Milk ( Dr. Hüseyin BOZKURT )

Dr. Hüseyin Bozkurt

Milk and dairy products have made a major contribution to the diet. Composition of milk Component Whole Milk Skimmed Milk Butter Milk Cream (40% fat) Fat 3.82 0.06 0.50 40.0 Protein (Nx6.38) 3.25 3.35 3.35 2.00 Casein 2.50 2.60 2.60 1.56 Whey Protein 0.60 0.62 0.62 0.37 Lactose 4.80 4.95 4.95 2.90 Minerals 0.70 0.73 0.73 0.44 Water 87.4 91.0 90.5 54.6

Nutrients provided by pasteurized milk Nutrient Quantity in Milk Protein 34.0 g Fat 39.1 g Carbohydrate 49.4 g Calcium 1.2 g Iron 1.1 mg Vitamin A 471 mg Vitamin D 0.30 mg Thiamin 0.40 mg Riboflavin 1.6 mg Niacin 9.3 mg Vitamin C 10.4 mg

The total solids (TS) of milk are made up of butterfat (usually around 3.9 %) and solids-not-fat (SNF, around 8.6%). The principles components of the SNF of milk are proteins (casein and whey proteins, immunoglobulin’s, etc.) an lactose. Fat phase contain fat soluble vitamins and salts. Aqueous phase also contains antibiotic residue.

The fat in untreated milk floats freely and rises to the surface to form a creamline on the top. Centrifugal seperation of the milk is simply an accelereated form of the same phenomenon.

Thermisation Pasteurization Sterilization

Milk and dairy products are pasteurized to destroy pathogenic organisms, particularly Tuberculobacillus and to reduce the number of non-pathogenic organisms which might adversely affect product quality. • Batch pasteurization hold at least 30 min at temperature not less than 62.8C and not more than 65.6C. • Continuous pasteurization (HTST) hold for at least 15 s at a temperature of at least 71.7C

Prior to taking portions for each determination; ◦ The milk should be thoroughly mixed by continuous slow inversions of the sample bottle or by slowly pouring it into a beaker and back into another beaker and repeating the process many times. } In the routine examination of milk it is convenient to take ◦ the lactometer reading, ◦ determining the fat by the Gerber method, ◦ the total solids ◦ the non-fatty solids content can be calculated.

The development of sourness can be assessed by determining the acidity of the milk. ◦ The assessment of the degree of pasteurisation from the results of the phosphatase test is also a common routine procedure for milks which are sold as “Pasteurised”. } Other determinations are ◦ protein, ◦ lactose, ◦ ash, ◦ chloride and citric acid and ◦ examination for dirt, ◦ added dyes, ◦ preservatives, ◦ detergent and ◦ antibiotics. ◦ The methylene blue test and the bacteriological examination must be carried out on samples taken under aseptic precautions.

Cow milk Component Lowest Highest Total Acidity as Lactic acid (%) 0.135 0.202 Density 1.028 1.039 Fat Content (%) 3.0 — Solid Non-Fat Content % 8.5 — Lactose (%) 3.5 5.5 Protein (%) 2.8 5.0 Ash (%) 0.6 0.9 Dirt (mg/100 ml) — 6

Determination of Ash in Milk Ash is determined by heating the dried residue of milk at a temperature not exceeding 500°C so that the chlorides are not volatilized. Chloride in Ash: } Pipette and weigh 10 ml milk into a 250 ml flask. Then add by pipette 10 ml 0.05 M silver nitrate (Section 5.7.). } Add 10 ml conc. nitric acid and a few anti-bump granules and boil gently for a few min. The liquid should then be pale yellow. } Cool, add 60 ml water and 1 ml ammonium ferric sulphate (Fe (SO ) .(NH ) .SO .24H O) solution as indicator 2 4 3 4 2 4 2 } And titrate the excess silver nitrate with the potassium thiocyanate solution (Section 5.5.). } Perform a blank determination by repeating the procedure with 10 ml water instead of milk. 1 ml of 0.050 M potassium thiocyanate = 0.001773 g chloride.

