Measurement of 2-thiobarbituric acid values in dark chicken meat through derivative spectrophotometry: influence of various parameters

Several variables (kind of filter paper, amount of sample, antioxidant addition, stability of the spectrophotometric measurement, and handling and storage of samples) were found to influence 2-thiobarbituric acid (TBA) values in dark chicken meat when an acid aqueous extraction method with derivative spectrophotometry was used. Filter papers with larger pore diameter or increasing sample weight led to lower TBA values. After incubation of reaction mixtures at 70 degrees C and ice-cooling, tempering for 45 min at room temperature was necessary to stabilize the spectrophotometric measurement. Furthermore, addition of butylated hydroxytoluene (BHT) and ethylenediaminetetraacetic acid disodium salt (EDTA) in the early steps of the method prevented artifactual formation of TBA reactive substances during analysis. Vacuum packaging and storage of samples at -20 degrees C were useful to avoid sample oxidation. The method finally proposed has a coefficient of variation of 3.81 or 4.13% for raw or cooked samples, respectively.     

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.     

Solid phase microextraction-gas chromatography for quantifying headspace hexanal above freeze-dried chicken myofibrils

A method using solid phase microextraction (SPME) combined with gas chromatography/mass spectrometry (GC/MS) was developed and used to determine the oxidation of freeze-dried chicken myofibrils spiked with methyl linoleate. Freeze-dried chicken myofibrils were found to act as a significant reservoir for hexanal. Recovery of hexanal emissions from the headspace above spiked myofibrils was 95% using a 5 min sampling time, with a total analysis time of approximately 12 min/sample. The SPME-GC/MS working linear response was from 0.01 to 10 mg hexanal/L (r( 2) = 0.995). Freeze-dried chicken myofibrils with added methyl linoleate (0.6 mmol/g of protein) were stored at 50 degrees C at water activities of 0.30 and 0.75 for 0, 12, 27, and 50 h. Lipid oxidation was determined using SPME-GC/MS to measure headspace hexanal concentration, the thiobarbituric acid reactive substances assay (TBARS) to quantify malonaldehyde, and a conjugated diene assay. Lipid oxidation was influenced by storage time and water activity. A strong correlation (r = 0.938) existed between SPME-GC/MS and TBARS. The use of SPME-GC/MS was a sensitive and rapid method for detecting hexanal as an indicator of lipid oxidation in chicken myofibrils.     

Optimizing headspace temperature and time sampling for identification of volatile compounds in ground roasted Arabica coffee

Equilibration time and temperature were the factors studied to choose the best conditions for analyzing volatiles in roasted ground Arabica coffee by a static headspace sampling extraction method. Three temperatures of equilibration were studied: 60, 80, and 90 degrees C. A larger quantity of volatile compounds was extracted at 90 degrees C than at 80 or 60 degrees C, although the same qualitative profile was found for each. The extraction of the volatile compounds was studied at seven different equilibration times: 30, 45, 60, 80, 100, 120, and 150 min. The best time of equilibration for headspace analysis of roasted ground Arabica coffee should be selected depending on the chemical class or compound studied. One hundred and twenty-two volatile compounds were identified, including 26 furans, 20 ketones, 20 pyrazines, 9 alcohols, 9 aldehydes, 8 esters, 6 pyrroles, 6 thiophenes, 4 sulfur compounds, 3 benzenic compounds, 2 phenolic compounds, 2 pyridines, 2 thiazoles, 1 oxazole, 1 lactone, 1 alkane, 1 alkene, and 1 acid.     

Mass spectrometry analysis of volatile compounds in raw meat for the authentication of the feeding background of farm animals

The authentication of the conditions of animal production, based on the analysis of meat commercial cuts, is a major challenge on both societal and analytical grounds. The aim of the present work was to propose a method for the extraction of the volatile compounds from ruminant raw muscles trimmed of fat and to assess by mass spectrometry-based techniques the relevance of these compounds for the authentication of the type of feeding offered to the animals. The first step of the study consisted of validating conditions of dynamic headspace (DH) extraction of volatile compounds that enabled us to minimize the appearance of heat-induced artifacts and to maximize the richness of the DH-gas chromatography-mass spectrometry profile (DH-GC-MS) of raw lamb muscle. An extraction temperature of 35 degrees C (vs 60 and 90 degrees C) and a sample mass of 6.25 g (vs 12.5, 25, and 50 g) were shown to be suitable. The second step aimed at identifying volatile compounds enabling us to discriminate muscle samples from 16 experimental lambs fed either concentrate (n = 8) or pasture (n = 8). Before, to carefully explore the information given by the DH-GC-MS signal, the MS spectra acquired along the chromatogram were summed and then converted in a virtual-DH-MS spectral fingerprint to have a quick overview of the discriminative potential of the volatile fraction. According to univariate (analysis of variance) and to multivariate (principal component analysis) data treatments performed on virtual-DH-MS fingerprints, the meat volatile fraction was relevant to reveal the type of feeding of the living animal. The detailed examination of the information given by the GC dimension showed that 33 volatile compounds among the 204 detected in the muscle by DH-GC-MS enabled us to discriminate the type of feeding of the lambs. The relevance of these results is discussed in light of previous studies performed on adipose tissues.     

