Accurate determination of hexanal in beef bouillons by headspace solid‐phase microextraction gas‐chromatography mass‐spectrometry

Lipid oxidation has great impact on the quality of food products through flavor and taste deterioration, reduction in nutritive value, and potential toxicity of the oxidized food components. Flavor and taste deterioration can be easily perceived and it represents one of the major causes of consumer complaints in the food industry. The deterioration of sensory properties is due to the decomposition products of hydroperoxides that easily isomerize and degrade into volatile compounds. Volatile products are responsible for flavor and taste deterioration. In this study, we present the development of the solid‐phase microextraction gas chromatography‐mass spectrometry (SPME‐GC‐MS) technique to quantify low amounts (μg/g range) of secondary oxidation products, i.e. hexanal. The optimization of SPME parameters is a difficult task because of the possibility of further formation of volatile products during analysis. Different parameters such as type of fiber, exposure time of the fiber to the sample headspace and the optimal temperature of absorption have also been investigated. The complete validation of the method was achieved by the determination of linearity, limits of detection and quantification and repeatability. We demonstrated that the SPME method is a valuable tool for the quantification of low amounts of secondary oxidation products such as hexanal. Therefore, this technique can be used to detect early formation of volatiles.     

Solid‐phase microextraction (SPME) in polymer characterization—Long‐term properties and quality control of polymeric materials

Solid‐phase microextraction (SPME) in combination with GG‐MS was applied to quality control polyamide 6.6 collected for recycling and to study the long‐term properties and degradation of nitrile rubber, polyethylene, and polyamide 6.6. The migration of plasticizer and other additives reduces the service‐life and changes the properties of the material. It is also a possible health hazard, for example, legislation against the use of brominated flame retardants in plastic materials, is under discussion, and fast and reliable methods are required to detect such compounds in plastic materials collected for recycling. SPME rapidly and effectively extracted several brominated compounds from in‐plant collected polyamide 6.6. Migration of tris(2‐butoxyethyl)phosphate plasticizer and its degradation products from nitrile rubber during long‐term thermal ageing at 60 and 80°C was shown by SPME‐GC‐MS, while the plasticizer was not volatile enough to be detected by traditional HS‐GC‐MS. In accordance the number of degradation products extracted from thermo‐oxidized PE by HS‐SPME was three times larger than the number detected after HS‐GC‐MS analysis. SPME‐GC‐MS could also detect early signs of degradation in thermo‐oxidized virgin and in‐plant recycled polyamide 6.6 before any signs of degradation were observed by, for example, tensile testing or FTIR. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 867–873, 2003     

Fish oil sensory properties can be predicted using key oxidative volatiles

The high level of PUFA in fish oil, primarily eicosapentaenoic acid (EPA) and DHA result in rapid oxidation of the oil. Current methods used to assess oxidation have little correlation with sensory properties of fish oils. Here we describe an alternative method using solid phase microextraction (SPME) combined with GC‐MS to monitor volatile oxidation products. Stepwise discriminant function analysis (DFA) was used to classify oils characterized as acceptable or unacceptable based on sensory analysis; a cross‐validated success rate of 100% was achieved with the function. The classification function was also successfully validated with tasted samples that were not used to create the method. A total of 14 variables, primarily aldehydes and ketones, were identified as significant discriminators in the classification function. This method will be useful as a quality control method for fish oil manufacturers. Practical applications: This paper describes an analytical method that can be used by fish oil manufacturers for quality control purposes. Solid phase microextraction and GC‐MS were used to monitor volatile oxidation products in fish oil. These data, combined with results of analyses by a sensory panel, were used to create a function that classified fish oil samples as acceptable or unacceptable. The volatile oxidation products used to in the function were primarily aldehydes and ketones. This method can be used by fish oil manufacturers as an alternative to expensive sensory panels.     

