Vitamins - PDF

VITAMINS Dr Hanisah Rosli [email protected] © 2019, University of Cyberjaya. Please do not reproduce, redistribute or share without the prior express permission of the author.  Introduction Vitamins are minor components of foods that play an...

VITAMINS Dr Hanisah Rosli [email protected] © 2019, University of Cyberjaya. Please do not reproduce, redistribute or share without the prior express permission of the author.  Introduction Vitamins are minor components of foods that play an essential role in human nutrition. The vitamins are usually divided into two main groups, the water-soluble and the fat-soluble vitamins. The occurrence of the vitamins in the various food groups is related to their water-or fat- solubility. The contribution of foods to vitamins in the diet is varies significantly between food groups and specific products within the food groups. © 2019, University of Cyberjaya. Please do not reproduce, redistribute or share without the prior express permission of the author.  Some vitamins function as part of a coenzyme, without which the enzyme would be ineffective as a biocatalyst. Frequently, such coenzymes are phosphorylated forms of vitamins and play a role in the metabolism of fats, proteins, and carbohydrates. Some vitamins occur in foods as provitamins—compounds that are not vitamins but can be changed by the body into vitamins. Vitamers are members of the same vitamin family. © 2019, University of Cyberjaya. Please do not reproduce, redistribute or share without the prior express permission of the author.  Many vitamins are unstable under certain conditions of processing and storage, and their levels in processed foods, therefore, may be considerably reduced. Synthetic vitamins are used extensively to compensate for these losses and to restore vitamin levels in foods. Stability of vitamins under different conditions © 2019, University of Cyberjaya. Please do not reproduce, redistribute or share without the prior express permission of the author.  Healthy levels of vitamins in the diet refers to the absence of disease based on clinical signs and symptoms of deficiency or excess, and normal function of the individual. The concept of protective nutrient intake for some vitamins refers to an amount which may be protective against a specified health or nutritional risk, for example vitamin C intake of 25 mg with each meal to enhances iron absorption and prevent anemia) (Cook and Reddy 2001). © 2019, University of Cyberjaya. Please do not reproduce, redistribute or share without the prior express permission of the author.  Malaysian Recommended Nutrients Intakes (RNI) Recommended Nutrients Intakes (RNI) are nutrient standards that may be used to plan and assess dietary nutrient intakes. The first edition of the Recommended Nutrient Intakes (RNI) Malaysia was published by the National Coordinating Committee on Food and Nutrition (NCCFN) (2005). Revision of RNI is an ongoing activity and nutrient recommendations will continue to evolve and be updated as new research findings using new methods of analysis are reported. These recommendations (RNI, 2017), part of an effort to update the original RNI (2005) are for healthy people and may not meet the specific nutritional requirements of individuals with various diseases or conditions, pre-term infants, or people with specific genetic profiles. © 2019, University of Cyberjaya. Please do not reproduce, redistribute or share without the prior express permission of the author. Fat-Soluble Vitamins © 2019, University of Cyberjaya. Please do not reproduce, redistribute or share without the prior express permission of the author.  Vitamin A (Retinol) Vitamin A is an alcohol that occurs in nature predominantly in the form of fatty acid esters. Highest levels of vitamin A are found in certain fish liver oils, such as cod and tuna. Other important sources are mammalian liver, egg yolk, and milk and milk products. Structural formula of vitamin A. Acetate: R=CO CH3. Palmitate: R=CO (CH2)14 CH3 © 2019, University of Cyberjaya. Please do not reproduce, redistribute or share without the prior express permission of the author.  