Extraction of phenolic acids

Fiamegos, Y.C. et al.. Analytical procedure for the in-vial derivatization-extraction of phenolic acids and flavonoids in methanolic and aqueous plant extracts followed by gas chromatography with mass-selective detection, J. Chromatogr. A, 1041, 11, 2004. 

Hayat K. Hussain S. Abbas S. Farooq U. Ding B. Xia S. Jia C. Zhang X. Xia W. 2009. Optimized microwave-assisted extraction of phenolic acids from citrus mandarin peels and evaluation of antioxidant activity in vitro. Sep. Purif. Technol. 70 63-70. 

Knutsson M, Lundh J, Mathiasson L, Jdnsson JA, and Sundin P. Supported liquid membranes for the extraction of phenolic acids from circulating nutrient solutions. Anal. Lett. 1996 29 1619-1635. 

The analytical chemistry of phenolic compounds was summarized in detail by several authors including [53,69,87,88]. From these articles it can be concluded that the extraction of phenolic acids can be achieved using methanol and ethanol (mostly with different proportions of water), ethyl acetate, acetone, chloroform, pressurized low-polarity water [89] or, rarely, with water itself. In some samples, snch as in wine or clear juices, direct HPLC injection can be applied after several minor alterations [90]. But in a majority of the studies, aqueous methanol or ethyl acetate was used as extraction solvent. As a general treatment, free phenolics were extracted with diethylether from the extract and the water phase was treated with HCl or in common with NaOH under nitrogen to liberate the insoluble-bound esterifled phenolic acids. The use of solid-phase cartridges is also another application to remove undesired compounds. To avoid losses in... 

Extraction Techniques Most Widely Used for the Extraction of Phenolic Acids from Eruits and Vegetables 3 Q ... 

According to Luthria [63], PLE is effective for the extraction of phenolic acids from potato peels, and a variety of parameters were optimized. The results indicated that the optimum recoveries were obtained when phenolic acids were extracted using methanohwater (90 10, v/v) at 160°C. It has been shown that static time variations (5-15 min), pressure (35-138 bars), and flush volume (10-100%) variations did not significantly improve the extraction. Luthria [64] also optimized the extraction conditions of phenolic acids in parsley, with similar results as in potato peels, but in this case, all extractions were carried out with either one or two solvent mixtures, ethanoliwater (50 50, v/v) and/or acetone water (50 50, v/v), as it has been indicated in Table 16.4. 

Luthria, D.L. 2012. Optimization of extraction of phenolic acids from a vegetable waste product using a pressurized liquid extractor. J. Funct Foods 4 842-850. 

The most common solvents used for the extraction of phenolic acids from plant matrices are ethyl acetate, diethyl ether, methanol or aqueous methanol [24]. Enzymatic hydrolysis with b-glucosidase or hydrocinnamoyl-quinate esterase... 

Identity of phenolic acids occurring in soils. . Extraction of phenolic acids from soils... 

The Phenox process (254) removes phenol (qv) from the efduent from catalytic cracking in the petroleum industry. Extraction of phenols from ammoniacal coke-oven Hquor may show a small profit. Acetic acid can be recovered by extraction from dilute waste streams (255). Oils are recovered by extraction from oily wastewater from petroleum and petrochemical operations. Solvent extraction is employed commercially for the removal of valuable... 

Preparation of seedlings for treatments with extract-amended nutrient solution was similar to that described for testing the effects of phenolic acids, except 40 plants were used per treatment and no replacement of the nutrient solution was made during the treatment period. Data collection procedures were modified in that only ab-axial leaf resistance was obtained and water potential was determined from four plants each day. Prior work established that abaxial resistance provided an adequate indicator of stomatal effects. The data were analyzed as described in experiments with pCA and FA. 

Michalkiewicz A, Biesaga M and Pyrzynska K. 2008. Solid-phase extraction procedure for determination of phenolic acids and some flavonols in honey. J Chromatogr A 1187( 1-2) 18-24. 

The ability of quaternary ammonium halides to form weakly H-bonded complex ion-pairs with acids is well established, as illustrated by the stability of quaternary ammonium hydrogen difluoride and dihydrogen trifluorides [e.g. 60] and the extractability of halogen acids [61]. It has also been shown that weaker acids, such as hypochlorous acid, carboxylic acids, phenols, alcohols and hydrogen peroxide [61-64] also form complex ion-pairs. Such ion-pairs can often be beneficial in phase-transfer reactions, but the lipophilic nature of H-bonded complex ion-pairs with oxy acids, e.g. [Q+X HOAr] or [Q+X HO.CO.R], inhibits O-alkylation reactions necessitating the maintenance of the aqueous phase at pH > 7.0 with sodium or potassium carbonate to ensure effective formation of ethers or esterification [49,64]. 

Among the numerous applications of SPE are separations of phenolic acids and flavonoids from wines and fruit juices. Sep-Pak Cig cartridges have been used for the fractionation of flavonol glycosides and phenolic compounds from cranberry juice into neutral and acidic parts before HPLC analysis. Antimutagenic flavonoids were identified in aqueous extracts of dry spinach after removal of lipophilic compounds by SPE. ... 

TABLE 5.7 Types and levels (mg/100 g sample) of phenolic acids and flavonoids in acidified methanol extracts of morama bean seed coat and cotyledon determined using reversed-phase HPLC" (adapted from van Zyl (2007))... 

Mass-Ion Fragments of Phenolic Acids in Potato Extracts... 

The distribution ratios obtained were compared to the corresponding distribution ratios between water and Toctanol. The authors also calculated solvent parameters of [C4Cilm][PFg] (Section 9.3). It was shown that phenolate-ion associates with [C4CiIm][PFg] more strongly than other ions. The authors also mention the possibility of extraction of amino acids into [C4CiIm][PPg] in the presence of crown ether dibenzo-18-crown-6, though at rather moderate efficiency. 

Retention times of the peaks are subject to the particular type of column. The acidic fraction from solid-phase extraction consists of phenolic acids such as cis-coutaric, trans-coutaric, and trans-caftaric acids. Isocratic elution is suitable because of the limited number of compounds found in the acidic fraction. Analysis of the acidic fraction is completed within 30 min. See Figure 11.3.1 for an HPLC chromatogram of the acidic polyphenolics isolated from Niagara grapes. 

Commonly used extraction solvents are ethyl acetate, diethyl ether, methanol, and aqueous methanol, but the majority of the free phenolic compounds can be extracted with alcohols (methanol or ethanol) or alcohol-water mixtures (1). Due to the differences in polarity between components (40), neither diethyl ether nor ethyl acetate are able to extract completely all the phenolic compounds in a liquid-liquid extraction. Thus, successive extraction with diethyl ether and then ethyl acetate has been used for phenolics in fruit juices (41). When using alcohol-water mixtures (40), repeated extraction or reflux for 1 h are necessary to extract free phenolic acids as well as their glycosides. 

Aqueous samples were extracted for phenol and 4-chlorophenol using pure carbon dioxide in a specially designed phase separator apparatus (111). The extraction efficiency for these phenols was reported to be over 85%, with a RSD of 8% for eight samples. Additional liquid sample extractions have been investigated for the extraction of phenol from a 6M sulfuric acid solution as well as the extraction of the components of commercial soft drinks and orange juice (112-113). In all cases, specifically designed extraction vessels were utilized. 

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