Yvette Naude

Multi-channel open tubular traps for headspace sampling, gas chromatographic fraction collection and olfactory assessment of milk volatiles.

A headspace sampling method is described for concentrating milk volatiles onto a multi-channel open tubular silicone rubber trap (MCT) for thermal desorption into a GC-FID. Sections of the chromatographic profile, single peaks or combinations of compounds are recaptured with secondary MCTs during a subsequent run. The recaptured aroma is released in a controlled manner by heating the MCT in a portable heating device. An aroma release window of several minutes allows up to six people the opportunity to sniff each aroma fraction more than once. Olfactory results suggest that a synergistic combination of 2-heptanone and 2-nonanone could be responsible for a pungent cheese, sour milk-like aroma. MCTs containing single components or fractions can be desorbed into a GC-MS for compound identification.

Investigating the coffee flavour in South African Pinotage wine using novel offline olfactometry and comprehensive gas chromatography with time of flight mass spectrometry

Pinotage wine from several South African wine cellars has been produced with a novel coffee flavour. We have investigated this innovative coffee effect using in house developed solventless sampling and fractionating olfactometric techniques, which are unique in their ability to study synergistic aroma effects as opposed to traditional gas chromatography olfactometry (GC-O) which is designed to, ideally, evaluate single eluting compounds in a chromatographic sequence. Sections of the chromatogram, multiple or single peaks, were recaptured on multichannel open tubular silicone rubber (polydimethylsiloxane (PDMS)) traps at the end of a GC column. The recaptured fractions were released in a controlled manner for offline olfactory evaluation, and for qualitative analysis using comprehensive gas chromatography coupled to time of flight mass spectrometry (GC×GC-TOFMS) for compound separation and identification, thus permitting correlation of odour with specific compounds. A combination of furfural and 2-furanmethanol was responsible for a roast coffee bean-like odour in coffee style Pinotage wines. This coffee perception is the result of a synergistic effect in which no individual compound was responsible for the characteristic aroma.

Monitoring of atmospheric gaseous and particulate polycyclic aromatic hydrocarbons in South African platinum mines utilising portable denuder sampling with analysis by thermal desorption-comprehensive gas chromatography-mass spectrometry

Concentrations of diesel particulate matter and polycyclic aromatic hydrocarbons (PAHs) in platinum mine environments are likely to be higher than in ambient air due to the use of diesel machinery in confined environments. Airborne PAHs may be present in gaseous or particle phases each of which has different human health impacts due to their ultimate fate in the body. Here we report on the simultaneous sampling of both phases of airborne PAHs for the first time in underground platinum mines in South Africa, which was made possible by employing small, portable denuder sampling devices consisting of two polydimethylsiloxane (PDMS) multi-channel traps connected in series separated by a quartz fibre filter, which only require small, battery operated portable personal sampling pumps for air sampling. Thermal desorption coupled with comprehensive gas chromatography-mass spectrometry (TD-GC×GC-TofMS) was used to analyse denuder samples taken in three different platinum mines. The samples from a range of underground environments revealed that PAHs were predominantly found in the gas phase with naphthalene and mono-methylated naphthalene derivatives being detected at the highest concentrations ranging from 0.01 to 18 μg m(-3). The particle bound PAHs were found in the highest concentrations at the idling load haul dump vehicle exhausts with a dominance of fluoranthene and pyrene. Particle associated PAH concentrations ranged from 0.47 to 260 ng m(-3) and included benzo[k]fluoranthene, benzo[a]pyrene, indeno[1,2,3-cd]pyrene and benzo[ghi]perylene. This work highlights the need to characterise both phases in order to assess occupational exposure to PAHs in this challenging sampling environment.

Determination of endocrine disrupting chemicals and antiretroviral compounds in surface water : a disposable sorptive sampler with comprehensive gas chromatography - time-of-flight mass spectrometry and large volume injection with ultra-high performance liquid chromatography-tandem mass spectrometry

