The Potential of NIR Spectroscopy and Chemometrics to Discriminate Roast Degrees and Predict Volatiles in Coffee.

This study aimed to establish a rapid and practical method for monitoring and predicting volatile compounds during coffee roasting using near-infrared (NIR) spectroscopy coupled with chemometrics. Washed Arabica coffee beans from Ethiopia and Congo were roasted to industry-validated light, medium, and dark degrees. Concurrent analysis of the samples was performed using gas chromatography-mass spectrometry (GC-MS) and NIR spectroscopy, generating datasets for partial least squares (PLS) regression analysis. The results showed that NIR spectroscopy successfully differentiated the differently roasted samples, similar to the discrimination achieved by GC-MS. This finding highlights the potential of NIR spectroscopy as a rapid tool for monitoring and standardizing the degree of coffee roasting in the industry. A PLS regression model was developed using Ethiopian samples to explore the feasibility of NIR spectroscopy to indirectly measure the volatiles that are important in classifying the roast degree. For PLSR, the data underwent autoscaling as a preprocessing step, and the optimal number of latent variables (LVs) was determined through cross-validation, utilizing the root mean squared error (RMSE). The model was further validated using Congo samples and successfully predicted (with R2 values > 0.75 and low error) over 20 volatile compounds, including furans, ketones, phenols, and pyridines. Overall, this study demonstrates the potential of NIR spectroscopy as a practical and rapid method to complement current techniques for monitoring and predicting volatile compounds during the coffee roasting process.

The Effect of Sound Frequency and Intensity on Yeast Growth, Fermentation Performance and Volatile Composition of Beer.

This study investigated the impact of varying sound conditions (frequency and intensity) on yeast growth, fermentation performance and production of volatile organic compounds (VOCs) in beer. Fermentations were carried out in plastic bags suspended in large water-filled containers fitted with underwater speakers. Ferments were subjected to either 200-800 or 800-2000 Hz at 124 and 140 dB @ 20 µPa. Headspace solid-phase microextraction (HS-SPME) coupled with gas chromatography-mass spectrometry (GC-MS) was used to identify and measure the relative abundance of the VOCs produced. Sound treatment had significant effects on the number of viable yeast cells in suspension at 10 and 24 h (p < 0.05), with control (silence) samples having the highest cell numbers. For wort gravity, there were significant differences between treatments at 24 and 48 h, with the silence control showing the lowest density before all ferments converged to the same final gravity at 140 h. A total of 33 VOCs were identified in the beer samples, including twelve esters, nine alcohols, three acids, three aldehydes, and six hop-derived compounds. Only the abundance of some alcohols showed any consistent response to the sound treatments. These results show that the application of audible sound via underwater transmission to a beer fermentation elicited limited changes to wort gravity and VOCs during fermentation.

Comparison of Four Extraction Techniques for the Evaluation of Volatile Compounds in Spray-Dried New Zealand Sheep Milk.

Recent growth and diversification of sheep milk products means more sophisticated methods are required to ensure their flavour quality. The objective of this study was to compare four extraction techniques for the analysis of volatile compounds in sheep milk by gas chromatography-mass spectrometry (GC-MS). Solvent Assisted Flavour Evaporation (SAFE), Solid Phase Microextraction (SPME), Headspace Sorptive Extraction (HSSE) and Stir Bar Sorptive Extraction (SBSE) were evaluated for their sensitivity, selectivity, reproducibility, and overall efficiency. A total of 48 volatile compounds from nine compound classes were identified in the spray-dried sheep milk. Alcohols, aldehydes, alkanes, carboxylic acids, ketones, lactones, sulphur compounds, nitrogen compounds, and terpenes were all present, but the differences between the methods were most apparent for lactones. SBSE extracted eight lactones, SAFE extracted four lactones and HSSE and SPME only detected trace levels of two lactones. Six of the lactones-δ-hexa-lactone, δ-octalactone, γ-decalactone, γ-dodecalactone, δ-tetradecalactone, and δ-hexadeca-lactone-were identified for the first time in spray-dried sheep milk. The present work demonstrated that SBSE is an effective tool for the extraction and analysis of volatiles, especially lactones, in sheep milk and dairy products in general. A discussion of the benefits and limitations of each method is included.

