Phenolic compounds optimizations

Pelander et al. [81] developed a computer program for optimization of the mobile phase composition in TLC. They used the desirability function technique combined with the PRISMA model to enhance the quahty of TLC separation. They apphed the statistical models for prediction of retardation and band broadening at different mobile phase compositions they obtained using the PRISMA method the optimum mobile phase mixtures and a good separation for cyanobacterial hepatotoxins on a normal phase TLC plate and for phenolic compound on reversed-phase layers. 

The extraction conditions used in the study were optimized on the basis of approximately 70% extraction of typical phenolic compounds. 

The complexity of the problems relative to maceration explain how difficult it is to optimize the extraction of phenolic compounds during vinification. 

Most plants suffer damage, both physiological and biochemical by exposure to temperatures higher or lower than optimal for growth [99]. The results of these injuries, which are reflected in most metabolic processes may be a reduced growth capacity of the crops and therefore lower commercial yield [100]. It has been demontrated that thermal stress induces the production of phenolic compounds [3,4,101]. 

P Hayes, MR Smyth, I McMurrough. Comparison of electrochemical and ultraviolet detection methods in high-performance liquid chromatography for the determination of phenolic compounds commonly found in beers. Part 1. Optimization of operating parameters. Analyst 112 1197-1203, 1987. 

De Ruiter et al. [4] observed that photochemical decomposition by ultraviolet irradiation of dansyl derivatives of chlorinated phenolic compounds in methanol-water mixtures led to the formation of highly fluorescent dansyl-OH and dansyl-OH3 species. The optimal irradiation time was 5.5s. This reaction was utilised in a post-column photochemical reactor in the high performance liquid chromatography determination of highly chlorinated phenols in river water. The method calibration curve (for dansylated pentachlorophenol) was linear over three orders of magnitude. 

The following GC operating conditions are optimal for phenolic compounds, including those present in spent pulping liquor or bleaching effluent with or without prior O-acetylation and subsequent O-methylation or O-ethylation ... 

Ghafoor K. Choi Y.Fl. Jeon J.Y. Jo I.H. 2009. Optimization of ultrasound-assisted extraetion of phenolic compounds, antioxidants, and anthocyanins from grape (Vitis vinifera) seeds. J. Agric. Food Chem. 57 4988 994. 

Catechins and proanthocyanidins can be detected at 280 nm using a UV detector. However, peak intensity at this wavelength is low, and many other phenolic compounds also adsorb light at 280 nm. Fluorescent detection provides better sensitivity and specificity than UV detection. The excitation and emission spectra of procyanidin dimers are shown in Figure 8.5. Excitation at 276 nm and emission at 316 nm had been used in earlier studies however, an examination of the fluorescent spectra indicated this was not the optimal condition. Excitation and emission wavelengths were set to 230 and 321 nm, respectively, in our most recent study, which caused a 5-fold increase in peak intensity (Robbins et ah, 2009). 

An optimization strategy was presented for the validation of a unique LC method, including the use of a single solvent gradient, for the LC analysis with DA-UVD of the most representative phenolic compounds from different food sources . 

A crnde extract of sweet potato Ipomoea-batatas (L.) Lam.) was nsed as a source of phenol oxidases (polyphenoloxidase, tyrosinase, catecholoxidase, EC 1.14.18.1). The extract was directly placed in the carrier of a FIA system with UVD, to promote oxidation of phenolic compounds to o-quinones that condense to form melanin-like pigments with a strong absorption at 410 nm. The determination of phenols in industrial wastewaters showed good agreement with conventional methods (correlation coefficient 0.9954) LOD was 10 p,M, with RSD <2.7% (w = 6). Under optimal storage conditions the enzymatic activity did not vary for at least five months . 

In a closely related paper [121] the calculated oxidation potentials for eight phenolic compounds for which experimental results are known were correlated to develop a calibration curve. From these data the oxidation potentials of coniferyl alcohol, sinapyl alcohol, anisole, guaiacol, and a pinoresinol dimer were predicted. This paper applied B3LYP/6-31G(d) optimizations to both gas phase and solvated models, and compared the results to experimental data at pH = 0. Based on a correlation coefficient of 0.93 for the calibration curve, the oxidation potentials of the nnknowns were determined. The relative results from both of these papers are similar, with dimethoxy compounds having lower oxidation potentials than the mono-methoxy compounds. 

The role of phenolic compounds as stabilizers and antioxidants has been studied very extensively in polymers and copolymers (refs. 18, 19). Many papers are devoted to this problem. Studies have been made on the optimization of phenolic structure based on hydroquinone (ref. 20) or catechol (ref. 21) as an antioxidant in polypropylene for example. Others have dealt with the influence of the polarity or stearic effect for different phenolic compounds or substituted phenols on the kinetics of antioxidation reactions - for example in polyvinyl acetate (ref. 22). Lastly, many papers have discussed on kinetic effects. 

Chirinos, R., Rogetz, FI., Campos, D., Pedreschi, R., and Larondelle, Y. (2007). Optimization of extraction conditions of antioxidant phenolic compounds from mashua (Tropaeolum tuberosum Ruiz Pavon) tubers. Sep. Purif. Technol. 55, 217-225. 

Chea V, Paolucci-Jeanjean D, Belleville M-P, and Sanehez J. Optimization and eharacterization of an enzymatie membrane for the degradation of phenolic compounds. Catal. Today 2012 193 49-56. 

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