Measurement of the acetoin content (Type IV)
OIV-MA-VI-18 Measurement of the acetoin content
Type IV method
- Introduction
Acetoin (CH3COCHOHCH3) is always present in wines and in vinegars. According to the bibliography its content in wines is of the order of 10 mg/L. In vinegars, contents can vary with the manufacturing technology between 100 mg/L and over 400 mg/L.
The acetoin content in the wine vinegars is an important reference factor for quality and origin.
- Principle
Neutralization of the sample at pH 7.00 with calcium hydroxide. Direct measurement of the acetoin via gas chromatography.
- Reagents
3.1. purified acetoin. Eliminate any diacetyl via distillation.
3.2. acetoin reference solutions: dilute acetoin (3.1) with water to prepare 10 to 500 mg/L reference solutions.
3.3. Pentan-1-ol (in-house standard solution)
3.4. Ethanol
3.5. in-house standard solution sample: in a 100 ml volumetric flask, dissolve 2 ml of pentan-1-ol in an aqueous-alcoholic solution at 50%. Make up to the mark with this solution.
3.6. calcium hydroxide
- Devices and utensils
Standard laboratory material, plus:
4.1. gas chromatograph with a flame ionization detector.
4.2. column for gas chromatography 2 m long and 1/8" in diameter: FFAP 2.5% on G Chromosorb (HP), with the addition of 0.5% of 1500 Carbowax (or any other system able to perform an acceptable separation of acetoin).
- Technique
Add some in-house standard solution (3.5) to the acetoin reference solutions (3.2), in sufficient quantity for these solutions to have, per L, 15 or 35 μL of pentan-1-ol (according to their acetoin content, that is respectively < or > 50 mg/L).
Neutralize the sample at pH 7.00 by addition of calcium hydroxide (solid). Add enough of the in-house standard solution (3.5), for the solution to have, per L, 15 or 35 μL of pentan-1-ol (according to the acetoin content).
Inject into the chromatograph 2 μL of the neutralized sample, the reference solutions, and the in-house standard solution. Temperature of the oven is 70° C, output of the vector gas (nitrogen) is 12.5 ml/min. Temperature of the detector is 180° C.
- Results
6.1. Calculation
Taking:
- the surface of the peak of the acetoin in the reference solution 1
- the surface of the peak of pentan-1-ol in the reference solution 1
- the surface of the peak of the acetoin in the solution to be measured
- the surface of the peak of pentan-1-ol in the solution to be measured
Calculate the ratios / for the various reference solutions.
Draw two curves to express graphically these ratios according to the acetoin content of the reference solutions (0 to 50 mg/L and 50 to 500 mg/L).
The acetoin content of the sample, expressed in mg/L, is shown by the ratio .
6.2. Presentation
Round results as mg per L to integer values.
- Bibliography
- Anonymous, 1993. Métodos Oficiales de Anàlisis, (Official Analytical Methods) Tomo II (Part II) Ministério de Agricultura, Pesca y Alimentación, (Ministry for Agriculture, Fishing and Food) Madrid, Spain.
- Gorostiza E., Gil de la Peña, M. et Cordobés M., La Semana Vitivinícola: 1577-1578 (1976).
- Llaguno C. and Polo M.C., 1991. El Vinagre de Vino (The Wine Vinegar) Consejo Superior de Investigaciones Cientificas (High Council of Scientific Research) Madrid, Spain.