Metabolic fingerprinting of hard and semi-hard natural cheeses using gas chromatography with flame ionization detector for practical sensory prediction modeling

Metabolic fingerprinting using gas chromatography with flame ionization detector (GC/FID) was used to generate a practical metabolomics-based tool for quality evaluation of natural cheese. Hydrophilic low molecular weight components, relating to sensory characteristics, including amino acids, fatty acids, amines, organic acids, and saccharides, were extracted and derivatized prior to the analysis. Data on 12 cheeses, six Cheddar cheeses and six Gouda cheeses, were analyzed by multivariate analysis. Prediction models for two sensory attributes relating to maturation, "Rich flavor" and "Sour flavor", were constructed with 4199 data points from GC/FID, and excellent predictability was validated. Chromatograms from GC/FID and gas chromatography/time-of-flight-mass spectrometry (GC/TOF-MS) were comparable when the same column was used. Although GC/FID alone cannot identify peaks, the mutually complementary relationship between GC/FID and GC/MS does allow peak identification. Compounds contributing significantly to the sensory predictive models included lactose, succinic acid, l-lactic acid, and aspartic acid for "Rich flavor", and?lactose, l-lactic acid, and succinic acid for "Sour flavor". Since similar model precision was obtained using GC/FID and GC/TOF-MS, metabolic fingerprinting using GC/FID, which is a relatively inexpensive instrument compared with GC/MS, is easy to maintain and operate, and is a valid alternative when metabolomics (especially using GC/MS) is to be used in a practical setting as a novel quality evaluation tool for manufacturing processes or final products.     

Determination of phthalates in raw bovine milk by gas chromatography/time-of-flight mass spectrometry (GC/TOF-MS) and dietary intakes

Low levels of phthalates, including di(2-ethylhexyl) phthalate (DEHP), in raw bovine milk were determined using gas chromatography/time-of-flight mass spectrometry (GC/TOF-MS). A fast and convenient process of sample treatment combined with TOF-MS analysis (medium resolution >5000), yielded good recoveries (85–125%) and low limits of detection (<0.002 mg kg^?1). The most commonly used phthalate, DEHP, was found in 15 out of 30 samples monitored in this study. DEHP concentrations in raw milk ranged from not detected to 0.154 mg kg^?1, and the mean concentration was 0.057 mg kg^?1. The dietary intake of DEHP was about 0.004 mg kg^?1 body weight day^?1 if a child (24 months, 13 kg body weight) drinks 1 L day^?1 of milk that contains the mean concentration of DEHP found in raw milk. The estimated dietary intake corresponded to 8% of the European Union tolerable daily intake (TDI) of 0.05 mg kg^?1 body weight day^?1. Dimethyl phthalate (DMP) and di-n-butyl phthalate (DBP) were found from two and 20 samples, respectively, at low levels. Diethyl phthalate (DEP), butylbenzyl phthalate (BBP), and di-n-octyl phthalate (DnOP) were not found in any of the samples.     

Endogenous steroid profiling by gas chromatography-tandem mass spectrometry and multivariate statistics for the detection of natural hormone abuse in cattle

For years it has been suspected that natural hormones are illegally used as growth promoters in cattle in the European Union. Unfortunately there is a lack of methods and criteria that can be used to detect the abuse of natural hormones and distinguish treated from non-treated animals. Pattern recognition of steroid profiles is a promising approach for tracing/detecting the abuse of natural hormones administered to cattle. Traditionally steroids are analysed in urine as free steroid after deconjugation of the glucuronide (and sulphate) conjugates. The disadvantage of this deconjugation is that valuable information about the steroid profile in the sample is lost. In this study we develop a method to analyse steroids at very low concentration levels (ng l^?1) for the free steroid, glucuronide and sulphate conjugates in urine samples. This method was used to determine concentrations of natural (pro)hormones in a large population (n?=?620) of samples from male and female bovine animals and from bovine animals treated with testosterone-cypionate, estradiol-benzoate, dihydroepiandrosterone and pregnenolone. The data acquired were used to build a statistical model applying the multivariate technique ‘Soft Independent Modeling of Class Analogy’ (SIMCA). It is demonstrated that by using this model the results of the urine analysis can indicate which animal may have had illegal treatment with natural (pro)hormones.     