Comparison of four extraction methods for analysis of volatile hop-derived aroma compounds in beer.

The volatile organic compound profile in beer is derived from hops, malt, yeast, and interactions between the ingredients, making it very diverse and complex. Due to the range and diversity of the volatile organic compounds present, the choice of the extraction method is extremely important for optimal sensitivity and selectivity. This study compared four extraction methods for hop-derived compounds in beer late hopped with Nelson Sauvin. Extraction capacity and variation were compared for headspace solid-phase micro extraction, stir bar sorptive extraction, headspace sorptive extraction, and solvent-assisted flavor evaporation. Generally, stir bar sorptive extraction was better suited for acids, headspace sorptive extraction for esters and aldehydes, while headspace solid-phase microextraction was less sensitive overall, extracting 40% fewer compounds. Solvent-assisted flavor evaporation with dichloromethane was not suitable for the extraction of hop-derived volatile organic compounds in beer, as the profile was strongly skewed towards alcohols and acids. Overall, headspace sorptive extraction is found to be best suited, closely followed by stir bar sorptive extraction.

Yeast Strain Influences the Hop-Derived Sensory Properties and Volatile Composition of Beer.

The perception of hop-derived flavour in beer is not well understood, particularly regarding the effect that different yeast strains and fermentation parameters have on perceived hop aroma and the mechanisms responsible for these changes. To evaluate the influence of yeast strain on the sensory properties and volatile composition of beer, a standard wort, late-hopped with New Zealand Motueka hops (5 g·L-1), was fermented with one of twelve yeast strains under constant conditions (temperature and yeast inoculation rate). The bottled beers were evaluated using a free sorting sensory methodology, and their volatile organic compounds (VOC) were assessed using gas chromatography mass spectrometry (GC/MS) with headspace solid-phase microextraction (SPME) sampling. Beer fermented with SafLager W-34/70 yeast was associated with a hoppy flavour attribute, whereas WY1272 and OTA79 beers were sulfury, and WY1272 was also metallic. WB06 and WLP730 beers were perceived to be spicy, with WB06 beer also perceived as estery, whereas VIN13 beer was sour, and the WLP001 beer was astringent. Beers fermented using the twelve yeast strains had clearly distinct VOC profiles. Beer made with WLP730, OTA29, SPH, and WB06 yeasts had the highest 4-vinylguaiacol levels, which contributed to their spicy attribute. Beer made with W3470 had high levels of nerol, geraniol, and citronellol, which supported its sensory characterisation as being 'hoppy'. This research has illustrated the important role that yeast strain has on modulating hop flavour in beer.

Online monitoring of higher alcohols and esters throughout beer fermentation by commercial Saccharomyces cerevisiae and Saccharomyces pastorianus yeast.

Higher alcohols and esters are among the predominant classes of volatile organic compounds (VOCs) that influence the quality of beer. The concentrations of these compounds are determined through a specific yeast strain selection and fermentation conditions. The effect of yeast strains on the formation of higher alcohols and esters throughout fermentations (at 20°C) was investigated. Flavour-relevant esters (ethyl acetate, isoamyl acetate, ethyl hexanoate and ethyl octanoate) and higher alcohols (isoamyl alcohol, isobutyl alcohol and phenylethyl alcohol) were monitored throughout the fermentation using proton transfer reaction-time of flight-mass spectrometry (PTR-ToF-MS) coupled with an automated sampling system for continuous measurements. Compound identification was confirmed by analysis of samples using gas chromatography-mass spectrometry (GC-MS). Results demonstrated the specific time points where variation in higher alcohol and ester generation between yeast strains occurred. In particular, the concentrations of isoamyl acetate, ethyl octanoate and isoamyl alcohol between yeast strains were significantly different over the first 2 days of fermentation; whereas, after Day 3, no significant differences were observed. The two Saccharomyces pastorianus strains produced comparable concentrations of the key higher alcohols and esters. However, the key higher alcohol and ester concentrations varied greatly between the two S. cerevisiae strains. The use of PTR-ToF-MS to rapidly measure multiple yeast strains provides new insights on fermentation for brewers to modify the sensory profile and optimise quality.