The rapid determination of protein in the milk can be made by formal titration method. } The protein in Milk can also be determined on 10 g milk by the macro Kjeldahl method using the factor N*6.38. } Formal titration method depends on the fact that when formaldehyde is added to neutralised milk, free acid(which can be titrated by alkali) is produced in proportion to the amount of protein present. } The protein content is then obtained by multiplying the titration by an empirical factor, which depends on the ratio of casein to albumin and also the particular technique employed in which interference due to calcium is prevented by addition of oxalate give reasonably accurate results.

To 10 ml of milk add 0.5 ml of 0.5 % phenolphthalein indicator and 0.4 ml of neutral saturated potassium oxalate ((COOK) .H O or C K O .H O). 2 2 2 2 4 2 } Mix and allow to stand for a few min. and neutralise with 0.1 M NaOH to the standard pink color. } Add exactly 2 ml. of formalin. } Mix and allow to stand for a few minute and titrate the new acidity produced with 0.1 M NaOH (Section 5.3.) to the same pink color (a). } Titrate separately 2 ml. of formalin and 10 ml. of water with the same alkali (b) as blank. } Then the protein content of the milk is % Pr otein = 1.7 *(a -b) } If the oxalate is omitted, the first titration gives the acidity and a higher formal factor is usually appropriate; % Pr otein = 1.95 *(a -b)

The specific gravity of milk varies according to the proportions of fat (sp. gr. 0.93), non-fatty solids, NFS, (sp. gr. 1.614) and water (sp. gr. 1.0). The density of milk can be conveniently measured by means of the lactometer which is a special hydrometer calibrated over the range 1.025-1.035 (25 ° – 35 ° as lactometer degrees). For determination, the milk should be reasonably fresh and be thoroughly but gently mixed, avoiding incorporation of air. The temperature of the sample being measured must always be taken. } If the percentage of fat is determined by Gerber method, the total solid (T) figure can be calculated from the modified Richmond’s formula T = 0.25 *D + 1.22 *F + 0.72 where D is the density hydrometer reading (lactometer degrees) at 20 °C and F is the fat in percentage. NFS = T -F

The acidity value can be expressed in different manners. These are: } Degree of Soxhlet Henkel ( SH° ) : Amount of N/4 NaOH required to neutralise 100 ml of milk. Or use 25 ml of milk then multiply the amount of alkali consumed by 4. Generally, SH° of milk is about 6-7. } Degree of Dornic (D°): Amount of 0.1 N NaOH required to neutralise 10 ml milk multiplied by 9. Generally the acidity of milk is 15-16 D° (1 SH° º 2.25D°). } % Lactic Acid. } } Procedure: } Take 20 g milk into a flask and dilute with twice its volume of CO2-free water. } By using ( 1% in alcohol) phenolphthalein (Section 5.1.1.) as indicator. } Titrate the sample with 0.1 N NaOH (Section 5.3.) to the first persistent pink color. } Calculate the percent acidity as lactic acid. 1 ml of 0.1 N NaOH = 0.0090 g lactic acid

When milk is heated at 80°C or above, all the albumin becomes denatured and if solutions of inorganic salts or acids are added the albumin separates with the casein. Procedure: } Weigh out 4.0 g of ammonium sulphate into a 50 ml conical flask. } Add 20.0 ml of milk sample and shake the mixture for 1 min. to dissolve the ammonium sulphate. } Allow the solution to stand 5 min., then filter it. } When at least 5 ml of clear filtrate have been collected, place the tube in boiling water for 5 min. } Then cool it in cold water and examine the solution for turbidity. } A sterilised milk that has been satisfactorily heat treated gives no turbidity. UHT milk gives a faint turbidity and raw pasteurised milk give a white precipitate.

Procedure: Put some milk into dish. Replace into microvawe oven. Run the program.


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