Novel approach for the determination of volatile compounds in processed onion by headspace gas chromatography-mass spectrometry (HS GC-MS)

Diversity of the Morphometric and Biochemical Traits of Allium cepa L. Varieties

Several Allium cepa L. varieties, representing a versatile set of vegetables widely utilized by consumers, are appreciated for their bioactive properties, including antimicrobial, anticarcinogenic, and antioxidant capacities. The aim of this study is to compare the morphometric characteristics and biochemical profiles of four cultivars of A. cepa, two of them represented by the perennial Sicilian landrace "Cipudda agghiarola" (Allium × proliferum (Moench) Schrader), widely known as the Egyptian walking onion (WO), and by the landrace "Cipudduzza" belonging to the variety known as aggregatum (ON), which were compared with two commercial cultivars of A. cepa var. cepa (onion), Stoccarda (OS) and Rossa Carmen (OR). The experimental trial was conducted in Catania (Sicily), following organic growing practices. The randomized complete block experimental design was adopted with one experimental factor, the genotype (GE) effect. The harvested plants were characterized for their main morphometric parameters, according to the International Plant Genetic Resources (IGPR) descriptors. The biochemical activity was assessed by analyzing the total phenolic content (TPC) and the total flavonoid content (TFC). The antioxidant capacity was determined by 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical scavenging, ferric reducing antioxidant power (FRAP), and oxygen radical absorbance capacity (ORAC). The sugar profile (total sugars, sucrose, glucose, fructose, and fructooligosaccharides-FOS) and the volatile compounds by headspace-gas chromatography/mass spectrometry (HS-GC/MS) were also determined. The OR bulb exhibited the highest TPC (16.3 mg GAE/g d.w., p < 0.01) and TFC (8.5 mg QE/g d.w., p < 0.01), with the highest antioxidant capacity measured by the FRAP (27.1 µmol TE/g d.w., p < 0.01) and DPPH assays (46.2 µmol TE/g d.w., p < 0.01). The ON bulb showed the highest ORAC value (209 µmol TE/g d.w., p < 0.01). Generally, the bulbs were richer in sugars (584 mg/g d.w., p < 0.01) than the leaf blade (239 mg/g d.w., p < 0.01), except for OR. Significant interaction between the genotype and plant organ was noted in the volatile compound profiles (p < 0.05) except for total ketones and carboxylic acids, where higher content was observed in the leaf blade compared to the bulb, regardless of the genotype. These findings highlight WO's potential for use in ready-to-eat products, enhancing its market value.

Generation of Meaty Aroma from Onion (Allium cepa L.) with Polyporus umbellatus: Fermentation System, Sensory Profile, and Aroma Characterization

One of the main reasons for consumer rejection of plant-based meat alternatives is the lack of meaty flavor after cooking. In this study, a platform was developed to generate meaty flavors solely from Allium substrates (chives, leeks, ramsons, and onions) using basidiomycete-mediated submerged fermentations. Polyporus umbellatus-mediated fermentation of onions resulted in an intense meaty and liver sausage-like flavor under proper fermentation parameters. Using multisolvent and solvent-free aroma extractions coupled with gas chromatography-mass spectrometry-olfactometry, 5 odorants with high assigned flavor dilution (FD) factors (≥ 256) were identified in the fermented sample that have been reported in the literature as important aroma compounds of meat products: methyl palmitate, bis(2-methyl-furyl) disulfide, (E,E)-2,4-decadienal, γ-nonalactone, and eugenol. Using selected ion monitoring, the presence of bis(2-methyl-furyl) disulfide (meaty, savory, FD 256) after fermentation was confirmed. It was proposed that P. umbellatus enzymatically forms bis(2-methyl-furyl) disulfide from intermediates derived from the thermal degradation of thiamine.

Application of Direct Thermal Desorption-Gas Chromatography-Mass Spectrometry for Determination of Volatile and Semi-Volatile Organosulfur Compounds in Onions: A Novel Analytical Approach

The population is now more aware of their diets due to the connection between food and general health. Onions (Allium cepa L.), common vegetables that are minimally processed and grown locally, are known for their health-promoting properties. The organosulfur compounds present in onions have powerful antioxidant properties and may decrease the likelihood of developing certain disorders. It is vital to employ an optimum approach with the best qualities for studying the target compounds to undertake a thorough analysis of these compounds. In this study, the use of a direct thermal desorption-gas chromatography-mass spectrometry method with a Box-Behnken design and multi-response optimization is proposed. Direct thermal desorption is an environmentally friendly technique that eliminates the use of solvents and requires no prior preparation of the sample. To the author's knowledge, this methodology has not been previously used to study the organosulfur compounds in onions. Likewise, the optimal conditions for pre-extraction and post-analysis of organosulfur compounds were as follows: 46 mg of onion in the tube, a desorption heat of 205 °C for 960 s, and a trap heat of 267 °C for 180 s. The repeatability and intermediate precision of the method were evaluated by conducting 27 tests over three consecutive days. The results obtained for all compounds studied revealed CV values ranging from 1.8% to 9.9%. The major compound reported in onions was 2,4-dimethyl-thiophene, representing 19.4% of the total area of sulfur compounds. The propanethial S-oxide, the principal compound responsible for the tear factor, accounted for 4.5% of the total area.

