Structure of polyphenolics

Figure 1 Chemical structure of polyphenolics in citrus. (A) Bergamottin, (B) 6 7 dihydroxybergamottin, (C) Naringenin, (D) Naringin, (E) Rutin, (F) Tangeretin, and (G) Nobiletin.

RELATION BETWEEN STRUCTURE OF POLYPHENOL OXIDASE AND PREVENTION OF BROWNING... 

The extraction of phenolic compounds from plant materials is considerably influenced by some factors such as the nature of the sample, the chemical structure of polyphenols, the extraction method employed, the extractirMi agent involved, sample particle size, as well as the presence of interfering substances. 

Fig. 18.3. Chemical structures of polyphenols Hydroxybenzoic acids (Hba), Hydroxy cinammic acids (Hca), Flavonoids (F), Chalcones (C), Stilbenes (S, cf. 20.2.6.6), Lignans (L). R H, OH or OCH3...

Polyphenolic compounds are separated mainly in the reversed phase on the column with C18 sorbent, with inside diameter from 1.7 to 2.1 mm, filled with small size particles (about 1.7 p,m). In the event of nonpolar stationary phases the order of elution of polyphenols is consistent with the number of hydroxyl groups in the molecule, the degree of methoxylation, as well as the amount of sugar molecules in the structure of polyphenol. 

In addition to the bitter acids and essential oils, the flowers of hops offer a rich array of polyphenolic compounds, primarily chalcones and their accompanying flavanones, many of which are prenylated derivatives (Stevens et al., 1997,1999a, b). The most prominent flavonoid in all plants studied was xanthohumol [342] (3 -prenyl-6 -0-methylchalconaringenin chalconaringenin is 2, 4, 6, 4-tetrahydroxychalcone) (see Fig. 4.11 for structures 342-346). Several additional chalcones—variously adorned with 0-methyl and/or C-prenyl functions—were also encountered, along with their respective flavanones. Three new compounds were described in the Stevens et al. 

Hanamura, T., Hagiwara, T., and Kawagishi, H., Structural and functional characterization of polyphenols isolated from acerola Malpighia emarginata DC) fruit, Biosci. Biotechnol. Biochem., 69, 280, 2005. 

Wolfender JL, Ndjoko K and Hostettmann K. 2003. Application of LC-NMR in the structure elucidation of polyphenols. In Santos-Buelga C, Williamson G, editors. Methods in Polyphenol Analysis. Cambridge, UK Royal Society of Chemistry, pp. 128-156. 

In recent years, numerous papers have been published about one of the most important groups of phytochemicals, the polyphenols (Manach and others 2004). These compounds, which possess an array of healthy properties, but also some disadvantages that will be discussed in this chapter, are present in a variety of plants used in both human and animal diets. However, the structure of this type of compound means that they can be oxidized by several pro-oxidant agents. The objective of this chapter is to describe the main enzymatic agents responsible for the degradation of polyphenols. In order to understand the mechanisms of degradation that will be described in the following sections, a brief summary of the main properties of the polyphenols is required. 

Because of the easily oxidizable structure of the polyphenols previously described, many studies have been published about the enzymatic degradation of these antioxidant compounds. This chapter exhaustively reviews the main publications concerning the degradation of this type of antioxidant compound by several enzymes. 

Flavonoids are a complex group of polyphenolic compounds with a basic C6-C3-C6 structure that can be divided in different groups flavonols, flavones, flavanols (or flavan-3-ols), flavanones, anthocyanidins, and isoflavones. More than 6,000 flavonoids are known the most widespread are flavonols, such as quercetin flavones, such as lu-teolin and flavanols (flavan-3-ols), such as catechin. Anthocyanidins are also bioactive flavonoids they are water-soluble vegetable pigments found especially in berries and other red-blue fruits and vegetables. 

Kusuda M, Inada K, Ogawa TO, Yoshida T, Shiota T, Shiota S, Tsuchiya T, Hatano T. (2006) Polyphenolic constituents structures of Zanthoxylum piper-itum fruit and the antibacterial effects of its polymeric procyanidin on methicillin-resistant Staphylococcus aureus. Biosci Biotechnol Biochem 70 1423-1431. 

Polyphenol adsorbents are mainly polyamides (Dadic, 1973). At one time various nylons were used, but PVPP is most frequently used today (McMurrough et ah, 1997). The structure of PVPP (see Fig. 2.23) resembles that of polyproline (Fig. 2.6) both have five-membered, saturated, nitrogen-containing rings and amide bonds. 

Nishioka. Tannins and related compounds. CXIV. Structure of novel fermentation products, theogallinin, theaflavonin and desgalloyl thea-flavonin from black tea and changes of tea leaf polyphenols during fermentation. Chem Pharm Bull 1992 40(6) 1383-1389. 

Poncet-Legrand, C. et ak, Flavan-3-ol aggregation in model ethanolic solutions incidence of polyphenol structure, concentration, ethanol content and ionic strength. Langmuir 19, 10563, 2003. 

Tanaka, T., Mine, C., and Kuono, I., Structures of two new oxidation products of green tea polyphenols generated by model tea fermentation. Tetrahedron, 58, 8851, 2002. 

Comparative Aspects of Polyphenol Metabolism - Proanthocyanidins and the complex esters of gallic and hexahydroxydiphenic acid show many structural similarities as plant metaijol i tes. The shape and size of the ester (5) is thus very similar to that of a proanthocyanidin hexamer (1, n = 4). The most striking feature of both structures however s the manner in which free phenolic groups are distributed over the surface of the molecule providing a structure with the inbuilt capacity for multidentate attachment to other species by hydrogen bonding. 

---