Study of light-induced volatile compounds in goat's milk cheese

Light-induced volatile compounds in goat cheese were studied by a combination of solid phase microextraction (SPME)-gas chromatography (GC)-mass spectrometry (MS), headspace oxygen depletion, and sensory evaluation. Samples stored under fluorescent light for 2 days at 30 degrees C had 90% more volatile compounds and 4 times more headspace oxygen depletion than samples stored in the dark at 30 degrees C. The volatiles 1-heptanol, heptanal, nonanal, and 2-decenal were formed and increased only in the light-stored samples, which may be formed from singlet oxygen oxidation of unsaturated fatty acids. Sensory evaluation showed that samples stored under light had significantly more off-flavor than samples stored in the dark at 30 degrees C (P < 0.05), and 1-heptanol, heptanal, nonanal, and 2-decenal increased the goat cheese off-flavor significantly (P < 0.05).     

Optimization of headspace solid-phase Microextraction (SPME) for the odor analysis of surface-ripened cheese

Fifty volatile compounds of surface smear-ripened cheese were detected and identified using headspace solid-phase microextraction (HS-SPME) and vacuum distillation coupled to gas chromatography-mass spectrometry. Changes in the headspace of aroma compounds were monitored over the whole packaging period (47 days) using the HS-SPME method. Initially, the concentration of methanethiol increased before reaching a plateau. This evolution could be linked to the growth of Brevibacterium linens. During the shelf life of cheese, levels of acetic acid and 3-methylbutanoic acid remained constant, whereas butane-2,3-dione, 3-hydroxybutan-2-one, and hydroxypropan-2-one levels gradually declined and acetone and 3-methylbutanol levels dropped sharply to a plateau. Changes in odor could be related to changes of the rind, which behaved as a barrier, strongly influencing the distribution of volatile compounds in the headspace. Using a gas chromatography-olfactometry technique without separation, it was shown that the SPME extract was representative of the cheese odor.     

Characterization of Citrus unshiu (C. unshiu Marcov. forma Miyagawa-wase) blossom aroma by solid-phase microextraction in conjunction with an electronic nose

The volatile composition of the headspace from Citrus unshiu Marcov. forma Miyagawa-wase blossom was investigated. The volatile constituents were absorbed by a solid-phase microextraction (SPME) fiber and directly transferred to a GC-MS. Volatile compositional changes of C. unshiu blossom prepared via different drying methods (shade, microwave, and freeze-drying methods) were also determined. A total of 96 volatile constituents were confirmed in the headspace from these samples. Monoterpene hydrocarbons were prominent in the headspace volatiles of C. unshiu blossom: fresh, 84.1%; shade-dried, 60.0%; microwave-dried, 88.4%; and freeze-dried, 29.9%. p-Cymene (23.3%) was the most abundant component in the headspace of fresh C. unshiu blossom; gamma-terpinene was the most abundant in shade- and microwave-dried samples (26.8 and 31.2%, respectively) and beta-caryophyllene (10.5%) in freeze-dried sample. By using an electronic nose consisting of six metal oxide sensors, principal component analysis of the volatile compounds showed a clear aroma discrimination of the fresh and all dried blossom samples.     

Typicality and geographical origin markers of protected origin cheese from The Netherlands revealed by PTR-MS

Volatile fingerprints of 30 cumin cheese samples of artisanal farmers' cheese of Leiden with EU Protected Designation of Origin (PDO) and 29 cumin cheese samples of varying commercial Dutch brands without PDO protection were used to develop authentication models. The headspace concentrations of the volatiles, as measured with high sensitivity proton-transfer mass spectrometry, were subsequently subjected to partial least-squares discriminant analysis (PLS-DA). Farmers' cheese of Leiden showed a distinct volatile profile with 27 and 9 out of the 60 predominant ions showing respectively significantly higher and lower concentrations in the headspace of the cheese in comparison to the other cumin cheeses. The PLS-DA prediction models developed classified in cross-validation 96% of the samples of PDO protected, artisanal farmers' cheese of Leiden correctly, against 100% of commercial cumin cheese samples. The characteristic volatile compounds were tentatively identified by PTR-time-of-flight-MS. A consumer test indicated differences in appreciation, overall flavor intensity, creaminess, and firmness between the two cheese groups. The consumers' appreciation of the cumin cheese tested was not influenced by the presence of a name label or PDO trademark.     

