The concept of food physical performance index density and relative density

1.

Density refers to the mass per unit volume of a substance at a certain temperature, and is represented by the symbol p _t (the right subscript represents the temperature at the time of measurement, and can be represented by p at 20°C, and t is omitted)

Relative density refers to the ratio of the mass of a substance at temperature 4 to the mass of pure water of the same volume at temperature _t2, represented by the symbol d ^t1 _t2 , and the dimension is one

When measuring the relative density of a solution with a densitometer or a density bottle, the test procedure can be simplified when the temperature of the solution to be tested and the pure water are set to 20°C.

d ₄ ²⁰ = d ₂₀ ²⁰ ×p ₂₀

Wherein P _{20 is} -20 deg.

Second, the significance of density determination

The purity and concentration of liquid food are related to its relative density, and the quality of the food can be evaluated through the detection of relative density

Liquid food in the water is completely evaporated to a residual substance obtained was dried at constant weight, it referred to the solids (dry matter), including salts, organic acids , proteins and the like

3.

"GB/T5009.

Density meters commonly used in the food industry can be divided into ordinary density meters, hammer meters, milk thick meters, Baume meters, etc.

1.

Ordinary densitometers are directly scaled with the density value at 20°C (the density value of the substance at 20°C is equal to d ₄ ²⁰ in numerical value, so it can be said to be scaled with d ₄ ²⁰ )

2.

The Baume meter measures the concentration of a solution in units of Baume ( ^o Be)

3.

Brix scale, also known as Brixscale (abbreviated as ^o Bx), is a density meter dedicated to measuring the concentration of sugar liquid
.
It is based on the mass fraction of the sucrose solution as the scale, expressed by the symbol oBx
.
Which method is based on a scale of standard temperature 20 ℃ in distilled water for 0 ^O Bx, 1% sucrose solution for.
1 ^O Bx (i.
e.
100g sucrose solution containing 1g of sucrose), and so on
.
The scale range of the hammer meter has many kinds, the commonly used ones are: 0～6 ^o Bx, 5～11 ^o Bx, 10～16 ^o Bx, 15～21 ^o Bx and so on
.

If the measured temperature is not at the standard temperature of 20°C, the temperature should be corrected according to the observed hammer temperature correction table (see appendix 1)
.
When the measured temperature is higher than 20°C, the relative density decreases due to the volume expansion of the sugar solution, that is, the hammer is reduced, so the corresponding temperature correction value should be added, otherwise, the corresponding temperature correction value should be subtracted
.

[Example 2-1] The observed hammerness at 17°C is 22.
00 ^o Bx, and the correction value is 0.
18 ^o Bx in the attached table, then the sugar hammerness at the standard temperature of 20°C is 22.
00-0.
18=21.
82( ^o Bx)
.

[Example 2-2] The observed hammerness at 24°C is 16.
00 ^o Bx, and the correction value is 0.
24 ^o Bx by looking up the attached table .

The sugar hammer degree at a standard temperature of 20°C is 16.
00+0.
24=16.
24( ^o Bx)
.

The reading of the brix meter is an approximation of the mass fraction of the solution (solids)
.

4.
Milk Thickness Meter

The milk thick meter is a density meter specially used to determine the relative density of milk.
The measuring range of the relative density is 1.
015～1.
045
.
It is the relative density minus 1.
000 and then multiplied by 1000 as the scale, expressed in degrees (symbol: marked "o" in the upper right corner of the number), and the scale range is 15°～45°
.
When in use, the measured reading can be converted into a relative density value according to the above relationship
.
There are two types of milk consistency meters according to their different calibration methods: one is calibrated at 20°/4°, and the other is calibrated at 15/15°
.

The relationship between the two is: the latter reading is the mantissa of the former reading plus 2, namely:

d ₁₅ ¹⁵ = d ₄ ²⁰ +0.
002

The relative density of normal milk d ₄ ²⁰ =1.
030 and d ₁₅ ¹⁵ =1.
032
.

The relative density of cow's milk changes with temperature.
In the range of 10-25°C, for every 1°C change in temperature, the relative density differs by 0.
0002, which is equivalent to 0.
2 degrees of the milk consistency meter reading
.

For the 20/4° milk consistency meter, when the milk temperature is higher than the standard temperature of 20°C, 0.
2° should be added to the obtained milk consistency meter reading for every 1°C higher.
When the milk temperature is lower than 20°C, every 1°C lower 0.
2° should be subtracted
.

[Example 2-3] The reading of the 20/4° milk consistency meter at 16°C is 31°, converted to 20°C, it should be:

31-(20-16)×0.
2=31-0.
8=30.
2°

That is, d ₄ ²⁰ =1.
0302, and d ₁₅ ¹⁵ =1.
0302+0.
002=1.
0322
.

[Example 2-4] The reading of the 20°/4° milk consistency meter at 25°C is 29.
8°, which should be converted to 20°C

29.
8+(25-20)×0.
2=29.
8+1.
0=30.
8°

That is, d ₄ ²⁰ =1.
0308, and d ₁₅ ¹⁵ =1.
0308+0.
002=1.
0328
.

Use a 20°/4° milk consistency meter and a 15°/15° milk consistency meter to check the temperature correction in Appendix 2 and Appendix 3 respectively
.

5.
Alcohol Meter

The alcohol meter is a density meter specially used to measure the alcohol content in liquor or alcohol solution.
It is calibrated with an alcohol solution of known ethanol concentration.
It is 0 degrees in distilled water at 20°C and in 1% alcohol solution.
1 degree, that is, 100 mL of alcohol solution contains 1 mL of ethanol, so the volume fraction of the alcohol solution can be read directly from the alcohol meter
.

When the measuring temperature is not 20℃, it needs to be corrected to the actual concentration of alcohol at 20℃ according to the alcohol temperature concentration calibration table (see appendix 4)
.
For example, the direct reading at 25.
5°C is 96.
5%, and the actual content at 20°C is 95.
35% by checking the calibration table
.

Related Links: Statistical Inspection of Food Physical and Chemical Testing Results (2)