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


6. Determination of the nitrite in meat products - Procedure 1

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
  • funnel
  • automatic pipettes
  • Erlenmeyer flask
  • homogenizer
  • analytical balance
  • SpektraTM spectrometer

 

REAGENTS

  • saturated solution of Na2B4O7 x 10 H2O
  • Carrez solution II (300 g ZnSO4 x 7H2O/ 1L distilled water)
  • NH3 solution (25 % NH3 is diluted  1:4 with distilled water)
  • HCl solution (0.1 mol/L)
  • Griess reagent I (to 0.6 g of sulfanilic acid and 20 mL CH3COOH, add distilled water to the 100-mL mark)
  • 0.03 g of naphthyl-1-amine - boil three times with 10 mL of distilled water and filter
  • NaNO2 solution (g - 10mg/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

Prepare 100 g of well-homogenized sample. Weigh out 12.5 (±0.01 g) on an analytical balance. Put the sample in the 250-mL volumetric flask; add 5 mL of saturated solution Na2B4O7 x 10H2O and cca.150 mL of hot, distilled water. Stir well and heat for 15 minutes on the water-bath (90-100°C). After heating, add by dropping, 1 mL of Carrez solution II while mixing. Cool the solution completely. Add distilled water to the 250-mL mark. Filter the cold diluted solution into a glass beaker. With a pipette, transfer 20 mL of the cold and filtered solution into a 100-mL volumetric flask. Add 25 mL of diluted NH3 solution and 10 mL of HCl solution. Fill the volumetric flask with distilled water to the 100-mL mark.

Determination of nitrites

The procedure is shown in the table. Pipette transfer into the hollows of a blister the volumes of sample and other solutions, as shown in the following table. Stir well and wait for 15 minutes. After the waiting time measure the transmittance with the SpektraTM spectrometer using the green LED light.

 

Vsample
(µL)

VNaNO2
(µL)

VH2O
(µL) 

VGriess I
(µL)

VGriess II
(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