Trap GC-MS Research Articles

Acetylcholinesterase (AChE) Reversible Inhibitors: The Role of Oxamyl in the Production of Poisoned Baits

Oxamyl is a highly toxic carbamate molecule with toxicological risk from contamination, used as an insecticide, nematicide, and acaricide on many field crops, vegetables, fruits, and ornamentals. Suspected poisoned animals and baits were collected between January 2018 and August 2021 from Lombardy and Emilia-Romagna regions and analyzed at the chemical toxicology laboratory of the Experimental Zooprophylactic Institute of Lombardy and Emilia-Romagna, located in Brescia. The analyses were carried out by an ion trap GC-MS system in 2467 suspected samples and showed the presence of oxamyl in 67 of these. In this study, we analyzed 47 (out of 67) positive baits: the provinces in which more cases have been recorded are Mantua, Ferrara, and Cremona, which overall had 72% of positivity. The nature of the analyzed samples was mostly corn (55.3%), followed by bird carcasses (19.1%), apples (14.8%), meatballs (2.1%), bread (2.1%), and other (8.5%). The use of oxamyl to produce poisoned baits is constantly increasing, proving that it must be considered as a public health risk for the possible consequences on target and non-target organisms, including humans.

Characteristics of Volatile Organic Compounds Pollution and Risk Assessment of Nansi Lake in Huaihe River Basin

This study aimed to investigate the pollution characteristics of the volatile organic compounds in Nansi Lake and evaluate the ecological and health risks. In November 2017, water samples collected from 25 sampling points in Nansi Lake using the purge and trap technique and GC-MS detected 52 types of VOCs. The detection rate of ethylbenzene, m-/p-xylene, o-xylene, 1,2-dichlorobenzene, and naphthalene reached 100%, and cis-1,3-dichloropropene and toluene reached 96%. The detection rate of 1,2,4-trimethyl benzene was the lowest, at only 12%, the average concentration of 1,2-dichlorobenzene was the highest, reaching 3.49 μg·L-1, and 1,2,4-trimethyl benzene was only 0.02 μg·L-1. The concentration of 1,2-dichlorobenzene in Nansi Lake was generally higher than that of other VOCs. Meanwhile, the concentrations of m-/p-xylene and ethylbenzene at point NSH-24 far exceeded the other VOCs, but the median value of all VOCs did not exceed 4 μg·L-1. The spatial distribution of the VOCs concentrations in Nansi Lake presented high values in the northwest and southeast, and low in the middle. The leading cause of VOCs pollution in Nansi Lake may be the exhaust gas emitted by shipping vessels during navigation, and the secondary cause is the collection of VOCs in the upstream and downstream tributaries and the influence of human factors. The health risk assessment of Nansi Lake found that, overall, there was no carcinogenic or non-carcinogenic health risk, but the risk value of individual points was relatively high, even exceeding the risk threshold set by the US EPA. There were 12 points in Nansi Lake where the ecological risk quotient exceeded 1, indicating an ecological risk to aquatic organisms.

GC-MS fragmentation patterns of sprayed endosulfan and its sulphate metabolite in samples of Theobroma cacao L from a field kinetic study.