Headspace solid‐phase microextraction with gas chromatography/mass spectrometry reveals a correlation between the degradation product pattern and changes in the mechanical properties during the thermooxidation of in‐plant recycled polyamide 6,6

The increased susceptibility of in‐plant recycled polyamide 6,6 toward thermooxidation was shown by headspace solid‐phase microextraction with gas chromatography/mass spectrometry (HS‐SPME/GC‐MS), tensile testing, differential scanning calorimetry (DSC), and Fourier transform infrared spectroscopy (FTIR). A correlation between the deterioration in mechanical properties and the formation of degradation products due to thermooxidation was found, and the most prominent decrease in mechanical properties coincided with the largest increase in the abundance of degradation products. The recycled materials had a shorter induction period toward oxidation, and their mechanical properties deteriorated faster than the mechanical properties of virgin material. The same trend was observed with HS‐SPME/GC‐MS because degradation products were found for recycled materials after oxidation times shorter than those for virgin material. Furthermore, larger amounts of degradation products were formed in the recycled materials. The high sensitivity of HS‐SPME/GC‐MS as an analytical tool was demonstrated because it was able to detect changes caused by oxidation considerably earlier than the other methods. Unlike DSC and FTIR, it could also show differences between samples recycled for different times. Four groups of degradation products—cyclic imides, pyridines, chain fragments, and cyclopentanones—were identified in thermooxidized polyamide 6,6. After 1200 h of thermooxidation, 1‐pentyl‐2,5‐pyrrolidinedione was the most abundant degradation product. Approximately four times more 1‐pentyl‐2,5‐pyrrolidinedione was formed in polyamide recycled three times than in virgin polyamide. Pyridines and chain fragments behaved toward oxidation and repeated processing like cyclic imides; that is, their amounts increased during oxidation, and larger amounts were formed in recycled materials than in virgin material. The cyclopentanone derivatives were present already in unaged material, and their amounts decreased during oxidation. Cyclopentanones were not formed because of the thermooxidation of polyamide 6,6. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 3396–3407, 2002     

Characterization of virgin olive oil from Southern Tunisia

Fruits from three Tunisian cultivars of Olea europea L. grown in the southeast of Tunisia were harvested at the maturity stage of ripeness and immediately processed with a laboratory mill. There are as yet no data on the chemical composition of virgin olive oils from the southeast of Tunisia, an area characterized by an arid condition of growth for olive trees. Our results showed significant differences in the analytical parameters examined for the three cultivars such as fatty acid composition, total phenols and o‐diphenols, and the content of chlorophylls and carotenoids, confirming the importance of genetic factors in the chemical characteristics of the oil. Headspace solid‐phase microextraction (HS‐SPME) was applied to the analysis of volatile compounds of virgin olive oils. Forty‐eight compounds were isolated and characterized by GC‐RI and GC‐MS, representing 94.1–98.1% of the total amount. (E)‐Hex‐2‐enal, the main compound extracted by SPME, characterized the olive oil headspace for all samples. So, it was clearly shown that there were qualitative and quantitative differences in the proportion of volatile constituents from oils of the various cultivars.     

Photoinduced and thermal oxidation of rapeseed and sunflower oils

The aim of the present study was to compare oxidative stability of different sunflower and rapeseed oils. Ultra violet (UV) irradiation was used as an accelerator of the oil oxidation process. After UV irradiation, the formed volatile compounds were extracted by headspace solid‐phase microextraction HS‐SPME (DVB/CAR/PDMS fibre) and analysed by gas chromatography coupled with a flame ionization detector (GC/FID). At the same time, the same oil samples were thermally oxidized. The induction periods were determined on the basis of hexanal to 2‐trans‐nonenal ratio in the analysed samples. Finally, the obtained results were compared with induction period values obtained through the determination of peroxide and anisidine values, and from the Rancimat method, manostatic test and differential scanning calorimetry (DSC) method. The results obtained using the new method were well correlated with those achieved with the well‐established analytical techniques. The values of the induction period obtained after UV/HS‐SPME/GC/FID were up to three times higher than those from Rancimat, but the correlation between these two methods was on a very good level (correlation coefficient R>0.98). Similar correlation was also observed between these new methods and the DSC or manostatic test. In all cases, better results were obtained for rapeseed oils than sunflower oils.     