Comparison of static headspace, headspace solid phase microextraction, headspace sorptive extraction, and direct thermal desorption techniques on chemical composition of French olive oils

Static headspace (SHS), headspace solid phase microextraction (HS-SPME), headspace sorptive extraction (HSSE), and direct thermal desorption (DTD) were applied to the analysis of four French virgin olive oils from Corsica. More than 60 compounds were isolated and characterized by GC-RI and GC-MS. SHS was not suited to the characterization of olive oil volatile compounds because of low sensitivity. The SPME and HSSE techniques were successfully applied to olive oil headspace analysis. Both methods allow the characterization of volatile compounds (mainly C(6) aldehydes and alcohols), which contribute significantly to the "green" flavor note of virgin olive oils. The PDMS stir bar showed a higher concentration capacity than a DVB/CAR/PDMS SPME fiber due to the higher volume of polymeric coating. DTD was a very good tool for extracting volatile and especially semivolatile compounds, such as sesquiterpenes, but requires a significant investment like that for HSSE. Finally, SPME may be a more appropriate technique for routine quality control due to its operational simplicity, repeatability, and low cost.     

Analysis of volatile compounds released during the grinding of roasted coffee beans using solid-phase microextraction

A dynamic solid-phase microextraction (SPME) method to sample fresh headspace volatile compounds released during the grinding of roasted coffee beans was described and the analytical results using gas chromatography/mass spectrometry (GC/MS) and GC/olfactometry (GC/O) were compared to those of the conventional static SPME sampling methods using ground coffee. Volatile compounds released during the grinding of roasted coffee beans (150 g) were obtained by exposing the SPME fiber (poly(dimethylsiloxane)/divinylbenzene, PDMS/ DVB) for 8 min to nitrogen gas (600 mL/min) discharged from a glass vessel in which the electronic coffee grinder was enclosed. Identification and characterization of volatile compounds thus obtained were achieved by GC/MS and GC/O. Peak areas of 47 typical coffee volatile compounds, separated on total ion chromatogram (TIC), obtained by the dynamic SPME method, showed coefficients of variation less than 5% (n = 3) and the gas chromatographic profile of volatile compounds thus obtained was similar to that of the solvent extract of ground coffee, except for highly volatile compounds such as 4-hydroxy-2,5-dimethyl-3(2H)-furanone and 4-ethenyl-2-methoxyphenol. Also, SPME dilution analysis of volatile compounds released during the grinding of roasted coffee beans showed linear plots of peak area versus exposed fiber length (R (2) > 0.89). Compared with those of the headspace volatile compounds of ground coffee using GC/MS and GC/O, the volatile compounds generated during the grinding of roasted coffee beans were rich in nutty- and smoke-roast aromas.     

Effect of variety and maturation of cheese on supercritical fluid extraction efficiency

Supercritical fluid extraction (SFE) has been utilized by the food industry in many applications to extract, fractionate, and recover compounds from various food matrices. However, little research has been conducted using SFE as an alternative process for producing reduced-fat cheese. Lipids in cheeses may be selectively extracted due to the nonpolar properties of supercritical carbon dioxide (SC-CO2), without leaving residual chemicals as is the case in solvent extraction. The objective of this study was to evaluate the influence on the extraction process due to cheese variety and protein breakdown by age. A Latin square design was utilized to test the extractability of lipids from Parmesan and Cheddar cheeses, aged young (9-10 months) or old (24 months). Extraction took place in a 500 mL SFE vessel using 100 g of grated cheese samples. The SFE parameters of the extraction were 350 bar, 35 degrees C, and supercritical carbon dioxide at a flow rate of 20 g/min for 55 min. Compositional analysis measured all treated samples and controls of total lipids, lipid profiling, total protein, protein/peptide analysis, moisture, ash, and pH. Cheese type was a major variable in fat extraction. The extraction in Cheddar showed an average fat reduction of 53.56% for young cheese, whereas that in old Cheddar was 47.90%. However, young Parmesan was reduced an average of 55.07%, but old Parmesan was reduced at 68.11%, measured on a dry basis. SFE extracted triglycerides and cholesterol, but did not remove phospholipids. This investigation introduces the observations of the effect of Cheddar and Parmesan varieties on SFE, offering data on the important parameters to consider in the design of SFE processes to reduce fat in cheese.     

Aroma-active components in fermented bamboo shoots.

Bamboo shoots (Phyllostachys pubescens) were fermented and prepared in a traditional Taiwanese manner. Static and dynamic headspace extractions of volatile compounds were conducted by solid phase microextraction (SPME) and by cryogenic focusing purge and trap, respectively. Volatile analysis was conducted with gas chromatography and mass spectrometry. Gas chromatography-olfactometry (GCO) was conducted utilizing the Osme time-intensity method. Of 70 volatile compounds detected, 29 possessed aroma activity, and the most odor active included p-cresol (barn-like), 2-heptanol (mushroom), acetic acid (vinegar), and 1-octen-3-ol (mushroom). SPME extracted 66 compounds, purge and trap extracted 14 compounds, and 12 compounds were common to both methods. The Osme GCO technique coupled with SPME is an effective tool for the extraction and evaluation of aroma-active headspace volatiles.     