System design for integrated comprehensive and multidimensional gas chromatography with mass spectrometry and olfactometry.

An integrated system having the combined capability to perform gas chromatography (GC), comprehensive two-dimensional GC (GC × GC), and target heart-cut multidimensional GC (MDGC) using olfactometry (O), flame ionization (FID), and/or mass spectrometry (MS) detection is described. This combines a number of contemporary GC methods into a single instrument to provide very high resolution profiling of a sample. This provides initial assessment of volatile compound composition through GC × GC analysis with FID, which can be correlated with GC analysis using parallel O and FID detection. Subsequent microfluidic (Deans) switching selects regions (heart-cuts) of the chromatographic elution from the first dimension ((1)D) column for further resolution on a long second dimension ((2)D(L)) column for parallel detection of O and MS. Various (2)D(L) operational conditions, as well as the effect of different heart-cut (H/C) duration, were compared. The favored mode involves cryotrapping of heart-cuts, cooling the oven, and reducing carrier flow to offer greater efficiency. An analytical strategy that incorporates GC-FID/O, GC × GC-FID, and MDGC-MS/O analyses with cumulative solid phase microextraction (SPME) sampling for volatile sample enrichment is presented in this work. Excellent qualitative and quantitative performance was demonstrated with a Shiraz wine sample and an allergens mixture, with tentative identification of acetic acid, octen-3-ol, and ethyl octanoate as aroma contributors in Shiraz wine and determination of ß-damascenone (floral odor) well separated from hexanoic acid (sweaty odor). A novel approach to obtain (2)D retention indices is reported, allowing matching of mass spectral, (1)I (retention index in (1)D) and (2)I (retention index in (2)D) data. The method employs the same olfactory detector at the end of the (1)D and (2)D(L) columns.

Impact of sourdough culture on the volatile compounds in wholemeal sourdough bread.

Sourdough bread has a complex flavour profile, which is strongly influenced by the compounds generated during fermentation by the diverse array of microorganisms present, mainly yeasts and lactic acid bacteria (LAB). Twelve complex sourdough cultures, comprised of mixtures of yeast and bacteria, were propagated using wholemeal flour and used in the production of sourdough breads. The volatile organic compounds (VOCs) present in the sourdough bread crumb were characterised by gas chromatography-mass spectrometry (GC-MS) and proton transfer reaction-mass spectrometry (PTR-MS). Multiple factor analysis (MFA) relating the VOCs and physicochemical features of the sourdough breads (pH, TTA, lactic acid, colour and size) identified three distinct clusters. Cluster 1 was distinguished by VOCs, such as ethanol, 3-methyl-1-butanol, phenylethanol, 2-methyl-1-propanol, acetaldehyde and 2,3-butanedione, along with size related measures and increased production of lactic acid, indicating that yeast activity and homofermentative or facultative heterofermentative LAB were dominant. In contrast, cluster 2 was associated with acetic acid and acetate esters along with acidity related measures indicating a dominance of obligate heterofermentative LAB. Cluster 3 was also related to yeast fermentation activity, but particularly fermentation of lipids with greater production of aldehydes and lactones. The distinct differences between clusters of sourdough breads in their volatile and non-volatile features could be attributed to their fermentation activity and whether the culture was dominated by yeast or the different classes of LAB.

Association of metabolomic and lipidomic data with Chinese and New Zealand consumer clusters showing preferential likings for lamb meat from three production systems.