The structural formula of vitamin A shows its unsaturated character. The all-trans form is the most active biologically. The 13-cis isomer is known as neovitamin A; its biological activity is only about 75% of that of the all- trans form. There are several provitamins A; these belong to the carotenoid pigments. The most important one is β-carotene, and some of the pigments that can be derived from it are of practical importance. Beta-carotene occurs widely in plant products and has a high vitamin A activity. In theory, one molecule of β-carotene could yield two molecules of vitamin A. The enzyme 15-15'-dioxygenase is able to cleave a β-carotene molecule symmetrically to produce two molecules of vitamin A. This enzyme occurs in intestinal mucosa, but the actual conversion is much less efficient. © 2019, University of Cyberjaya. Please do not reproduce, redistribute or share without the prior express permission of the author. Structural formulas of some provitamins A. (a) β-carotene, and (b) apocarotenal (R=CHO) and apocarotenoic acid ester (R=COOC2H5)  After cleavage of the β-carotene, the first reaction product is retinal, which is reduced to retinol (Rouseff and Nagy 1994). Citrus fruits are a good source of provitamin A, which results mostly from the presence of β- cryptoxanthin, β-carotene, and α-carotene. Gross (1987) reported a total of 16 carotenoids with provitamin A activity in citrus fruits. © 2019, University of Cyberjaya. Please do not reproduce, redistribute or share without the prior express permission of the author.  Conversion of beta-carotene to vitamin A © 2019, University of Cyberjaya. Please do not reproduce, redistribute or share without the prior express permission of the author.  Vitamin A, or retinol, is also known as vitamin A1. Another form, vitamin A2, is found in fish liver oils and is 3-dehydroretinol. The Food and Agriculture Organization and the World Health Organization of the United Nations (FAO/WHO) and the National Academy of Sciences of the United States have recommended that vitamin A activity be reported as the equivalent weight of retinol. By definition, 1 retinol equivalent is equal to 1 μg of retinol, or 6 μg of β-carotene, or 12 μg of other provitamin A carotenoids. © 2019, University of Cyberjaya. Please do not reproduce, redistribute or share without the prior express permission of the author.  Vitamin A occurs only in animals and not in plants. The A1 form occurs in all animals and fish, the A2 form in freshwater fish and not in land animals. The biological value of the A2 form is only about 40% of that of A1. Good sources of provitamin A in vegetable products are carrots, sweet potatoes, tomatoes, and broccoli. In milk and milk products, vitamin A and carotene levels are subject to seasonal variations. Butter contains an average of 2.7 μg of carotene and 5.0 μg of vitamin A per g during winter and 6.1 μg of carotene and 7.6 μg of vitamin A per g during summer. Vitamin A is used to fortify margarine and skim milk. It is added to margarine at a level of 3525 IU per 100 g. Some of the carotenoids (provitamin A) are used as food colors. © 2019, University of Cyberjaya. Please do not reproduce, redistribute or share without the prior express permission of the author.  Vitamin A is relatively stable to heat in the absence of oxygen. Because of the highly unsaturated character of the molecule, it is quite susceptible to oxidation—especially under the influence of light, whether sunlight or artificial light. Vitamin A is unstable in the presence of mineral acids but stable in alkali. Vitamin A and the carotenoids have good stability during various food processing operations. Losses may occur at high temperatures in the presence of oxygen. These compounds are also susceptible to oxidation by lipid peroxides Pasteurization of milk does not result in vitamin A loss, but exposure to light does. It is essential, therefore, that sterilized milk be packaged in lightimpervious containers. Possible losses during storage of foods are more affected by duration of storage than by storage temperature. Blanching of fruits and vegetables helps prevent losses during frozen storage. © 2019, University of Cyberjaya. Please do not reproduce, redistribute or share without the prior express permission of the author.  Vitamin D Vitamin D occurs in several forms; the two most important are vitamin D2, or ergocalciferol, and vitamin D3, or cholecalciferol. Structural formulas of (a) vitamin D2 and (b) vitamin D3 © 2019, University of Cyberjaya. Please do not reproduce, redistribute or share without the prior express permission of the author.  