Identification of volatile compounds in soybean at various developmental stages using solid phase microextraction

Identification of volatile organic compounds in purple and white soybean flowers by HS-SPME/GC-MS

This study aimed to establish a method for the extraction, enrichment, and identification of volatile organic compounds (VOCs) released by the flowers of purple (BRS 399) and white (DONMARIO 6563) soybean varieties. We tested the Static Headspace (HS) and Solid Phase Microextraction (SPME) methods using various fibre types: PDMS (Polydimethylsiloxane), PDMS/DVB (Divinylbenzene), and PDMS/DVB/CAR (Carboxen). We employed gas chromatography-mass spectrometry (GC-MS) to identify the VOCs. The SPME method with PDMS/DVB and PDMS/DVB/CAR fibres yielded the highest number of extracted compounds for both soybean cultivars. Notably, 67 compounds were detected in Glycine max. L for the first time. Using the developed method, we were able to detect 52 and 57 VOCs in the purple and white soybean varieties, respectively, including ketones, alcohols, aldehydes and benzenoids. In conclusion, the method we developed effectively identified VOCs in soybean flowers, thus enriching our understanding of the interactions between soybean flowers and their pollinators.

Antennal transcriptome analysis of odorant-binding proteins and characterization of GOBP2 in the variegated cutworm Peridroma saucia

Odorant-binding proteins (OBPs) are expressed at extremely high concentrations in the chemo-sensilla lymph of insects and have long been thought to be crucial for delivering the semiochemicals to the odorant receptors. They are represented by multiple classes: general odorant-binding proteins (GOBP1 and GOBP2) and pheromone-binding proteins. In the current study, we identified a total of 35 OBPs in the antennal transcriptome of Peridroma saucia, a worldwide pest that causes serious damage to various crops. A gene expression value (TPM, transcripts per million) analysis revealed that seven OBPs (PsauPBP1/2/3, PsauGOBP1/2, PsauOBP6, and PsauOBP8) were highly abundant in the antennae. Next, we focused on the expression and functional characterization of PsauGOBP2. Real-time quantitative-PCR analysis demonstrated that PsauGOBP2 was predominantly expressed in the antennae of both sexes. Fluorescence binding assays showed that the recombinant PsauGOBP2 strongly binds to the female sex pheromone components Z11-16: Ac (Ki = 4.2 μM) and Z9-14: Ac (Ki = 4.9 μM) and binds moderately (6 µM ≤ Ki ≤ 13 µM) to the host plant volatiles phenylethyl acetate, β-myrcene, and dodecanol. Further 3D structural modeling and molecular docking revealed that several crucial amino acid residues are involved in ligand binding. The results not only increase our understanding of the olfactory system of P. saucia but also provide insights into the function of PsauGOBP2 that has implications for developing sustainable approaches for P. saucia management.

Volatile compounds from soybeans under multiple on herbivores infestations attract the predatory mite Neoseiulus californicus (Acari: Phytoseiidae)

Plant-induced resistance can be an important component of soybean mites biological control programs. This work evaluates the preference of predatory mite Neoseiulus californicus (Acari: Phytoseiidae) to soybean plants under single and multiple herbivory conditions by two-spotted spider mite Tetranychus urticae (Acari: Tetranychidae), and velvetbean caterpillar Anticarsia gemmatalis (Lepidoptera: Noctuidae). Using a Y olfactometer, the following scenarios were evaluated: soybean with no infestation and soybean infested with A. gemmatalis; soybean infested with T. urticae and A. gemmatalis, and soybean infested with T. urticae and with both T. urticae and A. gemmatalis. Volatile compounds released by plants were analyzed and identified by a Trace GC Ultra gas chromatograph coupled to a mass spectrometer with a solid phase micro-extraction ion-trap. The predatory mite N. californicus preferred soybean plants infested with T. urticae compared to those infested with A. gemmatalis. Multiple infestation did not interfere with its preference to T. urticae. Multiple herbivory of T. urticae and A. gemmatalis modified the chemical profile of volatile compounds emitted by soybean plants. However, it did not interfere with the search behavior of N. californicus. Out of the 29 identified compounds only five promoted predatory mite response. Thus, regardless of single or multiple herbivory by T. urticae with or without A. gemmatalis, the indirect induced resistance mechanisms operate similarly. As such, this mechanism contributes to an increase in the encounter rate between predator and prey for N. Californicus and T. urticae, and the efficacy of biological control of mites on soybean.