Most environmental analytical methods for the determination of organochlorine pesticides (OCPs) are multi-residual with other organic compounds co-extracted and co-eluted. This has been observed in GC spectra using classical detectors like electron-capture detector (ECD) even after appropriate clean-up. This limitation could be resolved by using GC-MS methods which are more specific and selective. Thus, a commercial-grade endosulfan treated Theobroma cacao plantation was sampled. Representative samples comprising leaves, stem bark and pulp were obtained between 0.5 h and 60 days after treatment. Samples were analyzed for residual parent endosulfan (α- and β-isomers) as well as the metabolite endosulfan sulphate using an ion trap GC-MS. The retention times and chromatogram peaks obtained for various endosulfan were identified and compared with reference standards, and confirmed with National Institute of Standards and Technology library. Results showed that the molecular ion at m/z 407 was exhibited by α- and β-endosulfan, representing the parent molecular ion M+• ([C9H6Cl6SO3]+•). The α-isomer was more thermally stable, hence exhibited more relative abundance. Other predominant peaks were 339, 307, 277, 265, 243, 241, 207, 195, 160, 159, 99 and 75 m/z. The peak at m/z 159 was the base molecular ion. For endosulfan sulphate, the peak at m/z 422 corresponded to parent molecular ion (M+•), while m/z 424 was due to isotopic pattern characteristic of the chlorine atom. The peaks at 387, 357, 289, 272, 229, 206, 170, and 120 m/z were characteristic for the sulphate metabolite. The m/z peak at 272 was the base molecular ion, while m/z 143 may be due to metabolite diol and lactone. These results showed that the various endosulfan species can be identified and confirmed simultaneously using a GC-MS.

Technical Note: A fully automated purge and trap GC-MS system for quantification of volatile organic compound (VOC) fluxes between the ocean and atmosphere

Abstract. The oceans are a key source of a number of atmospherically important volatile gases. The accurate and robust determination of trace gases in seawater is a significant analytical challenge, requiring reproducible and ideally automated sample handling, a high efficiency of seawater–air transfer, removal of water vapour from the sample stream, and high sensitivity and selectivity of the analysis. Here we describe a system that was developed for the fully automated analysis of dissolved very short-lived halogenated species (VSLS) sampled from an under-way seawater supply. The system can also be used for semi-automated batch sampling from Niskin bottles filled during CTD (conductivity, temperature, depth) profiles. The essential components comprise a bespoke, automated purge and trap (AutoP & T) unit coupled to a commercial thermal desorption and gas chromatograph mass spectrometer (TD-GC-MS). The AutoP & T system has completed five research cruises, from the tropics to the poles, and collected over 2500 oceanic samples to date. It is able to quantify >25 species over a boiling point range of 34–180 °C with Henry's law coefficients of 0.018 and greater (CH22l, kHcc dimensionless gas/aqueous) and has been used to measure organic sulfurs, hydrocarbons, halocarbons and terpenes. In the eastern tropical Pacific, the high sensitivity and sampling frequency provided new information regarding the distribution of VSLS, including novel measurements of a photolytically driven diurnal cycle of CH22l within the surface ocean water.

Organochlorine pesticide residues: An extensive monitoring of Italian fishery and aquaculture

A sampling campaign from 21 sites in Italy was carried out to investigate the presence of organochlorine pesticide residues in different fish species. Samples came from marine fishery and either from sea- or freshwater aquaculture. Fish feed used in some fish farms were also analyzed. Pesticides studied belong to Persistent Organic Pollutants widely used in the past such as DDT, chlordane, heptachlor, and others. To ensure good quality results and proper data validation the main existing guidelines in the field were applied. The instrumental technique was a Dual column–Dual detector Gas Chromatography (GC–ECD and Ion Trap GC–MS) which allowed that complementary data on the same sample were acquired. Results for fishery showed a wide range of concentrations depending from the area and species examined. DDT, the major OC pesticide detected, varied from 0.02 to 130.03ngg−1 edible portion. As regards the products of aquaculture we observed slightly lower average levels of pollutants in a more narrow range of concentration: this is probably due to fish feed used as shown by some measures performed in the present study. Organochlorine pesticide residues were detected in all samples examined but they were generally well below the existing tolerance or action levels. Also the estimated daily intakes are well below than those recommended by WHO. This is a good indication about OCPs in the areas investigated but some further considerations on fish safety must be taken into account. An example on how fishes may act as bioindicators is reported.

