Flavonoids are a widely distributed group of polyphenolic compounds with health-related properties, which are based in their antioxidant activity. These properties have been found to include anticancer, antiviral, antiinflammatory activities, effects on capillary fragility, and an ability to inhibit human platelet aggregation. The antioxidant capacity of any flavonoid will be determined by a combination of the O-dihydroxy structure in the B-ring, the 2,3-double bond in conjugation with a 4-oxo function and the presence of both hydroxyl groups in positions 3 and 5. Flavanones, flavones, and flavonols are the flavonoids present in Citrus, and although flavones and flavonols have been found in low concentrations in Citrus tissues, in relationship to flavanones, these types of compounds have been show to be powerful antioxidants and free radical scavengers. Some Citrus flavonoids can be used directly as repellents or toxins or be used in plant improvement programs to obtain more resistant crops. In addition, some Citrus flavonoids and their derivates, in the field of food technology, are principally known for their ability to provide a bitter or sweet taste and as bitterness inhibitor. Keywords: Free radicals, antioxidant; anticarcinogenic; antiinflammatory; platelet aggregation; antiallergic; analgesic; antimicrobial; food additives

The quantitative distribution of several flavan-3-ols was determined using HPLC in a grape (Vitis vinifera) seed extract (GSE) of four cultivars grown in the region of Murcia. Polymer >/= C(4) units made up the largest group of procyanidins in the GSE (90.92%, expressed as HPLC % area). The antioxidant activity of GSE and other reference compounds was investigated by measuring their ability to scavenge the ABTS(*)(+) radical cation (TEAC). The most effective compounds were, in order: GSE > rutin > (+)-catechin > diosmin >/= ascorbic acid. The radioprotective effects of GSE and other reference compounds were determined by using the micronucleus test for anticlastogenic activity, any reduction of the frequency of micronucleated polychromatic erythrocytes (MnPCEs) being evaluated in the bone marrow of mouse exposed to X-rays. The most effective compounds were, in order: GSE > rutin > dimethyl sulfoxide (DMSO) > ascorbic acid > 6-n-propyl-2-thiouracil-6c (PTU) > diosmin. The higher ABTS(*)(+) scavenging capacity and anticlastogenic activity of GSE can be explained, structurally, by the high number of conjugated structures between the catechol groups in the B-rings and the 3-OH free groups of the polymeric polyphenolic skeleton and, in addition, by the stability of the aroxyl flavonoid radical generated in the above processes.

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The effects of variety, rootstock, and geographical location were studied as to their effects on secondary metabolite production in grapefruit and pummelo. The concentration of the flavanones narirutin, naringin, and neohesperidin and of the sesquiterpene nootkatone, which is principally responsible for the grapefruit's aroma, varies during h i t development. The highest flavanone levels are detected during the juvenile stages of fruit development, while nootkatone expression is associated with the processes of maturation and senescence. The possibility of increasing the levels of these metabolites by regulating the associated processes of growth and cell differentiation is discussed.

The distribution of seven flavonoids, eriocitrin, luteolin 3'-O-beta-d-glucuronide, hesperidin, diosmin, isoscutellarein 7-O-glucoside, hispidulin 7-O-glucoside, and genkwanin, has been studied in Rosmarinus officinalis leaves, flowers, stems, and roots during plant growth. The maximum level reached by luteolin 3'-O-beta-d-glucuronide in leaves during June-August suggests the existence of a delay between the activation of the enzymes involved in the flavanone and flavone biosynthesis. The presence of hesperidin and diosmin in the vascular system is significant, and hesperidin shows even higher levels than the phenolic diterpenes and rosmarinic acid. The distribution of flavonoids observed in R. officinalis suggests a functional and structural relationship between phytoregulators and flavonoids, where flavonoids would be "protectors" of the activity of phytoregulators. A hypothesis for the general pathway of biosynthesis of these compounds in plants of the family Labiatae is proposed.