Gas chromatography-mass spectrometry based metabolic profiling for the identification of discrimination markers of Angelicae Radix and its application to gas chromatography-flame ionization detector system

Gas chromatography (GC)-based metabolomics technologies were applied for quality control of Angelicae Radix, an herbal medicine commonly used in Japan and China. Since Angelica roots are priced and graded differently based on their species and cultivation area, there is a need for a simple and reproducible method to discriminate Angelica roots. Here, we used GC-MS profiling data to construct a discrimination method for species and cultivation area of A. Radix. Seventy-six primary metabolites were identified. The quality factors of A. Radix were successfully classified using metabolic profiling and the orthogonal projections to latent structures-discriminant analysis (OPLS-DA) technique. Sorbitol and a glucose/4-aminobutyric acid combination were chosen as bio-markers from S-plot of OPLS-DA. Application of these selected bio-markers to a more practical and cost-efficient system, namely gas chromatography-flame ionization detector (GC-FID) system were also assessed. As a result, the same separations of sorbitol, glucose and 4-aminobutyric acid in box plots were obtained from GC-FID data. Our results demonstrate that GC-based metabolic markers can be readily applied for the establishment of a practical quality control method for A. Radix.     

Metabolite profiling of Cheonggukjang, a fermented soybean paste,during fermentation by gas chromatography-mass spectrometry and principal component analysis

Metabolite profiling by applying principal component analysis (PCA) to a GC–MS data set was performed to assess changes in a select number of pre-defined metabolites during the fermentation of Cheonggukjang. A total of 20 amino acids, 12 organic acids, and nine fatty acids were found as targeted metabolites in Cheonggukjang. As fermentation proceeded, the levels of most amino acids decreased during the early stage of fermentation, but increased in the later part of fermentation. On the other hand, amounts of fatty acids increased throughout the fermentation process, while those of most organic acids, except for tartaric acid, decreased. A PCA score plot illustrated good separation of the Cheonggukjang samples according to fermentation period by combining principal component 1 (PC 1) (36.8%) with PC 2 (30.3%). Tryptophan, citric acid, β-alanine, itaconic acid, 2-hydroxyglutaric acid, γ-aminobutyric acid, leucine, malic acid, and tartaric acid were the major components that differentiated the various samples.     

Differentiation of volatile aroma components in organically and conventionally produced apples by stir bar sorptive extraction combined with gas chromatography and EI/CI TOF mass spectrometry

Volatile aroma components and contents of organically and conventionally produced apples of the cultivars Elstar, Jonagold, Jonagored and Braeburn were studied. In three cultivars investigated, the aroma contents of organically produced apples were significantly lower (Elstar 16%, Jonagold 29%, Jonagored 68%). For Braeburn, no statistically significant difference was observed. In particular, the main aroma components were present at much lower concentrations in organically produced apples. In all apple cultivars, these were hexanal, trans-2-hexenal, 2-methylbutylacetate and hexylacetate. twenty-three aroma components were identified in total, in different relative ratios in the different apple cultivars: saturated esters, saturated and unsaturated aldehydes and alcohols. Some components identified in the conventionally produced cultivars were not present in the organically produced cultivars at all. The aroma components were extracted from juice freshly prepared from the apples by stir bar sorptive extraction (SBSE) technique and characterised by FID gas chromatography and EI/CI TOF mass spectrometry.     

Headspace solid-phase microextraction and gas chromatography/ion trap-mass spectrometry applied to a living system: Pieris brassicae fed with kale

The influence of Pieris brassicae feeding on kale was monitored, by evaluating its effect on the volatiles released by the plant through time. This is the first study applying headspace solid-phase microextraction (HS-SPME) and gas chromatography/ion trap-mass spectrometry to an isolated insect, as most studies analyse the insect–plant system as a whole, being unable to evaluate the contribution of the insect itself. Substantial differences were noticed between the volatiles composition of kale before and after the insect’s attack. More than 60 compounds were found, including terpenes, lipoxygenase pathway by-products, ketones, norisoprenoids, etc. After insect attack, l-camphor, sabinene and α-thujene were found and limonene and eucalyptol suffered a noticeable increase. A considerable rise in (Z)-3-hexenyl acetate was also observed. In vivo accumulation of limonene and camphor by the insect was detected. The findings contribute to the knowledge of the ecological interactions between the two species.     

