Milk can be adulterated by many ways, the most important one's are:
1- diluted milk with water
2- defatted milk
3- above two ways together
4- foreign matter is add such as starch, dextrin, etc
5- add anti deterioration and coloring agents.
Remove water from the milk by heat. It can be detected like liquid milk by dilute 1(dry milk):6-8 (water).
Detect starch and dextrin in milk:
To detect starch in milk by:
a- microscopic examination of starch granules.
b- boiling 5ml of milk, then I2 is added, white color of milk converted to blue color due to the presence of starch.
Few drops of vinegar are added to milk (condensate the milk), then solution is filtered using F.P wetted with absolute alcohol. The precipitate is dissolved in water, I2 is added, deep red or violet blue color is formed depend on the concentration of dextrin present. This confirm the presence of dextrin.
Potassium dichromate is the most popular preservative that added to milk.
1- 1ml of 2% silver nitrate is added to 1ml of milk in test tube then few calcium carbonate powdered is added, shake, yellowish red color, confirm presence of chromate.
2- take 25ml of milk then evaporated until dryness, ashing, dissolved ash with 2ml of water, filtered using filter paper. If filter paper get yellow stain, so detect the presence of chromate. Take this f.p., acidify using dilute sulfuric acid, few drops of H2O2 and 2ml of ether are added, blue color is formed in ethereal layer.
Distinguish between cow and human milk:
Can be distinguished by Umikoff reaction.
Take 4ml of milk in T. T., 1ml of water and 1ml of ammonia are added, put in water bath (60-65C) for 35', cold. If violet color is develop, this indicate the presence human milk. If yellow color is develop, this indicate the cow milk.
milk is fermented by adding yoghurt contains milk bacteria that affect on milk sugar which convert part of it to acidify milk (get acid taste of milk).
Thick milk can be adulteration by starch, shabb, powdered rice. It can be determined the presence of shabb by detect aluminum in ash as well as detect starch and powdered rice by iodine.
Milk is put in open cooking pot leave it for hours, fatty material is float on surface.
Cream can be adulterant by substituting fatty material with cheaper fat or emulsifying agent is added such as gum, gelatin to make thick consistency.
Detect gelatin in cream:
Mix 10 ml of cream with 10ml of water, 10ml of mercuric nitrate solution is added, stay 10', then filter using filter paper, if f.p. is turbid this detect the present of gelatin.
Determination of protein content by the formol titration:
Can't be determined protein directly with base due to weak carboxylic group in it. By adding formalin (formaldehyde) that react with NH2 group and form methelen amino (N=CH2) and carboxylic group COOH can be easily titration.
HOOC-CHR-NH2 + HCHO → HOOC-CHR-N=CH2 +H2O
Take 10 ml of milk in conical flask then 1ml ph.ph. and 0.4 ml of potassium oxalate are added to milk. Stay 2 mints. In piuret, 0.1 M of NaOH. Milk titrate by 0.1 M NaOH, end point is convert milk to pink color. 2ml of 40% formaldehyde is added to flask, then complete titration, end point is reach to pink color that appear first time, then measure the volume used in 0.1 M NaOH after titration of second time.
% protein present in milk = mls of 0.1 M NaOH needed for 100 ml of milk to neutralized acid formed from aldehyde x 0.17.
Cheese is a food product made from the separated crud obtained by coagulating the casein of milk, skimmed milk, or milk enriched with cream.
The coagulation is accomplished by rennet or other suitable enzyme, lactic fermentation, or by a combination of the two.
The crud may be modified by heat, pressure, ripening ferments, special molds, or suitable seasoning.
Cheese is adulterated in a number of ways:
1- it may contain excessive amount of water.
2- it may contain foreign fat, after original fat is separated from milk that used for prepare cheese.
3- It may contain emulsifying agent or binder
4- It may contain starch, flour, or metallic agent such as CaCO3
Kinds of cheese:
1- cheddar cheese: is the food prepared from milk by the procedure "a". it contains not more than 39% of moisture and its solids contain not less than 50% of milk fat.
Milk, procedure "a" which may be pasteurized and warmed. It is subjected to the action of harmless lactic acid producing bacteria, present in such milk or added. Harmless artificial coloring may be added. Sufficient rennet is added to the milk to the semi-solid mass.
The mass is cut, stirred and heated with continued stirring to promote the separation of whey and curd.
The whey is drained off and the crud is matted into a cohesive mass.
The mass is cut into slabs which are piled and handled to promote the drainage of whey and the development of acidity.
The slabs are then cut into pieces, it rinsed by water, so the whey is removed.
The crud is salted, stirred, further drained and pressed into forms.
2- washed crud cheese, soaked crud cheese. It contain not more than 42% of moisture and its solids contain not less than 50% of milk fat.
3- Colby cheese, it contains not more than 40% of moisture and its solids contain not less than 50% of milk fat.
4- cream cheese: it contains not less than 33% of milk fat and not more than 55% of moisture.
5- Neufchatel cheese it contains not less than 20% of milk fat and not more than 65% of moisture.
6- cottage cheese, it contains not more than 80% of moisture.
7- creamed cottage cheese, it contains not more than 80% of moisture.
Determination of fat by the soxtec methods:
In cheese, fat bind to protein, proteins should be free from fat before extract of fats.