Quantitation of free and glycosidically bound volatiles in and effect of glycosidase addition on three tomato varieties (Solanum lycopersicum L.)

The volatile fractions of three tomato cultivars (p73, Jorge, and Durinta) were studied in both free and glycosidically bound forms. The possibility of increasing the concentration of free volatile compounds by adding selected glycosidases was also tested. The free volatile fraction (FVF) of tomato juice was directly determined by headspace solid-phase microextraction (SPME). To analyze the glycosidically bound fraction (GBF), tomato juice samples were extracted with C18 cartridges and the resulting glycoside extracts were enzymatically hydrolyzed. The released aglycons were determined by headspace SPME. Of these compounds, six were not previously reported to belong to the tomato GBF. The concentration of 21 of 24 compounds detected in the FVF was significantly different between cultivars, the majority of them being greater in p73 than in Durinta and Jorge cultivars. In the GBF, 19 of 26 compounds that were detected were significantly different between cultivars but only the amount of trans-linalool oxide was significantly the greatest in the p73 cultivar. The addition of Candida molischiana beta-glucosidase (BGLN) and Saccharomyces cerevisiae exoglucanase (EXG1) to tomato juice samples led to increases in the concentration of 10 compounds, with variations depending on the cultivar or enzyme. These results provide scientific support for using glycosidases as a tool to improve tomato aroma.     

Gas chromatography-olfactometry (GC-O) and proton transfer reaction-mass spectrometry (PTR-MS) analysis of the flavor profile of grana padano,parmigiano reggiano,and grana trentino cheeses

Gas chromatography-olfactometry (GC-O) and proton transfer reaction-mass spectrometry (PTR-MS) techniques were used to deduce the profile of odor-active and volatile compounds of three grana cheeses: Grana Padano (GP), Parmigiano Reggiano (PR), and Grana Trentino (GT). Samples for GC-O analysis were prepared by dynamic headspace extraction, while a direct analysis of the headspace formed over cheese was performed by PTR-MS. The major contributors to the odor profile were ethyl butanoate, 2-heptanone, and ethyl hexanoate, with fruity notes. A high concentration of mass 45, tentatively identified as acetaldehyde, was found by PTR-MS analysis. Low odor threshold compounds, e.g., methional and 1-octen-3-one, which contributed to the odor profile but were not detected by FID, were detected by PTR-MS. Principal component analysis on both GC-O and PTR-MS data separated the three cheese samples well and showed specific compounds related to each sample.     

Analysis of terpenoids from hemlock (Tsuga) species by solid-phase microextraction/gas chromatography/ion-trap mass spectrometry

A sampling method for determining the volatile terpenoid composition from single needles of seven Tsuga species was developed using headspace solid-phase microextraction (SPME). A reproducible sampling method for the volatile components was generated by examination of sample storage, method of needle cutting, and headspace sampling duration. Following SPME collection of the volatile compounds from the seven Tsuga species, gas chromatography/ion-trap mass spectrometry was used to identify 51 terpenoids present in the needle headspace. A semiquantitative method was devised to express individual terpenoid amounts as a percentage of all of the identified peaks in the chromatogram. The semiquantitative results permitted facile interspecies comparison using principal component analysis. Two components were able to account for 90% of the variance and were interpreted as a "species" component and a "resistance/susceptibility" component. Three interspecies groupings were evident from the principal component analysis: (1) Tsuga canadensis and Tsuga caroliniana; (2) Tsuga chinesnsis, Tsuga diversifolia, Tsuga heterophylla, and Tsuga sieboldii; and (3) Tsuga mertensiana. The finding that T. mertensiana was grouped alone and far removed from the other species adds to the morphological evidence that this species should be segregated from other Tsuga.     

