Apple dihydrochalcones

Phlorizin, the glucoside of the dihydrochalcone phloretin, is a constituent of the tissues of the apple tree. Its distribution and bio-... 

Chalcones and dihydrochalcones have been reported in a restricted number of foods (Robards and others 1999 Tomas-Barbcran and Clifford 2000). Chalconaringenin occurs in tomato skin, but the acid extraction conditions of the usual polyphenol analyses convert the chalcone to the corresponding flavanone (naringenin) in the tomato. The most common dihydrochalcones found in foods are phloretin glucoside (phloridzin) and phloretin xylogalactoside, which are characteristic of apples (see Table 2.2) and derived products such as apple juice, cider, and pomace (Robards and others 1999 Tomas-Barbcran and Clifford 2000). 

Dihydrochalcones (DHCs) are characteristic of apples and derived products (apple juice, cider, pomace etc.), and their content depends on... 

The phenolic composition of apple consists of cinnamic acids, flavonols, dihydrochalcones, and flavan-3-ols (50,56). In the apple fruit processing industry, hydroxycinnamic acid derivatives and flavan-3-ols are important due to their contribution to the astringency, haze, and browning in apple juice and cider. Chlorogenic acid represents the major hydroxycinnamic acid derivative. The flavan-3-ols (catechins) are present in the monomeric form as well as in oligomeric and polymeric forms (procyanidins) in apple and apple products (56). 

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... 

FA Tomas-Barberan, C Garcia-Viguera, JL Nieto, F Ferreres, F Tomas-Lorente. Dihydrochalcones from apple juices and jams. Food Chem 46 33-36,1993. 

A Versari, S Biesenbruch, D Barbanti, PJ Famell. Adulteration of fruit juices dihydrochalcones as quality markers for apple juice identification. Lebensm Wiss Technol 30 585 -589, 1997. 

Chalcones, such as butein (1.26), are yellow pigments in flowers. An example of a dihydrochalcone is phloridzin (phloretin-2 -0-D-glucoside) (1.27), a compound found in apple leaves, and which has been reported to have anti-tumor activity (Nelson and Falk, 1993). 

Figure 4. HPLC chromatograms of Granny Smith apple juice phenolics. A, Cinnamics, flavonols, and dihydrochalcones B, procyanidins. (Reproduced from ref. 2. Copyright 1989 American Chemical Society.)...

The most characteristic compounds of apple are the dihydrochalcones, analysis of which can be applied to apple-derived food characterisation (juices, jams, purges, cider, etc.). Phloretin 2 -glucoside (phloridzin) (Fig. 5) and phloretin 2 -(2"-xylosylglucoside) are the only dihydrochalcones reported in apple so far [20]. 

Although tomato was the matrix most studied with this technique, other matrices such as pepper, eggplant, apple, pear, beans, mango, orange, citrus fruit, onion, garlic, potato, chillies, and strawberries were also studied by UAE. The extracted phenolic compounds included phenolic acids, isoflavones, flavonols, flavonones, fla-vones, flavonones, cinnamic acids, dihydrochalcones, chalcones, flavanols, and pro-cyanidins (Table 16.3). 

Phlorhizin, pUoridziK a dihydrochalcone found in the root bark of pears, apples and other members of the Rosaceae. P specific y blocks resorption of glucose by kidney tubules, thus inducing ucosuria. It therefore finds use in experimental physiology. Its activity may be due to inhibition of mutarotase. 

Phlorizin is a dihydrochalcone. Apart from its common occurrence in rosaceous trees, and especially in the root bark, it is otherwise reported as occurring only in Micromelum teprocarpum, a relative of Citrus. Although present in the seeds, shoots, and leaves of apples, it appears to be entirely absent from the flesh—a fortunate fact in view of its poisonous character. 

Apple polyphenols are present in different parts of the fruit. A major source is the skin, which contains all the flavonols and anthocyanins in addition to an important amount of dihydrochalcones. ° Phenolic acids are present in the flesh whereas most of the dihydrochalcones are in the core and the seeds. This distribution in different parts of the fruit also affects polyphenol concentration of apple juice where only small amounts of quercetin glycosides and dihydrochalcones are present. However, polyphenol content is also affected by the technological procedure. The oxidative conditions and the clarification process during the production of clear apple juice reduces the phenolic content. In contrast, the anaerobic conditions and the lack of a clarification step during cloudy apple juice production prevents an important loss of polyphenols. ... 

The dihydrochalcone glycoside phloridzin (Formula 18.31) occurs in apples. 

The main substrates of polyphenol oxidases in apples are hydrox-ycinnamic acid derivatives, especially caffeic add depsides, such as chlorogenic acid, and some groups of flavonoid compounds, such as flavan-3-ols, flavonols, dihydrochalcones and (in red-skinned apple varieties) also anthocyanins. In the flesh of apples, the main phenohcs are chlorogenic (3-caffeoylquinic) add, flavan-3-ol epicatechm, and procyanidin B2 representing condensed tannins. These three compounds represent more than 90% of the phenolic compounds present. The main substrates in apple peel are flavan-3-ols and flavonols (quercetin glycosides) and to a lesser extent derivatives of hydroxydnnamic acids are present (chlorogenic add and some other depsides). 

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