Study on Cut Tobacco Drying Process Based on HS-GC/MS: Principal Component Analysis, Similarity Analysis, Drying Conditions, and Drying Mechanism

In order to study the volatile and semivolatile components changes of cut tobacco in the drying process, the cut tobacco were determined by headspace-gas chromatography/mass spectrometry (HS-GC/MS). Principal component analysis (PCA) and similarity analysis were used to analyze the HS-GC/MS results. Based on the similarity, the drying conditions and drying mechanism have been studied. The results showed that the increase in water content would reduce the dying rate, and if the temperature increased, the dying rate increased. The preliminary study on the drying kinetics of the drying process shows that Henderson and Pabis model appeared to be the most suitable for describing the drying process of cut tobacco, and the drying activation energy is 111.9 kJ.

Relationship between Volatile Composition and Bioactive Potential of Vegetables and Fruits of Regular Consumption-An Integrative Approach

In recent years, there has been a growing interest in studying and exploring the potential health benefits of foods, mainly from vegetables and fruits from regular intake. The presence of secondary metabolites, namely polyphenols, carotenoids and terpenes, in certain food matrices seems to contribute to their functional properties, expressed through an increased prevention in the development of certain chronic diseases, namely coronary heart diseases, neurodegenerative diseases, cancer and diabetes. However, some foods' volatile secondary metabolites also present important bioactive properties, although this is a poorly scientifically explored field. In this context, and in order to explore the potential bioactivity of volatile metabolites in different vegetables and fruits from regular consumption, the volatile composition was established using a green extraction technique, solid phase microextraction in headspace mode (HS-SPME), combined with gas chromatography tandem mass spectrometry (GC-MS). A total of 320 volatile metabolites, comprising 51 terpenic compounds, 45 organosulfur compounds, 31 aldehydes, 37 esters, 29 ketones, 28 alcohols, 23 furanic compounds, 22 hydrocarbons, 19 benzene compounds, 13 nitrogenous compounds, 9 carboxylic acids, 7 ethers, 4 halogenated compounds and 3 naphthalene derivatives, were positively identified. Each investigated fruit and vegetable showed a specific volatile metabolomic profile. The obtained results revealed that terpenic compounds, to which are associated antimicrobial, antioxidant, and anticancer activities, are the most predominant chemical family in beetroot (61%), orange carrot (58%) and white carrot (61%), while organosulfur compounds (antiviral activity) are dominant in onion, garlic and watercress. Broccoli and spinach are essentially constituted by alcohols and aldehydes (enzyme-inhibition and antimicrobial properties), while fruits from the Solanaceae family are characterized by esters in tamarillo and aldehydes in tomato.

Narrowband Blue and Red LED Supplements Impact Key Flavor Volatiles in Hydroponically Grown Basil Across Growing Seasons

The use of light-emitting diodes (LEDs) in commercial greenhouse production is rapidly increasing because of technological advancements, increased spectral control, and improved energy efficiency. Research is needed to determine the value and efficacy of LEDs in comparison to traditional lighting systems. The objective of this study was to establish the impact of narrowband blue (B) and red (R) LED lighting ratios on flavor volatiles in hydroponic basil (Ocimum basilicum var. "Genovese") in comparison to a non-supplemented natural light (NL) control and traditional high-pressure sodium (HPS) lighting. "Genovese" basil was chosen because of its high market value and demand among professional chefs. Emphasis was placed on investigating concentrations of important flavor volatiles in response to specific ratios of narrowband B/R LED supplemental lighting (SL) and growing season. A total of eight treatments were used: one non-supplemented NL control, one HPS treatment, and six LED treatments (peaked at 447 nm/627 nm, ±20 nm) with progressive B/R ratios (10B/90R, 20B/80R, 30B/70R, 40B/60R, 50B/50R, and 60B/40R). Each SL treatment provided 8.64 mol ⋅ m^-2 ⋅ d^-1 (100 μmol ⋅ m^-2 ⋅ s^-1, 24 h ⋅ d^-1). The daily light integral (DLI) of the NL control averaged 9.5 mol ⋅ m^-2 ⋅ d^-1 during the growth period (ranging from 4 to 18 mol ⋅ m^-2 ⋅ d^-1). Relative humidity averaged 50%, with day/night temperatures averaging 27.4°C/21.8°C, respectively. Basil plants were harvested 45 days after seeding, and volatile organic compound profiles were obtained by gas chromatography-mass spectrometry. Total terpenoid concentrations were dramatically increased during winter months under LED treatments, but still showed significant impacts during seasons with sufficient DLI and spectral quality. Many key flavor volatile concentrations varied significantly among lighting treatments and growing season. However, the concentrations of some compounds, such as methyl eugenol, were three to four times higher in the control and decreased significantly for basil grown under SL treatments. Maximum concentrations for each compound varied among lighting treatments, but most monoterpenes and diterpenes evaluated were highest under 20B/80R to 50B/50R. This study shows that supplemental narrowband light treatments from LED sources may be used to manipulate secondary metabolic resource allocation. The application of narrowband LED SL has great potential for improving overall flavor quality of basil and other high-value specialty herbs.

Use of Multiple Bacteriophage-Based Structural Color Sensors to Improve Accuracy for Discrimination of Geographical Origins of Agricultural Products

A single M13 bacteriophage color sensor was previously utilized for discriminating the geographical origins of agricultural products (garlic, onion, and perilla). The resulting discrimination accuracy was acceptable, ranging from 88.6% to 94.0%. To improve the accuracy further, the use of three separate M13 bacteriophage color sensors containing different amino acid residues providing unique individual color changes (Wild sensor: glutamic acid (E)-glycine (G)-aspartic acid (D), WHW sensor: tryptophan (W)-histidine (H)-tryptophan (W), 4E sensor: four repeating glutamic acids (E)) was proposed. This study was driven by the possibility of enhancing sample discrimination by combining mutually characteristic and complimentary RGB signals obtained from each color sensor, which resulted from dissimilar interactions of sample odors with the employed color sensors. When each color sensor was used individually, the discrimination accuracy based on support vector machine (SVM) ranged from 91.8–94.0%, 88.6–90.3%, and 89.8–92.1% for garlic, onion, and perilla samples, respectively. Accuracy improved to 98.0%, 97.5%, and 97.1%, respectively, by integrating all of the RGB signals acquired from the three color sensors. Therefore, the proposed strategy was effective for improving sample discriminability. To further examine the dissimilar responses of each color sensor to odor molecules, typical odor components in the samples (allyl disulfide, allyl methyl disulfide, and perillaldehyde) were measured using each color sensor, and differences in RGB signals were analyzed.