Composition of the water-soluble fraction of different cheeses

Volatile and nonvolatile compounds present in the water-soluble fraction (WSF) and water-soluble fraction with molecular weight lower than 1000 Da (WSF < 1000 Da) of six Spanish cheeses, Cabrales, Idiazábal, Mahón, Manchego, Roncal, and a goat's milk cheese, were analyzed. Different nitrogen fractions (determined by Kjeldahl method), caseins (by capillary electrophoresis), peptides and amino acids (by HPLC), and volatile components (by dynamic headspace coupled to GC-MS) as well as mineral content in the cheese fractions were analyzed and compared. The different nitrogen and volatile compounds identified in the WSF were characteristic of each cheese variety. Cabrales cheese displayed the highest content of free amino acids and the highest quantity and variety of volatile compounds. The WSF < 1000 Da fraction was less representative, especially for volatile compounds, as some of the components were lost in the ultrafiltration. Alcohols were better recovered than ketones and esters.     

Solid-phase microextraction in the analysis of virgin olive oil volatile fraction: characterization of virgin olive oils from two distinct geographical areas of northern Italy

SPME was employed to characterize the volatile profile of virgin olive oils produced in two geographical areas of northern Italy: the region of the Gulf of Trieste and the area near Lake Garda. There are as yet no data on the headspace composition of virgin olive oils from these regions, characterized by particular conditions of growth for Olea europaea. Using the SPME technique coupled to GC-MS and GC-FID, the volatile components of 42 industrially produced virgin olive oil samples were identified and the principal compounds quantitatively analyzed. Significant differences in the proportion of volatile constituents from oils of different varieties and geographical origins were detected. The results suggest that besides the genetic factor, environmental conditions influence the volatile formation.     

Headspace solid-phase microextraction method for the study of the volatility of selected flavor compounds

Changes in the volatility of selected flavor compounds in the presence of nonvolatile food matrix components were studied using headspace solid-phase microextraction (HS-SPME) combined with GC-MS quantification. Time-dependent adsorption profiles to the SPME fiber and the partition coefficients between different phases were obtained for several individual volatiles, showing that HS-SPME analysis with a short sampling time can be used to determine the "true" headspace concentration at equilibrium between the headspace and a sample matrix. Equilibrium dialysis followed by HS-SPME/GC-MS was carried out to confirm the ability of HS-SPME extraction for monitoring the free volatile compounds in the presence of proteins. In particular, a short sampling time (1 min) avoided additional extraction of volatiles bound to the protein. Interactions between several selected flavor compounds and nonvolatile food matrix components [beta-lactoglobulin or (+)-catechin] were also studied by means of HS-SPME/GC-MS analysis. The volatility of ethyl hexanoate, heptanone, and hexanal was significantly decreased by the addition of beta-lactoglobulin compared to that of isoamyl acetate. Catechin decreased the volatility of ethyl hexanoate and hexanal by 10-20% and increased that of 2-heptanone by approximately 15%. This study indicates that HS-SPME can be a useful tool for the study of the interactions between volatile compounds and nonvolatile matrix components provided the kinetic and thermodynamic behavior of the volatiles in relation to the fiber chosen for the studies is carefully considered.     

Screening for 2-acetyl-1-pyrroline in the headspace of rice using SPME/GC-MS

Solid phase microextraction (SPME) is used to collect and concentrate the compounds in the headspace of rice. This research describes optimization parameters of temperature, moisture, and sampling time. Optimization was based upon the recovered levels of 2-acetyl-1-pyrroline (2-AP), the popcorn aroma in aromatic rice. The method uses a sampling temperature of 80 degrees C and adds 100 microL of water to a 0.75 g sample of rice. The rice was preheated for 25 min, a carboxen/DVB/PDMS SPME fiber was exposed to the headspace for 15 min, and a subsequent GC-MS analysis took 35 min. Samples of rice can be analyzed as the flour, milled kernels, or brown rice. Twenty-one experimental rice varieties were analyzed by the SPME method and compared to a wet technique. Recoveries of several nanograms of 2-AP from 0.75 g samples of aromatic rice were observed, whereas only trace amounts of 2-AP were recovered from nonaromatic rice. Recovery from a single SPME headspace analysis is calculated to be 0.3% of the total 2-AP in the sample.     

Characterization of the chemical composition of a byproduct from siam benzoin gum

The mixture of bark and gum obtained after size-grading of Siam benzoin gum was studied to establish its potential application as a valuable new grade of the balsamic resin. An analysis of its volatile constituents by means of static headspace and SPME led to the identification of 26 and 50 compounds, respectively. Significant differences were observed in both the headspace composition and olfactory properties of the byproduct as compared to those of Siam benzoin gum. This prompted the further analysis of its volatile extract and its resinoid by GC techniques, resulting in the identification of 60 (99.5%) and 16 (89.1%) components, respectively. To examine the influence of bark pieces, different extracts obtained from the raw material and from a sorted sample were analyzed by GC and HPLC techniques. The chemical compositions and the yields determined for the two resinoids lead to the conclusion that this harvesting byproduct is a new grade of Siam benzoin gum, providing interesting olfactory notes that differ from those of other grades.     