A new purge and trap headspace technique to analyze low volatile compounds from fluid inclusions of rocks and minerals

A new method for the analysis of trace gases from fluid inclusions of minerals has been developed. The purge and trap GC–MS system is based on the system described by Nolting et al. (1988) and was optimized for the analyses of halogenated volatile organic compounds (VOCs) having boiling points as low as −128°C (carbon tetrafluoride).The sample preconcentration cold trap consists of a U-shaped glass lined steel tube (GLT™), that is immersed into a small liquid nitrogen Dewar vessel for cooling. A rapid desorption step heats up the preconcentration tube in <30s from −196°C to 200°C. The process is carried out by using a pressurized air stream to dissipate the liquid nitrogen followed by resistive heating of the trap. The design of the cold trap and the direct transfer of desorbed analytes onto the GC column via a deactivated capillary column retention gap made sample refocusing within the GC oven unnecessary. Furthermore, a special air-tight grinding device was developed in which samples ranging from soft halite (hardness 2, Mohs scale) to hard quartz (hardness 7) are effectively ground to average diameters of 1000nm or below, thereby releasing gases from fluid inclusions of minerals. The gases are then purged from the grinding chamber with a He carrier gas flow. The detection and quantitative determination of gases, such as SF6 and CF4 released from fluorites and CH3Cl from halite samples is demonstrated.

Biosynthesis, isolation, and NMR analysis of leukotriene A epoxides: substrate chirality as a determinant of the cis or trans epoxide configuration

Leukotriene (LT)A₄ and closely related allylic epoxides are pivotal intermediates in lipoxygenase (LOX) pathways to bioactive lipid mediators that include the leukotrienes, lipoxins, eoxins, resolvins, and protectins. Although the structure and stereochemistry of the 5-LOX product LTA₄ is established through comparison to synthetic standards, this is the exception, and none of these highly unstable epoxides has been analyzed in detail from enzymatic synthesis. Understanding of the mechanistic basis of the cis or trans epoxide configuration is also limited. To address these issues, we developed methods involving biphasic reaction conditions for the LOX-catalyzed synthesis of LTA epoxides in quantities sufficient for NMR analysis. As proof of concept, human 15-LOX-1 was shown to convert 15S-hydroperoxy-eicosatetraenoic acid (15S-HPETE) to the LTA analog 14S,15S-trans-epoxy-eicosa-5Z,8Z,10E,12E-tetraenoate, confirming the proposed structure of eoxin A₄. Using this methodology we then showed that recombinant Arabidopsis AtLOX1, an arachidonate 5-LOX, converts 5S-HPETE to the trans epoxide LTA₄ and converts 5R-HPETE to the cis epoxide 5-epi-LTA₄, establishing substrate chirality as a determinant of the cis or trans epoxide configuration. The results are reconciled with a mechanism based on a dual role of the LOX nonheme iron in LTA epoxide biosynthesis, providing a rational basis for understanding the stereochemistry of LTA epoxide intermediates in LOX-catalyzed transformations.

Application of semi-permeable membrane dialysis/ion trap mass spectrometry technique to determine polybrominated diphenyl ethers and polychlorinated biphenyls in milk fat

Polychlorinated biphenyls (PCBs) and polybrominated diphenyl ethers (PBDEs) are hazardous food contaminants, their maximum legally allowable levels in food and environment are in the low pgg−1 range. Therefore some highly selective and sensitive analytical methods must be used to determine them. The 96/23/EC Directive implemented by EC Decision of 12 August 2002 requires recovery rate of an analyte at a concentration below 1ngg−1 within the 50–120% range at relative standard deviation (RSD) as low as possible.A method to determine low level PCBs and PBDEs in milk fat based on the semi-permeable membrane dialysis/ion trap GC MS technique was developed. Validation experiments proved that the method performance was within bounds set by the currently standing UE regulations. Recovery rates calculated on the basis of labeled internal standards for majority of the studied indicator PCB congeners and PBDE congeners were close to 100% at RSD below 20%. Also, dioxin-like PCBs recovery rates were compatible with the 1883/2006 EC Regulation (80–120%, RSD below 15%).The developed method turned out to be linear within a far broader concentration range than the studied 0.0025–10pgμL−1 range entirely sufficient for analyses of PCB and PBDE in milk fat. Within that range coefficient of linear correlation (R2) of calibration curves exceeded 0.98.