Determination of Organosulfides from Onion Oil

Qualitative and semi-quantitative analysis of organosulfides extracted from oil obtained by steam distillation of yellow onions was performed by gas chromatography-mass spectrometry (GC-MS). The extraction efficiency of organosulfides from onion oil was evaluated across four solvents: dichloromethane; diethyl ether; n-pentane; and hexanes. Analysis of solvent extracted organosulfides by GC-MS provided qualitative results that support the use of dichloromethane over other solvents based on identification of 27 organosulfides from the dichloromethane extract as compared to 10 from diethyl ether; 19 from n-pentane; and 17 from hexanes. Semi-quantitative evaluation of organosulfides present in the dichloromethane extract was performed using diallyl disulfide as the internal reference standard. Three organosulfides were detected in the extract at ≥5 mg/kg; 18 organosulfides between 3-5 mg/kg; and six organosulfides at <3 mg/kg. The E/Z isomers of 1-propenyl propyl trisulfide were among the most prevalent components extracted from the onion oil across all solvents; and 3,6-diethyl-1,2,4,5-tetrathiane was among the most abundant organosulfides in all solvents except hexanes. The method described here for the extraction of organosulfides from steam distilled onion oil surveys common solvents to arrive at a qualitative and semi-quantitative method of analysis for agricultural products involving onions; onion oil; and secondary metabolites of Allium spp.

A comparative analysis of the essential oils from two species of garlic seedlings cultivated in China: chemical profile and anticoagulant potential

Garlic seedlings (GS) and blanched garlic seedlings (BGS) are two kinds of common garlic-derived vegetables in China, but little information is available on their bioactive constituents. In this work, chemical profiles and anticoagulant activities of essential oils from GS (EOGS) and BGS (EOBGS) were disclosed and compared for the first time. Sixteen and fourteen volatile compounds were identified in EOGS and EOBGS by GC-MS analysis, and both of them were rich in sulfur-containing compounds, particularly diallyl sulfides accounting for 74.77% and 85.87%, respectively. EOGS and EOBGS exerted anticoagulant activities via intrinsic, extrinsic, and common coagulation pathways as well as by lowering the content of fibrinogen; EOGS exceeded EOBGS in the activation of intrinsic and extrinsic coagulation pathways, while EOBGS outperformed EOGS on the activation of the common coagulation pathway, which was even superior to that of heparin at the same dose. Herein, the results of the present investigation will give a strong clue that EOGS and EOBGS are more likely to lead to a promising way to vegetable-based anticoagulants.

A rapid dispersive liquid-liquid microextraction of antimicrobial onion organosulfur compounds in animal feed coupled to gas chromatography-mass spectrometry

A rapid analytical procedure is proposed for determining two antimicrobial onion organosulfur compounds, propyl disulfide (PDS) and propyl propane thiosulfonate (PTSO), in animal feed. The use of PTSO as a natural ingredient in animal feed is allowed due to its antimicrobial activity against pathogenic organisms. Two analytical methodologies using gas chromatography coupled to mass spectrometry (GC-MS) are compared. After the extraction of the compounds from animal feed with acetonitrile, dispersive solid phase extraction (DSPE) as a cleaning stage with C18, or dispersive liquid-liquid microextraction (DLLME), using 100 μL of CHCl3, was tried. Both the methods were validated using a pig feed sample and the best results were achieved by DLLME. This technique provided cleaner extracts, five-times greater linear ranges and lower detection limits than simple cleaning due to the enrichment factor achieved. The relative standard deviation decreased from 22% with DSPE to 13% with DLLME. The usefulness of the DLLME-GC-MS methodology was tested by analysing 10 different samples of chicken, calf, hen, cow and fish feed. The concentrations of PDS were in the 0.1-1.7 μg g-1 range and those of PTSO were between 0.09 and 2.1 μg g-1.

Typicality Assessment of Onions (Allium cepa) from Different Geographical Regions Based on the Volatile Signature and Chemometric Tools

Onion (Allium cepa L.) is one of the main agricultural commodities produced and consumed around the world. In the present work, for the first time, the volatile signature of onions from different geographical regions of Madeira Island (Caniço, Santa Cruz, Ribeira Brava, and Porto Moniz) was tested with headspace solid-phase microextraction (HS-SPME/GC-qMS) and chemometric tools, showing that the volatile signature was affected by the geographical region of cultivation. Sulfur compounds, furanic compounds, and aldehydes are the most dominant chemical groups. Some of the identified volatile organic metabolites (VOMs) were detected only in onions cultivated in specific regions; 17 VOMs were only identified in onions cultivated at Caniço, eight in Porto Moniz, two in Santa Cruz, two in Ribeira Brava, while 12 VOMs are common to all samples from the four regions. Moreover, some VOMs belonging to sulfur compounds (dipropyl disulfide, 3-(acetylthio)-2-methylfuran), furanic compounds (dimethylmethoxyfuranone, ethyl furanone, acetyloxy-dimethylfuranone), and lactones (whiskey lactone isomer), could be applied as potential geographical markers of onions, providing a useful tool to authenticate onions by farming regions where the influence of latitude seems to be an important factor for yielding the chemical profile and may contribute to geographical protection of food and simultaneously benefiting both consumers and farmers.