Headspace solid phase microextraction and gas chromatography-olfactometry dilution analysis of young and aged Chinese "Yanghe Daqu" liquors

The aroma compounds of young and aged Chinese "Yanghe Daqu" liquor samples were extracted by solid phase microextraction (SPME) and analyzed by gas chromatography (GC)-olfactometry dilution analysis. The original liquor samples were diluted with deionized water to give a final alcohol content of 14% (v/v). The samples were stepwise diluted (1:1) with 14% (by volume) ethanol-water solution and then extracted by headspace SPME. The samples were preequilibrated at 50 degrees C for 15 min and extracted with stirring at the same temperature for 30 min prior to injection into GC. The aroma compounds were identified by both GC-MS and GC-olfactometry using DB-Wax and DB-5 columns. The results suggested that esters were the major contributors to Yanghe Daqu liquor aroma. Ethyl hexanoate, ethyl butanoate, and ethyl pentanoate had very high flavor dilution values in both young and aged liquors (FD > 8192). Methyl hexanoate, ethyl heptanoate, ethyl benzoate, and butyl hexanoate could also be very important because of their high flavor dilution values (FD > or = 256). Moreover, two acetals, 1,1-diethoxyethane and 1,1-diethoxy-3-methylbutane, also were shown high flavor dilution values in Yanghe Daqu liquors (FD > or = 256). Other aroma compounds having moderate flavor dilution values included acetaldehyde, 3-methylbutanol, and 2-pentanol (FD > or = 32). Comparing young and aged liquors, the aroma profiles were similar, but the aroma compounds in the aged sample had higher flavor dilution values than in the young ones.     

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 solid phase microextraction analysis for the headspace volatile compounds of parmesan cheese

Optimum conditions of solid phase microextraction (SPME) analysis of the headspace volatile compounds of Parmesan cheese in airtightly sealed 100-mL bottles were developed. The coefficient of variation of SPME analysis on the headspace volatile compounds of Parmesan cheese was 2%. The reproducibility of SPME was improved by a combination of sampling at -10 degrees C, controlling the sample temperature, and uniform magnetic stirring of samples during equilibrium and isolation steps. The sensitivity of SPME increased by 125% in total peak areas by a combination of 40 min of sonication and 25% (w/v) sodium phosphate solution, compared with that of samples containing deionized water only (P < 0.05). The addition of salt solution or sonication treatment in samples increased the headspace volatile compounds of cheese quantitatively without producing any new volatile compounds.     

Ultrasonic determination of chicken composition.

An ultrasonic technique has been developed for measuring the composition of chicken meat. The relationship between the composition and ultrasonic velocity of chicken meat was determined using chicken analogues of different composition, prepared from dried chicken powder, corn oil, and distilled water. The ultrasonic velocity of chicken analogues was measured at temperatures from 5 to 35 degrees C using an ultrasonic spectrometer. The ultrasonic velocity increased with solids-nonfat (SNF) content at all temperatures but had a more complex dependence on fat content. Around 15 degrees C the ultrasonic velocity was independent of fat content; however, at lower temperatures it increased with fat content, and at higher temperatures it decreased. Semiempirical equations were developed to describe the relationship between ultrasonic velocity and chicken composition. To determine the usefulness of these equations, the ultrasonic velocities of various chicken meats were measured. The compositions of the chicken meats predicted on the basis of ultrasonic measurements were in good agreement with those determined by using standard methods (r(2) > 0. 97). The ultrasonic technique could also be used to measure the solid fat content of chicken fat. This study shows that ultrasonic velocity measurements can be used to characterize chicken composition. This method has great potential for application in the food industry because it is simple, fast, nondestructive, and reliable.     