Determination of Aroma Profiles of Olive Oils from Turkish Olive Cultivars

This study analyzed volatile aromatic compounds present in the oils of Turkish olive cultivars. The cultivars Gemlik, Ayval?k, Memecik, Domat, Uslu, Halhal?, Kilis ya?l?k, Nizip ya?l?k, Ha?ebi and Karamani were harvested from important Turkish olive‐growing locations, such as Bal?kesir, Bursa, Manisa, Ayd?n, Mu?la, ?zmir, Kilis, Mersin, Hatay and Gaziantep during the 2007–2008 and 2008–2009 growing seasons. Olive samples were collected in two harvest years, at almost the same maturity stage, and processed under the same conditions. Headspace solid‐phase microextraction (HS‐SPME) was used to analyze volatile aroma compounds in the olive oil samples. Forty‐seven compounds were characterized and quantified using gas chromatography‐mass spectrometry/flame ionization detector (GC–MS/FID). The most abundant identified compounds were trans‐2‐hexenal, hexanal and 3‐methyl‐1‐butanol. The trans‐2‐hexenal, hexanal and 3‐methyl‐1‐butanol contents of oil samples varied between 0.86–67.15, 3.93–61.82 and 0.48–84.74 %, respectively.     

A new analytical method to monitor lipid peroxidation during bleaching

Whereas solid phase microextraction (SPME) combined with gas chromatography is a wide‐spread technique in certain fields of food analysis this technique is quite new for the analysis of vegetable oils. The method is sensitive enough to follow changes in the oxidative state of vegetable oils by measuring the amount of volatile materials produced during storage and the refining process. In the present study degummed rapeseed oil was bleached using different activated bleaching earths applied in four dosages. Their effect on lipid degradation was determined both by traditional methods (e.g. UV absorbance, p‐anisidine value) and by the SPME‐HS method. Although the p‐anisidine value (p‐AV) gives only the concentration of β‐unsaturated aldehydes it correlates well to the amount of total volatile substances as determined by SPME at the headspace of the sample. The extracted volatile materials were separated and identified by gas chromatography combined with mass spectrometry. SPME gives more information about the stage of oxidation and the applied bleaching earth by quantifying the volatile compounds. Additionally SPME does not require any toxic reagent such as p‐methoxy aniline which is used to determine the p‐AV. Although bleaching is very important it was disregarded in recent years. Therefore one of the aims of the present study is to draw back more attention towards bleaching.     

Changes in Volatile Compounds of Black Cumin Oil and Hazelnut Oil by Microwave Heating Process

Black cumin and hazelnut oils were subjected to a heating process in a microwave oven for a duration of 2, 4, 6 and 8 min at a constant frequency of 2450 MHz and a power of 0.45 kW. The ultraviolet absorption and volatile products of the oils were investigated in detail during the processes. The experimental evidences obtained show that K₂₃₂ and K₂₇₀ parameters reach values of 4.69 and 1.30 for black cumin oil, 3.22 and 1.75 for hazelnut oil, respectively with the increment of heating time. The headspace SPME method was used to analyze volatile compounds extracted from black cumin and hazelnut oils being exposed to the microwave heating process. The SPME–GC/MS method allowed the detection of 17 identified volatile compounds (hexanal, α‐thujene, α‐pinene, sabinene, β‐pinene, 2‐heptenal, α‐terpinene, limonene, p‐cymene, γ‐terpinene, E‐2‐octenal, nonanal, 4‐terpineol, thymoquinone, E,E‐2,4‐decadienal, α‐longipinene and isolongifolene) in black cumin oils. Of the products, hexanal, 2‐heptenal, E‐2‐octenal, nonanal and E,E‐2,4‐decadienal were determined to be the predominant volatile oxidation products. In fact, the hexanal was found as a major volatile oxidation compound and reached a local maximum point of 7.41 × 10⁶ AU at the end of heating. On the other hand, only 8 volatile oxidation products (hexanal, heptanal, 2‐heptenal, nonanal, E‐2‐decenal, E,Z‐2,4‐decadienal, E,E‐2,4‐decadienal and E‐2‐tridecenal) were identified in hazelnut oils as a consequence of the heating process. Based on the experimental evidence observed, it is reasonable to conclude that the nonanal content dramatically increased at the end of heating and reached a value of 9.22 × 10⁶ AU.     

