252 The nutrition handbook for food processors or cholecalciferol is derived in animals, including man, from ultra-violet irra- diation of 7-dehydrocholesterol found in the skin. Human requirements are obtained both from the endogenous production in the skin and from dietary sources. Vitamin D,(ergocalciferol) is produced by the ultraviolet irradiation of ergosterol, which is widely distributed in plants and fungi. Both vitamins D2 and D3 are manufactured for commercial use. Both vitamins D2 and D3 are sensitive to light and can be destroyed relatively pidly if exposed to light. They are also adversely affected by acids. Prepara- tions of vitamin D in edible oils are more stable than the crystalline forms, and the vitamin is normally provided for commercial usage as an oil preparation or stabilised powder containing an antioxidant(usually tocopherol). The prepara tions are normally provided in lightproof containers with inert gas flushing The presence of double bonds in the structure of both forms of vitamin D can make them susceptible to isomerisation under certain conditions. Studies have shown that the isomerisation rates of ergocalciferol and cholecalciferol are almost equal. Isomerisation in solutions of cholecalciferol resulted in an equilibrium being formed between ergocalciferol and precalciferol with the ratios of the isomers being temperature dependent. The isomerisation of ergocalciferol has been studied in powders prepared with calcium sulphate, calcium phosphate, talc and magnesium trisilicate. It was found that the isomerisation was catalysed by he surface acid of these additives 6 Crystalline vitamin D2 is sensitive to atmospheric oxygen and will show signs of decomposition after a few days storage in the presence of air at ambient temperatures. Crystalline cholecalciferol, D,, is also destroyed by atmospheric oxygen but is relatively more stable than D,, possibly due to the fact that it has one less double bond The vitamin D3 naturally occurring in foods such as milk and fish, appears to be relatively stable to heat processing. 104. 4 Vitamin K Vitamin K occurs in a number of forms. Vitamin K(phytomenadione or phyl loquinone) is found in green plants and vegetables, potatoes and fruits, while vitamin K2(menaquinone) can be found in animal and microbial materials. The presence of double bonds in both vitamins K and K, makes them liable to isomerisation. Vitamin K has only one double bond in the side chain in the 3-position whereas in K double bonds recur regularly in the side chain. Vitamin KI exists in the form of both trans and cis isomers. The trans isomer is the naturally occurring form and is the one that is biologically active. The cis form has no significant biological activity The various forms of vitamin K are relatively stable to heat and are retained after most cooking processes. The vitamin is destroyed by sunlight and is decomposed by alkalis. Vitamin Ki is only slowly decomposed by atmospheric oxygen. Vitamin K is rarely added to food pre roducts and the most common commer-
or cholecalciferol is derived in animals, including man, from ultra-violet irradiation of 7-dehydrocholesterol found in the skin. Human requirements are obtained both from the endogenous production in the skin and from dietary sources. Vitamin D2 (ergocalciferol) is produced by the ultraviolet irradiation of ergosterol, which is widely distributed in plants and fungi. Both vitamins D2 and D3 are manufactured for commercial use. Both vitamins D2 and D3 are sensitive to light and can be destroyed relatively rapidly if exposed to light. They are also adversely affected by acids. Preparations of vitamin D in edible oils are more stable than the crystalline forms, and the vitamin is normally provided for commercial usage as an oil preparation or stabilised powder containing an antioxidant (usually tocopherol). The preparations are normally provided in lightproof containers with inert gas flushing. The presence of double bonds in the structure of both forms of vitamin D can make them susceptible to isomerisation under certain conditions. Studies have shown that the isomerisation rates of ergocalciferol and cholecalciferol are almost equal. Isomerisation in solutions of cholecalciferol resulted in an equilibrium being formed between ergocalciferol and precalciferol with the ratios of the isomers being temperature dependent. The isomerisation of ergocalciferol has been studied in powders prepared with calcium sulphate, calcium phosphate, talc and magnesium trisilicate. It was found that the isomerisation was catalysed by the surface acid of these additives.6 Crystalline vitamin D2 is sensitive to atmospheric oxygen and will show signs of decomposition after a few days storage in the presence of air at ambient temperatures. Crystalline cholecalciferol, D3, is also destroyed by atmospheric oxygen but is relatively more stable than D2, possibly due to the fact that it has one less double bond. The vitamin D3 naturally occurring in foods such as milk and fish, appears to be relatively stable to heat processing. 10.4.4 Vitamin K Vitamin K occurs in a number of forms. Vitamin K1 (phytomenadione or phylloquinone) is found in green plants and vegetables, potatoes and fruits, while vitamin K2 (menaquinone) can be found in animal and microbial materials. The presence of double bonds in both vitamins K1 and K2 makes them liable to isomerisation. Vitamin K1 has only one double bond in the side chain in the 3-position whereas in K2 double bonds recur regularly in the side chain. Vitamin K1 exists in the form of both trans and cis isomers. The trans isomer is the naturally occurring form and is the one that is biologically active. The cis form has no significant biological activity. The various forms of vitamin K are relatively stable to heat and are retained after most cooking processes. The vitamin is destroyed by sunlight and is decomposed by alkalis. Vitamin K1 is only slowly decomposed by atmospheric oxygen. Vitamin K is rarely added to food products and the most common commer- 252 The nutrition handbook for food processors