Determination of enantiomers of synthetic pyrethroids in water by solid phase microextraction - enantioselective gas chromatography

Solid phase microextraction (SPME) is an ideal sample preparation technique because of its speed and solvent-free features. Sampling by SPME is selective and only the dissolved concentration is measured, which allows measurement of the bioavailable fraction of a contaminant in aqueous media. One potential application of SPME is for analysis of enantiomers of chiral contaminants in environmental samples. In this study, a method was developed for determining enantiomers of (Z)-cis-bifenthrin and cis-permethrin in water using coupled SPME and enantioselective gas chromatography (GC). Following SPME sampling, enantiomers of (Z)-cis-bifenthrin and cis-permethrin were separated at the baseline on a beta-cyclodextrin-based enantioselective column, and analyte enrichment onto the SPME fiber was not enantioselective. The GC response increased as sampling time was increased from 0 to 240 min, and as sampling temperature was increased from 20 to 40 degrees C. Organic solvents such as methanol, acetone, and acetonitrile enhanced, while soil extracts slightly decreased, the GC response. The integrated SPME-enantioselective GC method was used to analyze surface runoff samples. The analysis showed preferential degradation of the 1S-3S enantiomer over the 1R-3R enantiomer for both (Z)-cis-bifenthrin and cis-permethrin. The concentrations detected by SPME-GC were substantially smaller than those determined following solvent extraction, suggesting that SPME-enantioselective GC analysis selectively measured the dissolved fraction.     

Optimization of solid-phase microextraction analysis for studying change of headspace flavor compounds of banana during ripening

The changes of headspace flavor compounds of banana during ripening were studied by a solid-phase microextraction (SPME) method. Three temperatures, 20, 25, and 30 degrees C, were used to investigate the temperature effect on the changes of headspace flavor compounds of banana during ripening over a period of 8 days. Banana juice concentration, salt concentration, time, and temperature were investigated for optimizing the SPME method. The most suitable concentrations of banana juice and salt were 33.3 and 20%, respectively. The optimal temperature and time are about 50 degrees C and 48 min, respectively. Increasing ripening temperature could accelerate ripening rate. Ethanol developed most rapidly at 30 degrees C, whereas amounts of the other investigated flavor compounds stored at 25 degrees C were greater than those of the ones stored at 20 or 30 degrees C.     

Gas-liquid chromatographic-mass fragmentographic determination of low levels of diethylcarbonate in beverages.

Sodium chloride and ethanol (omitted for samples with greater than 10% alcohol) are added to the beverage sample and the sample is allowed to equilibrate in a 30 degrees C water bath. An aliquot of the headspace is injected into a gas chromatography containing a column packed with 0.2% Carbowax 1500 on 80--100 mesh Carbopack C. During the elution of diethylcarbonate (DEC), an impurity that is present in diethylpyrocarbonate, the column effluent is vented to a mass spectrometer with a multiple ion detection system and operated in the electron impact mode. The ions at m/e 63 and 91 are monitored. Lemonade, fruit drinks, wine, and beer samples (138 total) were analyzed for DEC. Sixteen samples had greater than 30 ppb DEC. Eight analyses of a lemonade sample gave a mean of 88 ppb with a coefficient of variation of 11%.     

Effect of high-pressure-moderate-temperature processing on the volatile profile of milk

The effects of high hydrostatic pressure on volatile generation in milk were investigated in this study. Raw milk samples were treated under different pressures (482, 586, and 620 MPa), temperatures (25 and 60 degrees C), and holding times (1, 3, and 5 min). Samples submitted to heat treatments alone (25, 60, and 80 degrees C for 1, 3, and 5 min) were used for comparison. Trace volatile sulfur compounds were analyzed using solid-phase microextraction (SPME) and gas chromatography (GC) with pulsed-flame photometric detection (PFPD), whereas the rest of the volatile compounds were analyzed using SPME-GC with flame ionization detection (FID). Multivariate analysis of variance (MANOVA) and principal component analysis (PCA) were used to study the effect of pressure, temperature, and time on volatile generation. Relative concentration increases of 27 selected volatile compounds were compared to an untreated sample. It was found that pressure, temperature, and time, as well as their interactions, all had significant effects (P < 0.001) on volatile generation in milk. Pressure and time effects were significant at 60 degrees C, whereas their effects were almost negligible at 25 degrees C. The PCA plot indicated that the volatile generation of pressure-heated samples at 60 degrees C was different from that of heated-alone samples. Heat treatment tended to promote the formation of methanethiol, hydrogen sulfide, methyl ketones, and aldehydes, whereas high-pressure treatment favored the formation of hydrogen sulfide and aldehydes.     

