Universal method for online enrichment of target compounds in capillary gas chromatography using in-oven cryotrapping.

A method is described that permits automated online enrichment of injected compounds in multidimensional gas chromatography by using a microfluidic heart-cut (H-C) device to direct target compounds into a cryogenically cooled internal trap (cryotrap, CT). By performing multiple injections of a sample, selected compounds or regions of a primary column separation can be collected in the CT. Remobilizing the trapped species allows elution and further resolution on the second column. Using a well-balanced H-C device, compounds can be fully excluded from the collection step or quantitatively transferred to the CT. Peak areas of the remobilized compound correlate well with the number of sample injections. Trapping on various column phases shows the method is suited to quantitative trapping of alkanes of mass greater than about dodecane and fatty acid methyl esters greater than the C8 homologue. Caffeine and menthol standards of concentration 100 µg mL(-1) gave peak area correlation coefficients for 1-10 and 1-50 replicate split injections of 1 µL volume of 0.999 and 0.996, respectively. Peak height correlations were less favorable as a result of peak broadening on the second column, presumably due to overloading at greater collected mass. The method was applied to 0.2% solutions of peppermint oil (menthol; a major component; 44%) and 1.0% lavender oil (α-terpineol and neryl acetate; minor components of 1.05 and 0.42% abundance). The minor components gave good area and height correlations, and good recovery around 90% was observed for menthol compounds recovered from 15 accumulations. Response amplification was further demonstrated for menthol from mint oil headspace sampling using solid phase microextraction. This approach should be a valuable adjunct for improved detection specificity, for detectors of low sensitivity, and when prior sample concentration provides insufficient response of selected target analytes.

Physicochemical characteristics of pork fed palm oil and conjugated linoleic acid supplements.

The experiment was conducted to determine chemical and physical characteristics of pork fed palm oil in the diets and with two levels of CLA (0.5% and 1.0%) supplementation. Chemical compositions and CLA contents were analyzed from raw loins and ham portions. Color and shear force values were measured in raw and cooked meats. The pork fed CLA supplements contained higher (P<0.05) moisture, less fat, and lower MUFA:SFA, PUFA:SFA and n-6:n-3 ratios. Fatty acid compositions were noticeably changed in the loin meats when palm oil was supplemented with CLA in the pig diets, but not in the hams. The CLA contents of meats increased (P<0.05) with increasing amounts of CLA in the diets, with the c9,t11 CLA isomer was the highest concentration. The loins from pigs fed CLA supplements had lighter (P<0.05) color while the ham portions showed darker color. Cooked loins from pigs fed CLA supplements gave higher (P<0.05) shear forces compared with that fed palm oil only, while cooked hams had lower forces in spite of higher forces were observed in raw state.

Genotype and gender differences in carnosine extracts and antioxidant activities of chicken breast and thigh meats.

The aim of this work was to investigate the effects of genotypes and gender of chickens on carnosine contents and their antioxidant activities. The carnosine content of fresh meat from Thai indigenous and hybrid native chickens differed between breeds (p<0.01) and genders (p<0.01). Regardless of these differences, breast meat contained 2-4-fold higher carnosine than thigh meat. After water and heat extraction at 80°C and ultrafiltration, the carnosine content of meat extracts had the same distribution as in fresh meat. No relationship between total iron and carnosine content on antioxidant activity of the extract was detected. However, when compared in the extracts on the basis of mM carnosine in oxidation system, the extracts of chicken meat showed greater antioxidant activity than pure carnosine (p<0.05). Furthermore, at equal concentrations, thigh meat extract had higher effective inhibiting ability than breast extract.

Heat and ultrafiltration extraction of broiler meat carnosine and its antioxidant activity.

This study examined the effects of extraction and further ultrafiltration on the carnosine content, antioxidant activity and total iron content of chicken muscle extracts. Fresh breast meat had 7-fold higher carnosine than fresh thigh meat (2900 versus 419µg/g meat, respectively). Carnosine extracts of breast and thigh were prepared by heating at 60, 80 and 100°C, and ultrafiltration (UF) using a 5000MW cut-off. At increasing temperatures, protein concentrations decreased while carnosine, total iron and antioxidant activity increased. Antioxidant abilities of the 80 and 100°C-heated extracts were greater than that of the 60°C extract (p<0.05). The ultrafiltrate from the 80°C-heated extract had approximately 20% higher carnosine, but 40% lower protein and 10-30% lower iron than the 80°C-heated ultrafiltrate. However, compared in terms of carnosine concentration, the meat extracts had greater antioxidant activity than pure carnosine (p<0.05).

Aroma-impact compounds in dried spice as a quality index using solid phase microextraction with olfactometry and comprehensive two-dimensional gas chromatography.

A systematic experimental procedure is used to identify the aroma-impact compounds, leading to a shelf quality index based on head space solid-phase microextraction. Dried (ground) fennel seeds, having shelf life of 6 months (0.5Y) and 5 years (5Y), were used as a spice model for assessment of comparative aroma quality. Aroma-impact odorants were analysed by GC-olfactometry (GC-O) in parallel with comprehensive two-dimensional GC-flame ionisation detection (GC×GC-FID) using a polar/non-polar phase combination for the GC×GC column set. Tentative identification of aroma-impact odorants involved correlating data from the GC-O/FID system with GC×GC-time-of-flight mass spectrometry analysis by means of retention indices. Major compounds responsible for aroma perception were limonene, 1,8-cineole, terpinen-4-ol, estragole and trans-anethole, and showed an average decrease of 30-50% NIF from 0.5Y to 5Y. Monoterpenes which represent 'freshness', e.g. ß-pinene and ß-myrcene, exhibited identifiable aroma-impact only for the 0.5Y product. Sesquiterpenes and sesquiterpene oxides are suggested as an aging index, being present in increased amounts in 5Y. p-Anisaldehyde odour intensity for both samples remained the same (aroma perception sweet creamy, floral odour and Chinese seasoning powder).

Development of a switchable multidimensional/comprehensive two-dimensional gas chromatographic analytical system.

In this study, a new system for analysis using a dual comprehensive two-dimensional gas chromatography/targeted multidimensional gas chromatography (switchable GC x GC/targeted MDGC) analysis was developed. The configuration of this system not only permits the independent operation of GC, GC x GC and targeted MDGC analyses in separate analyses, but also allows the mode to be switched from GC x GC to targeted MDGC any number of times through a single analysis. By incorporating a Deans switch microfluidics transfer module prior to a cryotrapping device, the flow stream from the first dimension column can be directed to either one of two second dimension columns in a classical heart-cutting operation. Both second columns pass through the cryotrap to allow solute bands to be focused and then rapidly remobilized to the respective second columns. A short second column enables GC x GC operation, whilst a longer column is used for targeted MDGC. Validation of the system was performed using a standard mixture of compounds relevant to essential oil analysis, and then using compounds present at different abundances in lavender essential oil. Reproducibility of retention times and peak area responses demonstrated that there was negligible variation in the system over the course of multiple heart-cuts, and proved the reliable operation of the system. An application of the system to lavender oil, as a more complex sample, was carried out to affirm system feasibility, and demonstrate the ability of the system to target multiple components in the oil. The system was proposed to be useful for study of aroma-impact compounds where GC x GC can be incorporated with MDGC to permit precise identification of aroma-active compounds, where heart-cut multidimensional GC-olfactometry detection (MDGC-O) is a more appropriate technology for odour assessment.