Analysis of dietary fats

FATTY ACIDS PROFILE : QUALITATIVE AND QUANTITATIVE INFORMATION


The establishment of a fatty acids profile makes it possible to know not only the distribution of saturated, mono-unsaturated and polyunsaturated fatty acids of a fat, but also the different relative proportions of each of them in relation to the total fatty acids content and the concentration of each fatty acid in the fat.

 

FATTY ACIDS PROFILE : QUALITATIVE AND QUANTITATIVE INFORMATION

 Principle

Fats are essentially composed of esters of fatty acids, notably triglycerides. Given their high molecular mass, they are not very volatile and must be derived for analysis by gas chromatography (GC).

A “fast” derivation method consists of transesterifying the triglycerides in an alkaline medium, thus forming esters of fatty acids. This method is applicable to vegetable oils. This method does not produce esters from free fatty acids.
 

Method adapted from the NF EN ISO 12966-2 standard ("fatty acid methyl esters/chromatography")

Principle

FREE FATTY ACIDS : markers of lipid hydrolysis

 Equipment & Reagents
 
  • Glassware
  • Gas phase chromatograph coupled with a flame ionization detector (GC-FID)
  • Petroleum ether 35-60°, anhydrous methanol
  • Sodium hydroxide 2 mol/L in methanol
  • Hydrochloric acid 1 mol/L in methanol
  • Petroleum ether containing an internal standard (triglyceride in C17 at 3 mg/mL).
  • Mixture of standard triglycerides in petroleum ether (approx. at 3 mg/mL each)


Method adapted from the NF EN ISO 12966-2 standard ("fatty acid methyl esters/chromatography")

Equipment & Reagents

FATTY ACIDS PROFILE:  QUALITATIVE AND QUANTITATIVE INFORMATION

 Experimental procedure
 
  • In a small stoppable glass tube, accurately weigh about 30 mg of matter (3 drops of vegetable oil).
  • Add 1 ml of petroleum ether containing the internal standard (C17 triglyceride). Shake for 10 seconds.
  • Introduce 0.2 mL of 2 mol/L methanolic NaOH. Insert the stopper. Shake vigorously for 10 seconds while holding the stopper down.
  • Place the tube in a water bath at 50ºC for 30 seconds while continuing to hold the stopper down (risk of overpressure).
  • Shake for 10 seconds and carefully uncork the tube.
  • Add 0.4 mL of 1 mol/L methanolic HCl. Shake and allow to decant.
  • Using the GC syringe, withdraw the appropriate amount of the upper phase (0.3 to 0.5 μL) and inject it in GC-FID.
  • chromatographic conditions: capillary column in DB-WAX grafted silica, 30 m in length, internal diameter of 0.32 mm, 0.50 µm film; hydrogen gas vector, 1 mL/min - split 10 mL/min; oven temperature 180°C, 250°C for the injector, 250°C for the detector.
 
 ≈ 45 minutes / sample

Method adapted from the NF EN ISO 12966-2 standard ("Gas chromatography of fatty acid methyl esters")

Experimental procedure
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