Demand and Occurrence

The normal recommended intake for biotin is age-dependent Infants require 10-20 pg/day, children 25-30 pg/day and adolescents and adults 30-100 pg/day. Biotin deficiency is rare, but can lead to seborrhoea (excessive secretion of sebmn from the sebaceous glands in the skin), dermatitis, loss of appetite, muscular pain, lethargy, and nervous disturbances (Tab. 7.3). [109] 

A deficiency of biotin in humans may result from an unbalanced diet, alcohol abuse, side-effects of medication (e.g. with sulfonamides, antiepileptics), or genetic defects. In babies, this deficiency may appear after prolonged breastfeeding ( 4 months), as the biotin content of the mother s milk decreases. There has 

47 Among a variety of plant species studied, cultured green cells of lavender (Lavandula angustifolla, syn. Lavandula officinalis, Lavandula vera) were found to contain the greatest amount of free biotin. 

For animal feed, biotin is also of high importance. [110] Whereas ruminants have normally a sufficient supply of biotin provided by their fodder and by the amounts of biotin synthesised in the gastrointestinal tract, deficiencies occur more often in pigs, especially in piglets. Poultry tends to underutilise the biotin in their feed, and their enteral biotin synthesis is poor. Turkeys have an especially high demand for biotin. The use of sulfonamides and other antibiotics in animal husbandry affects the intestinal flora and may necessitate biotin-fortified feed (Tab. 7.4). 

Many foodstuffs contain a metabolic intermediate of biotin, biocytin s-N-biotinyUysine), which is cleaved in the intestinal tract by the enzyme biotinidase. Only free biotin can be resorbed in the proximal small intestine, a process, which can be blocked by avidin, a glycoprotein with a molar mass of ca. 70,000. Avidin occurs in greater amounts in egg-white, and forms with biotin an extraordinarily stable molecular complex (dissociation constant at 25 °C K = 10 M), which can be cleaved neither by acids nor by peptidases. Only irradiation or longer exposure to heat leads to denaturation of avidin and thereby the release of biotin. This is another reason why a breakfast egg ought to be cooked for at least AVi minutes. In this way avidin is denatured and loses its harmful effect. Similarly stable complexes are formed by biotin with neutravidin (de-glycosyl-ated avidin), streptavidin and stravidin from certain Streptomyces and Saccharo-myces species respectively. 

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