Expression, affinity, and binding mode analysis of antennal-binding protein X in the variegated cutworm Peridroma saucia (Hübner)

The variegated cutworm Peridroma saucia (Hübner) is a worldwide pest that causes serious damage to many crops. Odorant-binding proteins (OBPs) are small soluble proteins involved in the first step of odorant reception. In moths, antennal-binding protein Xs (ABPXs) represent a main subfamily of classic OBPs. However, their functions remain unclear. Here, we cloned the ABPX gene from the antennae of P. saucia. RT-qPCR and western-blot analyses showed that PsauABPX is antenna-predominant and male-biased. Further temporal expression investigation indicated that the expression of PsauABPX started 1 day before eclosion and reached the highest 3 days after eclosion. Next, fluorescence binding assays revealed that recombinant PsauABPX had high binding affinities with P. saucia female sex pheromone components Z11-16: Ac and Z9-14: Ac. Then, molecular docking, molecular dynamics simulation, and site-directed mutagenesis were employed to identify key amino acid residues involved in the binding of PsauABPX to Z11-16: Ac and Z9-14: Ac. The results demonstrated that Val-32, Gln-107 and Tyr-114 are essential for the binding to both sex pheromones. This study not only give us insight into the function and binding mechanism of ABPXs in moths, but could also be used to explore novel strategies to control P. saucia.

Functionalization of soy residue (okara) by enzymatic hydrolysis and LAB fermentation for B2 bio-enrichment and improved in vitro digestion

The utilization of major edible soy-waste (okara) remains a challenge due to its poor digestion, nutritional imbalance (lack of B-vitamins), and undesirable off-flavors. Herein, fresh okara was enzymatically hydrolyzed and then fermented using the B2-overproducing Lactiplantibacillus plantarum UFG169 strain. SEM micrographs showed the microporous and honeycombed structures on the surface of okara. The off-flavors were reduced, and the essential amino acids content was significantly increased in fermented okara. The higher β-glucosidase activity, increased aglycone isoflavones, and in situ riboflavin (B2) were associated with the enhanced antioxidant potential of the fermented okara. The in vitro digestion of okara resulted in reduced particle size, higher protein digestibility, improved aggregation, lower protein molecular chains, and increased polyphenols. Overall, our study indicated the improved nutrition and digestibility of B2 bio-enriched okara.

Comparative Analysis and Development of a Flavor Fingerprint for Volatile Compounds of Vegetable Soybean Seeds Based on Headspace-Gas Chromatography-Ion Mobility Spectrometry

Evaluating the volatile compounds and characteristic fingerprints of the core cultivars of vegetable soybean would provide useful data for improving their aroma in the breeding programs. The present study used headspace-gas chromatography-ion mobility spectrometry (HS-GC-IMS) to evaluate the volatile compounds of vegetable soybean seeds at a specific growth stage. In total, 93 signal peaks were identified, 63 compounds qualitatively, with 14 volatile flavor compounds providing multiple signals. The 63 volatile compounds consisted of 15 esters, 15 aldehydes, 13 alcohols, 15 ketones, one acid, and four other compounds. The peak intensity of most of the volatile compounds varied greatly between the core cultivars. The alcohols and aldehydes determined the basic volatile flavor of the vegetable soybean seeds. Volatile flavors were determined by their respective esters, ketones, or other components. Characteristic fingerprints were found in some core vegetable soybean cultivars. Four cultivars (Xiangdou, ZHE1754, Zhexian 65018-33, and Qvxian No. 1) had pleasant aromas, because of their higher content of 2-acetyl-1-pyrroline (2-AP). A principal component analysis (PCA) was used to distinguish the samples based on the signal intensity of their volatile components. The results showed that the composition and concentration of volatile compounds differed greatly between the core cultivars, with the volatile flavor compounds of soybeans being determined by the ecotype of the cultivar, the direction of breeding selection, and their geographical origin. Characteristic fingerprints of the cultivars were established by HS-GC-IMS, enabling them to be used to describe and distinguish cultivars and their offspring in future breeding studies.

Sensory attributes and characterization of aroma profiles of fermented sausages based on fibrous-like meat substitute from soybean protein and Coprinus comatus

Plant-based meat substitutes are emerging as healthy, balanced, and sustainable non-animal alternatives to alleviate stress from the increased demand for meat products. In this study, fibrous-like extrudates acting as meat substitutes were manufactured from soybean protein and Coprinus comatus by thermos-extrusion and fermentation processing improved the meat-like physicochemical and textural properties, taste, and flavor of products. The fermentation period was greatly shortened than animal meat-based fermented sausage. For comparison reasons, the aroma profiles of meat substitute fermented sausages (MS-FS), fermented sausages without curing (MS-NCFS) and natural fermented sausages (MS-NFS) were systemically analyzed by headspace solid phase microextraction-gas chromatography-mass spectrometry (HS-SPME-GC-MS). A total of 156 volatile compounds were identified, and the curing and fermenting process contributed to the increased contents of volatile compounds greatly. Moreover, the MS-FS without curing evaded undesired off-flavors like grass and bean flavor from 1-octen-3-ol. Sensory evaluation was also showed higher scores for MS-FS than other processing.