Relationships between overall liking scores for cooked lamb from Chinese (n = 158) and New Zealand (n = 156) consumers, and metabolite and lipid profiles were evaluated. Consumers assessed meat from 6 to 8-month-old lambs of composite genetics fed chicory (CHIC) or grass (GRASS), and from 12 month-old Merino lambs fed a mixed pasture (PMER). On average, Chinese consumers rated the overall liking of all types of lamb similarly, while New Zealand consumers preferred meat from CHIC over PMER. However, three clusters with similar preferences were obtained for both Chinese and New Zealand consumers based on their overall liking scores. In Cluster-1 with a preference for GRASS, overall liking for Chinese and NZ consumers was positively associated with umami compounds, ortho- and pyrophosphates (related to water holding capacity of meat), triglycerides (TG) with<50 carbons (C50) and phospholipids with polyunsaturated fatty acids (PUFA); but negatively associated with amino acids and TG with > C50 with saturated (SFA) and monounsaturated (MUFA) fatty acids. In Cluster-2 with a preference for CHIC, overall liking for both types of consumers was positively associated with TG with > C50 with PUFA, and phospholipids with PUFA, but negatively associated with umami compounds, ortho- and pyrophosphates and L-anserine. In Cluster-3 with a preference for PMER, overall liking for Chinese and NZ consumers was positively associated with amino acids, ortho- and pyrophosphates, L-anserine, umami compounds, TG with > C50 with SFA and MUFA and phospholipids that contain C16:0, C16:1, C18:0 and C18:1; but negatively associated with phospholipids with PUFA and TG with < C50 that contain PUFA. Overall, the liking of lamb meat between Chinese and New Zealand consumers differed, but similar clusters were generated based on their overall liking scores. The clusters were characterized by different associations of the consumer overall liking scores with cooked meat metabolome and lipidome profiles.

Cross-Cultural Differences in the Perception of Lamb between New Zealand and Chinese Consumers in New Zealand.

This study investigated differences between general New Zealand consumers and ethnic Chinese consumers living in New Zealand regarding the importance of lamb attributes at the point of purchase and opinions of New Zealand lamb. A central location test survey was undertaken with 156 New Zealand consumers living in Dunedin, New Zealand, and 159 Chinese consumers living in Auckland, New Zealand. In terms of importance at the point of purchase, Chinese consumers rated a number of attributes as more important than New Zealand consumers by a difference of >1.0 on a 9-point Likert scale for importance: animal origin, feeding, age, presence of hormones/residues, traceability, food safety, place of purchase, brand/quality label, and label information (p < 0.05). New Zealand consumers rated the price of other meats and animal welfare as more important than Chinese consumers (p < 0.05); however, the differences in scores were <1.0. In terms of opinions, Chinese consumers also considered New Zealand lamb to be better value for money, more additive-free, and more likely to make people feel good (p < 0.05), by scores >1.0 on a 7-point Likert scale for agreement. New Zealand consumers considered New Zealand lamb more traditional and boring (p < 0.05); however, the differences in scores were <1.0.

Characterization of blue cheese volatiles using fingerprinting, self-organizing maps, and entropy-based feature selection.

Understanding which volatile compounds discriminate between products can be useful for quality, innovation or product authenticity purposes. As dataset size and dimensionality increase, linear chemometric techniques like partial least squares discriminant analysis and variable identification (PLS-DA-VID) may not identify the most discriminant compounds. This research compared the performance of self-organizing maps and entropy-based feature selection (SOM-EFS) and PLS-DA-VID to identify discriminant compounds in 17 blue cheese varieties. A total of 172 volatiles were detected using headspace solid phase microextraction, gas chromatography and mass spectrometry, including 1-nonene and 2,6-dimethylpyridine, which were newly identified in blue cheese. Despite SOM-EFS selecting only 14 volatiles compared to 78 for PLS-DA-VID, SOM-EFS proved more effectively discriminant and improved the median five-fold cross-validated prediction accuracy of the model to 0.94 compared to 0.82 for PLS-DA-VID. These findings introduce SOM-EFS as a powerful non-linear exploratory data analysis approach in the field of volatile analytical chemistry.

Differences in New Zealand Hop Cultivars Based on Their Unique Volatile Compounds: An Integrated Fingerprinting and Chemometrics Approach.

