No abstract

Static headspace gas chromatographic method for determination of hexanal as a marker of lipid oxidation was developed. Tetradecane was suggested as a matrix for hexanal release from the sample. Sample equilibration temperature and time, tetradecane volume, injection time were optimized. Benzaldehyde was selected as an internal standard. Under the optimized conditions quality parameters were determined. The calibration curve was linear in the concentration range from 25 µg l -1 to 2 g l -1 , the detection limit was 15 µg l -1 , RSD was determined by five replication analysis with hexanal concentration 0.1 g l -1 and was 1.2%. The technique was applied for hexanal determination in potato chips and fried potatoes.

Direct and headspace gas chromatographic analysis is compared for the determination of lactic, oxalic, succinic, malic and citric acids. For better chromatographic behaviour, prior to GC analysis carboxylic acids were derivatized using BSTFA as a silylation reagent. Three solvents – acetone, diethyl ether and dimethylformamide – were tested as a derivatization medium and DMF was considered as the best. Derivatization conditions were optimized and analytical characteristics of the direct gas chromatographic determination of analytes in solutions were determined. The method was applied for the determination of citric acid in food. For the analytes dissolved in DMF, the headspace gas chromatographic determination was not sensitive enough. Concentrations of the derivates in the headspace were very low, thus the limits of detection were high and the method was not of practical use. On the other hand, headspace gas chromatography can be applied for identifying of carboxylic acids in solid samples.

The feasibility of a new approach for the determination of volatiles in solid matrices by coupling microwave‐assisted extraction with static headspace gas chromatography has been demonstrated using hexanal as an analyte present in fat‐rich food. Eight polar and low volatility deep eutectic solvents were prepared using microwave heating and examined for hexanal extraction. Choline chloride‐glucose‐water showed the best transition efficiency of hexanal to the headspace and was applied to extract hexanal using microwave‐assisted extraction. Hexanal released from the fat‐rich food is poorly soluble in the hydrophilic deep eutectic solvent choline chloride‐glucose‐water so enters the gas phase and subsequently dissolves in coconut oil fixed above the extraction mixture in a polypropylene capillary. After cooling the capillary was transferred to a headspace vial and headspace gas chromatography was carried out. Under optimized conditions, the limit of detection was 3.1 μg g–1. The developed approach was successfully applied to analyze hexanal in fat‐rich food.

Oxidation of unsaturated fatty acids of edible oils results in off-flavours, in a decrease in the nutritional properties and in the formation of toxic compounds. Hexanal is a suitable marker of the oxidation process. A new solvent, coconut oil, was suggested for hexanal quantification by static headspace extraction-gas chromatography. Sample equilibration temperature, time, weight and injection time were determined to provide the highest extraction to the headspace efficiency. At the optimized extraction conditions, the hexanal detection limit was 30 µg kg–1, linearity was 0.9977 for a concentration range of 50 µg kg–1 – 2 g kg–1 and repeatability of the results was 1.1%. The effect of heating on hexanal formation in four edible oils (olive oil, sunflower oil, rapeseed oil and linseed oil) was investigated. The biggest quantity of hexanal was observed in sunflower oil and it significantly increased after heating. Rapeseed oil was the most resistant to the oxidation at elevated temperatures. For linseed oil hexanal is not the most relevant oxidation marker as hexanal is not the main volatile oxidation product.