A headspace solid-phase microextraction method for the determination of some secondary compounds of Brazilian sugar cane spirits by gas chromatography

A headspace solid-phase microextraction (SPME) method was developed for the determination of secondary compounds from Brazilian sugar cane spirits, or cacha?a, by GC-FID. An SPME holder with an 85 microm polyacrylate coating was utilized. The novel method is compared with an optimized method: liquid-liquid extraction (LLE). Both methods showed good linearity, but the repeatability for analyses done with the SPME technique (%RSD = 1.8-3.9) was better than for those done with LLE (%RSD = 10.3-11.7). The concentrations of the analytes obtained in the analysis of 12 cacha?a samples with the SPME technique were higher than those obtained with LLE. In the SPME method the extraction wastes are smaller. Cacha?a samples were qualitatively analyzed for GC-MS.     

Headspace solid phase microextraction (SPME) analysis of flavor compounds in wines. Effect of the matrix volatile composition in the relative response factors in a wine model.

The application of headspace solid phase microextraction (SPME) for flavor analysis has been studied. Headspace SPME sampling was tested for nine common wine flavor compounds in 10% (v/v) aqueous ethanol: linalool, nerol, geraniol, 3-methyl-1-butanol, hexanol, 2-phenylethanol, ethyl hexanoate, ethyl octanoate, and ethyl decanoate. The chemical groups (monoterpenoids, aliphatic and aromatic alcohols, and esters) showed specific behavior in SPME analysis. SPME sampling parameters were optimized for these components. Relative response factors (RRFs), which establish the relationship between the concentration of the compound in the matrix liquid solution and the GC peak area, were estimated for all compounds. Log(10)(RRF) varied from 0 (3-methyl-1-butanol) to 3 (ethyl decanoate), according to their molecular weight. Quantification by SPME was shown to be highly dependent on the matrix composition; the compounds with higher RRF were the less affected. As a consequence, the data obtained with this methodology should be used taking into consideration these limitations, as shown in the analysis of four monovarietal Bairrada white wines (Arinto, Bical, Cerceal, and Maria Gomes).     

Freshness assessments of Moroccan sardine (Sardina pilchardus): comparison of overall sensory changes to instrumentally determined volatiles

Freshness of ice-stored sardine was assessed by two sensory methods, the quality index method (QIM) and the European Union freshness grading system, and by instrumental means using the method of aroma extract dilution analysis. Screening of sardine potent volatiles was carried out at three freshness stages. In the very fresh state, the plant-like fresh volatiles dominated the odor pattern, with the exception of methional. Overall odor changes in sardine throughout storage correlated with changes in the concentration of some potent volatiles: after 2 days of ice storage, (Z)-4-heptenal, (Z)-1,5-octadien-3-one, and methional imparted an overall "fishy" odor character to sardine, whereas at a lower sensory grade (B), the compounds (E)-2-nonenal and (E,Z)-2,6-nonadienal could be, in part, associated with the slightly rancid aroma top notes. Trimethylamine was detected as a highly volatile odorant using solid-phase microextraction (SPME) headspace analysis of refrigerator-stored sardine. Intensity and sensory characteristics of some SPME determined volatiles, for example, 3-methylnonane-2,4-dione, were closely related to overall odor changes. SPME headspace analysis may be useful in the characterization of off-flavors in fish.     

Screening of tropical fruit volatile compounds using solid-phase microextraction (SPME) fibers and internally cooled SPME fiber

In this study, the optimization and comparison of an internally cooled fiber [cold fiber with polydimethylsiloxane (PDMS) loading] and several commercial solid-phase microextraction (SPME) fibers for the extraction of volatile compounds from tropical fruits were performed. Automated headspace solid-phase microextraction (HS-SPME) using commercial fibers and an internally cooled SPME fiber device coupled to gas chromatography-mass spectrometry (GC-MS) was used to identify the volatile compounds of five tropical fruits. Pulps of yellow passion fruit (Passiflora edulis), cashew (Anacardium occidentale), tamarind (Tamarindus indica L.), acerola (Malphigia glabra L.), and guava (Psidium guajava L.) were sampled. The extraction conditions were optimized using two experimental designs (full factorial design and Doehlert matrix) to analyze the main and secondary effects. The volatile compounds tentatively identified included alcohols, esters, carbonyl compounds, and terpernes. It was found that the cold fiber was the most appropriate fiber for the purpose of extracting volatile compounds from the five fruit pulps studied.