Potential Occurrence of MTBE and BTEX in Groundwater Resources of Amman–Zarqa Basin, Jordan

AbstractThis study investigates potential occurrence, distribution, and sources of the newly added gasoline oxygenate, methyl‐tert‐butyl ether (MTBE) and the petroleum derivatives benzene, toluene, ethylbenzene, and xylenes called collectively, BTEX, in Jordan's heavily populated Amman–Zarqa Basin (AZB). It presents the first data on the levels of MTBE and BTEX in the aquifers of this basin. One hundred and seventy‐nine (179) groundwater wells were sampled near petrol service stations, oil refinery storage tanks, car wrecks, bus stations, and chemical industries at different locations in the basin. Headspace GC and purge and trap GC–MS were utilized to determine the target substances in the samples. Concentrations of BTEX varied between no‐detection (minimum) for all of them to 6.6 µg/L (maximum) for ethylbenzene. MTBE was found in few samples but none has exceeded the regulated levels; its concentrations ranged between no‐detection to 4.1 µg/L. However, though the contamination levels are very low they should be considered alarming.

GC-MSによる芋焼酎揮発性硫黄化合物の測定とガス臭物質の特定

Volatile sulfuric compounds such as hydrogen sulfide were thought to be the source of off-flavor be-cause a sulfur-like odor was detected from just distilled sweet potato shochu. A highly sensitive purge and cold trap GC-MS method equipped with an ethanol removal system to analyze volatile sulfuric compounds was developed to demonstrate the above idea. Unblended sweet potato shochu A which exuded a strong off-flavor was analyzed with this method and the concentrations of hydrogen sulfide, methyl mercaptan, dimethyl sulfide, and dimethy disulfide were 0.10mg/L, 0.070mg/L, 0006mg/L, and 0.002mg/L respectively. It was confirmed that the hydrogen sulfide and methyl mercaptan having strong off-flavors were detected at higher concentrations compared to the other two sulfuric compounds.In order to confirm that the off-flavor is caused by hydrogen sulfide and methyl mercaptan, the column（φ14mm × 40mm）of copper balls（φ1 ∼ 2mm）was used to remove these two volatile sulfuric compounds. A total of 4000mL of unblended sweet potato shochu B which exuded a very strong off-flavor was passed through the column at a flow speed of 20mL/minute. It was found that hydrogen sulfide and methyl mercaptan were eliminated completely by the column and the off-flavor also disappeared at the same time. Hydrogen sulfide and methyl mercaptan were confirmed as the sources of the off-flavor.

Ethylene Glycol and Glycolic Acid in Postmortem Blood from Fatal Poisonings

Ethylene glycol (EG), a relatively infrequent cause of fatal intoxication, presents an analytical challenge for forensic confirmation in postmortem toxicology. We report EG and glycolic acid (GA) quantification in postmortem blood by gas chromatography coupled with ion trap mass spectrometry (GC-MS) analysis using a modification of a previously reported clinical method. The method is linear from 50 to 4000 mg/L with a limit of detection of 25 mg/L for both EG and GA. Interassay coefficient of variation (2.1-8.6%, 4.3-6.0%) and accuracy (96-101%, 92-105%) were determined for EG and GA, respectively. EG concentration by ion trap GC-MS correlated closely (R(2) = 0.995) with EG quantified by GC-flame-ionization detection. Analysis of blood from 20 autopsies with no evidence of EG exposure did not reveal detectable EG or GA. In 12 medical examiner cases with EG poisoning as cause of death, EG concentrations ranged widely from 58 to 7790 mg/L with a mean of 1830 mg/L, and the GA concentration averaged 1360 mg/L with a narrower range of 810-1770 mg/L. EG and GA levels correlate poorly (R(2) = 0.15) in postmortem blood with discordantly low EG concentrations in two cases. Birefringent oxylate crystals in renal tissue was a consistent finding. In conclusion, a sensitive and specific GC-MS method for detection and quantification of EG and GA has been validated and a study of fatal EG poisonings revealed forensic application of the method.