Vitamin D does not occur in plant products. Vitamin D2 occurs in small amounts in fish liver oils; vitamin D3 is widely distributed in animal products, but large amounts occur only in fish liver oils. Smaller quantities of vitamin D3 occur in eggs, milk, butter, and cheese The precursors of vitamins D2 and D3 are ergosterol and 7-dehydrocholesterol, respectively. These precursors or provitamins can be converted into the respective D vitamins by irradiation with ultraviolet light. In addition to the two major provitamins, there are several other sterols that can acquire vitamin D activity when irradiated. The provitamins can be converted to vitamin D in the human skin by exposure to sunlight. © 2019, University of Cyberjaya. Please do not reproduce, redistribute or share without the prior express permission of the author.  Because very few foods are good sources of vitamin D, humans have a greater likelihood of vitamin D deficiency than of any other vitamin deficiency. Enrichment of some foods with vitamin D has significantly helped to eradicate rickets, which is a vitamin D deficiency disease. Margarine and milk are the foods commonly used as carrier for added vitamin D. The unit of activity of vitamin D is the IU. The human requirement amounts to 400–500 IU but increases to 1000 IU during pregnancy and lactation. © 2019, University of Cyberjaya. Please do not reproduce, redistribute or share without the prior express permission of the author.  Adults who are regularly exposed to sunlight are likely to have a sufficient supply of vitamin D. Excessive intakes are toxic. Vitamin D is extremely stable, and little or no loss is experienced in processing and storage. Vitamin D in milk is not affected by pasteurization, boiling, or sterilization (Hartman and Dryden 1978). Frozen storage of milk or butter also has little or no effect on vitamin D levels, and the same result is obtained during storage of dry milk. © 2019, University of Cyberjaya. Please do not reproduce, redistribute or share without the prior express permission of the author.  Vitamin E (Tocophenols) The tocopherols are derivatives of tocol, and the occurrence of a number of related substances in animal and vegetable products has been demonstrated. Cottonseed oil was found to contain α-, β-, and γ-tocopherol, and a fourth, δ-tocopherol, was isolated from soybean oil. Tocopherols are important as antioxidants in foods, especially in vegetable oils. With few exceptions, animal and vegetable products contain from about 0.5 to 1.5 mg/100 g; vegetable oils from 10 to 60 mg/100 g; and cereal germ oils, which are a very good source, from 150 to 500 mg/100 g. Vegetable oils have the highest proportion of α-tocopherol, which amounts to about 60% of the total tocopherols © 2019, University of Cyberjaya. Please do not reproduce, redistribute or share without the prior express permission of the author.  Vitamin K This vitamin occurs in a series of different forms, and these can be divided into two groups. The first is vitamin K1, characterized by one double bond in the side chain. The vitamins K2 have a side chain consisting of a number of regular units of the type. Vitamin K1 is slowly decomposed by atmospheric oxygen but is readily destroyed by light. It is stable against heat, but unstable against alkali. The human adult requirement is estimated at about 4 mg per day. Vitamin K occurs widely in foods and is also synthesized by the intestinal flora. Good sources of vitamin K are dark green vegetables such as spinach and cabbage leaves, and also cauliflower, peas, and cereals. Animal products contain little vitamin K1, except for pork liver, which is a good source. Chemical structure of vitamin K © 2019, University of Cyberjaya. Please do not reproduce, redistribute or share without the prior express permission of the author. Water-soluble Vitamins © 2019, University of Cyberjaya. Please do not reproduce, redistribute or share without the prior express permission of the author.  Vitamin C (L-Ascorbic Acid) L-ascorbic acid (Fig. 9.10) is a lactone (internal ester of a hydroxycarboxylic acid) and is characterized by the enediol group, which makes it a strongly reducing compound. The D form has no biological activity. One of the isomers, D-isoascorbic acid, or erythorbic acid, is produced commercially for use as a food additive. Vitamin C is widely distributed in nature, mostly in plant products such as fruits (especially citrus fruits), green vegetables, tomatoes, potatoes, and berries. The only animal sources of this vitamin are milk and liver. The concentration varies widely in different tissues of fruits; for example, in apples, the concentration of vitamin C is two to three times as great in the peel as in the pulp. © 2019, University of Cyberjaya. Please do not reproduce, redistribute or share without the prior express permission of the author.  