The stability of vitamins during food processing 253 cially available form is Ki(phytomenadione), which is insoluble in water. A water-soluble K, is available as menadione sodium bisulphite 10.5 Water-soluble vitamins The water-soluble vitamin group contains eight vitamins collectively known as the B-complex vitamins plus vitamin C (ascorbic acid 10.5.1 Thiamin(vitamin B1) Thiamin is widely distributed in living tissues. In most animal products it occurs in a phosphorylated form, and in plant products it is predominantly in the non- phosphorylated form. Commercially it is available as either thiamin hydrochlo ride or thiamin mononitrate. Both these salts have specific areas of application and their use depends on the product matrix to which they are added A considerable amount of research has been carried out on the heat stability of thiamin and its salts, particularly in the context of cooking losses. Early work on thiamin losses during bread-making showed an initial cleavage of the thiamin to pyrimidine and thiazole. The destruction of thiamin by heat is more rapid in alkaline media. Vitamin B, losses in milk, which has an average fresh content of 0.04 mg thiamin per 100 g, are normally less than 10% for pasteurised milk, between 5 and 15% for Uht milk and between 30 and 40%o for sterilised milk Between 30 and 50% of the vitamin B, activity can be lost during the production of evaporated milk. Losses of thiamin during the commercial baking of white bread are between 5 and 20%. Part of this loss is due to the yeast fermentation, which can convert thiamin to cocarboxylase, which is less stable than thiamin. Thiamin is very sensitive to sulphites and bisulphite as it is cleaved by sulphite. This reaction is rapid at high pH, and is the cause of large losses of the vitamin in vegetables blanched with sulphite, and in meat products such as comminuted meats where sulphites and bisulphite are used as preservatives. Where the pH is low, such as in citrus fruit juices, the bisulphite occurs mainly as the unionised acid, and thiamin losses in such systems are not significantly different from those in prod ucts not containing bisulphite. Studies on the rate of sulphite-induced cleavage of thiamin during the prepa ration and storage of minced meat showed that losses of thiamin were linear with sulphur dioxide concentrates up to O.1%. The storage temperature did not have a significant effect on the losses. It has also been reported that thiamin is cleaved by aromatic aldehydes. Thiamin is decomposed by both oxidising and reducing agents. If it is allowed to stand in alkaline solution in air it is oxidised to the disulphide and small amounts of thiothiazolone. A range of food ingredients has been shown to have an effect on the stability of thiamin. In general, proteins are protective of the vitamin, particularly food proteins such as egg albumin and casein. When heated with glucose, either
cially available form is K1 (phytomenadione), which is insoluble in water. A water-soluble K3 is available as menadione sodium bisulphite. 10.5 Water-soluble vitamins The water-soluble vitamin group contains eight vitamins collectively known as the B-complex vitamins plus vitamin C (ascorbic acid). 10.5.1 Thiamin (vitamin B1) Thiamin is widely distributed in living tissues. In most animal products it occurs in a phosphorylated form, and in plant products it is predominantly in the nonphosphorylated form. Commercially it is available as either thiamin hydrochloride or thiamin mononitrate. Both these salts have specific areas of application and their use depends on the product matrix to which they are added. A considerable amount of research has been carried out on the heat stability of thiamin and its salts, particularly in the context of cooking losses. Early work on thiamin losses during bread-making showed an initial cleavage of the thiamin to pyrimidine and thiazole.7 The destruction of thiamin by heat is more rapid in alkaline media. Vitamin B1 losses in milk, which has an average fresh content of 0.04 mg thiamin per 100 g, are normally less than 10% for pasteurised milk, between 5 and 15% for UHT milk and between 30 and 40% for sterilised milk.7 Between 30 and 50% of the vitamin B1 activity can be lost during the production of evaporated milk. Losses of thiamin during the commercial baking of white bread are between 15 and 20%. Part of this loss is due to the yeast fermentation, which can convert thiamin to cocarboxylase, which is less stable than thiamin. Thiamin is very sensitive to sulphites and bisulphites as it is cleaved by sulphite. This reaction is rapid at high pH, and is the cause of large losses of the vitamin in vegetables blanched with sulphite, and in meat products such as comminuted meats where sulphites and bisulphites are used as preservatives. Where the pH is low, such as in citrus fruit juices, the bisulphite occurs mainly as the unionised acid, and thiamin losses in such systems are not significantly different from those in products not containing bisulphite.8 Studies on the rate of sulphite-induced cleavage of thiamin during the preparation and storage of minced meat showed that losses of thiamin were linear with sulphur dioxide concentrates up to 0.1%. The storage temperature did not have a significant effect on the losses. It has also been reported that thiamin is cleaved by aromatic aldehydes. Thiamin is decomposed by both oxidising and reducing agents. If it is allowed to stand in alkaline solution in air it is oxidised to the disulphide and small amounts of thiothiazolone. A range of food ingredients has been shown to have an effect on the stability of thiamin. In general, proteins are protective of the vitamin, particularly food proteins such as egg albumin and casein. When heated with glucose, either as a The stability of vitamins during food processing 253