Till Goldmann

Rapid determination of furan in heated foodstuffs by isotope dilution solid phase micro-extraction-gas chromatography – mass spectrometry (SPME-GC-MS)

An analytical method is reported to determine trace amounts of furan in several different commercial foodstuffs that are subjected to thermal treatment. The SPME-GC-MS method is rapid and robust, and entails the following steps: addition of deuterated furan to the sample, sodium chloride-assisted extraction into the headspace, cryofocussing, and finally fibre desorption and GC-MS analysis. Furan is quantified by the use of an external calibration curve, achieving a decision limit (CC alpha) and detection capability (CC beta) of 17 pg and 43 pg, respectively, as absolute furan concentration in a 10 ml headspace vial. The method is applicable to a wide variety of foods, including fruits juices, baby foods in jars, canned foods, pet food, coffee and coffee substitutes. Typical amounts of furan found in selected foodstuffs range from about 1 microg kg(-1) (fruit juice) to 110 microg kg(-1) (baby food containing cooked vegetables). In-house validation data show good precision and accuracy of the method, with a typical repeatability of between 5 and 16% in different food matrices, and trueness determined in orange juice and coffee as 87 and 93%, respectively. Moreover, the measurement uncertainty has been evaluated for two matrices (fruit juice and coffee). Studies on short-term stability of furan in certain foods are also presented, and show that the furan content decreases in food while heating for preparation or reconstitution.

Comparison of indirect and direct quantification of esters of monochloropropanediol in vegetable oil

The presence of fatty acid esters of monochloropropanediol (MEs) in food is a recent concern raised due to the carcinogenicity of their hydrolysable moieties 2- and 3-monochloropropanediol (2- and 3-MCPD). Several indirect methods for the quantification of MEs have been developed and are commonly in use until today, however significant discrepancies among analytical results obtained are challenging their reliability. The aim of the present study was therefore to test the trueness of an indirect method by comparing it to a newly developed direct method using palm oil and palm olein as examples. The indirect method was based on ester cleavage under acidic conditions, derivatization of the liberated 2- and 3-MCPD with heptafluorobutyryl imidazole and GC-MS determination. The direct method was comprised of two extraction procedures targeting 2-and 3-MCPD mono esters (co-extracting as well glycidyl esters) by the use of double solid phase extraction (SPE), and 2- and 3-MCPD di-esters by the use of silica gel column, respectively. Detection was carried out by liquid chromatography coupled to time of flight mass spectrometry (LC-ToF-MS). Accurate quantification of the intact compounds was assured by means of matrix matched standard addition on extracts. Analysis of 22 palm oil and 7 palm olein samples (2- plus 3-MCPD contamination ranged from 0.3 to 8.8 μg/g) by both methods revealed no significant bias. Both methods were therefore considered as comparable in terms of results; however the indirect method was shown to require less analytical standards, being less tedious and furthermore applicable to all type of different vegetable oils and hence recommended for routine application.

Mechanisms of Acrylamide Formation

The formation of acrylamide (AA) from L-asparagine was studied in Maillard model systems under pyrolysis conditions. While the early Maillard intermediate N-glucosylasparagine generated ∼2.4 mmol/mol AA, the Amadori compound was a less efficient precursor (0.1 mmol/mol). Reaction with α-dicarbonyls resulted in relatively low AA amounts (0.2–0.5 mmol/mol), suggesting that the Strecker aldehyde pathway is of limited relevance. Similarly, the Strecker alcohol 3-hydroxypropanamide generated low amounts of AA (0.2 mmol/mol). On the other hand, hydroxyacetone afforded more than 4 mmol/mol AA, indicating that α-hydroxycarbonyls are more efficient than α-dicarbonyls in transforming asparagine into AA. The experimental results are consistent with the reaction mechanism proposed, i.e. (i) Streckertype degradation of the Schiff base leading to azomethine ylides, followed by (ii) β-elimination of the decarboxylated Amadori compound to release AA, The functional group in β-position on both sides of the nitrogen atom is crucial. Rearrangement of the azomethine ylide to the decarboxylated Amadori compound is the key step, which is favored if the carbonyl moiety contains a hydroxyl group in β-position to the N-atom. The β-elimination step in the amino acid moiety was demonstrated by reacting under pyrolysis conditions decarboxylated model Amadori compounds obtained by synthesis.