Hop aroma characteristics originate from hop essential oils, which have complex chemical profiles that remain poorly understood, particularly for New Zealand hops. The aim of this study was to determine volatile compounds that distinguish New Zealand hop cultivars. Untargeted fingerprinting methods based on headspace gas chromatography mass spectrometry (GC-MS) were used to analyse nine hop cultivars. A total of 61 volatile compounds were identified as compounds that differentiated the commercial hop varieties using advanced chemometrics and feature selection techniques. Similarities in volatile composition were found between Wakatu, Wai-iti™ and Kohatu®, which are rich in alcohols. Another grouping was found between Waimea™ and Nelson Sauvin™, where ketones and esters were commonly found. Rakau™ was distinct from the other eight cultivars, distinguished by 2-methylbutyl 3-methylbutanoate and methanethiol hexanoate. Riwaka™ contained the greatest number of discriminating volatile compounds when compared to other cultivars, which was dominated by terpenoids, such as geranyl 2-methylbutanoate, perillene and D-limonene. The chemical fingerprinting approach successfully identified volatile compounds that had not been previously found in New Zealand hop cultivars and that discriminated the commercial cultivars. The data obtained in the present study further extend the knowledge of New Zealand hops and will help facilitate targeted breeding.

Relationships among Consumer Liking, Lipid and Volatile Compounds from New Zealand Commercial Lamb Loins.

Loin sections (m. Longissimus lumborum) were collected at slaughter from forty-eight lamb carcasses to evaluate consumer-liking scores of six types of typical New Zealand commercial lamb and to understand the possible underlying reasons for those ratings. A consumer panel (n = 160) evaluated tenderness, juiciness, flavor liking, and overall liking of the different types of lamb loins. Consumer scores differed among the types of lamb meat for all the evaluated attributes (p < 0.05). Further segmentation based on overall liking scores showed two consumer clusters with distinct ratings. Correlation and external preference map analyses indicated that one consumer cluster (n = 75) liked lamb types that had lower total lipid content, a lower proportion of branched-chain fatty acids, oleic and heptadecanoic acids; and a higher proportion of polyunsaturated fatty acids and volatile compounds (green and fruity descriptors). Consumer liking of the other segment (n = 85) was less influenced by fatty acids and volatiles, except hexanoic, heptanoic and octanoic acids (rancid, fatty, and sweaty descriptors). Thus, the fatty acid profile and the volatile compounds derived from their oxidation upon cooking seem to be a stronger driver of consumer liking of lamb for some consumers than others.

Application of a Novel Instantized Glycerol Monooleate Ingredient in a Protein-Stabilized Oil-In-Water Emulsion.

Glycerol monooleate (GMO), casein and whey proteins are surfactants that can stabilize emulsion systems. This study investigates the impact of instantized GMO powders on creaming stability and oxidative stability in protein-stabilized emulsions. Model emulsions with bulk GMO, two instantized GMO powders, and two controls (without GMO) were produced by microfluidization. The droplet size, ζ-potential, viscosity, and creaming index of the emulsions were measured, while oxidative stability was evaluated by analysis of volatile compounds during storage (28 days, 45 °C) using gas chromatography mass spectrometry. Emulsions with GMO produced smaller average droplet sizes (180.0 nm) with a narrower distribution (polydispersity index of 0.161) compared to the controls (197.6 nm, 0.194). The emulsion stability of instantized emulsions was as good as bulk GMO, which were both better than controls. Based on the relative abundance of 3-octen-2-one, 2,4-heptadienal isomer 2, and 3,5-octadien-2-one isomer 1, the oxidative stability of the instantized emulsions was not significantly different from controls; however, bulk GMO emulsion showed significantly lower stability than controls. Instantized GMO powders can successfully produce physically stable protein-stabilized emulsions with good oxidative stability in a convenient powdered format.

Fatty Acid Composition and Volatile Profile of M. longissimus thoracis from Commercial Lambs Reared in Different Forage Systems.

