. Cheynier, F. B
Page 13 and 14: [26] J.H. Yoon, H. Lee, B.H. Chung
Page 16 and 17: *Highlights (for review)Highlights
Page 18: Figure(s)Figure 2.2000180016001400m
Page 22: Figure(s)Figure 4.300025002000mg GA
Page 25 and 26: Table(s)Table 1. Kinetic parameters
Page 27: Table(s)Table 3. Chemical compositi

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