Quality control of milk and dairy derivatives

Overview

To ensure the safety of dairy products, it is essential to control quality throughout the manufacturing chain. Thereafter, we will address the most frequent inspections.

Determination of the density of milk

Principle

The density of milk is the ratio of densities of the milk and water at 20 ° C and at the same pressure. It is measured by a lactodensimètre, containing a thermometer and a table of correction, and graduated in 0.0005 units calibrated against water, +/- 20 ° C.

Procedure

Place sample in a water bath at 40° C for the mix and dissolve the fat. Then let it cool to 20 ° C and pour into a test tube. Then, immerse the test piece lactodensimètre in full to overflow, which may eliminate the foam. We must keep the camera vertically, to undergo a rotation and play when it is stationary at the top of the meniscus.

Determination of acidity of milk Dornic

Principle

Determine the acidity of milk, mainly due to lactic acid by NaOH in the presence of a color indicator. This may be useful to detect milk formalin, which in this case, have an acidity higher than normal (18 ° Dornic) following the conversion of formaldehyde, an aldehyde, lactic acid.
(One degree corresponds to a Dornic decigram of lactic acid per liter of milk).

• Reaction at stake:

CH3-CHOH-COOH   +   NaOH    —>  CH3-CHOH-CONa    +  H2O
Lactic acid        Souda       Sodium lactate

Procedure

The base used is sodium N/9, which is prepared by diluting to 1 liter, 111.1 ml of sodium hydroxide 1N.
Then insert into a test tube 10 ml of milk at 20 ° C and 0.1 ml of phenolphthalein.
Assayed by soda Dornic (N/9) until the pink color that persists for about ten seconds.

Determination of milk fat (by the method of butyric acid-GERBER)

Principle and utility

GERBER method is valid only for fresh milk. The constituents of milk other than fat are dissolved by sulfuric acid. And thanks to centrifugal force and the addition of a small quantity of amyl alcohol (C₅H₁₁OH), which dissolves fat, it separates and rises to the top of butyrometers.

This may be useful in several cases: detect fraud skimming milk, check the standardization of fat content of milk before pasteurization, sterilization, etc..

Procedure

Garnish the butyrometers: for each of the four butyrometers used to first 10 ml of sulfuric acid, taking care not to wet the top of the device by pipetting acid. Next, put 11 ml of milk and avoid mixing with acid for not increasing the temperature butyrometers, and careful not to blow into the pipette. Then add 1 ml of amyl alcohol and cap with corks dry.

Butyrometers shake to mix the milk, acid and alcohol to facilitate the acid attack. At the beginning of the mixture acid coagulates the casein, stir to dissolve the curd. To stir, and return the empty butyrometers terminal bulb every time. During mixing, the temperature increases. Take precautions to not stop turning.

Centrifugation: introduce butyrometers in centrifuge (1000 to 1200 rpm) prior to cooling in balancing it. Check the plugs: if they are not pressed, the reading of the column will be impossible after centrifugation. Centrifuge for 3 minutes.
Play: butyrometers to remove from the centrifuge and keep them immersed in a water bath at 65° C for 4 to 5 minutes. Can it be read quickly on the scale of butyrometers: every inch in the scale represents 10 grams of fat per liter of milk.

Search antiseptics in milk: Search for hydrogen peroxide

Purpose and principle

Whether the milk is inhibited by hydrogen peroxide and this by using sulfuric acid and ethyl ether.

Procedure

Place in a test tube 2 ml of milk, 2 ml of ethyl ether and 5 drops of dilute sulfuric acid. Stir the mixture without emulsifying.
If no blue color, the milk does not contain hydrogen peroxide as an antiseptic.

Search for starch

This manipulation is intended to detect the reconstituted milks containing starch provided the milk powder contains starch as revealing.

Principle

The idea is based on the reaction between starch and iodine gives a blue color.

Procedure

In a test tube, place 10 ml of milk, a few drops of iodine solution prepared by dissolving 0.53 g of iodine in 40 ml of alcohol.
If n 'is not blue, milk is not restored and contains no starch.

Determination of raw milk nitrogen by the Kjeldahl method

Principle

The purpose of this manipulation is to determine the total nitrogen of milk by the official Kjeldahl method which is then affected by a factor of 6.39 for the protein content of milk.

Organic compounds containing nitrogen heated in the presence of concentrated sulfuric acid and catalyst are decomposed. They quantitatively mineralize and release of ammonium sulphate. It is collected in a known amount of a solution of boric acid. Is determined finally back with a solution of sulfuric acid the amount in excess of H₃BO₃.

Procedure

1. Mineralization:

The mixture of reactants and product to be determined Matras takes place in a 400 ml or one introduces 5 ml of milk, 15 ml of sulfuric acid 95% purity, and in the presence of a catalyst on conducts heat to high, when the mixture becomes clear bluish or greenish clear on prolonged heating of 30 minutes and then allowed to cool after.

2. Distillation:

Nitrogen organic milk will be mineralized to the state of ammonium sulphate. Ammonia is moved in the presence of the soda and will be distilled to be collected in a solution of boric acid and titrated back by the sulfuric acid in the presence of a color indicator which is the methyl red to yellow.

Determination of Chloride Milk

Purpose and principle

The objective of this manipulation is to determine the chloride content in milk by the method of Charpentier Vollard after defecation by zinc ferrocyanide.

Procedure

It uses 100 ml of filtrate, 1 ml of nitric acid and 5 ml of silver nitrate solution and 2 ml of iron alum, and then we start the agitation and then titration with potassium thiocyanate in 0.1 N to turn red persistent.

Determination of homogeneity

Homogenization must be sufficiently effective to prevent crémage. The result can be verified immediately by determining the index of homogeneity, the latter may be determined in the manner described in the example below:

Store a sample of milk into a measuring cup for 48 hours at a temperature of 4 to 6 ° C. Siphoning the top layer (1 / 10 volume) and thoroughly mix the remaining volume (9 / 10 volume), and then determine the fat content of both fractions. The difference in fat between the upper and lower layers, expressed as a percentage of the upper layer is called the index of homogenization.

Example: If the fat content of 3.15% in the upper layer and 2.9% in the lower layer, the uniformity index is:

  [(3.15 - 2.9) / 3.15] x 100 = 7.9.  The index of homogenized milk is between 1 to 10.