GOBP1 from the Variegated Cutworm Peridroma saucia (Hübner) (Lepidoptera: Noctuidae) Displays High Binding Affinities to the Behavioral Attractant (Z)-3-Hexenyl acetate

The variegated cutworm Peridroma saucia (Hübner) is a worldwide pest that causes serious damage to many crops. To recognize sex pheromones and host plant volatiles, insects depend on olfactory chemoreception involving general odorant-binding proteins (GOBPs). In this study, PsauGOBP1 was cloned from the adult antennae of P. saucia. RT-qPCR and Western-blot analysis showed that PsauGOBP1 was specifically and equally expressed in the adult antennae of both females and males. Fluorescence competitive-binding assays with sex pheromones and host plant volatiles demonstrated that PsauGOBP1 bound to six host plant volatiles: (Z)-3-hexenyl acetate (K_D = 4.0 ± 0.1 μM), citral (K_D = 5.6 ± 0.4 μM), farnesol (K_D = 6.4 ± 0.6 μM), nonanal (K_D = 6.8 ± 0.3 μM), (Z)-3-hexen-1-ol (K_D = 8.5 ± 0.6 μM), and benzaldehyde (K_D = 9.4 ± 0.5 μM). Electroantennogram recordings with the six host plant volatiles indicated that (Z)-3-hexenyl acetate elicited the strongest responses from both male and female antennae. Further bioassays using Y-tube olfactometers showed that (Z)-3-hexenyl acetate was attractive to adult P. saucia of both sexes. These results suggest that PsauGOBP1 might be involved in detecting host plant volatiles and that (Z)-3-hexenyl acetate might serve as a potential attractant for the biological control of P. saucia.

Hexanal induces early apoptosis of Aspergillus flavus conidia by disrupting mitochondrial function and expression of key genes

Aspergillus flavus is a notorious saprophytic fungus that compromises the quantity and quality of postharvest grains and produces carcinogenic aflatoxins. The natural compound hexanal disrupts cell membrane synthesis and mitochondrial function and induces apoptosis in A. flavus; here, we investigated the molecular mechanisms underlying these effects. The minimum inhibition and fungicidal concentration (MIC and MFC) of hexanal against A. flavus spores were 3.2 and 9.6 μL/mL, respectively. Hexanal exposure resulted in abnormal spore morphology and early spore apoptosis. These changes were accompanied by increased reactive oxygen species production, reduced mitochondrial membrane potential, and DNA fragmentation. Transcriptomic analysis revealed that hexanal treatment greatly altered the metabolism of A. flavus spores, including membrane permeability, mitochondrial function, energy metabolism, DNA replication, oxidative stress, and autophagy. This study provides novel insights into the mechanism underlying the antifungal activity of hexanal, suggesting that hexanal can be used an anti-A. flavus agent for agricultural applications. KEY POINTS: • Hexanal exposure resulted in abnormal spore morphology. • The apoptotic characteristics of A. flavus were induced after hexanal treatment. • Hexanal could change the expression of key A. flavus growth-related genes.

Induced volatiles in the interaction between soybean (Glycine max) and the Mexican soybean weevil (Rhyssomatus nigerrimus)

The present study analyzed the volatile compounds emitted by Glycine max (cv. FT-Cristalina-RCH) soybean plants: healthy plants and plants damaged mechanically or by the Mexican soybean weevil Rhyssomatus nigerrimus. The SPME method was used to compare the volatile profile of soybean plants in four different conditions. The volatile profile of G. max plants infested by R. nigerrimus was qualitatively and quantitatively different from that of healthy and mechanically damaged plants. Emission of 59 compounds was detected in the four treatments. Of these compounds, 19 were identified by comparison of the Kovats index, mass spectrum and retention times with those of synthetic standards. An increase in concentration of the volatiles (Z)-3-hexenyl acetate and the compound 1-octen-3-ol was observed when the soybean plants were mechanically damaged. The compounds mostly produced by the soybean plant during infestation by male and female R. nigerrimus were 1-octen-3-ol, 6-methyl-5-hepten-2-one, (E)-β-ocimene, salicylaldehyde, unknown 10, linalool, methyl salicylate, (Z)-8-dodecenyl acetate (ester 5), ketone 2 and geranyl acetone. Behavioral effects of the identified compounds during the insect-plant interaction and their conspecifics are discussed.