On‐line biodegradation monitoring of nitrogen‐containing compounds by membrane inlet mass spectrometry

Membrane inlet mass spectrometry (MIMS) has been developed for the on‐line monitoring of compounds in a continuous stirred tank bioreactor (CSTB) used to simulate a wastewater treatment plant (WWTP). A mixture of four industrially relevant nitrogen‐containing volatile and semi‐volatile compounds was fed to a 3 dm³ CSTB with a hydraulic retention time (HRT) of 24 h. In‐membrane preconcentration/thermal desorption was used for the on‐line monitoring of semi‐volatile compounds (n‐methylpyrrolidinone and tetramethylethylenediamine), while volatile organic compounds (3‐bromopyridine and 2‐chloro‐5‐trifluoromethylaniline) were determined by continuous infusion through the membrane. Quantification of the four compounds was achieved by MS. The CSTB was run for 160 h and, after reaching steady state, n‐methylpyrrolidinone showed removal to levels below the limit of detection, while there was partial biodegradation of 2‐chloro‐5‐trifluoromethylaniline and 3‐bromopyridine. There was no evidence of significant biodegradation for tetramethylethylenediamine. Intermediates in the metabolite pathways of 2‐chloro‐5‐trifluoromethylaniline and 3‐bromopyridine were identified by MIMS, gas chromatography/mass spectrometry (GC/MS) or liquid chromatography/mass spectrometry (LC/MS). COD was measured off line, and results agreed well with MIMS, although COD data did not provide information on the removal of the individual compounds. Copyright © 2003 Society of Chemical Industry     

Volatile compounds of original African black and white shea butter from Tchad and Cameroon

Shea butter is used as an edible vegetable fat in many African countries. It can be utilized as a substitute or complete replacement for cocoa butter in various applications and plays an important role in traditional African medicinal practice. Although detection of volatile compounds by solid‐phase micro‐extraction gas‐chromatography mass‐spectroscopy (SPME‐GC‐MS) is a very reliable and reproducible technique, which can be used as an important part of authenticity checking, production monitoring and contamination detection, no published data about volatile compounds of shea butter are available so far. In this investigation, the characteristic volatiles in the headspace of original African shea butter samples were identified by using SPME‐capillary‐GC coupled to a mass selective detector. Almost 100 different volatile components were identified, e.g. fatty acids, saturated and unsaturated aldehydes and ketones, terpenes, and typical Maillard reaction products such as methylfuranes and pyrazines. Furthermore, the samples have been olfactorily evaluated by a panel of professional flavorists and trained analytical chemists. It can be stated that variations in processing conditions of shea butter result in considerable differences in the composition of headspace volatiles, detected by SPME‐GC‐MS and human olfaction.     

Volatile compounds and triacylglycerol composition of original Indian fatty plant oils

Some typical original Indian edible and non‐edible fatty plant oils were subject of our investigations. Fundamental research was done on analyzing volatile compounds using HS‐SPME‐GC‐MS. In addition, a sensorial evaluation was applied to receive data on the smell of the samples. Furthermore, the typical and prevailing triacylglycerols (TAG) were investigated by MALDI‐TOF‐MS. Mass spectra reflect the TAG profiles of the whole oil samples based on the detection of [M+Na]⁺ ions. Oil samples exhibit quite unique TAG profiles, which are suitable for rapid characterization of the original plant oils. The fatty acid composition of the corresponding TAG structures was calculated using lipid analysis software based on the known fatty acid composition. Relative quantification of TAG components was in good agreement with the literature, in case appropriate data are available so far.     

Comparison of two methods for extraction of volatiles from marine PL emulsions

The dynamic headspace (DHS) thermal desorption principle using Tenax GR tube, as well as the solid phase micro‐extraction (SPME) tool with carboxen/polydimethylsiloxane 50/30 µm CAR/PDMS SPME fiber, both coupled to GC/MS were implemented for the isolation and identification of both lipid and Strecker derived volatiles in marine phospholipids (PL) emulsions. Comparison of volatile extraction efficiency was made between the methods. For marine PL emulsions with a highly complex composition of volatiles headspace, a fiber saturation problem was encountered when using CAR/PDMS‐SPME for volatiles analysis. However, the CAR/PDMS‐SPME technique was efficient for lipid oxidation analysis in emulsions of less complex headspace. The SPME method extracted volatiles of lower molecular weights more efficient than the DHS method. On the other hand, DHS Tenax GR appeared to be more efficient in extracting volatiles of higher molecular weights and it provided a broader volatile spectrum for marine PL emulsion than the CAR/PDMS‐SPME method.     