Characterization of Volatile and Flavonoid Composition of Different Cuts of Dried Onion (Allium cepa L.) by HS-SPME-GC-MS, HS-SPME-GC×GC-TOF and HPLC-DAD

Onion is widely used worldwide in various forms for both food and medicinal applications, thanks to its high content of phytonutrients, such as flavonoids and volatile sulfur compounds. Fresh onion is very perishable and drying is widely applied for extending shelf-life, thus obtaining a very easy-to-use functional food ingredient. The flavonoid and volatile fractions of different onion cuts (flakes, rings) prepared through different drying cycles in a static oven, were characterized by high-performance liquid chromatography with a diode-array detector HPLC-DAD, Head Space-Solid Phase Micro Extraction followed by Gas Chromatography coupled with Mass Spectrometry (HS-SPME-GC-MS) and Head-Space Solid Phase Micro Extraction followed by comprehensive two-dimensional Gas-Chromatography (HS-SPME-GC×GC-TOF). Onion flakes showed a significantly higher flavonoid content (3.56 mg g⁻¹) than onion rings (2.04 mg g⁻¹). Onion flakes showed greater amount of volatile organic compounds (VOCs) (127.26 mg g⁻¹) than onion rings (42.79 mg g⁻¹), with different relative amounts of di- and trisulfides—disulfides largely predominate the volatile fraction (amounts over 60% on the total volatile content), followed by trisulfides and dipropyl disulfide and dipropyl trisulfide were the most abundant VOCs. HS-SPME-GC×GC-TOF allowed for the detection of the presence of allylthiol, diethanol sulfide, 4,6-diethyl1,2,3,5-tetrathiolane, not detected by HS-SPME-GC-MS, and provided a fast and direct visualization and comparison of different samples. These results highlight different nutraceutical properties of dried onion samples processed otherwise, only differing in shape and size, thus pointing out potentially different uses as functional ingredients.

Comparison of Organosulfur and Amino Acid Composition between Triploid Onion Allium cornutum Clementi ex Visiani, 1842, and Common Onion Allium cepa L., and Evidences for Antiproliferative Activity of Their Extracts

Species that belong to the genus Allium have been widely used for human food and traditional medicine. Their beneficial health effects, as well as the specific aroma, are associated with their bioactive chemical compounds, such as sulfur compounds and flavonoids. Gas chromatography and mass spectrometry (GC-MS) and reverse-phase high-performance liquid chromatography (reverse-phase HPLC) were used to identify organosulfur and amino acid content of triploid hybrid onion, Allium cornutum Clement ex Visiani, 1842, and common onion, Allium cepa L. Allium extracts were tested for their antiproliferative activity in three human cancer cell lines (HeLa, HCT116, and U2OS). DNA fragmentation and DAPI staining analysis were performed on HeLa cells to evaluate the effect of extracts on DNA damage and cell morphology. The mRNA expression of p53, Bax, and Caspase-3 genes involved in apoptosis were analyzed by real-time PCR. Using GC-MS, 27 compounds were found in two Allium species headspaces. Differences were noted among the main compound abundance in the headspace (although the major thiols and disulfides were qualitatively identic in both Allium species) and dipropyl disulfide, diisopropyl trisulfide, and (Z)-prop-1-enyl propyl trisulfide were predominant sulfides. Identification of amino acids and their quantities were determined by reverse-phase HPLC. Most abundant amino acids in both onions were arginine (Arg) and glutamic acid (Glu). The results of cytotoxicity testing confirmed antiproliferative effects of both species. The DNA fragmentation assay, DAPI staining and real time PCR analysis confirmed that A. cornutum and A. cepa extracts induced apoptosis in HeLa cells. This study presents the evidence for possible therapeutic use of A. cornutum and A. cepa extracts against human cervical carcinoma cell line.

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.

Metabolite variation in three edible Italian Allium cepa L. by NMR-based metabolomics: a comparative study in fresh and stored bulbs

INTRODUCTION

In fruits and vegetables, comparative analysis of metabolic plant profiles has a high potential for quality control of active components. Onion (Allium cepa L.) is used fresh or stored as food, spice, and in traditional medicine. Its metabolic content, often with nutraceutical value, makes its level an important factor in agronomic production.

OBJECTIVE

To describe for the first time the metabolome of "San Pietro" white onion (WP), and compare its chemical profile with the red onion var. Tropea (RT) and the yellow onion var. Montoro (CM). Furthermore, we also aim to obtain a multivariate model based on NMR fingerprints to discriminate the three Italian A. cepa L. cultivars.

METHODS

For the chemical fingerprinting we used NMR-based metabolomics. We investigated the aqueous and chloroform extracts of fresh onion at harvesting time, and after 9-month storage. Principal component analysis (PCA), Partial least squares discriminant analysis (PLS-DA) and Orthogonal partial least squares (OPLS-DA) were used to build reliable models.

RESULTS

We obtained a clear discrimination of A. cepa L. varieties for the fresh and stored batches. The statistical model highlighted higher levels of fructo-oligosaccharides (FOS) in the fresh WP; RT showed a high content of glucose, citrate and amino acids, while CM had many sulfur components. In the stored samples (CMS, RTS), carbohydrates and sulfur components decreased, while in WPS the free monosaccharides concentration increased. Linoleic acid was overexpressed in the apolar extracts of CMF and WPF cultivars.