Effects of roasting level on physicochemical, sensory, and volatile profiles of soybeans using electronic nose and HS-SPME-GC-MS

We applied oven-roasting on soybean in order to investigate their physicochemical, sensory, and volatile profiles using electronic nose and HS-SPME-GC-MS. Results revealed a temperature dependent kinetic on the physicochemical index except fat content. Roasting at 200 °C for 20 min decreased the protein dispersibility index about 38%; while, lipoxygenase and peroxidase were entirely inactivated. The primary heat sensitive amino acids were methionine, arginine, and cysteine. Electronic nose showed certain capacity to discriminate varying roasted soybeans. Out of 41 volatile compounds identified in soybean headspace, 2,5-dimethylpyrazine showed the highest abundance of 411.18 μg/Kg. Regression model suggested the association of hexanal and aliphatic alcohols with beany flavor, while pyrazines, heterocycles, and furanoids showed a positive correlation with roasted flavor. The selected flavor markers can be used to predict the development of flavor in roasted soybeans. Our study emphasized the effect of roasting level on nutritive value and flavor profiles of soybeans.

(E)-2-Heptenal in Soymilk: A Nonenzymatic Formation Route and the Impact on the Flavor Profile

Flavor is an essential quality characteristic of soymilk. (E)-2-Heptenal has a fatty and fruity flavor with the sensory threshold value of 13 μg/L in water. This study demonstrated that the formation of (E)-2-heptenal was independent of the lipoxygenase (LOX) and hydroperoxide lyase (HPL) activity as well as oxygen concentration but was related to the presence/absence of Fe²⁺ and chelators. In a dry matter base, soybean hypocotyls generated a much higher amount of (E)-2-heptenal than cotyledons. A phospholipid hydroperoxide was purified from the chloroform/methanol extract of soybean hypocotyls and was identified as 1-palmitoyl-2-(12-hydroperoxyoctadecadienoyl)-sn-glycerol-3-phosphatidylethanol-amine (12-PEOOH). The decomposition of 12-PEOOH in the presence of ferrous ions to form (E)-2-heptenal was studied in a model system. The rate of decomposition decreased sharply at pH values higher than 6, but the molar conversion of 12-PEOOH to (E)-2-heptenal increased with an increase of pH. At a constant pH of 5.8, the decomposition rate of 12-PEOOH was positively linearly related to the Fe²⁺ concentration, while the molar conversion to (E)-2-heptenal was 74% and independent of the Fe²⁺ concentration. The formation of radicals LOO^• and R^• showed similar pH and Fe²⁺ concentration dependence with those of (E)-2-heptenal. (E)-2-Heptenal displayed an enhancement of bean aroma and fruity flavor of soymilk at low concentrations, but a fatty flavor was noticed at high concentrations.

Mechanisms of Soybean Host-Plant Resistance Against Megacopta cribraria (Hemiptera: Plataspidae)

A number of soybean varieties traditionally bred for resistance to various soybean arthropod pests have been identified as resistant to Megacopta cribraria (F.) (Hemiptera: Plataspidae). However, the mechanisms of host-plant resistance (HPR) in this system are not understood. The goal of this study was to identify the mechanisms of resistance by examining the role of plant volatile organic compounds (VOCs) and free amino acids (FAAs) among 16 soybean varieties. Choice and no-choice cage experiments identified several soybean varieties that demonstrated antixenosis as well as antibiosis. However, resistance varied over time in certain soybean varieties, such as N02-7002 and PI567352B. Mean nymph number from choice experiments had positive correlations with the FAAs asparagine, tryptophan, alanine, phenylanaline, and serine; negative correlation with leucine and threonine. Four plant volatiles, hexanal, 2-pentylfuran, beta-cyclocitral, and cis-9-hexadecenal, were positively correlated with subsequent nymph development, whereas n-hexadecenoic acid was negatively correlated with nymph number only, in adult choice cage experiments. This study contributes to understanding the mechanisms of HPR through associations with plant VOCs and FAAs in relation to M. cribraria development and provides useful knowledge for developing soybean varieties for M. cribraria management.

Overlooked side effects of organic farming inputs attract soil insect crop pests

Organic farming has been praised for many sound reasons, but there are some negative effects of organic practices. Research on the interactions between soil insect pests and organic farming practices is still scarce, although such interactions might sometimes lead to severe crop damage. Here, we explore the influences of organic farming inputs and key host crops on the oviposition behavior of soil insect pests likely to infest crops. We also shed light on the factors driving this behavior and analyze 4 yr of data from an on-farm investigation. Our study offers clear support to the idea that decomposing organic matter and legume crops affect oviposition behavior and provides evidence that butyric acid and 1-hexanol are major attractants. The results suggest that poor management or returning decomposing organic matter to the field is risky. The silver lining, however, is that oviposition behavior can be disrupted by the identified key attractants to benefit crop protection.