Many rural dwellers and inhabitants of informal settlements in South Africa are without access to treated water and collect untreated water from rivers and dams for personal use. Endocrine disrupting chemicals (EDCs) have been detected in surface water and wildlife of South Africa. EDCs are often present in complex environmental matrices at ultra-trace levels complicating detection thereof. We report a simplified multi-residue approach for the detection and quantification of EDCs, emerging EDCs, and antiretroviral drugs in surface water. A low cost (less than one US dollar), disposable, sorptive extraction sampler was prepared in-house. The disposable samplers consisted of polydimethylsiloxane (PDMS) tubing fashioned into a loop which was then placed in water samples to concentrate EDCs and emerging pollutants. The PDMS samplers were thermally desorbed directly in the inlet of a GC, thereby eliminating the need for expensive consumable cryogenics. Comprehensive gas chromatography coupled to time-of-flight mass spectrometry (GC×GC-TOFMS) was used for compound separation and identification. Linear retention indices of EDCs and emerging pollutants were determined on a proprietary Crossbond® phase Rtx®-CLPesticides II GC capillary column. In addition, large volume injection of surface water into an ultra-performance liquid chromatograph tandem mass spectrometer (UPLC-MS/MS) was used as complementary methodology for the detection of less volatile compounds. Large volume injection reduced tedious and costly sample preparation steps. Limits of detection for the GC method ranged from 1 to 98pg/l and for the LC method from 2 to 135ng/l. Known and emerging EDCs such as pharmaceuticals, personal care products and pesticides, as well as the antiretroviral compounds, efavirenz and nevirapine, were detected in surface water from South Africa at concentration levels ranging from 0.16ng/l to 227ng/l.

Diversity and functionality of bacillus species associated with alkaline fermentation of bambara groundnut ( Vigna subterranean L. Verdc ) into dawadawa-type African condiment

The aim of this study was to investigate the diversity of Bacillus species in dawadawa; aiding potential starter cultures selection for alkaline fermentation of bambara groundnut into dawadawa-type condiments based on their genotypic and volatile compound profiles. Bacillus species (n = 71) isolated from spontaneously fermented dawadawa were identified using matrix assisted laser desorption ionization time of flight mass spectrometry (MALDI-TOF MS) as B. cereus (35%), B. licheniformis (30%), B. pumilus (21%), B. subtilis (10%) and B. amyloliquefaciens (4%). Further molecular typing was performed using GTG5 rep-PCR typing, 16S rRNA and gyrA gene sequencing. The gyrA gene sequence analysis exhibited the highest species discriminatory power with B. subtilis subsp. subtilis, B. amyloliquefaciens subsp. plantarum, B. pumilus and B. licheniformis as the distinct clusters. Representative strains from each cluster were then used as starter cultures for the production of dawadawa from bambara groundnut. Volatile compounds analysis using headspace solid phase microextraction (SPME) and comprehensive gas chromatography coupled to time of flight mass spectrometry (GC × GC–TOF MS) identified distinct chemical profiles produced by each of the four strains. Volatile compounds produced by B. subtilis subsp. subtilis (strain SFBA3) were categorized by dimethyl disulfide, methanethiol and nonanal while B. amyloliquefaciens subsp. plantarum (strain SFBA2) produced acetic acid and hexadecanoic acid. B. cereus (strain PALB7) produced 2,5-dimethyl pyrazine and 2-butanone which were not detected in the other condiments. Hexanal was the main compound produced by B. licheniformis (strain OALB7).

Volatile compounds produced by Bacillus species alkaline fermentation of bambara groundnut (Vigna subterranean (L.) Verdc) into a dawadawa - type African food condiment using headspace solid-phase microextraction and GC x GC-TOFMS

ABSTRACT The reports on the volatile compounds of a dawadawa-type African food condiment produced from the alkaline fermentation of bambara groundnut (Vigna subterranea (L.) Verdc.) using Bacillus starter cultures are limited. Volatile compounds were isolated from dawadawa-type condiments using headspace solid phase microextraction and analysed by comprehensive gas chromatography coupled to time of flight mass spectrometry. Acids, aldehydes and alcohols accounted for over 70% of the volatile compounds produced in the Bacillus fermented samples. B. subtilis subsp. subtilis SFBA3 produced the highest content of acids (4969.60 µg kg−1), while the highest content of aldehydes (2811.90 µg kg−1) and alcohols (1247.60 µg kg−1) was detected with Bacillus cereus PALB7 and Bacillus licheniformis OALB2, respectively. Sulphur-containing compounds concentration (85.80 µg kg−1) was highest for Bacillus amyloliquefaciens SFBA2. Maximum 2-methyl butanoic acid and 3-methyl butanoic acid concentrations, indicative of typical dawadawa aroma, were produced by B. subtilis subsp. subtilis SFBA3.