CONCLUSION

Metabolomics allows a reliable differentiation among onion varieties, and highlights the potential of fingerprinting for food authentication purposes.

Emission of volatile organic compounds from yellow onion (Allium cepa L.) bulbs during storage

Fresh onions (Allium cepa L.) emit volatile organic compounds (VOCs) naturally in very low concentrations. The aim of the present study was to determine the emission rate of low-boiling VOCs from healthy and naturally infected onion bulbs at 4, 15, and 25 °C and to evaluate the applicability of the VOC method to monitor quality changes during 12 weeks of storage of two cultivars ('Hystand' and 'Hoza') of yellow onions. VOCs were extracted from the headspace of bulbs by solid phase micro-extraction (SPME) up to 5 times during storage and analyzed by gas chromatography-mass spectrometry (GC-MS). A total of twenty-nine compounds were measured and twenty-seven of these were identified while thirteen were reported for the first time from yellow onion bulbs. Acetone (0.10-18.0 nmol kg^-1 day^-1), dimethyl disulfide (0.12-18.9 nmol kg^-1 day^-1) and hexanal (0.05-4.40 nmol kg^-1 day^-1) were among the most abundant volatiles emitted from healthy bulbs. The concentration of these compounds as well as the total volatiles decreased with time in storage. However, microbial infection resulted in higher emission of propene, carbon disulfide, isoprene, pentane, 2-methylfuran, 3-methylfuran, 1-propenethiol, hexane, and methyl propyl sulfide, indicating that VOC emission may be used as an indicator to monitor natural senescence and decay of stored onion bulbs.

Mass spectrometry-based metabolomics of volatiles as a new tool for understanding aroma and flavour chemistry in processed food products

BACKGROUND

When foods are processed or cooked, many chemical reactions occur involving a wide range of metabolites including sugars, amino acids and lipids. These chemical processes often lead to the formation of volatile aroma compounds that can make food tastier or may introduce off-flavours. Metabolomics tools are only now being used to study the formation of these flavour compounds in order to understand better the beneficial and less beneficial aspects of food processing.

AIM OF REVIEW

To provide a critical overview of the diverse MS-based studies carried out in recent years in food metabolomics and to review some biochemical properties and flavour characteristics of the different groups of aroma-related metabolites. A description of volatiles from processed foods, and their relevant chemical and sensorial characteristics is provided. In addition, this review also summarizes the formation of the flavour compounds from their precursors, and the interconnections between Maillard reactions and the amino acid, lipid, and carbohydrate degradation pathways.

KEY SCIENTIFIC CONCEPTS OF REVIEW

This review provides new insights into processed ingredients and describes how metabolomics will help to enable us to produce, preserve, design and distribute higher-quality foods for health promotion and better flavour.

Feasibility of using a bacteriophage-based structural color sensor for screening the geographical origins of agricultural products

An M13 bacteriophage-based color sensor, which can change its structural color upon interaction with a gaseous molecule, was evaluated as a screening tool for the discrimination of the geographical origins of three different agricultural products (garlic, onion, and perilla). Exposure of the color sensor to sample odors induced the self-assembled M13 bacteriophage bundles to swell by the interaction of amino acid residues (repeating units of four glutamates) on the bacteriophage with the odor components, resulting in a change in the structural color of the sensor. When the sensor was exposed to the odors of garlic and onion samples, the RGB color changes were considerable because of the strong interactions of the odor components such as disulfides with the glutamate residues on the sensor. Although the patterns of the color variations were generally similar between the domestic and imported samples, some degrees of dissimilarities in their intensities were also observed. Although the magnitude of color change decreased for perilla, the color change patterns between the two groups were somewhat different. With the acquired RGB data, a support vector machine was employed to distinguish the domestic and imported samples, and the resulting accuracies in the measurements of garlic, onion, and perilla samples were 94.1, 88.7, and 91.6%, respectively. The differences in the concentrations of the odor components between both groups and/or the presence of specific components exclusively in the odor of one group allowed the color sensor-based discrimination. The demonstrated color sensor was thus shown to be a potentially versatile and simple as an on-site screening tool. Strategies able to further improve the sensor performance were also discussed.

Fresh-Cut Onion: A Review on Processing, Health Benefits, and Shelf-Life

The ready-to-eat produce market has grown rapidly because of the health benefits and convenience associated with these products. Onion is widely used as an ingredient in an extensive range of recipes from breakfast to dinner and in nearly every ethnic cuisine. However, cutting/chopping of onion is a nuisance to many consumers due to the lachrymatory properties of the volatiles generated that bring tears to eyes and leave a distinct odor on hands. As a result, there is now an increasing demand for fresh-cut, value-added, and ready-to-eat onion in households, as well as large-scale uses in retail, food service, and various food industries, mainly due to the end-use convenience. Despite these benefits, fresh-cut onion products present considerable challenges due to tissue damage, resulting in chemical and physiological reactions that limit product shelf-life. Intensive discoloration, microbial growth, softening, and off-odor are the typical deteriorations that need to be controlled through the application of suitable preservation methods. This article reviews the literature related to the fresh-cut onion, focusing on its constituents, nutritional and health benefits, production methods, quality changes throughout storage, and technologies available to increase product shelf-life.

Antimicrobial activity and thiosulfinates profile of a formulation based on Allium cepa L. extract

Background

Allium species extracts including Allium cepa L. contain sulfur compounds, known for their antiplatelet, antimicrobial, antineoplasic activities.

