9/11/2023 0 Comments Composition of milk pptSince the density of a substance varies with temperature, it is necessary to specify the temperature when reporting densities or specific gravities. Whereas density of a substance is its mass (weight) per unit volume, specific gravity is the ratio of density of the substance to density of a standard substance (water). The acidity and pH of fresh milk vary with: Higher pH values for fresh milk indicate udder infection (mastitis) and lower values, bacterial action. The pH of normal, fresh, sweet milk usually varies from 6.4 to 6.6 for cow milk and 6.7 to 6.8 for buffalo milk. The titrable acidity is usually expressed as a ‘percentage of lactic acid’. Hence the titrable acidity of stored milk is equal to the sum of natural acidity and developed acidity. ‘Developed’ or ‘real’ acidity is due to lactic acid, formed as a result of bacterial action on lactose in the milk. The titrable acidity of cow milk varies on an average from 0.13 to 0.14 per cent and buffalo milk from 0.14 to 0.15 per cent. The higher the solids- not-fat content in milk, the higher the natural acidity (N.A.) and vice versa. The natural acidity of individual milk varies considerably depending on species, breed, individuality, stage of lactation, physiological condition of the udder, etc., but the natural acidity of fresh, herd milk is much more uniform. This acidity, also called Titratable Acidity (T.A.) as it is determined by titration, is known as ‘natural’ or ‘apparent’ acidity and is caused by the presence of casein, acid-phosphates, citrates, etc., in milk. However, it shows a certain acidity as determined by titration with an alkali (sodium hydroxide) in the presence of an indicator (phenolphthalein). it turns red litmus blue and blue litmus red. Lactose and a portion of the mineral salts are found in solution, proteins and the remainder of the minerals in colloidal suspension and fat as an emulsion.įreshly-drawn milk is amphoteric to litmus, i.e. Water is the continuous phase in which other constituents are either dissolved or suspended. In this article we will discuss about the physico-chemical properties of milk and milk constituents.
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