Analysis of vinylidene chloride and 1-chlorobutane in foods packaged with polyvinylidene chloride casing films by headspace gas chromatography/mass spectrometry (GC/MS)

A headspace gas chromatography/mass spectrometry method was developed for the simultaneous determination of vinylidene chloride and 1-chlorobutane in foods packaged with polyvinylidene chloride casing films. The solid foodstuff was homogenized with an equal mass of distilled water. The homogenate was incubated for 1 h at 90°C in a sealed headspace vial, and the headspace gas was then analysed by gas chromatography/mass spectrometry in selected ion-monitoring mode using a bonded porous polymer-coated capillary column. The recovery rates of vinylidene chloride and 1-chlorobutane in foodstuffs were 94.5-103.9 and 85.8-120.3%, respectively. Among 13 samples tested, vinylidene chloride was detected at 0.001-0.020 µg g^-1 in 11 foodstuffs, and 1-chlorobutane was detected at 0.004-0.040 µg g^-1 in all 13 foodstuffs. Furthermore, vinylidene chloride was detected at 0.04 µg g^-1 in one casing film, and 1-chlorobutane was detected in all casing films. The results indicate that these compounds migrated from the casing films into the foodstuffs.     

Rice vinegars of different origins: discriminative characteristics based on solid‐phase microextraction and gas chromatography with mass spectrometry,an electronic nose,electronic tongue and sensory evaluation

Eight kinds of commercial rice vinegars from Korea, China and Japan were selected to evaluate their flavour‐related discriminative characteristics based on solid‐phase microextraction and gas chromatography with mass spectrometry (SPME/GC–MS), an electronic nose (e‐nose), electronic tongue (e‐tongue) and subjective sensory evaluation. Principal component analysis patterns based on SPME/GC–MS provided a clear categorical discrimination among the vinegars of three origins. The distribution patterns of the samples were similar between SPME/GC–MS and e‐nose analyses and Korean vinegars were clearly discriminated. A high correlation coefficient was determined between SPME/GC–MS and e‐nose on acetaldehyde (0.948) and diacetyl (0.970). e‐Tongue‐based principal component analysis patterns were subdivided into three regions according to the origin, and Chinese vinegars were clearly discriminated. Sensory panelists recorded origin‐specific scores on flavours for all the samples. In conclusion, SPME/GC–MS, e‐nose and e‐tongue analyses may be useful for discrimination of flavour profiles of rice vinegars of different producer origin. Copyright © 2017 The Institute of Brewing & Distilling     

Multiresidue method for the determination of 77 pesticides in wine using QuEChERS sample preparation and gas chromatography with mass spectrometry

A method based on a QuEChERS (quick, easy, cheap, effective, rugged, safe) sample preparation method and gas chromatography with mass spectrometric detection by selected ion monitoring (GC/MS-SIM) was developed for simultaneous determination of 77 pesticide residues in wine. An extraction of 10 ml of sample with acetonitrile followed by liquid–liquid partition formed by the addition of 4 g MgSO₄ and 3 g NaCl was applied in the sample preparation. The clean-up was carried out by applying dispersive solid-phase with 150 mg MgSO₄ as well as 50 mg primary secondary amine (PSA). One quantitation ion and at least two identification ions were selected in the analytical method for each pesticide compound by GC/MS. The recovery data were obtained by spiking blank samples at two concentration levels (0.05 and 0.2 mg l^?1). The recoveries of all pesticides were in the range 70–110%, with intra-day precision of less than 15%, and the inter-day precision of less than 22% and 15% for 0.05 and 0.2 mg l^?1 fortification levels, respectively. Linearity was between 0.02 and 2 mg l^?1 with determination coefficients (R ²) greater than 0.98 for all compounds. The limits of quantification (LOQs) for the 77 pesticides ranged from 0.003 to 0.05 mg l^?1. This method was applied for routine analysis in market products.