Methodology

Antibacterial activity of a formulation based on A. cepa extracts-liquid and lyophilized samples, has been demonstrated using two classes of bacteria: Gram-positive (Staphylococcus aureus) and Gram-negative (Escherichia coli) and three methods: discs soaked with liquid extract, the wells method in the culture medium, filled with the liquid extract and lyophilized formulation extracts transformed by the incorporation of ultrapure water. The second part of this study includes identification of thiosulfinates compounds from the studied samples by high performance liquid chromatography - mass spectrometry (HPLC-MS).

Results

The most important inhibition and the highest antibacterial effficiency were observed against Gram-positive bacteria, such as Staphylococcus aureus. The HPLC-MS thiosulfinates profile of the tested formulation extracts shows the presence of seven thiosulfinate compounds, MeS(O)S 1-propenyl (E,Z); n-PrS(O)S 1-propenyl-(E); n-PrS(O)S 1-propenyl-(Z); trans-zwiebelane; n-PrS(O)CHEtSS-1propenyl; 1-propenylS(O)CHEtSS1-propenyl, which may be responsible for antibacterial activity.

Conclusion

Testing antimicrobial effects using the three mentioned methods confirmed the antimicrobial activity of the tested samples based on A. cepa extracts, with a demonstrated content of seven thiosulfinate compounds.

Volatile composition and sensory characteristics of onion powders prepared by convective drying

Volatile composition and sensory characteristics of onion powders prepared by convective drying at different temperatures (50, 70, and 90°C) were investigated. Dipropyl disulfide was the major volatile compound in fresh onion (77.70% of total volatile compounds). However it was considerably lost during drying, reaching 6.93-32.25µg/g solids. Dipropyl disulfide showed a positive correlation with green sensory attribute perceived by descriptive sensory analysis. Thiophenes, which were responsible for caramel and sweet attributes, were produced by drying especially when the drying temperature was high. Aldehydes, another type of volatile compound found in fresh onion, showed a positive correlation with humidity. The aldehyde content in dried onion was the highest at the lowest drying temperature, possibly because the aldehydes were produced by the residual enzymes in fresh onion. Using a low temperature for drying was ideal to retain the aroma of fresh onion.

The Anti-Inflammatory and Vasodilating Effects of Three Selected Dietary Organic Sulfur Compounds from Allium Species

The anti-inflammatory and vasodilating effects of three selected dietary organic sulfur compounds (OSC), including diallyl disulfide (DADS), dimethyl disulfide (DMDS), and propyl disulfide (PDS), from Allium species were investigated. In the anti-inflammatory activity assay, the three OSC demonstrated significant inhibition of nitric oxide (NO) and prostaglandin E₂ (PGE₂) production in LPS-induced RAW 264.7 cells. The expression of inducible nitric oxide synthase (iNOS) and cyclooxygenase (COX-2) in activated RAW 264.7 cells was inhibited by the three OSC, indicating that the three OSC prevented the LPS-induced inflammatory response in RAW 264.7 cells. For the vasodilative assay, the three OSC were ineffective in producing NO in SVEC4-10 cells, but they did enhance prostacyclin (PGI₂) production. The expression of COX-2 in SVEC4-10 cells was activated by DADS and DMDS. Pretreatment of SVEC4-10 cells with the three OSC decreased ROS generation in H₂O₂-induced SVEC4-10 cells. In addition, the three OSC significantly inhibited angiotensin-I converting enzyme (ACE). The up-regulation of PGI₂ production and COX-2 expression by DADS and DMDS and the reduction of ROS generation by DADS, DMDS, and PDS in SVEC4-10 cells contributed to the vasodilative effect of the three OSC. Collectively, these findings suggest that DADS, DMDS, and PDS are potential anti-inflammatory and vasodilative mediators.

Chemical Composition and Antioxidant Properties of Five White Onion (Allium cepaL.) Landraces

Five onion landraces belonging toBianca di Pompeicv., cultivated in Campania region (Italy), were characterized for their main quality parameters. The onion landraces were harvested at the end of the growth cycle corresponding to the ripening time and harvest month, respectively: February, March, April, May, and June. The total content of volatile compounds as well as the sulfur-containing compounds inAprilaticawas significantly (p≤0.05) higher than the other landraces investigated. The nutraceutical feature investigated through the total phenols, phenols profile, and antioxidant activity showed higher values for the samples harvested in spring months. High pungency values ranging from 9 to 14 μmol/g FW were found in all onion landraces investigated as enzymatically (alliinase) produced pyruvate (EPY). The organic acids profile (malic, citric, succinic, pyruvic, oxalic, ascorbic, and tartaric acids) highlighted malic and citric acids in higher amounts in all landraces. Fructose, glucose, and sucrose were found as soluble sugars and fructose was the most abundant. Generally, the results highlighted the growth temperature influence on the investigated quality parameters.

Comparison of Aroma-Active Volatiles in Oolong Tea Infusions Using GC-Olfactometry, GC-FPD, and GC-MS

The aroma profile of oolong tea infusions (Dongdingwulong, DDWL; Tieguanyin, TGY; Dahongpao, DHP) were investigated in this study. Gas chromatography-olfactometry (GC-O) with the method of aroma intensity (AI) was employed to investigate the aroma-active compounds in tea infusions. The results presented forty-three, forty-five, and forty-eight aroma-active compounds in the TGY, DHP, and DDWL infusions, including six, seven, and five sulfur compounds, respectively. In addition, the concentration of volatile compounds in the tea infusions was further quantitated by solid phase microextraction-gas chromatography (SPME)-GC-MS and SPME-GC-flame photometric detection (FPD). Totally, seventy-six and thirteen volatile and sulfur compounds were detected in three types of tea infusions, respectively. Quantitative results showed that forty-seven aroma compounds were at concentrations higher than their corresponding odor thresholds. On the basis of the odor activity values (OAVs), 2-methylpropanal (OAV: 230-455), 3-methylbutanal (1-353), 2-methylbutanal (34-68), nerolidol (108-184), (E)-2-heptenal (148-294), hexanal (134-230), octanal (28-131), β-damascenone (29-59), indole (96-138), 6-methyl-5-hepten-2-one (34-67), (R)-(-)-linalool (63-87), and dimethyl sulfide (7-1320) presented relatively higher OAVs than those of other compounds, indicating the importance of these compounds in the overall aroma of tea infusions.

