Studying Plant–Insect Interactions with Solid Phase Microextraction: Screening for Airborne Volatile Emissions Response of Soybeans to the Soybean Aphid, Aphis glycines Matsumura (Hemiptera: Aphididae)

Insects trigger plants to release volatile compounds that mediate the interaction with both pest and beneficial insects. Soybean aphids (Aphis glycines) induces soybean (Glycine max) leaves to produce volatiles that attract predators of the aphid. In this research, we describe the use of solid-phase microextraction (SPME) for extraction of volatiles from A. glycines-infested plant. Objectives were to (1) determine if SPME can be used to collect soybean plant volatiles and to (2) use headspace SPME-GC-MS approach to screen compounds associated with A. glycines-infested soybeans, grown in the laboratory and in the field, to identify previously known and potentially novel chemical markers of infestation. A total of 62 plant volatiles were identified, representing 10 chemical classes. 39 compounds had not been found in previous studies of soybean volatile emissions. 3-hexen-1-ol, dimethyl nonatriene, indole, caryophyllene, benzaldehyde, linalool, methyl salicylate (MeSA), benzene ethanol, and farnesene were considered herbivore-induced plant volatiles (HIPVs). For reproductive field-grown soybeans, three compounds were emitted in greater abundance from leaves infested with A. glycines, cis-3-hexen-1-ol acetate, MeSA and farnesene. In summary, SPME can detect the emission of HIPVs from plants infested with insect herbivores

Characterization of Livestock Odors Using Steel Plates, Solid Phase Microextraction, and Multidimensional-Gas Chromatography-Mass Spectrometry-Olfactometry

Livestock odor characterization is one of the most challenging analytical tasks. This is because odor-causing gases are often present at very low concentrations in a complex matrix of less important or irrelevant gases. The objective of this project was to develop a set of characteristic reference odors from a swine barn in Iowa, and in the process identify compounds causing characteristic swine odor. Odor samples were collected using a novel sampling methodology consisting of clean steel plates exposed inside and around the swine barn for up to one week. Steel plates were then transported to the laboratory and stored in clean jars. Headspace solid phase microextraction (SPME) was used to extract characteristic odorants collected on the plates. All analyses were conducted on a Gas Chromatography-Mass Spectrometry (GC-MS)-Olfactometry system where the human nose is used as a detector simultaneously with chemical analysis via MS. The effects of sampling time, distance from a source, and the presence of particulate matter (PM) on the abundance of specific gases, odor intensity, and odor character were tested. Steel plates were effectively able to collect key volatile compounds and odorants. The abundance of specific gases and odor was amplified when plates collected PM. The results of this research indicate that PM is major carrier of odor and several key swine odorants. Three odor panelists were consistent in identifying p-cresol as closely resembling characteristic swine odor as well as attributing the largest odor response out of the samples to p-cresol. Further research is warranted to determine how the control of PM emissions from swine housing could affect odor emissions

Solid-Phase Microextraction as a Novel Air Sampling Technology for Improved, GC-Olfactometry-Based, Assessment of Livestock Odors

Air sampling and characterization of odorous livestock gases is one of the most challenging analytical tasks. This is due to low concentrations, physicochemical properties, and problems with sample recoveries for typical odorants. Livestock operations emit a very complex mixture of volatile organic compounds and other gases. Many of these gases are odorous. Relatively little is known about the link between specific VOCs/gases and specifically, about the impact of specific odorants downwind from sources. In this research, solid-phase microextraction (SPME) was used for field air sampling of odors downwind from swine and beef cattle operations. Sampling time ranged from 20 min to 1 hr. Samples were analyzed using a commercial GC-MSOlfactometry system. Odor profiling efforts were directed at odorant prioritization with respect to distance from the source. Results indicated the odor downwind was increasingly defined by a smaller number of high priority odorants. These ‘character-defining’ odorants appeared to be dominated by compounds of relatively low volatility, high molecular weight, and high polarity. In particular, pcresol alone appeared to carry much of the overall odor impact for swine and beef cattle operations. Of particular interest was the character-defining odor impact of p-cresol as far as 16 km downwind of the nearest beef cattle feedlot. The findings are very relevant to scientists and engineers working on improved air sampling and analysis protocols and on improved technologies for odor abatement. More research evaluating the use of p-cresol and a few other key odorants as a surrogate for overall odor dispersion modeling is warranted

