color of sweet paprika

iron in condiments

iron in flour

phosphates in apple juice

phosphates in meat products

nitrite in meat products (1)

nitrite in meat products (2)

alcohol in spirit

color of beer

glucose


7. Determination of the nitrite in meat products - Procedure 2

BACKGROUND

Nitrites are added to meat during the production of certain meat products to accelerate the process of saturation with salt and to enable the meat product to maintain its typical red colour. The brine and the meat are acidic medias (the pH of meat is 5.5 or 5.6). In the acidic media nitrite is converted into NO, which bonds to mioglobine and then transforms into nitrosomioglobine. During long-term storage and at high temperatures, nitrosomioglobine turns into a red coloured substance. NaCl and nitrites together help prevent the activity of micro-organisms and prototypical ferments.

The allowed quantity of nitrites in meat products is 20 ppm (mg/kg).
 

EQUIPMENT
 

  • volumetric flasks
  • pipettes
  • Erlenmeyer flask
  • homogenizer
  • precise balance
  • SpectraTM spectrometer

 

 

REAGENTS

  • Griess-Ilosvay reagent made of two solutions:
    • 0.5 g sufanilic acid diluted in 30 mL of  CH3COOH and 120 mL of distilled water
    • 0.2 g a-naphthylamine diluted in 50 mL of concentrated  CH3COOH solution and completed with a 20% solution of CH3COOH to the 150 mL mark.
  • saturated solution of HgCl2
  • standard solution of  NaNO2 (g - 10 mg/L)
     

HAZARDS
 

Hydrochloric acid - C
R: 34-37
S: 26-45

Ammonia - C
R: 34-37
S: 7-26-45

Disodium tetraborate – Xn
R: 22
 

Zink sulphate – T

Acetic acid – C
R: 10-35
S: 23-26-45

Disodium nitrite – T,O
R: 8-25
S: 44

Naphthyl-1-amine - Xn
R:22
S:24

Sulfanilic acid – Xn
R: 20/21/22-52/53
S:25-28


PROCEDURE

Sample preparation

Weigh 100 g of the meat-product sample. Homogenize it (10 000 rpm). Weigh out 5 g (± 0.01 g) of homogenized sample and put it into a 500-mL volumetric flask. Add approximately 300 mL of distilled water and heat it in a water bath for 2 hours. Stir several times during the heating. After heating, add 5 mL of saturated solution of HgCl2 (in order to clear the solution). Cool the solution to room temperature and fill with distilled water to the 500 mL mark. Shake well and filter into a beaker. Then follow the procedure described in the table.

Determination of nitrites

The procedure is shown in the table. Pipette into the hollows of the blister the volumes of sample solution and other solutions, as shown in the following table. Stir well and after waiting 30 minutes, read the transmittance using the spectrometer. Use the green LED.

 

Vsample
(µL)

VNaNO2
(µL)

VH2O
(µL) 

Vsulfan.a.
(µL) 

Va-naph.
 (µL)

gNaNO2
(mg/L)

T
(%)

A
 

Blank sample

-

-

50

25

25

-

 

 

Calib.solut.1

-

5

45

25

25

1

 

 

Calib.solut.2

-

10

40

25

25

2

 

 

Calib.solut.3

-

15

35

25

25

3

 

 

Calib.solut.4

-

20

30

25

25

4

 

 

Calib.solut.5

-

25

25

25

25

5

 

 

Calib.solut.6

-

30

20

25

25

6

 

 

Calib.solut.7

-

35

15

25

25

7

 

 

Calib.solut.8

-

40

10

25

25

8

 

 

Calib.solut.9

-

45

5

25

25

9

 

 

Calib.solut.10

-

50

0

25

25

10

 

 

sample

50

-

-

25

25

-

 

 

 


CALCULATION

Draw the calibration line that indicates the absorbance dependence on the NaNO2 concentration. Read from the graph the concentration of nitrite ions in the sample and calculate the concentration of nitrite ions in the primary sample of the meat product.

 

Developed and prepared by: Irena Štrumbelj Drusany, Alma Kapun Dolinar and Simona Škerlavaj Golec, Srednja agroživilska šola Ljubljana