Using headspace solid-phase microextraction for comparison of volatile sulphur compounds of fresh plants belonging to families Alliaceae and Brassicaceae

In this study, an optimisation of extraction of sulphur volatile compounds (SVCs) has been performed using Central Composite Design. The conditions of the highest amount of eluated peaks and total peaks area have been treated. Factors such as coating of fiber for SPME (Solid Phase Microextraction), extraction temperature and extraction time have been optimised. The SVCs have shown the optimal extraction using a DVB/CAR/PDMS (divinylbenzene/carboxen/polydimethylsiloxane) fiber at 73 °C during 50 min. Furthermore, a pre-incubation step lasting 20 min at the extraction temperature has been used. In total, 12 samples have been investigated at the mentioned optimal conditions, eight from the Alliaceae and four from the Brassicaceae family. The highest number of SVCs (24) has been identified in the sample of chive. The most frequently identified compound found in 11 of 12 samples has been dimethyl trisulphide.

In vitro toxicological evaluation of essential oils and their main compounds used in active food packaging: A review

Essential oils (EOs) and their main constituent compounds have been extensively investigated due to their application in the food industry for improving the shelf life of perishable products. Although they are still not available for use in food packaging in the market in Europe, considerable research in this field has been carried out recently. The safety of these EOs should be guaranteed before being commercialized. The aim of this work was to review the scientific publications, with a primary focus on the last 10 years, with respect to different in vitro toxicological aspects, mainly focussed on mutagenicity/genotoxicity. In general, fewer genotoxic studies have been reported on EOs in comparison to their main components, and most of them did not show mutagenic activity. However, more studies are needed in this field since the guidelines of the European Food Safety Authority have not always been followed accurately. The mutagenic/genotoxic activities of these substances have been related to metabolic activation. Therefore, in vivo tests are required to confirm the absence of genotoxic effects. Considering the great variability of the EOs and their main compounds, a case-by-case evaluation is needed to assure their safe use in food packaging.

Potential therapeutic effect of Allium cepa L. and quercetin in a murine model of Blomia tropicalis induced asthma

BACKGROUND

Asthma is an inflammatory condition characterized by airway hyperresponsiveness and chronic inflammation. The resolution of inflammation is an essential process to treat this condition. In this study we investigated the effect of Allium cepa L. extract (AcE) and quercetin (Qt) on cytokine and on smooth muscle contraction in vitro and its therapeutic potential in a murine model of asthma.

METHODS

AcE was obtained by maceration of Allium cepa L. and it was standardized in terms of quercetin concentration using high performance liquid chromatography (HPLC). In vitro, using AcE 10, 100 or 1000 μg/ml or Qt 3.5, 7.5, 15 μg/ml, we measured the concentration of cytokines in spleen cell culture supernatants, and the ability to relax tracheal smooth muscle from A/J mice. In vivo, Blomia tropicalis (BT)-sensitized A/J mice were treated with AcE 100, 1000 mg/kg or 30 mg/kg Qt. We measured cell influx in bronchoalveolar lavage (BAL), eosinophil peroxidase (EPO) in lungs, serum levels of Bt-specific IgE, cytokines levels in BAL, and lung histology.

RESULTS

We observed a reduction in the production of inflammatory cytokines, a relaxation of tracheal rings, and a reduction in total number of cells in BAL and EPO in lungs by treatment with AcE or Qt.

CONCLUSION

AcE and Qt have potential as antiasthmatic drugs, as they possess both immunomodulatory and bronchodilatory properties.

Chemical and biochemical mechanisms underlying the cardioprotective roles of dietary organopolysulfides

Foods that are rich in organosulfides are highly regarded for their broad range of functions in disease prevention and health promotion since ancient time yet modern scientific study, particularly clinical studies could not agree with traditional wisdom. One of the complexities is due to the labile nature of organosulfides, which are often transformed to different structures depending on the processing conditions. The recent evidence on polysulfides as H₂S donors may open up a new avenue for establishing structure and health promotion activity relationship. To put this development into perspective, we carried out a review on the recent progress on the chemistry and biochemistry of organopolysulfides with emphasis on their cardioprotective property. First, we briefly surveyed the foods that are rich in polysulfides and their structural diversity. This is followed by in-depth discussion on the chemical transformations of polysulfides under various processing conditions. We further reviewed the potential action mechanisms of polysulfides in cardioprotection through: (a) hydrogen sulfide releasing activity; (b) radical scavenging activity; and (c) activity in enzyme inhibition and intervention of gene regulation pathways. Based on the literature trend, we can conclude that the emerging concept of organopolysulfides as naturally occurring H₂S donors is intriguing and warrants further research to establish the structure and activity relationship of the organopolysulfides as H₂S donors.

High-cholesterol diet enriched with onion affects endothelium-dependent relaxation and NADPH oxidase activity in mesenteric microvessels from Wistar rats

BACKGROUND

The aim of the present study was to examine the effects of onion as functional ingredient on the oxidative status, lipoprotein levels (total cholesterol-TC, HDL-C, LDL-C), triacylglycerides (TAG) and vascular reactivity of mesenteric arteries in hypercholesterolemic Wistar rats.