Chemical-Sensory Characterization of Dairy Manure Odor Using Headspace Solid-Phase Microextraction and Multidimensional Gas Chromatography Mass Spectrometry-Olfactometry

Livestock operations are associated with emissions of odor, gases, and particulate matter. The majority of previous livestock odor studies focused on swine operations whereas relatively few relate to dairy cattle. Identifying the compounds responsible for the primary odor impact is a demanding analytical challenge because many critical odor components are frequently present at very low concentrations within a complex matrix of numerous insignificant volatiles. The objective of this study was to describe a chemical-sensory profile of dairy manure odor using headspace solid-phase microextraction (HS-SPME) and multidimensional gas chromatography-mass spectrometry-olfactometry (MDGC-MS-O). Two analytical approaches were used: (1) HS-SPME time-series extractions (from seconds up to 20 hr) followed by gas chromatography-mass spectrometry-olfactometry (GC-MS-O) analyses, and (2) relatively short HS-SPME extractions (30 min) followed by MDGC-MS-O analyses on selected chromatogram heart-cuts. Dairy manure was collected at research dairy farms in the United States and Israel. Volatile organic compounds (VOCs) resolved from multiple analyses included sulfur-containing compounds, volatile fatty acids, ketones, esters, and phenol/indole derivatives. A total of 86 potential odorants were identified. Of them, 17 compounds were detected by the human nose only. A greater number of VOCs and odorous compounds were detected, as well as higher mass loading, on solid-phase microextraction (SPME) fibers observed for longer extractions with SPME. However, besides sulfur-containing compounds, other selected compounds showed no apparent competition and displacement on the SPME fiber. The use of MDGC-MS-O increased chromatographic resolution even at relatively short extractions and revealed 22 additional odorants in one of the regions of the chromatogram. The two analytical approaches were found to be parallel to some extent whereas MDGC-MS-O can also be considered as a complementary approach by resolving more detailed chemical-sensory odor profiles

Effects of Dietary Treatment on Odor and VOCs Emitted From Swine Manure

Odor and volatile organic compounds (VOCs) emissions associated with swine production facilities are major concerns for the swine industry. Swine manure is one of the major sources of odor from swine operations. Odor control approaches include ration manipulation, improved manure treatment processes, capture and treatment of odorous gases, and improved dispersion. This study was conducted to investigate the effects of a low level of crude protein and low sulfur content in diets of young swine on odor and VOCs emissions from the headspace of swine manure. Small pigs in metabolic stalls were fed twice daily over 28 days with diets containing either 19.36 % crude protein, 7.06 % cellulose and 2,296 mg/kg sulfur (diet B) or 17.83 % crude protein, 6.82 % cellulose and 1,772 mg/kg sulfur (diet H). Three replicate trials were conducted and three pigs were used for each diet. All excreted manure (feces and urine) were collected daily after morning feeding and added to the manure storage vessel designed to hold waste from the same growing pig. Gas samples were collected from the headspace of manure storage container using 85 µm Carboxen/PDMS SPME fibers at the end of each trial and three replicate gas samples were collected for each pig. All samples were analyzed simultaneously for chemicals and odors on a GC-MS-olfactometry system. Statistical analyses were performed to determine the effects on diets on target odorous chemicals and odor. A total of 40 compounds belonging to 14 chemical classes were identified in the headspace of swine manure. A subset of 14 odorous compounds responsible for the characteristic odor of swine manure were selected for statistical analyses. The lower sulfur and crude protein diet was associated with reduced methanethiol (p=0.0686), dimethyl sulfide (p=0.0006), 2,4-dithiapentane (p\u3c0.00001), acetone (p=0.0003), toluene (p=0.0133), 4-methyl phenol (p=0.0745), 4-ethyl phenol (p=0.00004) and skatole (p=0.0002). The total odor (p=0.0262) and some characteristic odors caused by specific gases were also significantly reduced, i.e. ‘sewer’ (H2S) (p=0.0014), ‘acetic’ (acetic acid) (p=0.00001), ‘skunky’ (2,4-dithiapentane) (p=0.0261), ‘onion’ (dimethyl trisulfide) (p=0.0122) and phenolic’ (4-ethyl phenol) (p=0.0168)