Effect of electron beam irradiation and storage at 5 degrees C on thiobarbituric acid reactive substances and carbonyl contents in chicken breast meat infused with antioxidants and selected plant extracts

This study evaluated the effectiveness of synthetic and natural antioxidants, green tea, commercial grape seed extracts/combinations, and TBHQ, with varying concentrations of lipid oxidation of nonirradiated and irradiated chicken breast meats stored at 5 degrees C for 12 days. Fresh boneless and skinless chicken breast meats were vacuum-infused with varying concentrations of antioxidants: green tea, grape seed extracts alone/in combination, and TBHQ. The irradiation dosage was 3.0 kGy. Carbonyl values of raw chicken meat and thiobarbituric acid reactive substances (TBARS) values of raw and cooked chicken meat were determined for 0-12 days at 5 degrees C storage. TBARS values for 0-12 days of storage at 5 degrees C ranged from 1.21 to 7.3 and 1.22 to 8.51 mg malondialdehyde/100 g chicken for nonirradiated and irradiated raw chicken, respectively. TBARS values of cooked chicken ranged from 2.19 to 35.83 and 2.45 to 45.72 mg malondialdehyde/100 g chicken for nonirradiated and irradiated chicken, respectively. Irradiation increased TBARS values of both controls and plant extracts. The carbonyl content in meat lipid ranged from 1.7 to 2.9 and 1.7 to 4.41 micromol acetophenone/10 g of nonirradiated and irradiated chicken meat, respectively, and meat protein ranged from 1.4 to 2.07 and 1.41 to 2.72 micromol/10 g meat. Infusion of chicken meat with selected plant extracts is an effective method to minimize lipid oxidation and volatiles developments caused by irradiation.     

Headspace solid-phase microextraction gas chromatography-mass spectrometry analysis of volatiles in orujo spirits from a defined geographical origin

A headspace solid-phase microextraction (HS-SPME) and gas chromatography-selective ion monitoring/mass spectrometry (GC-SIM/MS) method was optimized for analysis of 22 volatile compounds in orujo spirit samples from the Geographic Denomination "Orujo de Galicia/Augardente de Galicia". HS-SPME experimental conditions, such as fiber coating, extraction temperature, extraction and pre-equilibrium time, sample volume, and the presence of salt, were studied to improve the extraction process. The best results were obtained using a 65 microm Carbowax-divinylbenzene fiber during a headspace extraction at 40 degrees C with constant magnetic stirring for 15 min and after a 5 min period of pre-equilibrium time. The sample volume was 6 mL of orujo containing 25% of NaCl, placed in 12 mL glass vials equipped with a screw cap and PTFE/silicone septum. Desorption was performed directly in the gas chromatograph injector port for 5 min at 250 degrees C using the splitless mode. The proposed method is sensible (with detection limits between 0.0045 and 0.2399 mg/L), precise (with coefficients of variation in the range 0.99-8.18%), and linear over more than 1 order of magnitude. The developed method presented recoveries comprised between 76.0 and 112.4%. The applicability of the new method was demonstrated by determining the considered 22 volatile compounds in nine orujo commercial samples with quality and origin brands.     

Gas chromatography-mass spectrometry determination of phosphine residues in stored products and processed foods

A gas chromatography-mass spectrometry (GC-MS) method was used for the quantitative confirmation of phosphine residues in stored products and processed foods. An established extraction technique was utilized for the preparation of headspace samples, which were analyzed by GC-MS and gas chromatography-nitrogen-phosphorus detection (GC-NPD). Wheat, oats, maize, white rice, brown rice, cornflakes, tortilla cornchips, groundnuts, and raisins were validated, showing excellent agreement between detectors when spiked at levels equivalent to 0.001 and 0.01 mg/kg phosphine and for samples containing incurred residues. The GC-MS method was reproducible and accurate when compared to the GC-NPD method and allowed five samples to be quantified in a working day. Subambient GC-MS oven temperatures were most suitable for phosphine residues ranging from 0.001 to 0.005 mg/kg, and a GC oven temperature of 100 degrees C was appropriate for residues >0.005 mg/kg. The method was sufficiently robust to be evaluated for other similar commodities as the need arises.     

