Headspace-solid-phase microextraction-gas chromatography (HS-SPME-GC) was used to identify in total 74 volatile lipid oxidation compounds altogether in thermally stressed conventional and high-oleic sunflower (HOSF) oil samples (in accelerated storage conditions for 14 days at 80°C). Out of the volatile compounds identified, six volatile compounds were selected as marker compounds for the assessment of lipid oxidation of sunflower (SF) and HOSF oils due to their low odour threshold values and fatty-rancid odour impression. Additionally, other oxidation parameters such as fatty acid composition, peroxide value (PV), anisidine value and tocopherol and tocotrienol composition were determined. Multivariate statistical methods (principal component analysis and agglomerative hierarchical cluster analysis) were applied to identify sensitive oxidation marker compounds. Preliminary results revealed that hexanal, E-2-heptenal, E-2-decenal and E,E-2,4-nonadienal were the most suitable in differentiating HOSF and SF oil varieties from each other and SF samples with differing oxidative properties. Differentiation of SF samples according to their volatile compound composition was done in accordance with the results from the well-known oil quality parameters (e.g. PV or fatty acid composition). In conclusion, the combination of volatile compound analysis with HS-SPME-GC and multivariate statistical methods provides a sensitive tool in differentiating conventional SF and HOSF oils by means of volatile lipid oxidation marker compounds.

The aim of the study was to evaluate volatile compounds as marker compounds for the edible oil deterioration during the production of deep-fried French fries. Additionally the sensory characteristics (taste and smell) were assessed and results were compared with the results of the volatile compound analysis. A 32-h deep-frying experiment was performed and different frying oils, namely sunflower oil (SF), high-oleic sunflower oil (HOSF), rapeseed oil (RO), high-oleic rapeseed oil (HORO), and palm olein, were subsequently analyzed for their oxidative properties by the determination of their total polar material (TPM), polymerized triglycerides (PTG), peroxide value, anisidine value, as well as the fatty acid composition. In addition, analysis of the volatile compounds derived from the thermal degradation of the frying oils was performed by means of headspace-GC/MS techniques (HS-SPME-GC/MS and DHS-GC/MS). Multivariate statistical methods (principal component analysis with VARIMAX rotation) were applied to identify sensitive volatile lipid degradation indicators, enabling a differentiation of the various frying oils of different degrees of lipid oxidation just after 3 h of deep-frying. E,E-2,4-decadienal and heptanal showed the greatest ability to differentiate between samples of various oxidative states, whereas E,E-2,4-heptadienal and E-2-decenal showed a reasonable correlation with well-known lipid oxidation parameters, e.g., values for PTG or TPM. In addition to the chemical evaluation of the frying oils, the produced French fries were evaluated in terms of their taste and smell by an advanced scientific sensory method (balanced incomplete block design). French fries produced in conventional vegetable oils (SF and RO) were differentiated earlier from those prepared in fresh reference oil compared to HOSF and HORO. The perception of the French fries prepared in HOSF was comparable to those prepared in palm olein. Therefore, high-oleic vegetable oils, especially high-oleic SF, provide a frying oils alternative for the production of deep-fried French fries, delivering low proportions of trans and saturated fatty acids.Practical applications: The combination of volatile compound analysis by headspace-GC/MS techniques with multivariate statistical methods is a sensitive tool to detect quality changes in deep-frying oils at an early stage of lipid deterioration. Evolved volatile marker compounds, e.g., E,E-2,4-heptadienal and heptanal correlated reasonably with quality parameters for the assessment of the thermal stability of frying oils, e.g., content of TPM polymerized trigylcerides. Comprehensive scientific sensory evaluations of frying oils revealed high-oleic edible oils as promising frying oil alternatives for the processing of French fries providing low proportions of trans fatty acids and saturated fatty acids. of detection; LOQ, limit of quantification; PCA, principal component analysis; PO, palm olein; PTG, polymerized triglyceride; PV, peroxide value; r, coefficient of determination; RO, rapeseed oil; SF, s...

