Analysis of target volatile compounds related to fishy off‐flavor in heated rapeseed oil: A comparative study of different headspace techniques

Abstract

Off‐flavors, characterized by a fishy odor, are emitted during the heating of rapeseed oil in a fryer. In order to study the headspace composition of degraded rapeseed oil, and more specifically the compounds responsible for the fishy odor, four headspace techniques were evaluated: Static headspace (SHS), headspace trap (HS Trap), headspace solid phase microextraction (HS‐SPME), and headspace sorptive extraction (HSSE) coupled to gas chromatography‐mass spectrometry (GC‐MS). The selected model compounds to develop the headspace methods were 1‐penten‐3‐one, 1‐octen‐3‐one, and E,Z‐2,6‐nonadienal as known fishy odor markers. Extraction conditions for the four techniques were optimized and evaluated in terms of repeatability and sensitivity. They were then applied to the analysis of real samples of degraded rapeseed oil. SHS was not suitable for the analysis of odorant volatile compounds because of LOD values lower than those required for a quantitative analysis of the target compounds. Concerning HS‐SPME and HSSE, a discrimination against the more volatile compounds was observed. Finally, HS Trap‐GC‐MS was considered the most appropriate technique for the analysis of the headspace of rapeseed oil in this study with LOD values less than 2 μg/L for the three target compounds. More than 60 compounds were identified by HS Trap‐GC‐MS and two compounds responsible for the fishy odor could be detected. The evolution of the relative areas of these compounds was reported for fresh oil and rapeseed oil degraded by 1, 5, and 10 heating cycles. Practical applications: The characterization of the volatile compounds responsible for the fishy odor is a key industrial issue. Moreover, the developed method with HS‐Trap could be used to quantify several volatile compounds characteristic of the degradation of rapeseed oil, and to evaluate the possible effect of antioxidants on oils. Rapeseed oil is edible oil containing a substantial amount of omega 3, but the heating of this oil leads to the formation of off‐flavors, characterized by a fishy odor. The characterization of these off‐flavors is a key industrial issue, and different headspace techniques can be considered to study the molecules present in the headspace of degraded rapeseed oil.

Validation of a headspace trap gas chromatography and mass spectrometry method for the quantitative analysis of volatile compounds from degraded rapeseed oil

“…Considering the variability of the method, these results highlighted a concentration almost constant between 1 and 15 heating cycles. These results confirmed the observations described in a previous study [15]. They were formed at the first heating cycle and in significant amounts.…”

“…The LOQ values were between 0.2 mg/L, for 1‐penten‐3‐one, and 1.4 mg/L, for nonanal. The LOQ of 1‐penten‐3‐one was higher than that estimated during the development of the method and this result was due to the nonlinearity of the area versus concentration. The LOQ of ( E )‐2‐heptenal, hexanal, and nonanal were of the same order of magnitude than those obtained in another study using HS‐SPME–GC–FID .…”

Comparative Fingerprint Changes of Toxic Volatiles in Low PUFA Vegetable Oils Under Deep‐Frying

“…3. In general, regardless of oil type, these results were consistent with other studies which applied frying temperatures, even after a short time [2,13,17,[33][34][35][36][37][38][39]. An ability to induce toxicological effects has been attributed to these [36] being therefore the ones that require more attention from the safety point of view.…”

Coconut oil as a calibration matrix for headspace gas chromatographic determination of hexanal in edible oils

“…Edible oils are important components of human diet as they provide energy, are a source of essential fatty acids and other minor but very important constituents, such as sterols, carotenoids, tocopherols and others [1]. However, during storage and especially during heating, unsaturated fatty acids of edible oils undergo oxidation [2,3]. As a consequence, hydroperoxides are formed.…”

“…As a consequence, hydroperoxides are formed. Subsequently they decompose to volatile secondary oxidation products such as alkanes, alkenes, aldehydes, ketones, alcohols, esters, acids and hydrocarbons [2,4]. Oxidation has a great impact on the quality of food products be-cause of off-flavours, of a decrease in the nutritional properties and especially because of the formation of toxic compounds.…”