Citrus fruits, flavones

Flavanones are 2,3-dihydroderivatives of flavones which have a saturated C-ring, and are mainly present in their glycosidic forms. In contrast to other flavonoid classes found in a wide range of foods and plants, flavanones are present mainly in citrus fruit and in some aromatic herbs such as ntint. However, reports on the isolation of antinticrobial flavanones from medicinal plants mainly concerned those belonging to the Leguntinoseae family. 

Normal phases (unmodified silica gel) are rarely employed, except for the occasional separation of weakly polar flavonoid aglycones, polymethoxylated flavones, flavanones, or isoflavones. The polymethoxylated flavones present in citrus fruits can, for example, be separated on silica gel columns. The big drawback is that solvent gradients cannot normally be run with normal phases. 

A comprehensive and critical review of food flavonoid literature has led to the development of a food composition database for flavonols, flavones, procyanidins, catechins, and flava-nones. This database can now be used and continuously updated to estimate flavonoid intake of populations, to identify dietary sources of flavonoids, and to assess associations between flavonoid intake and disease. However, there is a need for better food composition data for flavones, procyanidins, and flavanones as current literature is sparse particularly for citrus fruits, fruit juices, and herbs. In addition, anthocyanin food composition data are lacking although validated methods of determination are becoming available. 

About 300 different aglycones have been identified, and the most frequently are luteolin, apigenin (especially in parsley) and diosmetin (in Citrus fruits). Among glycosides, the 1-0- and C-forms are very common, and are characterized by a carbon-carbon bond between the anomeric carbon of a sugar molecule and the Q or Cg carbon of the flavone nucleus. Table 8 describes the most common flavones [19]. 

Citrus fruits and associated products (fruit juices, peeled fresh fruit) are a major dietary source of flavanones (Table 13) [35]. However, the distribution is quite scattered, and much higher concentrations are found in the solid tissues compared to the juice. For example, an individual drinking orange juice (250 ml) will have a daily flavone intake (as aglycones) in the range of 25-60 mg eating the flesh of a whole orange (200 g) will provide about 125-375 mg. 

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]. 

Flavones Apigenin, luteolin, diosmin and diosmetin. Found mainly in herbs, parsley, celery, citrus fruits, olives, peppers, red grapes, and some beans. Antiproliferative effect [67,70-73], Antimitotic [79], Inactivation of carcinogenesis mediated by chemicals [90, 91, 92], Inhibition of angiogenesis [108, Cardiovascular properties [99,100, 114], 10-4,000... 

Citrus fruit Flavanones Flavones Methylated flavones... 

Flavones Apigenin Luteolin Tangeretin Nobiletin Citrus fruits and pear [11,13]... 

Flavones consist chiefly of glycosides of luteolin, chrysin, and apigenin. They are less common in fruits [8]. Polymethoxylated flavones, the most hydrophobic flavonoids, present in citrus fruits (mainly in the peel, the nonedible part of the fruit) are tangeretin and nobiletin. Apigenin and chrysin possess anti-inflammatory and free-radical scavenging properties in several cancer cell lines and inhibit tumor cell invasion, metastasis, and mitogen-activated protein kinases (MAPK) and their downstream oncogenes [26]. 

In addition to these flavones and flavanones, many varieties of citrus fruits contain anthocyanin pigment. This does not appear to have been identified, but that in blood oranges has been studied by Matlack (1931), Carrante (1941), and Patane (1948). The color of pink grapefruit and Indian pummelo is due to lycopene, a carotenoid (Matlack, 1934, 1935). 

Davis WB (1947) Determination of flavanones in citrus fruits. Anal Chem 19 467-478 del Rio JA, Benavente O, Castillo J, Borrego F (1992) Neodiosmin, a flavone glycoside of Citrus aurantium. Phytochemistry 31 723-724... 

Flavone Nobiletin (citrus fruit) Oxidative stress... 

Figure 7.28 Flavanone conjugates, polymethoxylated flavones, f)-carotene, f5-cryptoxanthin and its fatty acid esters are found in citrus fruit.

Flavones have a close structural relationship to the flavonols, but unlike flavonols they are not widely distributed in plants. The only significant occurrences in plants are in celery, parsley, and a few other herbs, and they predominantly occur as 7-0-glycosides (e.g., luteolin and apigenin). In addition, polymethoxylated flavones have been found in citrus fruits (e.g., nobiletin and tangeretin). 

Citrus aurantium (Christen.) Swingle var. amara Suan Cheng (Bitter orange) (unripe fruit) Synephrine, N-methyltyramine, flavones including tangeratin and nobiletin.33 Treat indigestion, relieve abdominal distension, ptosis of the anus or uterus. 

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