Discrimination of Cultivated Regions of Soybeans (Glycine max) Based on Multivariate Data Analysis of Volatile Metabolite Profiles

Soybean (Glycine max) is a major crop cultivated in various regions and consumed globally. The formation of volatile compounds in soybeans is influenced by the cultivar as well as environmental factors, such as the climate and soil in the cultivation areas. This study used gas chromatography-mass spectrometry (GC-MS) combined by headspace solid-phase microextraction (HS-SPME) to analyze the volatile compounds of soybeans cultivated in Korea, China, and North America. The multivariate data analysis of partial least square-discriminant analysis (PLS-DA), and hierarchical clustering analysis (HCA) were then applied to GC-MS data sets. The soybeans could be clearly discriminated according to their geographical origins on the PLS-DA score plot. In particular, 25 volatile compounds, including terpenes (limonene, myrcene), esters (ethyl hexanoate, butyl butanoate, butyl prop-2-enoate, butyl acetate, butyl propanoate), aldehydes (nonanal, heptanal, (E)-hex-2-enal, (E)-hept-2-enal, acetaldehyde) were main contributors to the discrimination of soybeans cultivated in China from those cultivated in other regions in the PLS-DA score plot. On the other hand, 15 volatile compounds, such as 2-ethylhexan-1-ol, 2,5-dimethylhexan-2-ol, octanal, and heptanal, were related to Korean soybeans located on the negative PLS 2 axis, whereas 12 volatile compounds, such as oct-1-en-3-ol, heptan-4-ol, butyl butanoate, and butyl acetate, were responsible for North American soybeans. However, the multivariate statistical analysis (PLS-DA) was not able to clearly distinguish soybeans cultivated in Korea, except for those from the Gyeonggi and Kyeongsangbuk provinces.

Rapid Profiling of Soybean Aromatic Compounds Using Electronic Nose

Soybean (Glycine max (L.)) is the world's most important seed legume, which contributes to 25% of global edible oil, and about two-thirds of the world's protein concentrate for livestock feeding. One of the factors that limit soybean's utilization as a major source of protein for humans is its characteristic soy flavor. This off-flavor can be attributed to the presence of various chemicals such as phenols, aldehydes, ketones, furans, alcohols, and amines. In addition, these flavor compounds interact with protein and cause the formation of new off-flavors. Hence, studying the chemical profile of soybean seeds is an important step in understanding how different chemical classes interact and contribute to the overall flavor profile of the crop. In our study, we utilized the HERCALES Fast Gas Chromatography (GC) electronic nose for identification and characterization of different volatile compounds in five high-yielding soybean varieties, and studied their association with off-flavors. With aroma profiling and chemical characterization, we aim to determine the quantity and quality of volatile compounds in these soybean varieties and understand their effect on the flavor profiles. The study could help to understand soybean flavor characteristics, which in turn could increase soybean use and enhance profitability.

Electrophysiological and Behavioral Responses of the Kudzu Bug, Megacopta cribraria (Hemiptera: Plataspidae), to Volatile Compounds from Kudzu and Soybean Plants

The kudzu bug, Megacopta cribraria, is a key pest of soybean in the United States. Electrophysiological and behavioral responses of adult M. cribraria to kudzu and soybean volatile compounds were examined to identify semiochemicals used for host location. Headspace volatiles collected from undamaged potted plants were analyzed by gas chromatography with electroantennographic detection (GC-EAD). Subsequently, six GC-EAD-active compounds were identified by gas chromatography-mass spectrometry (GC-MS). These six compounds, along with some previously reported insect attractants, were selected for electroantennogram (EAG) assays. The four chemicals that elicited the strongest EAG responses, 1-octen-3-ol, nonanal, benzaldehyde, and ocimene, were selected for evaluation in olfactometer bioassays. Both benzaldehyde and 1-octen-3-ol exhibited dose-dependent responses at higher concentration. Our results provide insight into host location compounds used by adult M. cribraria. These results may be evaluated in future field tests and ultimately useful to develop a semiochemical-based monitoring technique and integrated pest management program for M. cribraria.

Capturing and Explaining Sensory Differences among Organically Grown Vegetable-Soybean Varieties Grown in Northern California

Vegetable soybean (VS), known as edamame, is appreciated for its robust flavor and exceptional nutrient content. Although the United States is one of the world's leading producers of soy, only a fraction is harvested as edamame. Research involving varietal differences is very limited, particularly among U.S. consumers. Sensory attributes of three VS varieties grown in Northern California (with organic methods) were assessed: Giant Midori (GM), ButterBean (BB), and Kuroshinja (KU). Participants (n = 74) rated four characteristics: flavor, texture, appearance, and overall liking on unlabeled, 11-point hedonic scales and were asked if they would purchase the variety. A small portion of these participants would again evaluate the varieties, using free choice profiling (FCP) methodology. After these evaluations, texture analyzer, colorimeter, and high-performance liquid chromatography (free amino acids, sugars, and isoflavones) testing were performed. Among tested varieties, distinct differences in quality were found, with GM preferred first, followed by KU, and BB. GM was significantly harder, a more intense green, had more free sugars and isoflavones and fewer free amino acids, whereas KU and BB trended to be the opposite. Analyzing FCP data with a General Procrustes Analysis, varieties were separated in different factors for flavor and texture, but not appearance. Although repeated, and larger trials are needed, our study signifies that consumers are able to detect differences among VS varieties. Further research may influence producers to grow the variety likely to be most profitable and marketable.

