Commission Regulation (EC) No 273/2008 (repealed)Show full title

9. EXPRESSION OF RESULTS

9.1. Method of calculation and formulae

9.1.1. Calculation of the response factors R:

Peak II:

RII = 100/(AII[0])

where:

R_II

=

the response factors of peaks II,

A_II [0]

=

the areas of peaks II of the standard sample [0] obtained in 8.5.3.

Peak III:

RIII = W/(AIII[5] – AIII[0])

where:

R_III

=

the response factor of peak III,

A_III [0] and A_III [5]

=

the areas of peak III in standard samples [0] and [5] respectively obtained in 8.5.3,

W

=

the quantity of whey in standard sample [5], i.e. 5.

9.1.2. Calculation of the relative area of the peaks in the sample [E]

S_II[E] = R_II × A_II[E]

S_III[E] = R_III × A_III[E]

S_IV[E] = R_IV × A_IV[E]

where:

S_II [E], S_III [E], S_IV [E]

=

the relative areas of peaks II, III and IV respectively in the sample [E],

A_II [E], A_III [E]

=

the areas of peaks II and III respectively in the sample [E] obtained in 8.4.2,

R_II, R_III

=

the response factors calculated in 9.1.1.

9.1.3. Calculation of the relative retention time of peak III in sample [E]: RRT_III[E] = (RT_III[E])/(RT_III[5])

where:

RRT_III [E]

=

the relative retention time of peak III in sample [E],

RT_III [E]

=

the retention time of peak III in sample [E] obtained in 8.4.2,

RT_III [5]

=

the retention time of peak III in control sample [5] obtained in 8.5.3.

9.1.4. Experiments have shown that there is a linear relation between the relative retention time of peak III, i.e. RRT_III [E] and the percentage of whey powder added up to 10 %

• The RRT_III [E] is < 1,000 when the whey content is > 5 %;

• the RRT_III [E] is ≥ 1,000 when the whey content is ≤ 5 %.

The uncertainty allowed for the values of RRT_III is ±0,002.

Normally the value of RRT_III [0] deviates little from 1,034. Depending on the condition of the columns, the value may approach 1,000, but it must always be greater.

9.2. Calculation of the percentage of rennet whey powder in the sample:

W = S_III[E] – [1, 3 + (S_III[0] – 0, 9)]

where:

W

=

the percentage m/m of rennet whey in the sample [E];

S_III [E]

=

the relative area of peak III of test sample [E] obtained as in 9.1.2;

1,3

=

represents the relative average area of peak III expressed in grams of rennet whey per 100 g determined in non-adulterated skimmed-milk powder of various origins. This figure was obtained experimentally;

S_III [0]

=

represents the relative area of peak III which is equal to R_III × A_III [0]. These values are obtained in 9.1.1 and 8.5.3 respectively;

(S_III [0] – 0,9)

=

represents the correction to be made to the relative average area 1,3 when S_III [0] is not equal to 0,9. Experimentally the relative average area of peak III of the control sample [0] is 0,9.

9.3. Accuracy of the procedure

9.3.1. Repeatability

The difference between the results of two determinations carried out simultaneously or in rapid succession by the same analyst using the same apparatus on identical test material shall not exceed 0,2 % m/m.

9.3.2. Reproducibility

The difference between two single and independent results, obtained in two different laboratories on identical test material shall not exceed 0,4 % m/m.

9.4. Interpretation

9.4.1. Assume the absence of whey if the relative area of peak III, S_III [E] expressed in grams of rennet whey per 100 g of the product is ≤ 2,0 + (S_III[0] – 0,9) where

2,0

=

is the maximum value allowed for the relative area of peak III taking into account the relative area of peak III, i.e. 1,3, the uncertainty due to variations in the composition of skimmed-milk powder and the reproducibility of the method (9.3.2),

(S_III [0] – 0,9)

=

is the correction to be made when the area S_III [0] is different from 0,9 (see point 9.2)

9.4.2. If the relative area of peak III, S_III [E] is > 2,0 + (S_III[0] – 0,9) and the relative area of peak II, S_II [E] ≤ 160, determine the rennet whey content as indicated in point 9.2.

9.4.3.

If the relative area of peak III, S_III [E] is > 2,0 + (S_III[0] – 0,9) and the relative area of peak II, S_II [E] ≤ 160, determine the total protein content (P %); then examine graphs 1 and 2.

9.4.3.1. The data obtained after analysis of samples of unadulterated skimmed-milk powders with a high total protein content have been assembled in graphs 1 and 2.

The continuous line represents the linear regression, the coefficients of which are calculated by the least squares method.

The dashed straight line fixes the upper limit of the relative area of peak III with a probability of not being exceeded in 90 % of cases.

The equations for the dashed straight lines of graphs 1 and 2 are:

SIII = 0,376 P % – 10,7	(graph 1),
SIII = 0,0123 SII [E] + 0,93	(graph 2),

respectively where:

S_III

=

the relative area of peak III calculated either according to total protein content or according to the relative area of peak S_II [E],

P %

=

the total protein content expressed as a percentage, by weight,

S_II [E]

=

the relative area of sample calculated in point 9.1.2.

These equations are equivalent to the figure of 1,3 mentioned in point 9.2.

The discrepancy (T₁ and T₂) between the relative area S_III [E] found and the relative area S_III is given by means of the following: T₁ = S_III[E] – [(0,376 P% – 10,7) + (S_III[0] – 0,9)]T₂ = S_III[E] – [(0,0123 S_II[E] + 0,93) + (S_III[0] – 0,9)]

9.4.3.2.

If T₁ and/or T₂

are zero or less, the presence of rennet whey cannot be determined.

If T₁ and T₂

exceed zero, rennet whey is present.

The rennet whey content is calculated according to the following formula: W = T₂0,91

where:

0,91 is the distance on the vertical axis between the continuous and dotted straight lines.

Skimmed-milk powder

Skimmed-milk powder