Flavor of rapeseed oil: An overview of odorants, analytical techniques, and impact of treatment

Combining Targeted Metabolomics with Untargeted Volatilomics for Unraveling the Impact of Sprouting on the Volatiles and Aroma of False Flax (Camelina sativa) Cold-Pressed Oil

Sprouting of stored oilseeds due to improper storage can lead to quality defects of cold-pressed oils obtained from them. This study aimed to evaluate the effect of seed sprouting on volatile organic compounds (VOCs), aroma-active compounds, and the content of nonvolatile metabolites in cold-pressed false flax oil obtained from sprouted seeds. In this study, 88 unique VOCs were detected in sprouted oils, whereas only 42 were found in the control oils. The control oils were characterized by a higher abundance of alcohols, while all other groups of compounds were associated with sprouted seeds. The formation of many VOCs was reflected in changes in the nonvolatile precursors. Fifteen aroma-active compounds were identified in sprouted oil, with five compounds playing a significant role (FD ≥ 128) in aroma formation. The presented approach allowed identification of differences caused by seed sprouting, resulting in oils with a much stronger aroma and a richer profile of VOCs due to intensive metabolic changes. The origin of many VOCs can be explained by alterations in the content of nonvolatile metabolites.

Peanut oils from roasting operations: An overview of production technologies, flavor compounds, formation mechanisms, and affecting factors

Fragrant peanut oils (FPOs) are commonly defined as edible peanut oils having strong natural roasted peanut flavor without peculiar unpleasant odors and produced from peanut kernels through roasting/steaming and pressing operations, etc. The flavor of FPOs plays a crucial role in their acceptability and applications and their flavor profiles are an important factor in determining their overall quality. This paper presents a systematic literature review of recent advances and knowledge on FPOs, especially their flavors, in which it is focused on the evaluation of volatile compounds, the factors influencing the formation of flavor compounds, and formation mechanisms of those typical flavor compounds. More than 300 volatiles are found in FPOs, while some key aroma-active compounds and their potential formation pathways are examined. Factors that have big influences on flavor are discussed also, including the properties of raw materials, processing technologies, and storage conditions. Ultimately, the paper highlights the challenges facing, including the challenges in flavor analysis, the relationship between volatile compounds and sensory attributes, as well as the opening of the blackboxes of flavor formations during the processing steps, etc.

Anti-oxidant activity of 1-(1H-imidazo[4,5-c]pyridin-4-yl)ethenone, a Maillard reaction product derived from fructose and histidine

BACKGROUND

The Maillard reaction involves the interaction of various amino acids and reducing sugars, resulting in food browning. It often produces appealing aromas and flavors. The complexities of the reaction are such that it can be challenging to identify the often numerous and frequently volatile products formed by it. In the present study, we sought to identify and evaluate an unusual product with anti-oxidant activity arising from a fructose-histidine Maillard reaction model. The anti-oxidant profile of this product was assessed by computational means.

RESULTS

The fructose-histidine Maillard reaction products (FH-MRPs) were generated by heating a 2:1 mixture of the sugar and the amino acid at 140 °C for 2 h. Chromatographically separable fractions, labelled DM-1 to DM-8, were obtained using silica gel as the stationary phase and dichloromethane/methanol (DCM/MeOH) mixtures as the mobile one. Fraction DM-5 exhibited the highest 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical scavenging activity, and further bio-assay guided fractionation led to isolation and identification of 1-(1H-imidazo[4,5-c]pyridin-4-yl)ethenone (IMPE) as the active principal, the structure of which was established by nuclear magnetic resonance (NMR) spectroscopic and mass spectral techniques. A mechanism for the formation of IMPE from its precursors is proposed. Density functional theory (DFT) calculations suggest this novel heterocyclic compound exerts its anti-oxidant effects by interacting with DPPH and 2,2'-Azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) radicals. Essentially, IMPE was non-toxic below 300 ug mL-1, showing a concentration-dependent free radical clearance capacity and reducing power within the 100-1000 μg mL-1 range, and moreover, exhibiting significant Fe2+ chelating abilities wihin the 50-200 μg mL-1 range.

