Dr.D.H.Kankhare Assistant Professor Animal Science & Dairy Science College of Agriculture, Dhule

Transcription

1 MILK : COMPOSITION AND PHYSICAL PROPERTIES Dr.D.H.Kankhare Assistant Professor Animal Science & Dairy Science College of Agriculture, Dhule 1

2 WHAT IS MILK? BY FSSAI RULE: Is the normal mammary secretion derived from the complete milking of healthy milch animal without either addition thereto or extraction there from. It shall be free from colostrum. Milk of different classes & of different designations shall confirm to the standards laid down by FSSAI. 2

3 Chemical Point of view : Milk is a complex fluid with more than 100 separate chemical entities in level that vary with species. From Physical Point of view : Milk is opaque, white heterogeneous fluid, having various constituent in multi- dispersed phases of emulsion, colloidal suspension or solution. 3

4 MILK :DEFINITION Whole, fresh, lacteal secretion obtained by the complete milking of one or more healthy milch animals, excluding that obtained within 15 days before or 5 days after calving Term Market milk refers to fluid whole milk that is sold to individuals usually for direct consumption. It excludes milk consumed on the farm and that used for the manufacture of dairy products 4

5 MILK : CLASSIFICATION OF MILK CONSTITUENTS MILK Total Solids Water Fat SNF Lactose Protein Minerals Other constituents 5

6 MILK CONSTITUENTS : CLASSIFICATION Water Milk Total solids WATER : Water content varies from % to 87.2 % Most of it is free & very small portion is in bound portion Small % of water hydrated to the lactose & salts, while some portion is bound with protein,phospholipids etc. Cow : 86.5 % Buffalo : 82.8 % In commercial milk range is to % 6

7 MILK CONSTITUENTS : CLASSIFICATION Water Milk Total solids WATER : Water is the medium in which all the other components of milk (TS) are dissolved or suspended. Water serves as a carrier for the other constitute of milk. 7

8 MILK CONSTITUENTS : CLASSIFICATION FAT Milk TS WATER True fat Associate subs Phospholipids Cholesterol Carotene Vita. ADEK FAT: Lipids are large group of organic compound Lipid is a collective term used for Quite bland in taste, imparts richness/ smoothness Fat : in the form small globule ave. app.. (2-5 micron) Buffalo : 4.15 to 4.60 µm Cow : 3.36 to 4.15µm Oil-in-water type emulsion 8

9 Lipids are found in three diff phases fat globule,- membrane surrounding these globules & milk serum Membrane is imp. In keeping fat separating as free oil. Also protects against the action of enzymes. 9

10 MILK CONSTITUENTS : CLASSIFICATION FAT Milk TS WATER True fat Associate subs Phospholipids Cholesterol Carotene Vita. ADEK FAT: Surface of fat globule coated with FGM Membrane contains Major portion of milk lipids enveloped in the globule is milk fat tri, di,& mono glycerides (98%), FFA, carotene, fat soluble vit., Milk fat consist chiefly of the triglycerides of fatty acids which make up % of milk fat In general milk fat consists of 65 % saturated, 32 % monounsaturated & 3% polyunsaturated fatty acids 10

11 MILK CONSTITUENTS : CLASSIFICATION SNF LACTOSE PROTEIN MINERALS Phosphates, Citrate, Chlorides OTHER CONST. Vita.,Enzymes,Pigments, Dissolned gases PROTEIN : Casein principal milk protein, makes up 80% of the total protein content & 20% WP Major portion of casein protein is in the form of micelles, which are composed of water, casein protein, salts & minor components like lipase, & proteinase, enzymes Casein found in the form of a calcium caseinate- phospahte complex Present in the colloidal state Casein itself composed of alfa, beta, gamma fractions. 11

12 MILK CONSTITUENTS : CLASSIFICATION SNF LACTOSE PROTEIN MINERALS Phosphates, Citrate, Chlorides OTHER CONST. Vita.,Enzymes,Pigments, Dissolned gases PROTEIN : Casein is that fraction of raw skim milk which is precipited by acidifying to p H 4.6. USE if casein As such not used in food. Used in bacteriological works, plastic and paper industry. Confectionaries,bakery & pharmaceuticals. Sodium caseinate used as binder in meat products. Adhesive in number of insecticidal and fungicidal spray. 12

13 PROTEIN : Casein principal milk protein, makes up 80% of the total protein content & 20% WP Major portion of casein protein is in the form of micelles, which are composed of water, casein protein, salts & minor components like lipase, & proteinase, enzymes Casein found in the form of a calcium caseinate- phospahte complex Present in the colloidal state Casein itself composed of alfa, beta, gamma fractions. 13