Animal production factors can affect the fatty acid and volatile profile of lamb meat. The fatty acid and volatile composition of the M. longissimus thoracis was evaluated from 150 lambs from 10 groups of commercial lambs that differed in age, sex, diet and breed, from three farms, which represent typical forage lamb production systems in New Zealand. The meat from 4-month-old composite lambs slaughtered at weaning had a similar polyunsaturated to saturated fatty acid ratio compared to 6- to 8-month-old composite lambs, but a greater ratio than that of 12-month-old Merino lambs (p < 0.05), with all ratios being lower than the recommended ≥0.45. All lamb production systems produced meat with an omega-6 to omega-3 ratio below 1.5, well below the recommended ratio ≤ 4.0. Meat from 4-month-old lambs had higher C12:0, C14:0 and C16:0 and lower C18:0, reflecting the composition of the milk diet, resulting in higher atherogenic index than meat from other animal groups, while meat from 12-month-old Merino lambs, with lower content of polyunsaturated fatty acids, showed higher thrombogenic index. Meat from lambs processed at weaning contained the greatest concentration of eicosapentaenoic and docosahexaenoic acids, which would qualify as a 'source' or 'good source' of these target fatty acids based on the Commission of Regulation of the European Union or the Food Standards Australia New Zealand guidelines, respectively. Volatiles were extracted from the headspace of raw lean meat and 36 volatile compounds were identified. The abundance of carbon disulphide, isododecane, heptanal, 2,5-hexanediol and 3-octanone and pentanoic, octanoic, nonanoic and heptanoic acids was similar between all groups of lambs. Meat from 12-month-old Merino lambs had low abundance of acetic, propanoic, butanoic and hexanoic acids, and hexanal, octanal and dimethyl sulphide. For 6- to 8-month-old composite lambs, hexanal, octanal and nonanal were present at higher relative abundance in meat from lambs that grazed on chicory than perennial ryegrass. The significant differences in the fatty acid and volatile profiles in meat from 12-month-old Merino lambs compared with lambs slaughtered at weaning or further grazed on red clover, chicory or mixed pasture may result in distinctive nutritional value and lamb flavour.

Effect of milk protein composition on physicochemical properties, creaming stability and volatile profile of a protein-stabilised oil-in-water emulsion.

Casein, whey proteins and monoglycerides are emulsifiers that adsorb at the oil-water interface to form and stabilise emulsions. This study aims to understand the effect of different milk protein compositions (ratio of sodium caseinate and whey protein concentrate (WPC)) with glycerol monooleate (GMO) on physicochemical properties, creaming and oxidative stability of the emulsions. Model emulsions with five different protein compositions were prepared by microfluidisation. The physicochemical properties were characterised by droplet size, zeta potential, viscosity and creaming index. Oxidative stability was assessed using volatile lipid oxidation compounds during ageing (28 days at 45 °C). Results showed that the emulsion with only sodium caseinate produced smaller droplets (174.7 nm), higher zeta potential (-50.8 mV) and a more viscous emulsion (1.89 mPa s) compared to the emulsion with only WPC (191.4 nm; -38.8 mV; 1.65 mPa s). Protein composition had no significant effect on creaming stability. Eleven volatile compounds were identified as lipid oxidation markers and six compounds (2-pentylfuran, octanal, nonanal, 3-octen-2-one, 2,4-heptadienal, 3,5-octadien-2-one isomers) demonstrated that emulsions with mixed protein types (sodium caseinate and WPC) had better oxidative stability than emulsions with a single protein type. Therefore, mixed proteins with GMO form stable emulsions with both good physicochemical properties and oxidative stability.

Changes in the physicochemical properties and flavour compounds of beef bone hydrolysates after Maillard reaction.