1-2g of cheese put in themble containing 10g of acidify sand. Themble is heated in oven for 2-3 hrs 100◦C in vertical state. Extracted by pet.ether until boiling point, then decrease temperature, stay for one hour, remove round flask, dry, weight again, calculate the difference in weight.
% fat = w1-w2/w3 x 100
W1 = empty round flask in gm
W2 = residue in round flask in gm
W3 = weight of sample in gm.
Eggs are almost as complete a food as milk.
Eggs are not easy to be adulterant because they have shell.
How can be determined the eggs are new or not?
By one of these methods:
1- examine eggs in dark room, and use a focus light:
If the egg is new, it seems to be homogenous pink color and air room inside is very small.
If the egg is old, it seems patches of many dark spots and air room inside is big.
If the egg is deteriorate, the light not pass and its very dark inside.
2- dip an egg in 10% normal saline (NaCl):
If it is new, settled down.
If it is old, float on the surface.
3- shake the egg near to ear:
If its new, no hear any sound, due to the air room is very small, if it is old, you are heard a sound.
4- after break the eggs, egg is new, the yolk is round and yellow in color and it is not mix with white egg,. Old egg, yolk is not round, faint yellow, mix with white egg easily, have undesirable odor.
Prepared meat is the product obtained by subjecting meat to a process of comminuting, of drying, of curing, of smoking, of cooking, of seasoning or of flavoring or to any combination of such processes.
To examine meat, it includes:
1- physical examination
2- detect deterioration
3- microbial examination
if the meat exposure to the air lead to deteriorate in taste and odour.
To detect deterioration of meat, using litmus paper:
If new meat, L. P. red.
If deteriorate, L. P. blue.
Wheat flour is easily adulterated by different methods, the most common method is:
1- Metal material is added like CaCO3 and talk, we can detected by using ash. If ash is more than normal level than it should be, so it adulterated
2- Mixed with other grains, we can detected by microscopically.
3- Whitening material is added, the most common used are NO, Br, borate. All these are oxidizing agent can oxidize iodic acid solution then iodine is free, can be detected by usual method.
Meat, vegetables and others are preserve by one of these methods:
then they are added in canes.
Sterilization by heat:
Should be available in two things:
Cane containing food must be:
2-high level of sterilizing by using autoclave at 120 ◦C.
Is not used now for drying meat because it effects on its shape and properties. It is suitable for fruit and vegetable.
It is a suitable method for saving meat and fish if two criteria is present:
1- Temperature is very low and not change.
2- The air inside very clean and dry.
Both are applicable from -3 ◦C.
by two methods
1- anti-deteriorate is added or
2- isolate the surface of the food with a preservative material to preserve from contamination that pass air.
Kinds of cane:
1- Cane of meats:
A: meat is boiling with water for one hour at 100◦C. soup is separated after boiling, concentrate, cooling (gelling). The meat is added to the gelling soup in metal canes, cover, well sealed then sterilized in autoclave at 120◦C for10'.
B: salted meat is put in refrigerator at 3◦C, then meat is cooked, then added in cane by using pressure to press the meat. Close well, leave small pore in cover, sterilized then close this pore.
Examine canes meat:
A: examine the appearance properties of canes:
1- if the cover cane is convex---- not used
2- if the cover canes concave…. Ok
B: examine cane containing material:
The meat inside cane must be cooked well and the soup has gelling consistency with amber color, and not liquefied until increase temperature over 18◦C.
The deteriorate meat become soft, dark green in color and have bad smell and the surrounding viscose is melting and have black color.
C: examine by microscope:
Prepare a sample in slide, stain, examine under microscope. If observe large number of microbes, so unfit to human been.
The fish is preserve in olive oil and peanut oil after cleaned and salted then cooked in steam oven or fried in oil. After put fish in cane sink with oil, well sealed then sterilized.
Detection of fish:
Same in meat.
Preparation of vegetable:
1- cleaning and peeling
2- initial cooked or bleached with water and salt,
3- then return the green color that remove through bleaching by immerse in dilute solution of CuSO4.
Spices are aromatic vegetable substances used for the seasoning of food such as anise, caraway, paprika, cardamom .etc.
1- The v.o. is obtained from a spice by distillation (round bottom flask are placed the material containing v.o., separator: oil is automatically separated from distillate in a graduated tube, permitting a direct reading of the quantity of the oil, condenser.
2- Oils have densities lower or higher than water.
3- It is necessary to use collection traps that are suitable for each type of oil recovered.
4- transfer the v.o. in t.t and allow to stand over night or pass through anhydrous sodium sulfate, filter. Small amount of v.o. is obtain (0.75-1.5 ml).
5- Determination refractive index, specific gravity and optical rotation.
- Foods are analyzed to determine their radioactive content.
- Radioactive contamination in plants may result from either:
1- direct deposition on the surface of the plant tissues through stomata or epidermal cells or
2- from soil plant transfer in case of radio-nuclides reaching the soil.
The former way is the most significant of the two transfer ways.
Radioactive substances can enter the body either by:
1- ingestion of contaminated foodstuffs.
2- Inhalation uptake through wounds or
3- by direct absorption through the skin under normal conditions.
Ingestion is major pathways contributing to the total radioactive dose received by populations.
The amount of exposure to radiation depend on:
1- the intake of the radionuclide and other variables such as
3- metabolic kinetics and
4- size of the individual.
Radium-226: determined by alpha counting.
Strontium-90: AEC method.
Radium-226: goldin method.