Chemical Analysis of Value Added Dairy Products and Their Quality ...

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Chemical Analysis of Value Added Dairy Products and Their Quality AssuranceNutrients generally added to milkLiquid milk fortification with vitamins A and/D is mandated in several countries. β-carotene isadded as a colour-enhancing agent to some milk products such as butter. Dried milk is often fortifiedwith vitamins A and D, calcium, and iron. Milk based infant formula and weaning foods are fortifiedwith a range of vitamins, minerals, and other nutrients such as polyunsaturated fatty acids. Powderedmilk used for complementary feeding in Chile is fortified with vitamin C, iron, copper and zinc.Fortification of milk & milk products with vitaminsUnder ambient conditions the water soluble vitamin C and vitamins of the B-complex groupsuch as thiamin, riboflavin, vitamin B6, niacin, pantothenic acid, folic acid, biotin and vitamin B12 arepowdered and thus relatively easy to work with when producing most dairy products. The fat solublevitamins which include vitamin A, D, E and K, however, exist either as an oil or as crystals, which maycause processing difficulties during the production of certain types of dairy products (Mortensen andGotfredson, 1996).One of the problem encountered with the vitamins, is their limited stability in presence of heat,humidity and oxygen. Among the water soluble vitamins, vitamin C, folic acid, vitamin B6 and vitaminB12 are the less stable. While in the case of fat soluble vitamins vitamin A, D and E are least stable.In order to improve the stability of these vitamins, a number of different coating technologieshave been developed. One of the most important methods to protect the fat soluble vitamins ismicroencapsulation, which results in a highly sophisticated powder, where the vitamin is kept protectedfrom degradation by the coating material used for the encapsulation. During microencapsulation, thefat soluble vitamins are brought from the form of oil or a crystal – which in some processes would bedifficult to handle – to the form of a free flowing powder much easier to handle and mix with otherdry ingredients (Mortensen and Gotfredson, 1996).When two or more vitamins are added to a food product at the same manufacturing stage, thisis commonly done in the form of premix or as blend. Premix is a homogenous mixture of desiredvitamins in a dry powder from, whereas a blend is the same for the fat soluble vitamins, but in an oilyform. A premix can consist of both water soluble and fat soluble vitamins and carotenoids, in whichcase the fat soluble vitamins have to be microencapsulated.Fortification of milk and milk products with iron, calcium and other mineralsSelection of an appropriate mineral fortificant (iron, calcium etc) is based on its organolepticconsiderations, bioavailability, cost and safety. The colour of iron compounds is often a critical factorwhen fortifying milk and milk products. The use of more soluble iron compounds often leads tothe development of off-colours and off-flavours due to reactions with other components of the foodmaterial. Infant cereals have been found to turn grey or green on addition of ferrous sulphate. Offflavourscan be the result of lipid oxidation catalysed by iron. The iron compounds themselves maycontribute to a metallic flavour. Some of these undesirable interactions with the food matrix can beavoided by coating the fortificant with hydrogenated oils or ethyl cellulose (Jackson and Lee, 1991).Bioavailability of iron compounds is normally stated relative to a ferrous sulphate standard. Thehighly water soluble iron compounds have superior bioavailability (Richardson, 1990). Bioavailabilityof the insoluble or very poorly soluble iron compounds can be improved by reducing particle size.Unfortunately this is accompanied by increased reactivity in deteriorative processes. The problemof low bioavailability of some of the less reactive forms of iron is often circumvented by the use ofabsorption enhancers like, ascorbic acid, sodium acid sulphate and orthophosphoric acid, added alongwith the fortificant.The other important mineral for the fortification of milk and milk products, which has been studied,is calcium. Several commercial calcium salts are available for calcium fortification, which includecarbonate, phosphate, citrate, lactate and gluconate. In general, organic acid salts of calcium are morebioavailable than inorganic salts (Labin-Godscher and Edelstein, 1996). The pH of the milk should be30
Fortification of Milk and Milk Products for Value Additiontaken care of during Ca fortification. Manufacturers of calcium fortified milk products should consideradding, magnesium, riboflavin and perhaps vitamin D as well, in amounts that would normally beobtained in a serving of vitamin D fortified milk (Weaver, 1998).Milk and milk products can also be fortified with a range of other mineral salts such as Mg, P,Zn, Cu and Mn. Prudent selection of mineral compounds is based largely on consideration of mineralreactivity and solubility of the salt. To overcome problems of flavour, texture and colour deteriorationdue to addition of minerals, some companies have engineered new fortificant preparations, whichgenerally involve the use of stabilisers and emulsifiers to maintain the mineral in solution (FAO,1995).Technology for fortification:1. Liquid milkThe technology of milk fortification is relatively simple and no additional equipments are neededor can be practiced with minor modifications in the existing plant. Mineral/vitamin fortification can bepracticed at several stages in the production. But liquid milk is usually fortified prior to pasteurizationor ultra-heat treatment. Homogenization is essential for oily preparations of vitamins. Usually twomethods of additions are practiced i.e. batch process for small operations and metered additions forcontinuous process. A metered injection of the vitamin preparation upstream to the homogenizer hasbeen the standard set up in continuous operation plants (Cornell University, 1994).Oily preparations are diluted with 10 parts of warm oil (45 – 50°C), usually butter oil andhomogenized with a suitable quantity of skim milk or it can be mixed with appropriate quantity of milkand cream and finally homogenized. In the case of water soluble or water dispersible micronutrients,a premix can be made by diluting the nutrients to 20 times their weight with milk at 45°C, followed bystirring and thorough mixing (USAID, 2001).A simple procedure for fortification of skim milk with vitamins A without using homogenizer wasdeveloped by Bector and Rani (1998). This process is basically a batch process and is suitable for smallplants of low capital cost.Many iron compounds have been assessed in the fortification of pasteurised whole milk. Thebest fortification procedure was judged to be the addition of ferric ammonium citrate followed bypasteurisation at 81 °C. In this way fortified milk containing 30 ppm iron was found to be acceptableafter 7 days storage. Levels of vitamin E, vitamin A and carotene were not affected by the presenceof iron. At pasteurisation temperatures below 79 °C off-flavours developed due to lipolytic rancidity(Edmondson et al, 1971). De-aeration of the milk prior to the addition of iron compounds was also foundto reduce flavour problems. In the production of iron fortified evaporated milk, ferric orthophosphatewas shown to be useful (FAO, 1995).Calcium fortificant preparations including stabilizers and emulsifiers have been used forfortification of milk and milk-based beverages. It maintains calcium in suspension so as to improvemouth feel and appearance of products (FAO, 1995). In Germany a milk-based fruit beverage has beenmarketed which is fortified with calcium, phosphorous as well as vitamins A, E, B and C.Dried milkHere particle size of the fortificant as well as density of the fortificant has to be taken care as largeand heavier size particles will lead to separation. In order to achieve stability of vitamins, the safest wayto fortify dried milk is to blend dry forms of premix with the dried milk powder, thereby protectingthe effect of microencapsulation. However, this requires an effective mixing system. If blends are used,they are added directly to milk, provided homogenization is done before spray drying. If vitamins areadded before spray drying, overage addition (Table 2) will be necessary in order to compensate thelosses (Mortensen and Gotfredsen, 1996).31
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