Biochemistry

from the oxidizing effect of atmospheric oxygen and is little destroyed by heat treatment. With proper cooking without access of oxygen (cooking with the lid closed), about 70% of vitamin A is retained. Ultraviolet rays and fat oxidation products are detrimental to retinol. Fats and bile acids are needed to absorb retinol in the intestine. The presence of tocopherol (vitamin E) also contributes to the absorption of retinol. Calciferol (Vitamin D, antirachitic factor). This vitamin was discovered in 1916, but it was synthesized only in 1931. Vitamin D 3 -an effective drug for the treatment of rickets was obtained from fish oil in 1936. A year later, 7-dehydrocholesterol was isolated from the surface layers of the pig skin, which, under ultraviolet radiation, turns into active Vitamin Dj (Cholecalciferol) Vitamins D 2 and D 3 are colorless crystals with a melting point of 115-117 °C, insoluble in water, but well soluble in fats and solvents (acetone, ether, chloroform, alcohol). They are easily exposed to oxidizing agents and mineral acids, but are resistant to temperature effects and arc not destroyed by cooking. Biological role. Calciferol affects calcium phosphorus metabolism, affects the formation of bone tissue. Vitamin D promotes the absorption of calcium and phosphorus in the intestine; providing their transfer through the wall of the intestines, it maintains the ratio of calcium and phosphorus in the blood, necessary for the ossification of bones. He is involved in the regulation of bone 265