Phenolics in fruits

Imeh U and Khokhar S. 2002. Distribution of conjugated and free phenols in fruits antioxidant activity and cultivar variations. J Agric Food Chem 50(22) 6301-6306. 

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. 

Table 2 describes the HPLC procedure for phenolics in fruit juices, which is based on previous works (22,49,50). A typical extraction procedure for obtaining phenolics from fruit juices is shown in Figure 7. 

For phenolics in fruit purees and jams (54), an HPLC condition similar to that used for apple juice, but with acidified water (5% formic acid) and methanol, was utilized as a solvent system. In most cases, detection was achieved with diode array detection, at UV 280 nm and 320 nm. The different phenolic compounds were identified by their UV spectra and by chromatographic comparisons with authentic standards. Several classes of phenolic compounds (cinnamic acids, catechins, dihydrochalcones, and flavonol glycosides) could be detected along with arbutin in... 

Fig. 7 Sample preparation procedure for phenolics in fruit juices. (From Refs. 22, 49, and 50.)...

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-... 

Ascorbic acid browning is also inhibited by the addition of sulfite (Wedzicha and McWeeny, 1974). The same holds for polyphenol oxidase-catalyzed oxidation of natural phenols in fruit. The mechanism of the inhibition is by reaction of oquinone intermediates with sulfite, which leads to nonreactive sulfocatechols (Wedzicha, 1995). 

Vrhovsek, U., Masuero, D., Gasperotti, M., Franceschi, P., Caputi, L., Viola, R., and Mattivi, F. 2012. A versatile targeted metabolomics method for the rapid quantification of multiple classes of phenolics in fruits and beverages. J. Agr. Food Chem. 60 8831-8840. 

Phenolics reported in fruits and fruit products include 47 phenolic acids, 112 flavonoids, 7 stilbenes, 6 lignans, and 1 other polyphenol [9]. The major phenolics in fruits and fruit products are summarized in Tables 81.4 and 81.5. 

Table 81.5 TPC range (mg/100 g FW) and major phenolics in fruits and fruit products ...

Scalzo J, Politi A, Pellegrini N, Mezzetti B, and Battino M (2005), Plant genotype affects total antioxidant capacity and phenolic contents in fruit , Nutrition, 21, 207-213. 

Phytochemicals present in fruits and vegetables are very diverse, such as ascorbic acid, carotenoids, and phenolic compounds (Liu 2004 Percival and others 2006 Syngletary and others 2005 Yahia and others 2001a, 2001b). Plant polyphenols are ubiquitous in the diet, with rich sources being tea, wine, fruits, and vegetables they demonstrate considerable antioxidative activity in vitro, which can have important implications for health (Duthie and others 2000). 

Several in vitro studies have shown that phenolic compounds in fruits and vegetables have antiproliferative effect in different cancer cell lines (Eberhardt and others 2000 Chu and others 2002 Sun and others 2002 Liu and others 2005 Mertens-Talcott and others 2005 Percival and others 2006). 

The consumption of a mixture of phenolic compounds presented in apple or purple grape juice inhibited mammary carcinogenesis in 7,12-dimethylbenzo[a]anthracene (DMBA) treated rats (Liu and others 2005 Jung and others 2006). However, the individual antioxidants of these foods studied in clinical trials, including (3-carotene, vitamin C, and vitamin E, do not appear to have consistent preventive effects comparable to the observed health benefits of diets rich in fruits and vegetables, suggesting that natural phytochemicals in fresh fruits and vegetables could be more effective than a dietary supplement. 

Ju Z and WJ Bramlage. 1999. Phenolics and lipid-soluble antioxidants in fruit cuticle of apples and their antioxidant activities in model systems. Postharv Biol Technol 16 107—118. 

Robards K, Prenzler PD, Tucker G, Swatsitang P and Glover W. 1999. Phenolic compounds and their role in oxidative processes in fruits. Food Chem 66 4014-36. 

Velioglu YS, Mazza G, Gao L and Oomah DB. 1998. Antioxidant activity and total phenolics in selected fruits, vegetables, and grain products. J Agric Food Chem 46 4113—4117. 

Phenolic Compounds Chemistry and Occurrence in Fruits and Vegetables... 

In order to preserve, as much as possible, the phenolic content in fruit and vegetable samples, the literature proposed the application of cold temperatures, even reaching to freezing, when lyophilization is the objective. These procedures also could inactivate the enzymes. The freeze-drying is largely the main preservation technique used in the studies related to the identification and quantification of the phenolic compounds of fruit... 

Liquid chromatography, coupled to the different ionization sources, is generally the technique most used to characterize the phenolic profile in fruit and vegetable products. With regard to the source ionization, it seems that ESI is used more frequently than other sources, such as APCI or APPI. Another important aspect of this technique is the ionization of phenolic compounds. Negative ionization seems to be more suitable... 

Buta JG and Spaulding DW. 1997. Endogenous levels of phenolics in tomato fruit during growth and maturation. J Plant Growth Regul 16(1) 43—46. 

Colaric M, Veberic R, Solar A, Hudina M and Stampar F. 2005. Phenolic acids, syringaldehyde, and juglone in fruits of different cultivars of Juglans regia L. J Agric Food Chem 53(16) 6390-6396. 

Li P, Wang XQ, Wang HZ and Wu YN. 1993. High performance liquid chromatographic determination of phenolic acids in fruits and vegetables. Biomed Environ Sci 6(4) 389-398. 

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