Vitamin C is the least stable of all vitamins and is easily destroyed during processing and storage. The rate of destruction is increased by the action of metals, especially copper and iron, and by the action of enzymes. Exposure to oxygen, prolonged heating in the presence of oxygen, and exposure to light are all harmful to the vitamin C content of foods. Ascorbic acid is oxidized in the presence of air under neutral and alkaline conditions. At acid pH (for example, in citrus juice), the vitamin is more stable. There are many technical uses of ascorbic acid in food processing. It is used to prevent browning and discoloration in vegetables and fruit products; as an antioxidant in fats, fish products, and dairy products; as a stabilizer of color in meat; as an improver of flour; as an oxygen acceptor in beer processing; as a reducing agent in wine, partially replacing sulfur dioxide; and as an added nutrient. © 2019, University of Cyberjaya. Please do not reproduce, redistribute or share without the prior express permission of the author.  Vitamin B1 (Thiamin) This vitamin acts as a coenzyme in the metabolism of carbohydrates and is present in all living tissues. It acts in the form of thiamin diphosphate in the decarboxylation of α-keto acids and is referred to as cocarboxylase. Thiamin is available in the form of its chloride or nitrate Structural formula of thiamin. © 2019, University of Cyberjaya. Please do not reproduce, redistribute or share without the prior express permission of the author.  The molecule contains two basic nitrogen atoms; one is in the primary amino group, the other in the quaternary ammonium group. It forms salts with inorganic and organic acids. The vitamin contains a primary alcohol group, which is usually present in the naturally occurring vitamin in esterified form with ortho-, di-, or triphosphoric acid. In aqueous solution, the compound may occur in different forms, depending on pH. Small quantities of thiamin are present in almost all foods of plant and animal origin. Good sources are whole cereal grains; organ meats such as liver, heart, and kidney; lean pork; eggs; nuts; and potatoes Increased metabolic activity, such as that which results from heavy work, pregnancy, or disease, requires higher intake © 2019, University of Cyberjaya. Please do not reproduce, redistribute or share without the prior express permission of the author.  Thiamin is one of the more unstable vitamins. Various food processing operations may considerably reduce thiamin levels. Heat, oxygen, sulfur dioxide, leaching, and neutral or alkaline pH may all result in destruction of thiamin. Light has no effect. Because thiamin and other vitamins are located near the bran of cereal grains, there is a great loss during milling. White flour, therefore, has a greatly reduced content of B vitamins and vitamin E Because of the losses that are likely to occur in cereal grain processing and in the processing of other foods, a program of fortification of flour is an important factor in preventing vitamin deficiencies. © 2019, University of Cyberjaya. Please do not reproduce, redistribute or share without the prior express permission of the author.  Vitamin B2 (Riboflavin) The molecule consists of a d-ribitol unit attached to an isoalloxazine ring The vitamin is a constituent of two coenzymes, flavin mononucleotide (FMN) and flavin adenine dinucleotide (FAD). FMN is riboflavin-5′-phosphate and forms part of several enzymes, including cytochrome c reductase. The flavoproteins serve as electron carriers and are involved in the oxidation of glucose, fatty acids, amino acids, and purines. Structural formula of riboflavin. Riboflavin: R=OH; Riboflavin phosphate: R=PO3NaOH © 2019, University of Cyberjaya. Please do not reproduce, redistribute or share without the prior express permission of the author.  Very good sources of riboflavin are milk and milk products; other sources are beef muscle, liver, kidney, poultry, tomatoes, eggs, green vegetables, and yeast Riboflavin is stable to oxygen and acid pH but is unstable in alkaline medium and is very sensitive to light. When exposed to light, the rate of destruction increases as pH and temperature increase. Heating under neutral or acidic conditions does not destroy the vitamin. © 2019, University of Cyberjaya. Please do not reproduce, redistribute or share without the prior express permission of the author.  