Phenolic compounds chemical characterization

Biogenic amines and phenolic compounds were also characterized from the defensive secretion of other saturniid caterpillars such as Saturnia pavonia, S. pyri, and Eupackardia calleta [169] and the chemical ecology of Saturniidae and Lymantriidae was recently reviewed by Demi and Dettner [170]. 

Until recently, most of the chemical research on the contents of these structures was directed at the identification of the constituents of castoreum. In the late 1940s Lederer [72, 73] identified 36 compounds and some other incompletely characterized constituents in castoreum of uncertain origin. Other constituents were subsequently identified in the material [74-77]. In a reinvestigation aimed specifically at the phenol content of the material, Tang et al [69] identified 10 previously unreported phenols in the castoreum from the North American beaver, Castor canadensis. Of the 15 phenols reported elsewhere, only five were confirmed in this analysis, in addition to 10 phenolic compounds that were not reported elsewhere. It was concluded that the 10 previously identified phenols that were not found in the study by Tang et al. were either absent or were not volatile enough to be detected by the methods employed. This was most probably because a relatively low maximum column temperature of only 210 °C was employed in the GC-MS analyses. The compounds identified by Lederer,... 

Leighton, T. et al.. Molecular characterization of quercetin and quercetin glycosides in Allium vegetables their effects on malignant cell transformation. In Huang, M.T., Ho, C.T., and Lee, C.Y., eds.. Phenolic Compounds in Food and their Effects on Health II. Antioxidants and Cancer Prevention. New York American Chemical Society, 1992, p. 220. 

There are numerous synthetic and natural compounds called antioxidants which regulate or block oxidative reactions by quenching free radicals or by preventing free-radical formation. Vitamins A, C, and E and the mineral selenium are common antioxidants occurring naturally in foods (104,105). A broad range of flavonoid or phenolic compounds have been found to be functional antioxidants in numerous test systems (106—108). The antioxidant properties of tea flavonoids have been characterized using models of chemical and biological oxidation reactions. 

Many excellent discussions of natural occurrence, structure, characterization, and analysis of phenolic compounds are available in the literature, and a series of books devoted to flavonoid chemistry has also been published. Detailed discussions on various chromatographic modes, including HPLC, GC, column chromatography (CC), capillary electrophoresis (CE), PC, and TLC, of simple phenolics and polyphenols are also presented in the recent book, Handbook of Food Analysis, volume 1, edited by Nollet (1). Due to their diversity and the chemical complexity of phenolic compounds, this chapter is limited to phenolic compounds that are considered to be important to foods and the food industry. 

For phenolics in fruit by-products such as apple seed, peel, cortex, and pomace, an HPLC method was also utilized. Apple waste is considered a potential source of specialty chemicals (58,62), and its quantitative polyphenol profile may be useful in apple cultivars for classification and identification. Chlorogenic acid and coumaroylquinic acids and phloridzin are known to be major phenolics in apple juice (53). However, in contrast to apple polyphenolics, HPLC with a 70% aqueous acetone extract of apple seeds showed that phloridzin alone accounts for ca. 75% of the total apple seed polyphenolics (62). Besides phloridzin, 13 other phenolics were identified by gradient HPLC/PDA on LiChrospher 100 RP-18 from apple seed (62). The HPLC technique was also able to provide polyphenol profiles in the peel and cortex of the apple to be used to characterize apple cultivars by multivariate statistical techniques (63). Phenolic compounds in the epidermis zone, parenchyma zone, core zone, and seeds of French cider apple varieties are also determined by HPLC (56). Three successive solvent extractions (hexane, methanol, aqueous acetone), binary HPLC gradient using (a) aqueous acetic acid, 2.5%, v/v, and (b) acetonitrile fol-... 

In the previous chapters we have discussed the different classes of phenolic compounds, their chemical properties, and their biosynthesis. The characterization of phenolic compounds relied on the ability to isolate them from plant tissues. In this chapter we will discuss methods to isolate and characterize phenolic compounds, and methods to visualize them in planta. Chapter 5 focuses on techniques for the identification and characterization of some of these compounds using recently developed mass-spectrometry-based techniques. 

In the previous section methods to isolate (certain classes of) phenolic compounds were described. In general, however, these methods do not provide information on specific chemical composition. In order to characterize mixtures of phenolic compounds, a variety of separation and identification methods exist. They will be described below. 

The identification of phenolic compounds separated by TLC is somewhat challenging. The most common strategy is to include a set of reference compounds on the TLC plate. These compounds are applied individually, and if the mixture contains any of the reference compounds, they can be identified based on the i /-value. Note that this approach always leaves some room for uncertainty, because two different compounds can have the same /< /-value. Further characterization is necessary to establish compound identity with more confidence. This can be achieved by scraping off the area on the TLC plate where the compound of interest has migrated to, followed by solvent extraction of the matrix, and more detailed chemical analyses, such as, for example gas chromatography-mass spectrometry or mass spectrometry (see Section 1.5 and Chapter 5). 

Sunflower is a rich source of sesquiterpenes,21 especially sesquiterpene lactones.23,28 31 44 Due to its economic importance, sunflower has been extensively studied, thus leading to the isolation and chemical characterization of phenolic compounds (benzoic acid derivatives,9 39,51 coumarins,51 and flavonoids6,10,19), diterpenes, and triterpenes. Most of these studies were performed using... 

Fernandez de Simon, B., Sanz, M., Cadahfa, E., Poveda, R, Broto, B. (2006). Chemical characterization of oak heartwood from Spanish forests of Quercus pyrenaica (Wild.). Ellagitannins, low molecular weight phenolic, and volatile compounds. J. Agric. Food Chem., 54, 8314-8321. 

Little is known about the overall mechanism of cyclic oligomer formation, although the mechanism of the initial stages of the sequence seems fairly clear. The first chemical event is the reaction of formaldehyde (formed in the Petrolite procedures by depolymerization of paraformaldehyde) with phenol to form 2-hydroxy-methyl- and 2,6-6w(hydroxymethyl)phenols in a base-catalyzed process, as shown in Fig. 3. Such compounds were characterized many years ago50), obtained from the action of aqueous formaldehyde on phenol in basic solution at room temperature. Subsequent condensation between the hydroxymethylphenols and the starting phenol occurs to form linear dimers, trimers, tetramers, etc. via a pathway that might involve o-quinonemethide intermediates which react with phenolate ions in a Michael-like reaction, as portrayed in Fig. 4. The condensation of hydroxymethyl-... 

Attempts at characterizing peat humus through spectroscopy and chemical degradation procedures (Walmsley, 1973 Stevenson, 1974 Fuchsman, 1980) also have shown that peat humic substances are similar to those from mineral soils. For example Levesque et al. (1980b) found that humic substances extracted by sodium pyrophosphate from 10 different peat materials that varied in botanical origin and extent of humification yielded aliphatic and phenolic compounds and benzenecarboxylic acids (Table 14) in amounts... 

The presence of an exchangeable proton band at relatively low field and the relatively high field chemical shifts produced by the hydroxyl group on the ortho and para aromatic hydrogens makes the phenols a relatively simple group of compounds to characterize. 

With the rapid increase in the number of chemical industries, a great deal of waste-water is produced, which causes pollution and degrades the environment. Many of these industrial wastewaters, particularly the ones, containing phenolic compounds, are well known to be characterized by higher salinity, acidity, chemical oxygen demand (COD) value and low biodegradability, which means that the effluent cannot be treated by the conventional process [2, 3]. An alternative method of treating such... 

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