Fruit flavanols

Flavanols/Procyanidins Catechin, epicatechin, and their gallic acid esters Apples, grapes, plums, pears, mangoes, okra, peaches, Swiss chard, berry fruits and vegetables in general,... 

Flavanones In some cases, flavanones produced by CHI will accumulate to sizeable amounts instead of being diverted away to form flavonols, anthocyanins, and flavanols (see Fig. 5.4). These flavanone products, hesperetin and naringenin being the most common, are frequently encountered in citrus fruits and juices (USDA Flavonoids Database Release 2.1,2007). In most of these cases, essentially no flavonols or anthocyanins are encountered the flavonoid pathway is essentially blocked at the F3H step. 

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. 

Fruit juices processing may seriously affect flavanol content. For example, the preparation of commercial apple juice decreased the flavanol content in a stepwise manner. In particular, crushing and pressing, storage of the concentrated juice at room temperature and decolorization by treatment with activated carbon destroy the flavanols almost entirely [46]. 

The phenolics ( + )catechin and (— )epicatechin are common flavanols in several fruits (128). Apples and pears contain other phenolic compounds such as quinic, shikimic, chlorogenic, and caffeic acids (39). Durkee and Poapst (162) reported that the two major phenolic constituents of core tissues and seeds of McIntosh apples were chlorogenic acid and phloridzin. After hydrolysis of extracts from core tissues, the identified phenolics were phloretin, caffeic acid, p-coumaric acid, phloretic acid, and trace amounts of ferulic acid. Studies have shown that apple leucoanthocyanins yield catechin, epicatechin, cyanidin, and pelargonidin after hydrolysis (163, 164). Van Buren et al. (164) also reported that a purified leucoanthocyanin from apples was either a dimer or oligomer containing ( —) epicatechin, and 5,7,3, 4 -flavin-3,4-diol. 

For fruits and their products, HPLC techniques for phenolics have been used to study the effect of processing, concentration, and storage on the phenolic composition of juices as well as a potential precursor for an off-flavor compound in juices. Phenolic analysis has been further applied to the detection of economic adulteration and especially to verify the authenticity of fruit juices. This is especially important when cheaper fruits can be added to more expensive ones in a fraudulent manner. In most fruits, the nonanthocyanin flavonoids consist mainly of flavonols and flavanols, with trace amounts of flavones. Glycosides are the predominant forms present. These most often are separated by reversed-phase HPLC on Cl8 columns with gradients consisting of acidified H20 and ACN, MeOH, or EtOH. 

Flavonoids constitute a large class of polyphenols found in fruits and vegetables that share a common skeleton of phenylchromane. This basic structure allows a large number of substitution patterns leading to several subclasses of flavonoids, such as flavonols, flavones, flavanones, flavanols, anthocyanidins, isoflavones, dihydroflavonols, and chalcones. Among the diverse flavonoid subclasses, flavonols (especially quercetin) and flavanols (catechins) are the most abundant in our food. Flavonols are present in foods as diverse glycosides, whereas flavanols are usually found as aglycones. 

Flavanols are present in various vine plant tissues, including wood (Boukharta et al. 1988), leaves (Bogs et al. 2005 Tesnibre et al. 2006), stems (Souquet et al. 2000), and fruit. Within the grape berry, they are particularly abundant in seeds and skins. 

This effect can be modulated by environmental factors. Significant increases were found in skin proanthocyanidin content, proportion of (-)-epigallocatechin, and average DP in berries from zones with a low vine vigor (Cortell et al. 2005). In reaction to sun exposure, skin proanthocyanidin content tends to increase, particularly trihydroxylated subunits and mDP is enhanced (Downey et al. 2004 Cortell and Kennedy 2006). Shaded fruits reached a lower maximum in proanthocyanidin content than sun-exposed ones but the contents at harvest were similar. Most authors agree that water stress had only slight effects on tannin composition (Ojeda et al. 2002 Kennedy et al. 2002 Castellarin et al. 2006). Seed flavanol composition seems hardly affected by environmental factors. 

Flavanols with the hydroxyl group in the 3-position are often referred to as flavan-3-ols or catechins (Chung et al., 1998). As these compounds have two asymmetric carbon atoms (C-2 and C-3), four isomers exist for each flavan-3-ol molecule [Figure 3.3(b)], The flavan-3-ols most often occurring in grapes and berry fruits are... 

Anthocyanins, flavanols and phenolic acids are the main polyphenols of grapes and grape-derived foods, responsible for their major organoleptic properties. Anthocyanins are directly involved in the color of most red fruits including grapes (7) while flavanols are thought to make an important contribution to the astringency and bitterness of plant derived foods (2,3). 

Amperometric techniques are very useful for detecting analytes that have been separated by chromatographic means but have no chromophores or other easy means of detection. Adsorptive stripping voltammetry (ASV) can be used for the direct sensitive analysis of metals in many types of sample matrix. For example, ASV has been used to determine cadmium, lead and zinc in urine, copper and bismuth in human hair tin in fruit juice, zinc and copper in fish and lead in gunshot residue. Stripping analysis can also be used for other applications such as determining flavanols in wine °, inorganic compounds such as cyanide and pharmaceuticals. ... 

The flavonoids are a group of secondary metabolites widely distributed in the plant kingdom [63]. In 1984, more than 4000 flavonoids were identified in plants [64]. The major dietary sources of flavones are spices and pot herbs, such as parsley, rosemary, and thyme [65], whereas flavonols are predominantly found in onions, kale, broccoli, apples, berries and cherries, and in tea and red wine [66]. The flavanones are mainly restricted to citrus fruits [67], and flavanols are found in considerable amounts in tea, apricots, apples, and cherries [66]. 

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