Attractiveness of Host Plants at Different Growth Stage to Kudzu Bug, Megacopta cribraria (Heteroptera: Plataspidae): Behavioral Responses to Whole Plant and Constitutive Volatiles

The kudzu bug, Megacopta cribraria (Fabricius), is an invasive pest of soybeans, Glycine max (L.) Merr., that has recently been detected in the United States. This study investigated whether there was a differential attraction of adult bugs to soybean growth stages, and whether the attraction was related to soybean constitutive volatiles. Greenhouse choice assays examined the behavioral orientation preference of adult bugs exposed to four growth stages of whole soybean plants: vegetative (V2), flowering (R1), pod (R3), and seed (R5). Results show that significantly more adults landed on plants in the early reproductive stage R1 than in other stages. Laboratory olfactometer assays also demonstrate that significantly more adult bugs were attracted to R1 plants, with females responding more strongly than males. Both greenhouse and olfactometer assays indicate that the differential attraction of adult bugs to soybean growth stages was mediated by plant constitutive volatiles. These results offer an insight into kudzu bug chemical and behavioral ecology and thus are of great significance for optimizing the timing of field scouting and treatment as well as the development of soybean pest management programs.

Chemical Composition, Antioxidant and Biological Activities of the Essential Oil and Extract of the Seeds of Glycine max (Soybean) from North Iran

Glycine max (L.) Merrill (soybean) is a major leguminous crop, cultivated globally as well as in Iran. This study examines the chemical composition of soybean essential oil, and evaluates the antioxidant and antimicrobial activities of seeds on various plant pathogens that commonly cause irreparable damages to agricultural crops. The essential oil of soybean seeds was analyzed by gas chromatography coupled to mass spectrometry. Antimicrobial activity was tested against 14 microorganisms, including three gram-positive, five gram-negative bacteria, and six fungi, using disk diffusion method and the Minimum Inhibitory Concentration technique. The soybean seeds were also subjected to screening for possible antioxidant activity by using catalase, peroxidase, superoxide dismutase, and 2,2-diphenyl-1-picrylhydrazyl (DPPH) assay. Forty components were identified, representing 96.68% of the total oil. The major constituents of the oil were carvacrol (13.44%), (E,E)-2,4-decadienal (9.15%), p-allylanisole (5.65%), p-cymene (4.87%), and limonene (4.75%). The oil showed significant activity against Pseudomonas syringae subsp. syringae, Rathayibacter toxicus with MIC = 25 µg/mL, and Pyricularia oryzae with MIC = 12.5 µg/mL. In addition, the free radical scavenging capacity of the essential oil was determined with an IC50 value of 162.35 µg/mL. Our results suggest that this plant may be a potential source of biocide, for economical and environmentally friendly disease control strategies. It may also be a good candidate for further biological and pharmacological investigations.

Barley (Hordeum distichon L.) roots synthesise volatile aldehydes with a strong age-dependent pattern and release (E)-non-2-enal and (E,Z)-nona-2,6-dienal after mechanical injury

In the context of chemical ecology, the analysis of the temporal production pattern of volatile organic compounds (VOCs) in root tissues and the emission rate measurement of root-emitted VOCs are of major importance for setting up experiments to study the implication of these compounds in biotic interactions. Such analyses, however, remain challenging because of the belowground location of plant root systems. In this context, this study describes the evolution of the root VOC production pattern of barley (Hordeum distichon L.) at five developmental stages from germination to the end of tillering and evaluates the emission of the identified VOCs in an artificial soil. VOCs produced by crushed root tissues and released by unexcavated root systems were analysed using dynamic sampling devices coupled to a gas chromatography-mass spectrometry methodology (synchronous SCAN/SIM). The results showed that, at each analysed developmental stage, crushed barley roots produced mainly four volatile aldehydes: hexanal; (E)-hex-2-enal; (E)-non-2-enal; and (E,Z)-nona-2,6-dienal. Higher total and individual VOC concentrations were measured in 3-day-old seminal roots compared with older phenological stages. For each developmental stage, the lipoxygenase (LOX) activity was greater for linoleic acid than α-linolenic acid and the greatest LOX activities using linoleic and α-linolenic acids as substrates were measured in 7- and 3-day-old roots, respectively. The analysis of VOCs released by barley roots into the soil showed that (E)-non-2-enal and (E,Z)-nona-2,6-dienal were the only VOCs emitted in quantifiable amounts by mechanically injured roots.