METHODS

Twenty-four animals were fed with three different diets [control, high-cholesterol diet (HC) and high-cholesterol enriched with onion diet (HCO)]. After seven weeks of experimental feeding the rats were euthanized for blood and tissues collection. TC, HDL-C, LDL-C and TAG were measured, and 2,2'-azinobis-(3-ethylbenzothiazoline-6-sulfonic acid) radical cation (ABTS(•+)) scavenging capacity and ferric reducing antioxidant power (FRAP) were determined in plasma. Superoxide dismutase (SOD) and glutathione peroxidase (GPx) enzyme activities were assayed in erythrocyte lysates. Endothelium-dependent vasodilation to acetylcholine was evaluated in mesenteric arterial segments. NADPH oxidase (NOX) was also measured by lucigenin-derived chemiluminiscence.

RESULTS

The dietary cholesterol content significantly affected plasma lipoprotein levels, increased superoxide generation from NOX, and caused impaired endothelium-dependent vasodilation in the rat mesenteric arteries. Onion ingredient improved antioxidant status in HCO group, as it was evidenced by ABTS(•+) and FRAP values and SOD and GPx enzyme activities compared to the HC-fed group, reduced the increment in NOX activity and reversed endothelial dysfunction promoted by the HC diet. Scavenging of superoxide with TEMPOL or inhibition of NOX with apocynin improved endothelium-dependent vasodilation only in HC-fed rats.

CONCLUSIONS

Enrichment of diet with onion as functional ingredient could be proposed as a complementary approach to prevent or partially modulate vascular dysfunction, reducing some of the risk indexes linked to initial development of atherosclerosis.

Effect of processing conditions on the organosulfides of shallot (Allium cepa L. Aggregatum group)

There is a growing account of the health benefits of H2S as an endogenous cell-signaling molecule. H2S from organic polysulfides, in particular, is increasingly gaining attention for their beneficial effects to cardiovascular health. Here, we studied shallot as a potential dietary source of organic polysulfides and examined the effects of processing conditions on its polysulfide profiles. Boiling, autoclaving, and freeze-drying were tested on whole and crushed shallot bulbs, analyzing their effect on the yield of organosulfides. Seventeen organosulfides, including disulfides, trisulfides, and cyclic polysulfides, were identified. Significant differences in the quantitative and qualitative profiles of organosulfides in the hydrodistilled and solvent extracted oils were observed. Freeze-drying retained the majority of the organosulfides, but the whole-autoclaved and whole-boiled shallots lost more than 95% of their organic polysulfides. Crushed-boiled and crushed-autoclaved shallot lost 76-80% of their organosulfides, likely due to the thermal sensitivity of these compounds. The organosulfide profiles are sensitive to the pH values of the processing media. In general, disulfides increased at basic pH (pH 9.0) while trisulfides and cyclic organosulfides are much higher at the acidic to neutral pH values (pH 3.0-5.0). Our results provide important information on the effects of processing conditions that are relevant for optimizing extraction of organosulfides from shallot for further studies evaluating their H2S-releasing activity.

Evaluation of allium and its seasoning on toxigenic, nutritional, and sensorial profiles of groundnut oil

Mitigation of xerophilic storage fungi-associated aflatoxin threat in culinary oil will be a new technology advantage to food industries. Groundnut oil isolate Aspergillus flavus MTCC 10680 susceptibility to Allium species (A. sativum L., A. cepa L., and A. cepa var. aggregatum) extracts, composition, and in silico confirmation of extract's phytoconstituent aflatoxin synthesis inhibition were determined. The behavior of seasoning carrier medium groundnut oil in the presence of Allium was also determined. All the Allium species extracts exhibited concentration dependent in vitro inhibition on mycelial biomass, radial growth, and toxin elaboration. The gas chromatography-mass spectrometry revealed the presence of 28, 16, and 9 compounds in the extracts of A. sativum, A. cepa, A. cepa var. aggregatum, respectively. The Allium phytocostituents-like hexadecanoic acid, 5-Octanoyl-2,4,6(1H,3H,5H)-pyrimidinetrione, Guanosine, and so on, showed higher binding energy with aflatoxin synthesis key enzyme ver1. Allium seasoning increased the typical nutty odor of the groundnut oil with sweet aroma note as well as intensification of pale yellow color. Allium seasoning exhibited the highest aflatoxin detoxification and aroma development without any nutritional loss. Culinary oil Allium seasoning has anti-aflatoxin and food additive potential for use in food industries.

Selective spectrofluorimetric determination of sulfide ion using manganese doped ZnS quantum dots as luminescent probe

This work reports a spectrofluorimetric method for selective and sensitive determination of sulfide ion in aqueous solution. The ultra-small zinc sulfide quantum dots (QDs) doped with manganese (ZnS:Mn) were synthesized by using a simple and fast procedure based on the co-precipitation of nanoparticles in aqueous solution in the presence of 2-mercaptoethanol, as capping agent. The nanoparticles have exhibited two strong fluorescent emissions at about 424 and 594 nm. Luminescent surface-capped ZnS:Mn QDs, with particle size below 5 nm, have been applied for determination of sulfide anions in water samples. Under the optimum conditions, the fluorescence intensity of ZnS:Mn QDs is linearly proportional to the sulfide ion concentration in the range 1.2×10(-6) to 2.6×10(-5) mol L(-1) with a detection limit as 3.3×10(-7) mol L(-1). The relative standard deviation for five replicate measurements (for 8.0×10(-6) mol L(-1) of S(2-)) was obtained to be 2.6%. It was founded that the interference of the other anions was negligible on the quantitive determination of sulfide ion.