Direct determination of recombinant bovine somatotropin in plasma from a treated goat by liquid chromatography/high‐resolution mass spectrometry

Recombinant bovine somatotropin (rbST) is used in dairy cattle to enhance milk production. Despite the ban on this hormone in some countries, especially in Europe, there is so far no method available for the direct detection of rbST either in milk or in plasma. An analytical strategy has been developed to analyze rbST in plasma, including a purification procedure based on a precipitation with ammonium sulphate, followed by a solid-phase extraction (SPE)-based clean-up on C4 sorbent and precipitation with cold methanol. The hormone was then digested with trypsin and analyzed by liquid chromatography/high-resolution mass spectrometry (LC/HRMSn) on a linear ion trap coupled with an Orbitrap. The tryptic N-terminal peptide, specific to the difference between the endogenous and recombinant form of the somatotropin, was fragmented and product ions were analyzed at high mass resolution. Applying this approach to goat plasma allowed the direct detection of 10 ng mL(-1) of rbST in fortified samples. It also showed the presence of rbST in plasma collected from a goat treated with the hormone, even 2 days after administration. These results are of a great interest in the field of somatotropin control and undoubtedly constitute a first step in the development of a method for the detection of rbST not only in bovine plasma, but also in other biological matrices such as milk.

Determination of Seven Glycidyl Esters in Edible Oils by Gel Permeation Chromatography Extraction and Liquid Chromatography Coupled to Mass Spectrometry Detection

A method based on a gel permeation chromatography (GPC) extraction procedure combined with an additional cleanup by solid-phase extraction (SPE) on silica gel and liquid chromatography-mass spectrometry (LC-MS) detection has been validated for the analysis of seven glycidyl esters (GEs) including glycidyl laurate, myristate, palmitate, stearate, oleate, linoleate, and linolenate in various edible oils. This method was conjointly developed and validated by two different laboratories, using two different detection systems, a LC time of flight MS (LC-ToF-MS) and a LC triple-quadrupole MS (LC-MS/MS). The extraction procedure allowed targeting low contamination levels due to a highly efficient matrix removal from the 400 mg oil sample loaded on the GPC column and is suitable for routine analysis as 24 samples can be extracted in an automated and reproducible way every 12 h. GPC extraction combined with SPE cleanup and LC-MS/MS detection leads to a limit of quantification in oil samples between 50 and 100 μg/kg depending on the type of glycidyl ester. Recoveries ranged from 68 to 111% (average = 93%). Quantification was performed by automated standard addition on extracts to compensate matrix effects artifacts. To control recoveries of each sample four isotopically labeled GEs ((13)C(3) or (13)C(4)) were included in the method.

Impact of extraction conditions on the content of acrylamide in model systems and food.

It has recently been suggested that the analytical methods that have been developed to date for the determination of acrylamide (AA) may underestimate the concentration of AA in certain foods, because significantly higher results were obtained upon extraction of the food matrix under alkaline conditions. The present study employs food (potato, rye) and chemical model systems to better understand the tentative release of AA under high pH extraction conditions. The experimental design is based on the generation of AA in an environment containing an AA-isotopomer, and by comparing the ratio of AA, respectively the AA-isotopomer, after extraction at pHs 7 and 12. The results show that the additional AA released is not due to improved extractability of AA from the food matrix, and should therefore be regarded as an extraction artefact. Strongly alkaline conditions seem to induce net formation of AA from water-soluble precursors formed during thermolysis.

Formation of styrene during the Maillard reaction is negligible.

The elucidation of chemical pathways and the identification of intermediates leading to vinylogous compounds such as acrylamide by the Maillard reaction have proven challenging. This study was conducted to assess the formation of styrene from L-phenylalanine, employing binary mixtures of the amino acid heated together with simple C3-sugar analogue (1-hydroxyacetone) or methylglyoxal. The formation of the corresponding vinylogous product, i.e. styrene, was measured under different moisture, pH, and temperature conditions. The formation of intermediates over time was monitored by gas chromatography-mass spectrometry (GC-MS) and liquid chromatography-mass spectrometry (LC-MS) together with the target compound styrene. Two intermediates, i.e. 1-phenethylaminopropan-2-one and 2-phenylethylamine, play a role in the formation of styrene, the latter of more importance in high-moisture systems, whilst the former favours the release of styrene in low-moisture systems. The model further showed that Strecker-type reactions are of less importance in the formation of styrene, as the yield from single immediate precursors was maximally 0.03 mol%. The low conversion rate of L-phenylalanine to the vinylogous product and existing data on the occurrence of free L-phenylalanine in food plants suggests that the amounts of styrene expected in foods subjected to thermal treatment are negligible.

Chapter 20 Acrylamide, Chloropropanols and Chloropropanol Esters, Furan

Publisher Summary This chapter provides background and analytical considerations of acrylamide, chloropropanols and chloroesters, and furan. The analytical tools at the disposal of food analysts and chemists have evolved considerably over the past few decades. Progress has been made in the development of confirmatory techniques, based on mass spectrometry (MS), that enable detection limits in complex food matrices of basically any single compound (polar or nonpolar) in the low part-per-billion range. Extraction and clean-up techniques have also improved, but they are clearly adapted to the performance of the analytical detection system. The harmonization of validation approaches, the establishment of interlaboratory performance schemes, the availability of centralized databases that allow comparison of data have contributed positively to better and more reliable methods being developed and published at an exponential rate. The chapter highlights the proficiency tests of these compounds. In the past years, several proficiency tests for acryamide, chloropropanols and chloroesters, and furan in foods have been conducted.