Measurement of volatile organic compounds in bottled and tap waters by purge and trap GC–MS: Are drinking water types different?

Volatile organic compounds (VOCs) including major trihalomethanes (THMs) in bottled and tap waters from Central Missouri were quantified and compared with drinking water guidelines. Tap ( n = 34), spring (3 brands, n = 25), purified (8 brands, n = 58), distilled (3 brands, n = 12) and flavored waters (5 brands, n = 34) along with Missouri River water ( n = 30), were analyzed by purge and trap gas chromatograph–mass spectrometry (GC–MS) using USEPA method 524.2. The mean recoveries of the internal and surrogates standards were fluorobenzene: 100%, benzene d5-, chloro: 100% and 1,4-dichlorobenzene d4: 96%. Approximately 97% of all drinking water types were found to be safe for human consumption. However, two tap water samples recorded bromodichloromethane concentrations above the 60 μg/L World Health Organization (WHO) limit. Moreover, six tap water samples exceeded both the 80 μg/L USEPA Stage I limit and the 100 μg/L European Community (EC) maximum contaminant concentration (MAC) for total THMs (TTHMs) in drinking water. TTHMs in the water types ranged from 0–322 μg/L (tap), 0.1–0.3 μg/L (spring), 0–7.6 μg/L (purified), 0.1–18.1 μg/L (distilled), and 0–5.7 μg/L (flavored). Kruskal–Wallis Chi square approximation showed significant differences ( P < 0.001) in the levels of THMs found in the water types. Principal components (PC1 and PC2) with 97% total variance suggested similarities in most drinking waters except for Boonville and Columbia tap waters. Dendrogram plots of TTHMs and Σ VOCs revealed two principal clusters with Columbia and Boonville tap waters in a different cluster and also distant from other water types.

Monitoring changes in the volatile profile of cheese crackers during storage using GC–MS and PTR–MS

AbstractThe primary objective of this work was to determine the feasibility of using PTR–MS ion profiles to monitor changes in the volatile profile of cheese crackers during storage. This was done by obtaining PTR–MS ion profiles of cheese crackers during the early shelf‐life of the product (first 4 months of storage) and comparing these data to those obtained using a more traditional approach, i.e. purge and trap–GC–MS (PT–GC–MS). The PTR–MS profile of the samples was monitored for 47 ion masses, mainly corresponding to low molecular weight compounds or fragments of low mass. From the application of multivariate statistical analysis (cluster analysis, PCA, ANOVA) to the PTR–MS data of the samples of different storage times, it was shown that the age of the sample was an important factor for their classification. It was possible to differentiate two main groups of samples, the first group included samples of age &lt;3 months (1, 1.5 and 2 months). This group had low ion intensities relative to the second group. The second group comprised samples of age ≥3 months (3 and 4 months) that showed higher ion intensities. PT–GC–MS data on the same samples found 38 volatile compounds, primarily aldehydes, that increased during storage. A good correlation was found between changes in some PTR–MS masses and major volatile compounds of crackers. The compounds that increased were generally products of autoxidation. It appears that a PTR–MS could be a useful tool for monitoring volatile changes during storage in cheese crackers. Copyright © 2009 John Wiley &amp; Sons, Ltd.

On-Line Purge and Trap GC-MS for Monitoring 1,3-Dichloropropene in Agricultural Water and Soil Samples

A simple and reliable method using on-line purge and trap gas chromatography mass spectrometry has been developed for the determination of the fumigant 1,3-dichloropropene (1,3-DCP) in agricultural water and soil samples. The proposed analytical methodology was validated in the target environmental matrices by the analysis of spiked blank matrix samples. Limit of detection values of 0.05 microg/L for water and 0.005 microg/Kg for soils were obtained, while limits of quantitation were of 0.1 microg/L for water and 0.01 mg/kg for soils. Good recoveries (93-104%) and precision values (< 6%) were obtained for the target compound in the studied matrices. This methodology has been successfully applied to the analysis of incurred groundwater samples from an agricultural area, The Campo de Dalías (Almería, South Spain), although 1,3-DCP was not detected. The method was also applied to soil samples from greenhouse treated with a soil fumigant containing 1,3-DCP.