Influence of Fat and Emulsifier Content on Volatile Release of Butter Aroma Used in Water Phase and Physical Attributes of Model Margarines

Margarines are water‐in‐oil (W/O) emulsion‐type products produced with butter aroma. The aim of this study is to investigate the volatile release of the butter aroma compounds used in the water phase of model margarine and sensory properties influenced by the change of fat and emulsifier. A headspace/solid phase microextraction/gas chromatography/mass spectrometry (HS/SPME/GC/MS) system is used for the identification of the volatile compounds. It is determined that high fat content in model margarine samples results in an increase in the release of both 2,3‐butandione and butanoic acid. On the other hand, an increase in fat content reduces the release of butanoic acid ethyl ester and vanillin. In addition, an increase in the emulsifier content of the model margarines results in a decrease in butanoic acid ethyl ester release. The model margarines with 80% fat content have the highest hardness and storage modulus (G′) values. The perception of butter aroma and taste are more intense in high‐fat margarine samples, while fruity aroma and taste, vanilla aroma, and taste perception are higher in low‐fat margarine samples. However, emulsifier content does not affect the sensory properties of the model margarines. Practical Applications: Decreasing high fat content food intake has become increasingly popular among consumers. Thus, in order to meet consumer demands, manufacturers have begun to reduce the fat content of the foods they produce. However, the flavor properties of a product can change as a consequence of fat content reduction. In order to produce a product in accordance with the properties demanded by the consumer, the change in the flavor of that product should be foreseen depending on the change in fat content. This study aimed to determine the volatile compound release and sensory properties of margarine samples due to fat and emulsifier changes. The findings of this study are a guide for the production of low‐fat products.     

Monitoring of headspace volatiles in milk‐cereal‐based liquid infant foods during storage

The effect of storage (time and temperature) on the evolution of pentanal, hexanal, heptanal and pentane as volatile lipid oxidation products in two liquid ready‐to‐eat milk‐cereal‐based infant foods was studied. An SPME‐GC method was used to this effect. Samples were stored for 9 months at 25, 30 and 37 °C and tested eight times during this period. Freshly produced infant foods contained pentanal, hexanal and heptanal (mean values: 10.71, 71.5 and 1.2 µg/kg, respectively), which decreased during the first 3 months of storage, although from the fourth month onwards no significant differences among storage times were found. Aldehyde content was inversely proportional to storage temperature. Pentane content was directly proportional to storage temperature and increased (19.9 µg/kg at zero time) over all months of storage up to 43.1 µg/kg.     

Effect of cultivation area and climatic conditions on volatiles of virgin olive oil

To elucidate the influence of the cultivation area and climatic conditions on volatiles of virgin olive oil from Gemlik cultivar, an investigation was carried out. Five Turkish geographical zones (Bal?kesir, Ayd?n, Manisa, Antalya and Hatay) were chosen. From these areas, fruits were collected at the same maturity stage and processed using a small experimental olive oil mill, applying identical processing conditions for all olive samples. Headspace solid‐phase microextraction (HS‐SPME) technique coupled to GC/MS was used for volatile analysis. Twenty‐seven compounds were identified and characterised, representing 96.40–98.74% of the total GC area. The major volatile representing about 50% was the (E)‐2‐hexenal. This compound was found in higher concentrations on olive oils from Antalya than from Hatay area. Hexanal was the second most abundant volatile compound and varied between 13.89 and 28.96%. Comparing the olive growing areas Hatay and Antalya, the hexanal concentration was about 29 and 14%, respectively. Generally, a significant difference in the composition of volatile compounds between the oils from the same olive cultivar and from different geographic regions was recorded. The results suggest that climatic factors, latitude and longitude affect the formation of volatiles.     

