Organoleptic and physicochemical indicators of raw milk are important for determining its quality and suitability for different production processes.
When accepting raw milk firstly its organoleptic indicators are determined: taste, smell, color, texture. The sensory (organoleptic) evaluation of the milk by smell, taste and consistency is carried out for each batch of milk. In order to evaluate the smell it is recommendable to heat the sample of raw milk of 10 – 20 ml at water bath up to a temperature of 35 oC. The taste of milk has to be evaluated selectively after boiling the sample.
An important indicator is temperature of raw milk. It has to comply with the regulations of a certain country.
Milk samples are taken for analysis in compliance to the regulations. It is recommendable the samples to be canalized in the presence of the producers or suppliers of raw milk. The average milk samples are taken in containers with different volume, convenient for mixing depending on the volume of the sample. Vessels with a sample need to nave a label or attached label with information about the supplier and the date of product receipt.
Determining the purity is made for each milk batch. In cases when visual check determined presence of mechanical impurities, a sample is taken to determine the purity group of the milk. The filters with instructions for the purity group of the milk are sent to the suppliers if necessary (highly polluted milk).
An important indicator at accepting is the acidity of the milk. It is an important standard indicator. It determines the quality and suitability of milk for pasteurization and the production of dairy products. The acidity of milk is determined through titration according to the approved methods. This an indicator of freshness of raw milk and refrigeration conditions in which it has been stored.
Milk density is one of the most important physicochemical indicators for the quality of the milk and its technological value. The density of milk is understood as the ratio of a certain volume of milk at a temperature of 20 degrees C and the mass of the same volume of distilled water at a temperature of 4 degrees C. The density of milk is determiend by the content of its different compounds (fat, proteins, carbohydrates, salts etc.). Each change of the content of the milk leads to a change of its density. The density is determined in laboratory conditions accurately with a pycnometer and Mohr-Westwall scales and satisfactorily accurately with a hydrometer (lectodensimeter). It is also determined for each milk batch.
Determining the content of fats is reformed for each batch of raw milk and an average sample is taken from it. The sample is taken with metal pipe and the milk has to be mixed well before that. Milk fat is found in milk in the form of small fatty balls with an average diameter of 3-6 µm and it forms with plasma emulsion or suspension. Determining the content of fats in milk is one of the most important analyses since based on it payment is done and also it is an important technological indicator for production of dairy products. That is why quick and precise measurement is necessary. The most precise method is the weight-analytical method of Rose Gottlieb, but is applied only at arbitration. A quick method is the butyrometer method of Gerber (volume-analytical determination). The measurement is express with the ultrasonic milk analyzers of the company Milkotester Ltd – Lactomat and Master and with precise accuracy.
Protein substances are one of the most important compounds of milk. They are divided into two groups – caseins and whey. The main part of the milk proteins are caseins (78-85%), and the smaller one (15-22 %) – whey proteins. In order to determine the total amount of proteins different method are used- of formal titration, of dye binding, refractometric. Arbitration method is the method of Kjeldahl when determining the content of protein substances.
Lactose is important for the correct course of the fermentation process and for the production of low-calorie dairy products. The amount of lactose is determined by using the fermentative method: measurement of lactose is done through the use of ferment (for example lactase), which breaks down the lactose to glucose and galactose. The amount of the sugars formed is measured and is transformed into amount of lactose.
Mineral substances in milk are determined based on the ash content. The milk is dried, carbonized to constant mass. The ash obtained is calculated in percentage.
Dry substance determined the nutritional value of milk and the amount of dairy products obtained during its processing. It shows content of fats, proteins, carbohydrates and salts. By dry substance is meant the residue (%) that is obtained after drying the milk at a temperature of 102±2 oC to a constant mass..
The dry fat-free residue is obtained by subtracting the fat content (%) from the milk solids (%).
Check of the presence of added substances: when receiving milk suspected of adulteration, as well as systematic delivery of low-quality milk that does not meet the requirements of the current regulatory documentation (for example, acidity - less than 16 oT), the quality of the milk is checked for inhibiting substances (soda, formaldehyde, ammonia) by specific methods. The false milk is not accepted.
Each incoming batch of raw milk is examined for its compliance with the current regulatory documents and for arganoleptic abd main physichochemical indicators and on this basis a decision is made on its acceptance/ purchase.
Various analytical laboratory methods and tools are used to measure the above indicators, as well as spectrophotometry, chromatography, electrophoresis and others. Certain standards and methods are applied in compliance with the laws of a certain country or region.
The ultrasonic milk analyzers of the company Milkotester Ltd – Lactomat and Master determine all necessary physicochemical iindicators, with exceptional precision when determining the quality of raw milk: fat content, dry fat-free residue, density, proteins, lactose, salts, added water, freezing point, sample temperature. With their use, determining the quality of raw milk becomes fast, easy and precise.