Analysis of 2‐Acetyl‐1‐Pyrroline in Rice by HSSE/GC/MS

An extremely sensitive method for the analysis of 2‐acetyl‐1‐pyrroline (2AP) in rice, employing stir bar sorptive extraction (Twister) was studied. The Twister stir bar is placed in the headspace of a 20‐mL vial containing 1 g of rice kernels, 7.5 mL of 0.1M KOH, and 2.2 g of NaCl, along with a second Teflon‐coated stir bar for mixing. Analytes are adsorbed onto the Twister for 4 hr at 40°C and then desorbed at 270°C into a GC column while cryofocusing at –80°C. The headspace sorptive extraction (HSSE) method was able to detect <0.1 ppb of 2AP in rice. The precision of the HSSE method (>10%) was not as good as the GC/FID method (≈6%). Using HSSE, 2AP was observed in all samples generally considered to be aromatic and was not observed in any nonaromatic samples. Additionally, a modified method for the synthesis of 2‐acetyl‐1‐pyrroline was studied and the presence of a tautomer of 2‐acetyl‐1‐pyrroline was confirmed.     

Electrophoretic pattern, thermal denaturation, and in vitro digestibility of oxidized myosin

Physicochemical changes and in vitro digestibility of chicken breast myosin oxidized with a nonenzymic free-radical-generating system (FeCl(3)/H(2)O(2)/ascorbate) were studied by SDS-PAGE, differential scanning calorimetry, and o-phthaldialdehyde assay. Oxidation caused fragmentation and polymerization of myosin. Myosin polymers were cross-linked mainly through disulfide bonds. Hydroxyl radicals destabilized myosin, lowering its denaturation temperature by up to 4 degrees C. Oxidized myosin also produced a new thermal transition in the 60-80 degrees C temperature range, which could be attributed to the formation of disulfide-stabilized polymers. The proteolytic susceptibility of myosin to pepsin, trypsin, and chymotrypsin was increased by oxidation. Under nonreducing conditions, however, oxidized myosin showed decreased digestibility. The results may help explain variations in the functionality and nutritional quality of muscle foods in meat processing in which oxidation is involved.     

Protein and lipid oxidation during frozen storage of rainbow trout (Oncorhynchus mykiss)

This study aimed at investigating protein and lipid oxidation during frozen storage of rainbow trout. Rainbow trout fillets were stored for 13 months at -20, -30, or -80 degrees C, and samples were analyzed at regular intervals for lipid and protein oxidation markers. Lipid oxidation was followed by measuring lipid hydroperoxides (PV), as well as secondary oxidation products (volatiles) using dynamic headspace GC-MS. Free fatty acids (FFA) were measured as an estimation of lipolysis. Protein oxidation was followed using the spectrophotometric determination of protein carbonyls and immunoblotting. Significant oxidation was observed in samples stored at -20 degrees C, and at this temperature lipid and protein oxidation seemed to develop simultaneously. FFA, PV, and carbonyls increased significantly for the fish stored at -20 degrees C, whereas the fish stored at -30 and -80 degrees C did not show any increase in oxidation during the entire storage period when these methods were used. In contrast, the more sensitive GC-MS method used for measurement of the volatiles showed that the fish stored at -30 degrees C oxidized more quickly than those stored at -80 degrees C. Detection of protein oxidation using immunoblotting revealed that high molecular weight proteins were oxidized already at t = 0 and that no new protein oxidized during storage irrespective of the storage time and temperature. The results emphasize the need for the development of more sensitive and reliable methods to study protein oxidation in order to gain more explicit knowledge about the significance of protein oxidation for food quality and, especially, to correlate protein oxidation with physical and functional properties of foods.     

Automated dynamic headspace/GC-MS analyses affect the repeatability of volatiles in irradiated Turkey

Although a dynamic headspace/gas chromatography-mass spectrometry (DH/GC-MS) method is an effective tool for determining volatiles of irradiated turkey meat, the profile of volatiles may be changeable depending upon the availability of oxygen in the sample vial and sample holding time before purge. The objective of this study was to evaluate the effects of helium flushing and sample holding time before purge on the volatiles profiles of irradiated raw and cooked turkey breast meat. Vacuum-packaged turkey breasts were irradiated at 2.5 kGy, and the volatiles of irradiated raw and cooked samples were analyzed using a DH/GC-MS with different holding times up to 280 min. The amounts of dimethyl disulfide and dimethyl trisulfide decreased as sample holding time in an autosampler (4 degrees C) before purge increased, whereas those of aldehdyes increased as holding time increased due to lipid oxidation. Helium flush of sample vials before sample loading on an autosampler retarded lipid oxidation and minimized the changes of sulfur volatiles in raw meat but was not enough to prevent oxidative changes in cooked meat. Although DH/GC-MS is a convenient method for automatic analysis of volatiles in meat samples, the number of samples that can be loaded in an autosampler at a time should be limited within the range that can permit reasonable repeatabilities for target volatile compounds.