14 MILK : COMPOSITION SNF LACTOSE PROTEIN MINERALS Phosphates, Citrate, Chlorides OTHER CONST. Vita.,Enzymes,Pigments, Dissolned gases LACTOSE (milk sugar) Major milk carbohydrate It is in true solution in milk serum Composed of glucose & galactose Buffalo : % Cow : % 1/6 th as sweet as sucrose Contributes to nutritive value Responsible for texture & miscibility of some milk products Essential in fermented milk products 14

15 MILK : COMPOSITION SNF LACTOSE PROTEIN MINERALS Phosphates, Citrate, Chlorides OTHER CONST. Vita.,Enzymes,Pigments, Dissolned gases MINERALS Less than 1% but they influence the heat stability & clumping of fat globule All 22 minerals considered essential to human are present Good source of Calcium Major salt constituents : potassium, sodium, magnesium, calcium, phosphate, citrate, chloride. Minerals salts usually determine by ashing 15

16 MILK : COMPOSITION SNF LACTOSE PROTEIN MINERALS Phosphates, Citrate, Chlorides OTHER CONST. Vita.,Enzymes,Pigments, Dissolned gases Ave. normal milk contains 0.70 % ash, & this amount represents a salt contents of about 0.90 % Major salt constituents : potassium, sodium, magnesium, calcium, phosphate, citrate, chloride. Minor boron, cobalt, copper, Iron, manganese, Sulpher, Zinc Minerals salts usually determine by ashing Calcium influence firmness of curd during paneer & chhana making 16

17 MILK : COMPOSITION SNF LACTOSE PROTEIN MINERALS Phosphates, Citrate, Chlorides OTHER CONST. Vita.,Enzymes,Pigments, Dissolned gases Ash does not represent milk salt truly because organic salts are destroyed by the ashing and some non salt components. (e.g.sulphur of amino acid) contributes to ash. The % of salt and ash in milk varies with the breed, feed,season, and stage of lactation & disease. 17

18 MILK CONSTITUENTS : CLASSIFICATION Other constituents Vitamins Enzymes Pigments VITAMINS Milk contains both fat soluble (A,D,E,K) & water soluble B1,B6,B12, Folic acid For transfer of energy & to regulate metabolism in body Dissolved gases 18

19 MILK CONSTITUENTS : CLASSIFICATION Other constituents Vitamins Enzymes Pigments Dissolved gases ENZYMES Biological catalyst Over 20 enzymes isolated & characterized in cow milk Analase- starch splitting Lipase fat splitting Phospate- Protease- protein splitting 19

20 MILK CONSTITUENTS : CLASSIFICATION Other constituents Vitamins Enzymes Pigments Dissolved gases LACTOPEROXIDASE (LP) Naturally present in milk Unique biological function : antibacterial effect in presence of hydrogen peroxide & thiocyanate PIGMENTS These are fat soluble (carotene & xanthophylls) & water soluble such as riboflavin 20

21 MILK : COMPOSITION Species Water Fat Protein Lactose Ash Cow Buffalo Goat Sheep Human

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23 PHYSICAL PROPERTIES OF MILK Dr.D.H.Kankhare Assistant Professor Animal Science & Dairy Science College of Agriculture, Dhule 23

24 PHYSICAL PROPERTIES OF MILK Appearance Flavour Acidity p H Specific Gravity Freezing Point Boiling point Viscosity Refractive index Specific heat Thermal expansion Electrical conductivity, Surface tension

25 PHYSICAL PROPERTIES : 1.APPEARANCE Opacity Milk colour varies from white to yellow Colour of Buffalo milk is richer than that of Cow milk due to larger no. of fat particles in it Homogenized product whiter in colour Skim milk : slightly bluish tint Dense white colour of buffalo milk is due to absence of pigments as well larger size of casein micelles/colloidal calcium phosphate complex 25

26 PHYSICAL PROPERTIES :2. FLAVOUR Sensory property in which odour & taste interact Sweet taste of lactose is balanced by salty taste of chloride, & both are somewhat moderated by protein The fat, fatty acid & phospholipids also contributes to flavour The characteristic rich flavour of dairy products is due to the lactones, methylketones,certain aldehyde & certain short chain fatty acids Milk has clean pleasantly slightly sweet flavour Type of feed,season, stage of lactation,udder condition,sanitation may change flavour 26

27 3. ACIDITY AND ph p H is the activity of hydrogen ion concentration whereas acidity is the concentration of hydrogen ion donor compound TA of Cow milk : 0.13 to 0.14 Buffalo milk : 0.14 to 0.15 p H normal, fresh milk, sweet milk varies. Cow milk : 6.4 to 6.6 Buffalo milk : 6.7 to 6.8 Higher p H indicates udder infection, lower values, bacterial action p H of fresh milk vary with species, breed indivi.,lactn Skimming & dilution of water raise the p H of milk while sterilization usually lowers it Little practical value except to measure changes in acidity 27