Vitamin B6 (Pyridoxine) There are three compounds with vitamin B6 activity. The other two forms of this vitamin are different from pyridoxine—they have another substituent on carbon 4 of the benzene ring. Pyridoxal has a –CHO group in this position and pyridoxamine has a – CH2NH2 group. All three compounds can occur as salts. Vitamin B6 plays an important role in the metabolism of amino acids, where it is active in the coenzyme form pyridoxal-5-phosphate. Structural formula of pyridoxine © 2019, University of Cyberjaya. Please do not reproduce, redistribute or share without the prior express permission of the author.  Vitamin B6 is widely distributed in many foods (Table 9.21), and deficiencies of this vitamin are uncommon. Vitamin B6 occurs in animal tissues in the form of pyridoxal and pyridoxamine or as their phosphates. Pyridoxine occurs in plant products. Pyridoxine is stable to heat and strong alkali or acid; it is sensitive to light, especially ultraviolet light and when present in alkaline solutions. Pyridoxal and pyridoxamine are rapidly destroyed when exposed to air, heat, or light. Pyridoxamine is readily destroyed in food processing operations. milk as 0.54 mg per L. Other sources are meats, liver, vegetables, whole grain cereals, and egg yolk. © 2019, University of Cyberjaya. Please do not reproduce, redistribute or share without the prior express permission of the author.  The effects of processing on pyridoxine levels in milk and milk products have been reviewed by Hartman and Dryden (1978). No significant losses have been reported to result from pasteurization, homogenization, or production of dried milk. Heat sterilization of milk, however, has been reported to result in losses ranging from 36 to 49%. Losses occur not only during the heat treatment but also during subsequent storage of milk. These storage losses have been attributed to a conversion of pyridoxal to pyridoxamine and then to a different form of the vitamin. © 2019, University of Cyberjaya. Please do not reproduce, redistribute or share without the prior express permission of the author.  Niacin The term niacin is used in a generic sense for both nicotinic acid and nicotinamide Structural formulas of (a) nicotinic acid and (b) nicotinamide © 2019, University of Cyberjaya. Please do not reproduce, redistribute or share without the prior express permission of the author.  Nicotinamide acts as a component of two important enzymes, NAD and NADP, which are involved in glycolysis, fat synthesis, and tissue respiration. Niacin is also known as the pellagra preventive factor. The incidence of pellagra has declined but is still a serious problem in parts of the Near East, Africa, southeastern Europe, and in North American populations that subsist on corn diets. When corn is treated with alkali or lime, as for the tortilla preparation in Central America, the amount of available niacin can be greatly increased. Tryptophan can be converted by the body into niacin. Many diets causing pellagra are low in good quality protein as well as in vitamins. Corn protein is low in tryptophan. The niacin of corn and other cereals may occur in a bound form, called niacytin, that can be converted into niacin by alkali treatment. © 2019, University of Cyberjaya. Please do not reproduce, redistribute or share without the prior express permission of the author.  The human requirement of niacin is related to the intake of tryptophan. Animal proteins contain approximately 1.4% of tryptophan, vegetable proteins about 1%. A dietary intake of 60 mg of tryptophan is considered equivalent to 1 mg of niacin. Good dietary sources of this vitamin are liver, kidney, lean meat, chicken, fish, wheat, barley, rye, green peas, yeast, peanuts, and leafy vegetables. Niacin is probably the most stable of the B vitamins. It is unaffected by heat, light, oxygen, acid, or alkali. The main loss resulting from processing involves leaching into the process water. Blanching of vegetables may cause a loss of about 15%. Processes in which brines are used may cause losses of up to 30%. Processing of milk, such as pasteurization, sterilization, evaporation, and drying have little or no effect on nicotinic acid level. © 2019, University of Cyberjaya. Please do not reproduce, redistribute or share without the prior express permission of the author.  Vitamin B12 (Cyanocobalamine) This vitamin possesses the most complex structure of any of the vitamins and is unique in that it has a metallic element, cobalt, in the molecule Structural formula of cyanocobalamine © 2019, University of Cyberjaya. Please do not reproduce, redistribute or share without the prior express permission of the author.  