section 3.pdf

Food Hygiene Department Milk Hygiene Practical Part Scientific subject by: Prof. Dr. Nagah Mohamed Saad Prof. Dr. Enas El-Prince Mohammad Prepared by Marwa Gamal El-Dien Abd El-Kadar Marwa Gamal Mi...

Food Hygiene Department Milk Hygiene Practical Part Scientific subject by: Prof. Dr. Nagah Mohamed Saad Prof. Dr. Enas El-Prince Mohammad Prepared by Marwa Gamal El-Dien Abd El-Kadar Marwa Gamal Milk Hygiene Section (3) Marwa Gamal Physical examination of milk Marwa Gamal  ** Items ** Specific gravity of milk. ** Specific gravity of milk serum. ** Refractive index of milk serum Marwa Gamal  * Specific gravity of milk ** The ratio between the weight of given volume of milk to the same volume of standard substance (water). 1ml water weight at 4°C = 1 g * 1 litter x sp.gr. = ….kilo Sp.gr. of water at 4°C 1 So sp.gr. = W(k) * 1 L of milk 1.031 kilo milk V(l) Marwa Gamal ** Factors affecting specific gravity: 1) Total solids sp.gr. 2) Temp. temp. Density sp.gr. temp. Density sp.gr. 3) Fat%: fat of milk has lower sp.gr. (0.92) < of water 1 So fat% sp.gr. of milk So by removal of fat sp.gr. of milk. Marwa Gamal ** SP.gr. of milk is determined by lactometer Marwa Gamal  ** Procedure ** Milk must be left 2 h after milking before testing to avoid presence of gas bubbles which lower sp.gr. of milk. 1) Put 250 ml of milk in cylinder. 2) Put lactometer in milk prevent lactometer from touching wall ?? or bottom ?? of the cylinder (wait for fixation) lactometer must be in up right position & float. 3) Take 2 reading:. * Lactometer reading on scale 15-40 * Temp.°C mercury bulb of thermometer must remain in milk. Marwa Gamal Marwa Gamal  * Calculation: * Specific gravity = 1.0 C.L.R. C.L.R. (Correct Lactometer Reading(= L.R. ± ( (°F – 60) X 0.1) °F = (°C x 9/5 ) + 32 If of 60 + If of 60 - 1)L.R. at this specific gravity of milk no change (standard). 2)°C °F 3)C.L.R. 4)Sp.gr. then compared with whose of normal animal. Marwa Gamal  * Normal value: * Cow´s milk 1.028 : 1.034 (1.032) * Buffalo´s milk 1.033 : 1.036 (1.034) * Significance 1) Sp.gr. adulteration by H O. 2 2) Sp.gr. partial skimming. 3) No change both of them by the same level.?? 4) Addition of skim milk Sp.gr. but decrease of fat% , increase of SNF% Marwa Gamal  * Specific gravity of milk serum Milk plamsa (skim milk) = milk – fat. Milk serum (whey) = milk – (fat & Caesin) * Preparation of milk serum by two methods:. CuSo milk serum 4 Acetic acid milk serum PPt of fat & protein by addition PPt of fat & casein by of CuSo soln. (71.5 g/ litter) 4 addition of acetic acid 25%. Marwa Gamal  * 2 types of milk serum CuSo milk serum 4 Acetic acid milk serum 100 ml milk 50 ml milk 4 parts milk 2 ml acetic acid 1 ml acetic acid 1 part CuSo4 soln. Mixing, put in water bath 70°C for 5 minutes because (acetic acid is Mixing then filteration weak acid), cooling & filtration Fat & protein Fat & casein (curd) (curd) CuSo4 milk serum Acetic acid milk serum ( filtrate) (filtrate) Marwa Gamal  * 2 types of milk serum CuSo milk serum 4 Acetic acid milk serum ** Comparison between Cu SO milk serum & 4 acetic acid milk serum.  ** Comparison between Cu SO4 milk serum & acetic acid milk serum. Comparison CuSO4 milk serum Acetic acid milk serum 1) Action PPt of fat & protein PPt of fat & casein 2) Filter paper PPt of fat & protein PPt of fat & casein 3) Turbidity Clear (no presence of Turbid (presence of whey protein) protein) 4) Color Blue colorless 5) Refractive index 36 40 Marwa Gamal * Sp.gr. of milk serum determined by Westphal´s balance Marwa Gamal Westphal´s balance method * The balance is first standardized on water at 60°F, then using milk serum which is heavier than water in sp. gr. so lift the plumet so lift vertical scale up (above) & by addition of various weight on the vertical scale of the balance, to determine the specific gravity of milk serum (weigh as 5 g, 1 g, 0.5 g, 0.05 g, 0.005 g) Sp. gr. of milk serum = 1.+weight(1 to equal to water) * Normal value of milk serum: 1.026 at 60°F * Significance if adulteration by addition of water Marwa Gamal  * Refractive index of milk serum * Property of translucent materials, which results if a ray of light is being bent & passing through it. * Due to opacity of milk (due to presence of protein & fat), R.I. of milk serum is determined as lactose of milk is translucent liquid. Marwa Gamal ** R.I. is measuring by Zeiss immersion refractometer Marwa Gamal  * Procedure 1) The prism of the refractometer is dipped into a beaker contains milk serum, which is put in water bath at 20°C. 2) Light is reflected from a mirror fall on solution to the prism interface & the scale is moved untill a clear light boundary on the scale is obtained. 3) The scale is graduated from 15-45 or 0-100. Milk serum beaker Water bath 20°C Marwa Gamal  * Normal value of refractive index R.I. of CuSo4 milk serum R.I. of acetic acid milk serum Not less than 36 Not less than 40 ?? Refractometer degrees at 20°C. Refractometer degree at 20°C. * Significance If the result below these degrees adulteration by addition of water Marwa Gamal Marwa Gamal Marwa Gamal