Halogenated solvent interactions with N, N-dimethyltryptamine: Formation of quaternary ammonium salts and their artificially induced rearrangements during analysis

The psychoactive properties of N, N-dimethyltryptamine (DMT) 1a are known to induce altered states of consciousness in humans. This particular attribute attracts great interest from a variety of scientific and also clandestine communities. Our recent research has confirmed that DMT reacts with dichloromethane (DCM), either as a result of work-up or storage to give a quaternary N-chloromethyl ammonium salt 2a. Furthermore, this was observed to undergo rearrangement during analysis using gas chromatography–mass spectrometry (GC–MS) with products including 3-(2-chloroethyl)indole 3 and 2-methyltetrahydro-β-carboline 4 (2-Me-THBC). This study further investigates this so far unexplored area of solvent interactions by the exposure of DMT to other halogenated solvents including dibromomethane and 1,2-dichloroethane (DCE). The N-bromomethyl- and N-chloroethyl quaternary ammonium derivatives were subsequently characterised by ion trap GC–MS in electron and chemical ionisation tandem MS mode and by NMR spectroscopy. The DCE-derived derivative formed at least six rearrangement products in the total ion chromatogram. Identification of mass spectrometry generated by-products was verified by conventional or microwave-accelerated synthesis. The use of deuterated DCM and deuterated DMT 1b provided insights into the mechanism of the rearrangements. The presence of potentially characteristic marker molecules may allow the identification of solvents used during the manufacture of controlled substances, which is often neglected since these are considered inert.

Determination of Methylmercury in Biological Samples Using Dithizone Extraction Method Followed by Purge & Trap GC-MS

In this study, a dithizone extraction technique involving purge & trap GC-MS was developed for the determination of methylmercury in biological samples, especially blood and fish. After alkaline digestion, methylmercury in biological samples was extracted into dithizone and back-extracted into aqueous sulfide solution. The extracted methylmercury was converted to the volatile ethyl derivative, purged and trapped onto a solid-phase collection medium, and then introduced into the GC-MS system. The determined MDLs of the established method were 0.9 ng·g?1 for biological samples and its accuracy and precision were found to be 93% and 3.8%, respectively. The method was validated by analysis of CRMs such as SRM 966, BCR 463 and IAEA 407 and all analytical results were within certified ranges with average RSDs of less than 6%. The analytical results of field-sampled fish also showed that the method can be successfully used as an alternative for commonly used distillation method followed by GC-CVAFS detection.

Laboratory Generated Bitumen Fumes Under Standardized Conditions. Clean-up Scheme and Ion Trap GC-MS Analysis of VOC, Semi-Volatile and Particulate PAH and PASH

This article reports the applicability of an efficient clean-up and enrichment procedure for the determination of polycyclic aromatic compounds (PAC) including polycyclic aromatic hydrocarbons (PAH) and polycyclic aromatic sulfur heterocyclic hydrocarbons (PASH) in the gas and particulate phases in raw bitumen and bitumen fumes by gas chromatography-ion trap mass spectrometry. The scheme includes a liquid-liquid partition to eliminate the aliphatics, a solid phase extraction on SiO2 cartridge to remove the polar compounds and an HPLC fractionation to isolate the aromatic fraction. The purified extract enables the determination of PAH profile from 2 to 7 rings including their methyl derivatives and 3 carcinogenic benzonaphthothiophene isomers. The reproducibility of the method was estimated by analyzing 6 bitumen replicates and is around the 30% overall uncertainty or less. In bitumen fumes generated at 170°C under standardized conditions, VOC and semi-volatile PAH were sampled with XAD-2 tubes and were also determined in six replicates. The VOCs are mainly monoaromatic derivatives (4% of fumes) and aliphatics essentially from C6 to C17 (27%). With regards to the particulate phase PAC, the coefficients of variation from 6 replicates are 5–24% for PAH and 6–10% for PASH. Data on VOC and PASH represent new contribution in the characterization of bitumen fumes.