Cyanocobalamine is a component of several coenzymes and has an effect on nucleic acid formation through its action in cycling 5-methyltetrahydrofolate back into the folate pool. The most important dietary sources of the vitamin are animal products. Vitamin B12 is also produced by many microorganisms. It is not surprising that vitamin B12 deficiency of dietary origin only occurs in vegetarians. © 2019, University of Cyberjaya. Please do not reproduce, redistribute or share without the prior express permission of the author.  Folic Acid (Folacin) Folic acid is the main representative of a series of related compounds that contain three moieties: pterin, p-aminobenzoic acid, and glutamic acid Structural formula of folic acid © 2019, University of Cyberjaya. Please do not reproduce, redistribute or share without the prior express permission of the author.  It has been suggested that folic acid deficiency is the most common vitamin deficiency in North America and Europe. Deficiency is especially likely to occur in pregnant women. The vitamin occurs in a variety of foods, especially in liver, fruit, leafy vegetables, and yeast Many of the naturally occurring folates are extremely labile and easily destroyed by cooking. Folic acid itself is stable to heat in an acid medium but is rapidly destroyed under neutral and alkaline conditions. © 2019, University of Cyberjaya. Please do not reproduce, redistribute or share without the prior express permission of the author.  Pantothenic Acid Pantothenic acid plays an important role as a component of coenzyme A, and this is the form in which it occurs in most foods. Pantothenic acid occurs in all living cells and tissues and is, therefore, found in most food products. Good dietary sources include meats, liver, kidney, fruits, vegetables, milk, egg yolk, yeast, whole cereal grains, and nuts The vitamin is stable to air, and labile to dry heat. It is stable in solution in the pH range of 5–7 and less stable outside this range. Pasteurization and sterilization of milk result in very little or no loss. The production and storage of dried milk involves little or no loss of pantothenic acid. Manufacture of cheese involves large losses during processing, but during ripening the pantothenic acid content increases, due to synthesis by microorganisms. Blanching of vegetables may involve losses of up to 30%. © 2019, University of Cyberjaya. Please do not reproduce, redistribute or share without the prior express permission of the author.  Biotin The structural formula contains three asymmetric carbon atoms, and eight different stereoisomers are possible. Structural formula of biotin © 2019, University of Cyberjaya. Please do not reproduce, redistribute or share without the prior express permission of the author.  Biotin occurs in some products in free form (vegetables, milk, and fruits) and in other products is bound to protein (organ meats, seeds, and yeast). Good sources of the vitamin are meat, liver, kidney, milk, egg yolk, yeast, vegetables, and mushrooms Biotin is important in a number of metabolic reactions, especially in fatty acid synthesis. The biotin supply of the human organism is only partly derived from the diet. An important factor in biotin’s availability is that some of the vitamin is derived from synthesis by intestinal microorganisms; this is demonstrated by the fact that three to six times more biotin is excreted in the urine than is ingested with the food. Biotin is deactivated by raw egg white. This is caused by the glycoprotein avidin. Heating of avidin will destroy the inactivator capacity for biotin. © 2019, University of Cyberjaya. Please do not reproduce, redistribute or share without the prior express permission of the author.  The vitamin appears to be quite stable. Heat treatment results in relatively small losses. The vitamin is stable to air and is stable at neutral and acid pH. Pasteurization and sterilization of milk result in losses of less than 10%. In the production of evaporated and dried milk, losses do not exceed 15%. © 2019, University of Cyberjaya. Please do not reproduce, redistribute or share without the prior express permission of the author.  Thank you Address Telephone Website University of Cyberjaya 03 - 8313 7000 www.cyberjaya.edu.my Persiaran Bestari, Cyber 11, 63000 Cyberjaya, Facsimile Email Selangor Darul Ehsan, Malaysia. 03 – 8313 7001 [email protected]