MRC MIA-LA, Руководство по эксплуатации

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Ultrasonic milkanalyser
Operation manual 67/92
APPENDIX 2 FREEZING POINT DETERMINATION
1. Methods for determination.
The milk analyser determines the freezing point of each sample and the
quantity of added water. The milk analyser does not measure the freezing
point, but calculates it from the components it depends on. The basic
components in the milk are water, solids, lactose, FAT, proteins, minerals
(salts) and acids. The freezing point depends only on the diluted in the milk
components and quantity of the solvent (in the milk it is water). The ultrasonic
technology allows direct measurement of FAT, proteins, lactose + salts (the
soluble components, only influencing the freezing point), and the quantity of
the solvent in % is determined by 100 %
– total solids %, total solids = lactose
% + FAT % + proteins % + salts % + acids %.
Without understanding the meaning of the freezing point
– determined or
shown from the milk analyser added water result easily may lead to a mistake
for the value of this parameter.
2. The basic freezing point.
Milk freezes at lower temperature than water. The average freezing point of
the raw milk in the most regions is at about -0,540

С. The average reading
for your region is called
“basic” freezing point.
The freezing point of milk is a
“physiological constant”. This does not mean
that it will not vary. In fact feed, breed, season, time of lactation, climate,
whether the sample is taken at the beginning, middle or end of lactation
– all
these factors will have an effect on the freezing point of the individual sample.
This means that there is an average value of all these numbers. The more
samples used in obtaining this average, the more reliable it is as a base. Or
the basic freezing point is an average of freezing points of milk, taken from
many cows. When a laboratory checks a producer, it is only comparing the
average of the producer’s cows against a larger area average.
The Health authorities establish the basic freezing point or agriculture
departments in some regions, sometimes by universities, separate dairy
producers, or their associations. Frequently, tolerances have been
established on top of a basic freezing point to allow some variations in the
milk as well as device or operator variations.
Without mentioning the basic freezing point, the Association of Official
Analytical Chemists now recommends an upper limit freezing point at -
0,525

C (2,326 standard deviations above the most recently determined
North American average of
–0,5404

C), below which there will be at 95%