Aerobic degradation of methyl tert-butyl ether by a Proteobacteria strain in a closed culture system

The contamination of methyl tert-butyl ether (MTBE) in underground waters has become a widely concerned problem all over the world. In this study, a novel closed culture system with oxygen supplied by H 2O 2 was introduced for MTBE aerobic biodegradation. After 7 d, almost all MTBE was degraded by a pure culture, a member of β- Proteobacteria named as PM1, in a closed system with oxygen supply, while only 40% MTBE was degraded in one without oxygen supply. Dissolved oxygen (DO) levels of the broth in closed systems respectively with and without H 2O 2 were about 5-6 and 4 mg/L. Higher DO may improve the activity of monooxygemase, which is the key enzyme of metabolic pathway from MTBE to tert-butyl alcohol and finally to CO 2, and may result in the increase of the degrading activity of PM1 cell. The purge and trap GC-MS result of the broth in closed systems showed that tert-butyl alcohol, isopronol and acetone were the main intermediate products.

Evolution of the volatile components of ewes raw milk Zamorano cheese. Seasonal variation

The evolution during ripening and the seasonal variation of the volatile fraction of Zamorano cheeses were studied by using purge and trap extraction and GC-MS analysis. Concentrations of acetaldehyde, propanal and branched chain aldehydes, 2-methyl ketones, higher molecular weight alcohols, and most esters increased significantly with ripening time. Branched chain aldehydes were more abundant in spring and winter cheeses. 2-Heptanone showed lower concentrations in autumn cheeses, opposite to 2,3-butanedione and 2,3-pentanedione. Alcohols were in general lower in autumn cheeses, except ethanol and 2-propenol, which were lower in summer cheeses. Methyl-, propyl- and 2-butyl esters were in general less abundant in autumn cheeses. Discriminant analysis classified correctly 90% of the cheeses for the season of manufacture and 100% of the cheeses for the dairy of origin. Principal component analysis showed a positive correlation between odour intensity, aroma intensity, pungent taste and branched chain aldehydes, phenyl acetaldehyde and acetophenone. Odour and aroma qualities were negatively correlated with branched chain alcohols, butyl acetate and 2-butyl acetate.

Evolution of the volatile components of raw ewes’ milk Castellano cheese: seasonal variation

Abstract Fifteen batches of Castellano cheese were made in different seasons of the year from raw ewes’ milk without the addition of starter cultures. The volatile fraction of the cheeses, its evolution during ripening and the seasonal differences were studied by using purge and trap extraction and GC-MS analysis. Concentrations of aldehydes such as 2-propenal, hexanal and 2-methyl-1-butanal, 1- and 2-alkanols, 2-alkenols, and most classes of esters increased significantly with ripening time, while that of 2,3-butanedione decreased from 60 to 180 d. Branched chain aldehydes were more abundant in cheeses made in summer. 2-Propenal and 2-methyl ketones were more abundant in 180-d-old cheeses made in autumn. Alcohols were quantitatively the main chemical class found in the volatile fraction of Castellano cheese. Primary alcohol concentrations were significantly higher and 2-butanol significantly lower in autumn cheeses. α-Pinene, toluene and 3-methyl-1-heptene concentrations were higher in summer cheeses. Discriminant analysis classified all the cheeses at 60 and 180 d of ripening correctly for the season of manufacture. Principal component analysis showed a positive correlation between 2-methyl-ketones, 2-pentanol and 2-propanol with the Micrococcaceae counts at 60 d, and the gram-negative bacteria and coliform counts in 1-d-old-cheese. Ethyl esters and ethanol correlated positively with lactic acid bacteria counts and odour quality.