Citrus glycosides

Of this class of naturally occurring, sweet compounds, the flavanone glycosides found in citrus fruits have achieved considerable interest, owing to the systematic studies of Horowitz and Gentili " (see Fig. 20). 

The flavanone hesperetin has been detected in citrus honeys but not in honey samples of any other origins (Ferreres et al., 1993). It is a constitutive phenolic compound of citrus nectar, where it is present as a glycoside (hesperidin). 

McHale D, Khopkar PP and Sheridan JB. 1987. Coumarin glycosides from citrus flavedo. Phytochemistry 26(9) 2547-2549. 

Citrus species are well-known for their accumulation of flavone- and flavanone-glycosides, and thus should contain all of the enzyme activities necessary for the synthesis of these compounds. Two tentative consensus sequences for FNS-II have been identified by in silico analysis of the CitEST database, apparently representing the first identification of putative FNS-II genes in this genus [29]. Biochemical determination of function and analysis of the proteins encoded by these genes will be an important step toward elucidating flavone synthesis in Citrus. 

Lewinsohn E, Britsch L, Mazur Y, Gressel J (1989) Flavanone glycoside biosynthesis in Citrus chalcone synthase, UDP-glucose flavanone-7-0-glucosy-transferase and -rhamnosyltransferase activities in cell-free extracts. Plant Physiol 91 1321-1328... 

Kuoryanagi M, Ishii JH, Kawahara N, Sugimoto H, Yamada H, Okihara K, Shirota O (2008) Flavonoid glycosides and limonoids from Citrus molasses. J Nat Med 62 107-111... 

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. 

We know of thousands of flavonoids. They have a C6-C3-C6 skeleton and are responsible for the bright colors in flowers. The bitter taste in citrus fruits is caused by flavonone glycosides. 

Miyake, Y. et al., New potent antioxidative hydroxyflavanones produced with Aspergillus saitoi from flavanone glycoside in citrus fruit, Biosci. Biotechnol. Biochem., 67, 1443, 2003. 

Mouly, P.P. et ak, Differentiation of citrus juices by factorial discriminant analysis using liquid chromatography of flavanone glycosides, J. Agric. Food Chem., 42, 70, 1994. 

Marini, D. and Balestrieri, F., Multivariate analysis of flavanone glycosides in citrus juices, Ital. J. Food Sci., 1, 255, 1995. 

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]. 

Among aglycones, the best known are naringenin and hesperidin. Their glycosylated forms occur commonly as O- or C-glycosides, usually as rutinosides (6-O-a-L-rhamnosyl-D-glucosides) and neohesperidosides (2-O-a-L-rhamnosyl-D-glucosides) attached at position 7. Flavanones contribute to the flavour of citrus [19]. Table 12 reports the structures of some common flavanones. 

Pectin and related substances are widespread in the plant kingdom. They are normally obtained from the dilute acid extract of the inner portion of citrus peels or from apple pomace. The extraction of pectin is carried out at elevated temperatures at a controlled pH. The process must be very carefully checked in order to avoid a possible hydrolysis of glycosidic and ester linkages. The crude extract is concen-... 

The flavone glycoside hesperidin makes up 80% of the dry weight of orange peels. It has been claimed (but not proved) that this compound, also known as vitamin P and citrus bioflavonoid, is essential to... 

Hypertension is an important risk factor for coronary heart disease and stroke. Since ancient times, hypertensive patients have been treated orally with plant extracts based on folk medicine. However, and despite their in vitro vasodilator effects, little information about the protective effects of flavonoids on hypertension is available in the literature. Flavonoids have been considered as active principles of several antihypertensive plant extracts (e.g. rhamnoglycoside of limocitrin isolated from Citrus limonum, kaempferol 4 -0-glucose and hyperin from Euphorbia maddeni, moracenins from Morus alba, procyanidin glycoside from Rhamnus lycioides) [150,151]. In all cases, only the acute antihypertensive effects after i.v. administration in anaesthetised normotensive and/or hypertensive animals have been described. In addition to the direct vasodilator effects discussed above, the inhibition of angiotensin-converting enzyme reported... 

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