Effects of Aspergillus species inoculation and their enzymatic activities on the formation of volatile components in fermented soybean paste (doenjang)

The volatile components of rice-koji doenjang produced in association with various Aspergillus species (A. oryzae, A. sojae, and A. kawachii) during 8 weeks of fermentation were compared using gas chromatography-mass spectrometry analysis and multivariate statistical analysis. In addition, the activities of diverse enzymes (α-amylase, protease, lipase, and esterase) were determined to investigate their effects on the formation of volatile compounds. Regardless of the fungi types, carbonyls including 4-methylheptan-2-one, heptan-2-one, (E)-hept-2-enal, and hexanal were found to contribute mainly to early phase fermentation, whereas the contents of ethyl esters of long-chained fatty acids were considerably enhanced in the latter stage of fermentation. With the exception of α-amylase, the activities of the studied enzymes generally increased as fermentation proceeded, and there were significant differences in enzymes activities between the species of fungi. The lipase activity was strongly correlated with the formation of long-chain fatty acid esters, which could be related to the distinctive organoleptic properties of rice-koji doenjang.

Volatile compounds as markers of tofu (soybean curd) freshness during storage

Volatile compounds in packed and unpacked commercial tofu were extracted by solid phase microextraction fibers and analyzed by gas chromatography-mass spectrometry. The tofu samples were stored at 4 °C for 15 days to measure freshness and quality changes during storage. Totals of 41 and 35 volatile compounds were identified from packed tofu and unpacked tofu, respectively. Peak area ratio (PAR) of hexanal in packed tofu increased from 11.44 (day 0) to 496.30 (day 9) and finally decreased to 11.06 on day 15 of storage. PAR of ethanol and 1-hexanol increased from 5.41 and 0.76 (day 1) to 66.93 (day 9) and 47.46 (day 15), respectively. Changes in these volatiles in unpacked tofu were similar to those in packed tofu. The results show that hexanal, ethanol, and 1-hexanol are characteristic volatile compounds for providing quantitative and qualitative information regarding deterioration of tofu.

Inoculation with Bradyrhizobium japonicum enhances the organic and fatty acids content of soybean (Glycine max (L.) Merrill) seeds

Soybean (Glycine max (L.) Merrill) is one of the most important food crops for human and animal consumption, providing oil and protein at relatively low cost. The least expensive source of nitrogen for soybean is the biological fixation of atmospheric nitrogen by the symbiotic association with soil bacteria, belonging mainly to the genus Bradyrhizobium. This study was conducted to assess the effect of the inoculation of G. max with Bradyrhizobium japonicum on the metabolite profile and antioxidant potential of its seeds. Phenolic compounds, sterols, triterpenes, organic acids, fatty acids and volatiles profiles were characterised by different chromatographic techniques. The antioxidant activity was evaluated against DPPH, superoxide and nitric oxide radicals. Inoculation with B. japonicum induced changes in the profiles of primary and secondary metabolites of G. max seeds, without affecting their antioxidant capacity. The increase of organic and fatty acids and volatiles suggest a positive effect of the inoculation process. These findings indicate that the inoculation with nodulating B. japonicum is a beneficial agricultural practice, increasing the content of bioactive metabolites in G. max seeds owing to the establishment of symbiosis between plant and microorganism, with direct effects on seed quality.

Induction of hexanol dehydrogenase in Geotrichum spp. by the addition of hexanol

Excessive hexanol content distorts the flavor of foods and is harmful to human health. Previously, two strains of fungi were found capable of producing hexanol-degrading enzymes. The current study identified these strains as Galactomyces geotrichum according to the gene sequence of the 26 S rDNA D1/D2 region (strain S12) and genus Geotrichum according to the gene sequence of ITS region (strain S13). Parallel analysis of extracellular and intracellular enzyme activities showed that the enzymes mainly accumulated intracellularly. Native polyacrylamide gel electrophoresis with reactive dyes showed the enzymes were alcohol dehydrogenases induced by the addition of hexanol. Hexanol was catalyzed into hexanoic acid and hexanal by strain S12 and into hexanoic acid by strain S13. The optimum conditions for the induction of enzymes were determined to be 6-9 h in the presence of 0.7 g/l hexanol. The identification of two strains capable of enzymatically degrading hexanol and optimum conditions for their induction will facilitate their use in industrial applications.

