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Stabilisers in separation of nutrients in fortified milk products
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Friday, 17 July, 2020, 15 : 00 PM [IST]
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Srushty Patil
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Normal milk is considered as complex food emulsion and colloidal solution. The emulsion comprised of fat particles dispersed in the protein-containing aqueous phase. The protein exists both as colloidal particles in the form of casein micelles and solution as monomers of whey protein. But when the production of fortified milk products, the milk goes from a processing treatment like heating for flavoured as well as UHT milk, freezing for ice cream, and cooling for yoghurt. The nutrient in the milk and products gets separated such as protein gets destabilisation at a higher temperature, some minerals and vitamins are unstable to higher temperatures for this stabiliser is used.
Stabilisers are indispensable substances and come under a category such as food additives. Stabilisers smoothen the texture of the milk products by making the homogenous dispersion of two or more immiscible materials and give the definite framework with well maintained physicochemical attributes after their addition.
Apart from basic stabilisation and improvement in texture, they do behave as nanostructures to control, retain, and intensify an existing colour and flavour of the milk product. Stabilisers used in dairy products are polysaccharides like gum, fibres, and starches or protein like whey and gelatin. Stabiliser improves thinking, mouthfeel, product structure stability, water binding capacity for better shelf life of the product, creamy consistency, and viscosity. Different dairy products such as flavoured milk, ice cream, and yoghurt contain different stabilisers which are used on their requirement like texture and stability.
Flavoured milk
Flavoured milk is a sweetened dairy product manufactured by blending milk with sugar, colourings, and artificial or natural flavourings, stabilisers, and emulsifiers. This type of milk is often treated using the UHT technique offering it a longer shelf-life than plain milk. For the preparation of flavoured milk with desired properties like better mouthfeel, body, texture, consistency, and viscosity different stabilisers and emulsifiers or their blends are used. These blends are produced by mixing different ingredients that provide a steady fat emulsification process and prevent cream separation during storage and extended shelf life. Other functions of these additives include the prevention of vegetation juices separation, used in the recipe of the flavoured milks by offering certain desired levels of thickeners and, to increase the heat stability of milk protein along with perfect structure of dairy products.
A stabiliser has the quality to keep the ingredients in suspended form without making the product too thick while adding at low concentrations. This works in two ways: Firstly, a stabiliser like starch increases viscosity by minimising the gravitational effects to pull the particles out of the suspension, and secondly, a gum, such as carrageenan forms a colloidal network. This network supports particulate matter to remain suspended for longer duration and prevents settling. The stabilisers also prevent air bubbles from collapsing and encourage good flavour release and hold flavouring compounds well dispersed in solution, Although stabilisers help in the processing of flavoured milk processing parameters, such as pasteurisation and homogenisation are equally important in combination for the successful formulation of flavoured milk.
Ice cream
The main objectives for using stabilisers in ice cream are to produce smoothness in body and texture, reduction in ice, and lactose crystal growth during storage especially during heat shock and to provide consistency to the product and opposition to melting shock. The mechanism of action for stabilisers to improve frozen stability is primarily related to their effect on unfrozen serum phases and the ice.
Stabilisers added to ice cream perform numerous important functions, such as reduced whipping time, controlled fat destabilisation, improved dryness, and increased resistance to melting and shrinkage. To produce a more desirable body and texture in final product polysaccharide stabilisers are often added into ice cream mix which reduces the formation of large ice crystals during storage. Ice cream stabilisers are guar, locust bean gum, carboxymethyl cellulose, xanthan, carrageenan, and gelatin of animal origin. Generally, locust bean gum and carrageenan were most effective to retard ice crystal growth.
Yoghurt
Textural properties of yoghurt like viscosity, smoothness, thickness and structural resistance to stress are important attributes based on protein content, heat treatment of the mix. Natural and modified gums, seaweed extracts such as carrageenan, alginates and gelatin are examples of stabilisers used in yoghurt. These additives have the property to form gel networks and their addition allows the production of yoghurt with a firm texture and high resistance for water separation.
Sedimentation of the milk protein increased with lower levels of stabilisers, but once the level of stabiliser increased beyond the level of minimum viscosity the sedimentation decreased. Stabilisers can form a network of linkages between themselves and the milk constituents because of the hydrogen or carboxyl radicals present in their structure. The negative sides got attached at the interface and water-bound in basic mix due to the presence of stabilisers. Level of hydration improved by the attachment of water to milk constituents like proteins, forming a network, that reduces the free movement of water.
Cheese
Stabiliser used in cream cheese due to its high-fat content than the other cheese. Fat and liquid do not mix well in cream cheese so the stabiliser useful for syneresis control and prevents the liquid separated from fat. Also in the processed cheese sauces, the stabiliser like xanthan, ?–carrageenan, guar gum, pectin, and sodium alginate used to improve its properties and preserve the losses. In spreadable cheese mainly sodium aliginate and carrageenan used which improve its texture like thick and creamy, reduction in syneresis and increase in the shelf life of the cheese.
Sweetened condensed milk
The importance of stabilisers used in sweetened condensed milk is to improve its heat stability, sedimentation, lactose crystallisation and prevent the separation of fat and protein during storage. Increased concentration of milk solids to cause an increase in the amount of sediment produced and an increase in concentration necessarily increases Ca, Mg, citric acid, and PO4 content in the milk and thus provides the possibility of precipitation. This can be controlled by the addition of casein stabiliser.
(The author is from Dairy Chemistry Division, National Dairy Research Institute, Karnal, Haryana)
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