28 4. DENSITY AND SPECIFIC GRAVITY Density of a substance : defined as its mass per unit volume at a specific temperature Density of milk : g/cm3 (3-5 % fat ) Density increases from a maxi. 5.2 c to a min. at 40 c Specific gravity is the ratio of density of the substance to density of standard substance Usually reported/expressed at 15.5 c Spe. Grav. of fresh milk Ave Cow milk , Buffalo milk Skim milk :

29 4. DENSITY AND SPECIFIC GRAVITY Use- 1. To convert vol in to mass.2.to estimate TS More SNF in buffalo milk results in higher Sp.gr. 29

30 5. FREEZING POINT Milk : soluble constituent : lactose, soluble salts & dissolved gases are major contributor. Ave. freezing point Cow : C Buffalo : C Used to detect water adulteration in milk AOAC has specified that milk with freezing point of c or below may be presumed to be water free.but above this a strong suspicious As little as 3 % water added to milk can be determined Freezing point should be determined in fresh sample for grayest accuracy 30

31 5. FREEZING POINT Also used to determine lactose content in milk, estimate whey powder content in SMP Mastitis milk normal freezing point Boiling & sterilization increase freezing point Pasteurization do not have any effect Under feeding causes increased in freezing point There is deciding rupturing of fat globule of milk when frozen, a liberation of some free fat Fat and protein have little or no effect on freezing point. 31

32 6. BOILING POINT Milk constituent in true solution are responsible for elevation of the boiling point above C Boiling point.. Buffalo milk : C Cow milk : C Milk adulterated with water boils at a lower temp than that of normal water May help in detection of adulteration (not easily applicable ) 32

33 7. SPECIFIC HEAT Amount of heat required to raise the temperature of 1 gram of substance through 1 0 C Specific heat of milk at 15 0 C at (0 0 C ) Important in processing of milk to determine the quantity of heat either to be added or removed from milk to reach the desired temperature Heat capacity of milk & cream depend upon the fat content 33

34 8. VISCOSITY Viscosity refers to its resistance to flow; is a measure of the friction between molecules as they slid past one another Expressed in terms of centipoise (cp) Whole milk at 25 C is about 2 cp Viscosity of milk & cream gives an impression of richness to the consumer Organoleptic standpoint, contributes to mouth feel & flavour Depend on temp., concentration, & state of casein micelles & fat globule 34

35 8. VISCOSITY Casein micelle & fat globule are imp contributor to the viscosity of milk Imp in determining rate of creaming, rates of mass & heat transfer Low temp increase viscosity due to the increased voluminosity of casein micelle Ageing, souring & development of bacteria responsible for increased in viscosity At 27 C Buffalo milk Cp Cow milk cp Milk is more viscous than water. 35

36 9. REFRACTIVE INDEX When light passes at an angel from a less dense medium to more dense medium it is bent or refracted Used to indicate purity Indicate adulteration. Addtn of water lower the R.I. Refractive index of milk. Varies from to at 50 0 C The component of milk contributing to its R.I. in descending order of importance are ; water, protein, lactose, and minor constituents. 36

37 9. THERMAL EXPANTION When warmed, the volume of milk increase The volume of buffalo milk increase steadily by 1.26 per cent when heated from 4 to 40 0 C and by 6% when heated to 90 0 C Coefficient of thermal expansion for cow milk are Slightly lower compare to buffalo milk 37

38 10. ELECTRICAL CONDUCTIVITY Milk can conduct electric current because it contains various kinds of ions Measured in terms of specific resistance Specific resistance : resistance in ohm of a column of solution of 1 cm long and 1 sq cm in cross section to ohm at 25 C Dilution causes fall in conductance Mastitis condition increased the conductance (chloride ions increased) E.C. in dairy processing successfully employed as an index of added neutralizer 38

39 10. ELECTRICAL CONDUCTIVITY During fermentation (bacterial action) milk increases its conductance because of conversion of calcium & magnesium to ionic forms. By measuring E.C. progress of fermentation can be followed. 39

40 11. SURFACE TENSION May be defined as the force in dynes acting at right angels to the surface of a liquid along Milk has surface tension 50 dynes /cm at 20 C Heating, sterilization,homogenization increase the surface tension Surface activity related to protein, fat, phospholipids & FFA present in it. Process of homogenization increases the surface tension of milk and so does sterilization by heat. 40

41 12. Curd tension Imp in relation to the cheese making characteristics as well as digestibility of milk The curd tension of buffalo milk is significantly higher at g than that of cow milk, which is g Heat treatment of Buffalo milk causes reduction of curd tension,so also does the homogenization treatment Addition of some salt tend to reduce the curd tension 41

42 Acidity Cow % LA Buffalo % LA p H Cow Buffalo Density g/cm3 (3-5 fat %) Specific gravity Freezing point Cow C Buffalo C Boiling point Cow C Buffalo Specific heat at 15 0 C Refractive index at 50 0 C 42

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