Comparison of fermented soybean paste (Doenjang) prepared by different methods based on profiling of volatile compounds

In this study, 2 different extraction methods, namely solvent-assisted flavor evaporation (SAFE) and solid-phase microextraction (SPME), were employed to investigate the comprehensive volatile profile of Doenjang (one of Korean fermented soybean pastes) efficiently. Quantitatively, major volatiles of Doenjang isolated by SAFE were 3-methylbutanoic acid, butanoic acid, 3-hydroxy-2-methyl-4H-pyran-4-one (maltol), ethyl 2-methylbutanoate, 2-methylpropanoic acid, tetramethylpyrazine, and 4-ethyl-2-methoxyphenol, while ethanol, ethenylbenzene, ethyl benzoate, ethyl linoleate, ethyl acetate, ethyl butanoate, tetramethylpyrazine, and ethyl 2-methylpropanoate extracted by SPME. In addition, volatile profiling that applied principal component analysis to gas chromatography-mass spectrometry datasets allowed Doenjang samples that had been prepared using different traditional and commercial methods to be discriminated, and the volatile compounds that contributed to their discrimination were assigned. The major volatiles that were related to differentiation of traditional and commercial Doenjang samples were 2-pentylfuran, 4-ethylphenol, dihydro-5-methyl-2(3H)-furanone, butanoic acid, pyrazines (for example, 2-ethyl-5-methylpyrazine and 2,3-dimethylpyrazine), esters (for example, ethyl 4-methylpentanoate and diethyl succinate), maltol, dimethyl disulfide, 2- and 3-methylbutanal, hexanal, 4-vinylphenol, and ethanol.

Solid-phase micro-extraction (SPME-GC) and sensors as rapid methods for monitoring lipid oxidation in nuts

Dry foods with high fat content are susceptible to lipid oxidation, which involves a quality deterioration of the product, since this process is responsible for the generation of off-flavours. Hexanal is considered to be a good shelf-life indicator of such oxidation products. In addition, due to its high volatility, hexanal can be easily determined by fast headspace analytical techniques. For this reason an electronic nose comprising ten metal oxide semiconductors (MOS) and a solid-phase microextraction (SPME) coupled with gas chromatography and flame ionization detector (GC-FID) method were compared in order to determine hexanal formed in hazelnuts during storage under different conditions (room temperature, 40 degrees C, ultraviolet light, with and without oxygen scavenger). The results obtained by the two methods showed a good correlation, confirming the possibility of using a multi-sensor system as a screening tool for the monitoring of shelf-life and oxidation state of nuts.

Production of volatile compounds by Rhizopus oligosporus during soybean and barley tempeh fermentation

Rhizopus oligosporus Saito can ferment soybeans or cereal grains to tempeh, a sliceable cake with improved nutritional properties. Volatiles produced by different R. oligosporus strains grown on malt extract agar (MEA), barley and soybean were investigated. The effect of co-cultivation with Lactobacillus plantarum on the production of volatiles was also studied. Volatile compounds were collected in situ by headspace diffusion and identified by GC-MS. The ten R. oligosporus strains that had different colony morphologies on MEA produced very similar volatile profiles, except for slight variations among the minor volatile compounds (e.g. sesquiterpenes). Likewise, practically no differences in volatile profiles were observed between three of the strains grown on soybeans. In contrast, the R. oligosporus volatile profile on soybean was different from that on barley from the same strain. Co-cultivation with L. plantarum did not influence volatile production by R. oligosporus. The dominant compounds produced on all three substrates were ethanol, acetone, ethyl acetate, 2-butanone, 2-methyl-1-propanol, 3-methyl-1-butanol and 2-methyl-1-butanol. Acetaldehyde and 2-methyl-propanal were also produced on MEA and barley, while 2-pentanone, methyl acetate, 2-butanol and 3-methyl-3-buten-1-ol were observed on soybeans. Ethanol, 2-methyl-1-butanol and 3-methyl-1-butanol were the most abundant volatile compounds produced on MEA and barley, while 2-butanone was the dominant volatile metabolite on soybean. The mushroom odour compounds, 3-octanone and 1-octen-3-ol, were only detected from soybean and soybean tempeh.

Solid-phase microextraction method for the determination of hexanal in hazelnuts as an indicator of the interaction of active packaging materials with food aroma compounds

Fatty foods are susceptible to lipid oxidation resulting in deterioration of product quality due to the generation of off-flavours. Hexanal is a good indicator of rancidity. Therefore, a method based on solid-phase microextraction (SPME) coupled to gas chromatograph with flame ionization detection was developed to determine hexanal formation in hazelnuts during storage. Optimum conditions were as follows: carboxen-polydimethylsiloxane 75 microm fibre, extraction time 10 min, equilibrium time 10 min and equilibrium temperature 60 degrees C. The effect of oxygen scavengers on the oxidation process was also evaluated by measuring hexanal formation in hazelnuts stored with/without oxygen absorber sachets. Oxygen scavengers were shown to reduce oxidation; however, analysis of the sachet revealed that other volatile compounds from the headspace were also absorbed.