Oxidative Stability and Changes in Chemical Composition of Extra Virgin Olive Oils After Short‐Term Deep‐Frying of French Fries

We aimed at investigating oxidative stability and changes in fatty acid and tocopherol composition of extra virgin olive oil (EVOO) in comparison with refined seed oils during short‐term deep‐frying of French fries, and changes in the composition of the French fries deep‐fried in EVOO. EVOO samples from Spain, Brazil, and Portugal, and refined seed oils of soybean and sunflower were studied. Oil samples were used for deep‐frying of French fries at 180 °C, for up to 75 min of successive frying. Tocopherol and fatty acid composition were determined in fresh and spent vegetable oils. Tocopherol, fatty acid, and volatile composition (by SPME–GC–MS) were also determined in French fries deep‐fried in EVOO. Oil oxidation was monitored by peroxide, acid, and p‐anisidine values, and by Rancimat after deep‐frying. Differential scanning calorimetry (DSC) analysis was used as a proxy of the quality of the spent oils. EVOOs presented the lowest degree of oleic and linoleic acids losses, low formation of free fatty acids and carbonyl compounds, and were highly stable after deep‐frying. In addition, oleic acid, tocopherols, and flavor compounds were transferred from EVOO into the French fries. In conclusion, EVOOs were more stable than refined seed oils during short‐term deep‐frying of French fries and also contributed to enhance the nutritional value, and possibly improve the flavor, of the fries prepared in EVOO.     

Anaerobic lipoxygenase activity from Chlorella pyrenoidosa responsible for the cleavage of the 13‐hydroperoxides of linoleic and linolenic acids

An enzyme from the alga Chlorella pyrenoidosa, previously identified as a hydroperoxide lyase (HPLS), cleaves the 13‐hydroperoxide derivatives of linoleic and linolenic acids into a volatile C5 fragment and a C13 oxo‐product, 13‐oxo‐9(Z),11(E)tridecadienoic acid (13‐OTA). Gas chromatography/mass spectrometry (GC/MS) headspace analysis of the volatile products indicated the formation of pentane when the substrate was the 13‐hydroperoxide derivative of linoleic acid, whereas a more complex mixture of hydrocarbons was formed when the 13‐hydroperoxide derivative of linolenic acid was the substrate. Analysis of the nonvolatile products by GC/MS and liquid chromatography/mass spectrometry (LC/MS) indicated the formation of 13‐OTA along with the 13‐ketone derivative. This enzymatic activity was inhibited by oxygen but was restored with nitrogen. The enzymatic cleavage activity was coincidental in purified fractions with lipoxygenase activity that produced the 13‐ and 9‐hydroperoxide derivatives of linolenic acid. The results suggest that the enzymatic cleavage activity in Chlorella pyrenoidosa was not a consequence of hydroperoxide lyase activity as previously thought, but was due to anaerobic lipoxygenase activity. This enzyme fraction was purified by (NH₄)₂ SO₄ precipitation, gel filtration, and hydrophobic interaction chromatography. The purified enzyme has an approximate MW of 120 KDa and maximum activity at pH 8.0.     

Determination of Origin of Commercial Flavored Rapeseed Oil by the Pattern of Volatile Compounds Obtained via GC–MS and Flash GC Electronic Nose

Flavored rapeseed oil (FRO) is a typical hot‐pressed oil and is widely consumed in China due to its strong characteristic flavor and intensive color. In this study, volatile profiles of 33 representative commercial rapeseed oils in China are characterized by gas chromatography‐mass spectrometry (GC‐MS) and flash gas chromatography (GC) electronic nose system. 51 volatile compounds are identified and the nitriles (methallyl cyanide and 5‐cyano‐1‐pentene), aldehydes (nonanal, 3‐furaldehyde, and 5‐methyl‐2‐furancarboxaldehyde), alcohols (1,5‐hexadien‐3‐ol, 2‐furanmethanol, and phenylethyl alcohol), and pyrazines (2,5‐dimethyl‐pyrazine and 2,6‐dimethyl‐pyrazine) are the major volatile compounds in FROs. Glucosinolate degradation products account for the highest proportion of these volatiles, which are found to have a positive correlation with the erucic acid content (R² = 0.796, p < 0.01). FRO from Sichuan province in the southwest of China can be characterized by the obvious distinctions in flash GC electronic nose combined with principal component analysis, which indicates that the flash GC electronic nose can be used as a promising method to identify the origins of FRO. Practical Applications: This work is helpful for expanding the knowledge of volatiles of commercial flavored rapeseed oil. The data can also serve as a basis for the quality assessment of hot‐pressed rapeseed oil. Meanwhile, the flash GC electronic nose combined with principal component analysis can be used as a promising method for the classification of flavor rapeseed oil production areas.