Headspace-solid-phase microextraction-gas chromatography was used to identify in total 55 volatile lipid oxidation compounds in thermally stressed conventional and high-oleic rapeseed oil samples. Out of this profile, 17 volatile compounds with low odor threshold values were selected as target compounds for the assessment of lipid oxidation in rapeseed and high-oleic rapeseed oils. Additionally, other lipid oxidation parameters such as fatty acid composition, peroxide value, anisidine value, and induction time (Rancimat analysis) were determined. Multivariate statistical methods (principal component analysis in combination with agglomerative hierarchical cluster analysis) were applied to identify sensitive volatile lipid oxidation indicators enabling the differentiation of rapeseed oil samples of different varieties (high-oleic versus conventional). Moreover, these statistical methods were capable of differentiating rapeseed oils of different oxidative properties. Octanal and 3-octanone showed the highest ability to differentiate between samples of different rapeseed varieties, whereas propanal, E,E-2,4-hexadienal, and E-2-heptenal were most suitable in differentiating rapeseed oil samples with different oxidative properties from each other. Clustering of rapeseed oil samples according to their volatile compound composition was comparable with results of sensory duo-trio and paired comparison tests, but the analytical approach of the volatile compound analysis in combination with chemometric methods detected changes sooner in relation to the flavor composition of rapeseed oils and high-oleic rapeseed oil samples.Practical applications: The combination of volatile compound analysis by HS-SPME-GC with multivariate statistical methods and complementary sensory duo-trio and one-sided paired comparison tests are sensitive tools in differentiating conventional and high-oleic rapeseed oil samples with different lipid oxidation properties. The presented methods are suitable techniques for the detection of initial changes of lipid oxidation progress in edible oils.Abbreviations: AHC, agglomerative hierarchical cluster analysis; AV, anisidine value; FID, flame ionization detector; GC, gas chromatography; HORO, high-oleic rapeseed oil; HS-SPME, headspace solid-phase microextraction; LOD, limit of detection; LOQ, limit of quantification; PCA, principal component analysis; PV, peroxide value; RO, rapeseed oil Eur.

In the present study, 122 food samples from the German food market were analysed for their C18:1 trans fatty acid (TFA) content and profile. A particular focus of the survey were baked and fried foods. TFA analysis was performed by means of silver ion SPE (Ag+‐SPE) in combination with high‐resolution GC (HRGC‐FID). Overall, 51 bakery product samples were analysed of which 25 samples were prepacked bakery products purchased from local retail stores and 26 samples of unpacked bakery products purchased from local bakery shops. In addition, 14 French fries samples obtained from small local fast food restaurants as well as from internationally operating fast food chains, 27 potato and tortillas chips, 15 instant soups as well as 15 dry culinary sauces were analysed. The highest amounts of C18:1 TFA isomers were found in deep‐fried bakery products. Prepacked branded cookies and biscuits on the other hand contained only negligible C18:1 TFA amounts. Regarding their C18:1 trans isomer profile most deep‐fried bakery products exhibited a Gaussian‐distributed isomer profile. The analysed prepacked croissants, cookies and biscuits contained predominantly ruminant TFA (TFA) as suggested by the presence of vaccenic acid (C18:1 trans 11), which was the major C18:1 TFA isomer in these products. All non‐bakery samples (n = 71) contained less than 3 g C18:1 TFA per 100 g fat. In conclusion, TFA still occur in considerable amounts in a few German food products, especially in some deep‐fried bakery products (‘Berliner’ type of doughnuts). Practical applications: Trans fatty acids, in particular the trans octadecenoic fatty acid isomers (C18:1), are generally considered from the nutritional point of view as undesirable food components due to their negative health effects. Tremendous efforts have been made by major food processors in order to decrease or even eliminate the presence of TFA in some foodstuffs (e.g. in margarines in European countries). However, some food processors of other food sectors are still applying oils and fats containing partially hydrogenated vegetable oils, whereas others within the same food category have already switched their processing conditions and/or raw materials towards TFA alternatives. Therefore, actual TFA data of foodstuffs determined by means of state‐of‐the‐art analytical procedures (Ag+‐SPE in combination with GC‐FID) is necessary to detect areas of further improvement in the food supply chain and to provide data for an update of dietary TFA intake.

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