BIOFLAVONOIDS:
A. History. Albert Szent-Györgyi and his associates, in 1936, reported the presence, inlemon peel, of a material which they named citrin. It consisted of a mixture of flavonoids and was shown to be associated with the maintenance of normal capillary permeability and fragility. The
active principle in citrin was found to be hesperidin. It shows physiologic roles similar to those
exhibited by other structurally-related compounds such as flavanones, flavones and flavonols. The term vitamin P (for permeability) was at first assigned to this group of compounds. They are now more commonly referred to as bioflavonoids.
B. Occurrence. The bioflavonoids are widely distributed in nature. They are always of plant
origin. They are present in the juice, peel and pulp of citrus fruits, in tobacco leaves, in buckwheat (Fagopyrum esculentum), in grapes and in many other fruits and vegetables.
C. Structure. Hesperidin is 5,3′-dihydroxy-4′-methoxy-7-rhamnoglucosidoflavanone. Its aglycone hesperitin, rutin (5,7,3′,4′- tetrahydroxy-3-glucorhamnosidoflavone) and its aglycone,
quercitin all have comparable physiologic roles.
D. Properties. The bioflavonoids are water-soluble.
E. Metabolism. The bioflavonoids act as antioxidants and thus protect ascorbic acid from
oxidative destruction (Clemetson and Andersen, 1966). The effect is indirect due to the chelation
of heavy metal ions (Cu2+ etc., ) that catalyze oxidative degradation of ascorbic acid. Bioflavonoids, thus, decrease oxidative losses of ascorbic acid from foods during storage or in intestinal tract.
F. Deficiency. Bioflavonoid deficiency in animals results in a syndrome characterized by increased capillary permeability and fragility. In man, however, the deficiency symptoms have not been observed.
G. Human requirements. The dietary allowances for man are not known.
VITAMERS ( = ISOTELS):
The various forms of any vitamin are referred to as vitamers. Williams, however, prefers to call these as isotels or isotelic vitamins, since the name vitamer is misleading. Although the isotels, in general, are not the isomers but a few of them may be isomers. All the fat-soluble vitamins and a few water-soluble vitamins (vitamins B5 and B6) have isotels. The various isotelic forms of a vitamin may differ with respect to either the β-ionone ring (vitamin A), the side chain attached at carbon 17 of the steroid nucleus (Vitamin D), the substituents present at carbon atoms 6, 7 and 8 in the chroman ring (vitamin E) or the side chain attached at carbon 3 of naphthoquinone radical (vitamin K). The study of isotels helps in a better understanding of the various physiologic functions which the vitamins perform.
A. History. Albert Szent-Györgyi and his associates, in 1936, reported the presence, inlemon peel, of a material which they named citrin. It consisted of a mixture of flavonoids and was shown to be associated with the maintenance of normal capillary permeability and fragility. The
active principle in citrin was found to be hesperidin. It shows physiologic roles similar to those
exhibited by other structurally-related compounds such as flavanones, flavones and flavonols. The term vitamin P (for permeability) was at first assigned to this group of compounds. They are now more commonly referred to as bioflavonoids.
B. Occurrence. The bioflavonoids are widely distributed in nature. They are always of plant
origin. They are present in the juice, peel and pulp of citrus fruits, in tobacco leaves, in buckwheat (Fagopyrum esculentum), in grapes and in many other fruits and vegetables.
C. Structure. Hesperidin is 5,3′-dihydroxy-4′-methoxy-7-rhamnoglucosidoflavanone. Its aglycone hesperitin, rutin (5,7,3′,4′- tetrahydroxy-3-glucorhamnosidoflavone) and its aglycone,
quercitin all have comparable physiologic roles.
D. Properties. The bioflavonoids are water-soluble.
E. Metabolism. The bioflavonoids act as antioxidants and thus protect ascorbic acid from
oxidative destruction (Clemetson and Andersen, 1966). The effect is indirect due to the chelation
of heavy metal ions (Cu2+ etc., ) that catalyze oxidative degradation of ascorbic acid. Bioflavonoids, thus, decrease oxidative losses of ascorbic acid from foods during storage or in intestinal tract.
F. Deficiency. Bioflavonoid deficiency in animals results in a syndrome characterized by increased capillary permeability and fragility. In man, however, the deficiency symptoms have not been observed.
G. Human requirements. The dietary allowances for man are not known.
VITAMERS ( = ISOTELS):
The various forms of any vitamin are referred to as vitamers. Williams, however, prefers to call these as isotels or isotelic vitamins, since the name vitamer is misleading. Although the isotels, in general, are not the isomers but a few of them may be isomers. All the fat-soluble vitamins and a few water-soluble vitamins (vitamins B5 and B6) have isotels. The various isotelic forms of a vitamin may differ with respect to either the β-ionone ring (vitamin A), the side chain attached at carbon 17 of the steroid nucleus (Vitamin D), the substituents present at carbon atoms 6, 7 and 8 in the chroman ring (vitamin E) or the side chain attached at carbon 3 of naphthoquinone radical (vitamin K). The study of isotels helps in a better understanding of the various physiologic functions which the vitamins perform.
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