This study investigated the changes in physicochemical properties and volatile compounds of beef bone hydrolysates during heat treatment as a result of the Maillard reaction (MR). Five beef bone hydrolysates obtained from single (P-Protamex®, B-bromelain, and F-Flavourzyme®) and simultaneous (P + F and B + F) enzymatic hydrolysis treatments were combined with ribose in aqueous solutions and heated at 113 °C to produce Maillard reaction products (MRPs). Total free amino acids decreased after heat treatment indicating the occurrence of the MR. MRPs showed a decrease in pH and an increase in browning intensity as the degree of hydrolysis of hydrolysates increased. The volatiles compounds generated during heat treatment were evaluated using gas chromatography-mass spectrometry (GC-MS) with headspace solid phase microextraction (SPME) sampling. A total of 40 volatile compounds were identified in all MRPs and their concentration were found to increase with increasing degree of hydrolysis. Pyrazines were the most abundant class of compounds produced as a result of the MR. F-MRP showed the highest peak area intensity for 17 volatile compounds in single hydrolysis treatment followed by heat treatment. There was also no significant difference in those major volatile compounds between F-MRP and P + F-MRP or B + F-MRP from simultaneous hydrolysis treatment after heating. Hence, the use of Flavourzyme® alone to increase the flavour intensity of beef bone extract is recommended. Overall results indicated that enzymatic hydrolysis and MR could be used to modify the flavour characters of beef bone extract.

Structural Changes Induced by Pulsed Electric Fields Increase the Concentration of Volatiles Released in Red Onion (Allium cepa L. var. Red Pearl) Bulbs.

This study investigated whether pulsed electric field (PEF) treatment can induce structural changes of whole, intact red onion bulb (Allium cepa L. var. Red Pearl). Onion bulbs were treated at electric field strengths of 0.6 and 1.2 kV/cm combined with energy inputs of 6 and 60 kJ/kg at different onion orientations with respect to the high voltage electrode. Results showed that onion cells across all fleshy scales experienced uniform cell damage with a higher proportion (>80%) of non-metabolically viable cells after PEF treatment at 1.2 kV/cm when the root end was positioned facing toward the PEF electrode. The findings were supported by cryogenic-scanning electron micrographs (cryo-SEM), where the underlying storage circular cells were completely damaged owing to the PEF treatment. In this study, it was found that the treatment intensity of PEF to induce structural damage across all the scale layers of an onion bulb coincided with an increase in dipropyl disulfide (DPDS) released from the onion bulbs. Therefore, DPDS was used as a volatile marker indicating cellular disruption within whole, intact onion bulbs. A considerable increase of DPDS, up to 52-fold, was detected from PEF-treated onion bulbs compared to untreated bulbs.

Method for small-molecule discovery based on microscale-preparative multidimensional gas chromatography isolation with nuclear magnetic resonance spectroscopy.

Absolute chemical identification requires obtaining a pure compound followed by structure elucidation using spectroscopic techniques, principally NMR spectroscopy and mass spectrometry. Classical isolation techniques suffer from insufficient resolution for complex samples, requiring time-consuming fractionation in multiple steps. Here, a novel preparative technique based upon capillary column multidimensional gas chromatography (MDGC) with 2D NMR to resolve, isolate, and identify pure volatile components from a complex sample is described. As a model application, geraniol was isolated from an essential oil matrix using MDGC and quantitatively resolved from 15 partially coeluting compounds from the first column. Geraniol was recovered from 10 (8.6 microg) and 100 injections (77.6 microg; purity >99%) for subsequent NMR analysis at 500 and 800 MHz (with cryoprobe). Proton and gCOSY NMR experiments were successfully performed at 12.3 microg/mL (10 injections), while gHSQC and gHMBC NMR experiments were obtained at 110.8 microg/mL (100 injections). This approach is applicable to the biodiscovery of volatile molecular species or, indeed, any volatile compound in a complex matrix that requires confirmation of component identity.

Application of microscale-preparative multidimensional gas chromatography with nuclear magnetic resonance spectroscopy for identification of pure methylnaphthalenes from crude oils.

Mass spectrometry is often insufficient to distinguish between structural isomers, requiring confirmation using NMR spectroscopy. Here, a novel preparative technique based upon capillary multidimensional gas chromatography to isolate pure volatile components from complex samples is described. The method was developed through isolation of 1,4-dimethoxybenzene (5.2 microg, 10 injections) from a peppermint essential oil. Then isomers of 1- and 2-methylnaphthalene were isolated from a complex crude oil in sufficient amounts (3.1 microg, 38 injections and 5.0 microg, 35 injections) for discrimination using (1)H NMR spectroscopy. This methodology is applicable to identify any volatile molecule in complex matrices requiring confirmation using NMR spectroscopy.