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Milk and its diverse array of derivative products have a rich and enduring history in human nutrition. The significance of analysing milk and milk products cannot be emphasised, both historically and in the context of dairy farming today. Milk is a comples food that includes superior macromolecules such as fat, protein, and carbohydrates. They are crucial in determining and preserving the stability and quality of milk and milk products. This manual’s main goal is to offer helpful guidelines for evaluating milk and milk products’ quality at the laboratory scale, along with a range of traditional methods for analysing them. This comprehensive guide on milk and milk product analysis is intended to serve as a useful tool for experts, scholars, and students working in the area of dairy science and technology.

1 Analysis of Chemical Composition of Milk  1.1 Determination of Acidity of Milk  Introduction The acidity of milk can be determined by titrating the milk against standard sodium hydroxide solution using an indicator like phenolphthalein and is expressed in the terms of lactic acid. Though natural acidity in milk is due to its constituents such as casein, albumin, citrates, phosphates and carbon dioxide but it is customary to express in terms of lactic acid. As one gram equivalent weight of an alkali neutralizes one gram equivalent weight of an acid, the volume of standard alkali required to neutralize lactic acid of fixed volume of milk gives percent acidity of milk according to the reaction.

1 Analysis of Cream  Sample Preparation Warm the cream sample to 40 - 50oC if the sample is very viscous. Then pour from one vessel to another 3 to 4 times to mix well. Sample should be tested daily and always within three days after collection since enzymatic deterioration of the cream will cause low tests. 1.1 Determination of Fat Content in Cream  1.1.1 Gerber Method  Introduction Sulphuric acid is added to cream in order to dissolve the protein and other solids and create heat which liquefy and de-emulsify the fat. Iso-amyl alcohol is added to aid the separation of fat. Upon centrifugation, fat being lighter will be separated on top of solution in the cream butyrometer.

Sample Preparation  Cheese sample is prepared by passing through 8 mesh sieve three times or grate sample and mix thoroughly or grind to a uniform mass in a glass pestle and mortar. Keep the sample in an airtight container until the time of analysis.  1 Determination of Moisture Content in Cheese  Introduction The moisture content of cheese is defined as the loss in mass, expressed as a percentage by mass when the product is heated in a hot air oven at 102 ± 2°C to constant mass.

Sample Preparation a) Plain products: Sample should be softened at room temperature. Since the melted fat tends to separate and rise to the surface, it is not advisable to soften the sample by heating on a water bath or oven or flame. Mix thoroughly by stirring with spoon or eggbeater or by pouring back and forth between beakers. b) Ice-cream containing Fruits and Nuts: Fill one third part of the cup with ice cream sample. Melt the product at room temperature and mix until insoluble particles are finely divided (about 3-5 minutes for fruit pieces and upto 7 minutes for nut pieces). Otherwise, the product may be ground in a porcelain or glass pestle and mortar. Don’t let temperature exceed 25oC at any time during softening and mixing steps. If fat separation occurs, discard sample otherwise immediately pour mixture into wide jar and cap tightly. If allowed to stand, shake vigorously before taking sample for analysis.

Sample Preparation Sample should be taken at six or more points on the top of the surface by means of a tubular trier of sufficient length to extend to the bottom of the barrel. Remove this cores and transfer to clean, dry, air tight container and seal immediately. Before opening sample for analysis, make homogenous either by shaking or by alternately rolling and inverting container. If lump are present, sift sample through No 20 sieve, rubbing material through sieve and tapping vigorously, if necessary. Avoid sampling on rainy day or when humidity is high, so as to reduce moisture absorption from air. 1 Determination of Moisture Content by Moisture Balance Introduction In this procedure, infra-red radiation is used to accomplish rapid drying. The tester has a sensitive torsion balance which permits rapid determination directly from the balance scale, eliminating the need for computing or calculation to obtain results. This method is useful for the in-process determination of moisture because the results may be obtained in minutes.

1 Detection of Starch Introduction Starch is widely available in several forms such as wheat flour, corn flour and commercially manufactured starch. It is extensively used by adulterators to raise the SNF content in the milk. When high amounts of starch are added to milk, it can cause diarrhea due to the indigestion of starch in colon. Apart from this, accumulation of starch in the body may prove very fatal for diabetic patients. In this method, starch in milk can be detected by using iodine solution. Iodine from the iodine solution gets absorbed on the starch molecule surface and resultant product of adsorption has deep blue colour. Reagents  • Potassium iodide  • Iodine solution - 1% (Add 1 g of iodine and 5 g of potassium iodide in distilled water and dilute to 100 ml)

1. Preparation of Standard Sodium Hydroxide Solution  Introduction  When oxalic acid reacts sodium hydroxide, sodium oxalate and water are form. Phenolphthalein indicator detects the end point by its characteristics colour change.  Apparatus  Burettes, pipette, volumetric flask, beaker  Reagents  • Oxalic acid crystals  • Sodium hydroxide – 0.1 N approximate  • Phenolphthalein solution – 0.1 percent in ethyl alcohol Procedure Preparation of 0.1 N oxalic acid solution 1. Weight accurately 1.575 g of oxalic acid into a 250 ml beaker using a weighing bottle. 2. Add some distilled water to the beaker and dissolve the oxalic acid with the help of glass rod. 3. Transfer the solution into a 250 ml volumetric flask through a funnel. 4. Wash the beaker 3- 4 times with small quantities of distilled water and transfer the washing into the flask. 5. Make up the volume up to the mark with distilled water and mix thoroughly. 6. Preparation of approximately 0.1 N sodium hydroxide solution 7. Weigh about 4.25 g of sodium hydroxide pellets and dissolve into 200 ml of distilled water.

1. Calibration of Milk Butyrometer Introduction Butyrometer is used for determination of fat for milk and milk products by Gerber method. The milk butyrometer is a graduated vessel, which are designed in such a way that the internal volume of each unit is 0.125 ml which is corresponding to 1 percent fat. Sometimes due to manufacturer’s error, the volume of one unit of milk butyrometer is not exactly equal to 0.125 which leads to subsequent error in results in milk fat. So before starting to use a new butyrometer, it is essential to calibrate for its efficiency in the laboratory. Mercury is used to calibrate milk butyrometer. Apparatus Milk butyrometer (0 – 10% graduation), analytical balance