CONCLUSION

This study identified the unique FH-MRP, IMPE, and found that it acts as food antioxidant through the chelation of metal ions. © 2024 Society of Chemical Industry.

Microwave pretreatment effects on the aroma precursors, sensory characteristics and flavor profiles of fragrant rapeseed oil

Microwave technology offers a rapid and uniform heating method. This study investigated how microwave pretreatment affects the aroma precursors and flavor of fragrant rapeseed oils (FROs). Microwave pretreatment led to decreased levels of polyunsaturated fatty acids, sugars, protein-bound amino acids, and glucosinolates. Using gas chromatography-mass spectrometry, we identified 66 volatile compounds in the oil samples. Among these, based on odor activity values (OAV ≥ 1), we found 9 aldehydes, 1 ketone, 6 pyrazines, 1 isothiocyanate, and 7 nitriles as the key aroma-active compounds, contributing fatty-like, nutty-like, and pungent-like odors, respectively. The electronic nose results highlighted W5S and W1W as primary sensors for determining the flavor profiles of FROs. Notably, aroma-active pyrazines exhibited strong negative correlations with sucrose, cysteine, lysine, and isoleucine. This research provides essential insights for enhancing the aroma of FROs.

Contribution of lipid to the formation of characteristic volatile flavor of peanut oil

Lipid is an important precursor for volatile flavor formation, but it is not clear how to study the reactions involved in forming key volatile flavor compounds in peanut oil. In this paper, we innovatively established a flavor research model to investigate the contribution of different chemical reactions to the aroma compounds of peanut oil. The results showed that lipid participation in thermal reactions is necessary for forming major aroma compounds in hot-pressed peanut oil. Compared to the Maillard reaction, the lipid oxidation-Maillard reaction produces more compounds with 46 volatile substances identified. During the heating process, six new key substances were formed and the level of unsaturated fatty acids decreased by 7.28%. Among them, linoleic acid may be an important precursor for the formation of aroma components of hot-pressed peanut oil. Our study could provide theoretical guidance for understanding the volatile flavor mechanism of peanut oil and improving volatile flavor.

Recent advances in the contribution of glucosinolates degradation products to cruciferous foods odor: factors that influence degradation pathways and odor attributes

As one of the most important vegetables and oils consumed globally, cruciferous foods are appreciated for their high nutritional value. However, there is no comprehensive knowledge to sufficiently unravel the "flavor mystery" of cruciferous foods. The present review provides a comprehensive literature on the recent advances regarding the contribution of glucosinolates (GSL) degradation products to cruciferous foods odor, which focuses on key GSL degradation products contributing to distinct odor of cruciferous foods (Brassica oleracea, Brassica rapa, Brassica napus, Brassica juncea, Raphanus sativus), and key factors affecting GSL degradation pathways (i.e., enzyme-induced degradation, thermal-induced degradation, chemical-induced degradation, microwave-induced degradation) during different processing and cooking. A total of 93 volatile GSL degradation products (i.e., 36 nitriles, 33 isothiocyanates, 3 thiocyanates, 5 epithionitriles, and 16 sulfides) and 29 GSL (i.e., 20 aliphatic, 5 aromatic, and 4 indolic) were found in generalized cruciferous foods. Remarkably, cruciferous foods have a distinctive pungent, spicy, pickled, sulfur, and vegetable odor. In general, isothiocyanates are mostly present in enzyme-induced degradation of GSL and are therefore often enriched in fresh-cut or low-temperature, short-time cooked cruciferous foods. In contrast, nitriles are mainly derived from thermal-induced degradation of GSL, and are thus often enriched in high-temperature, long-time cooked cruciferous foods.

CARM30: China annual rapeseed maps at 30 m spatial resolution from 2000 to 2022 using multi-source data

Rapeseed is a critical cash crop globally, and understanding its distribution can assist in refined agricultural management, ensuring a sustainable vegetable oil supply, and informing government decisions. China is the leading consumer and third-largest producer of rapeseed. However, there is a lack of widely available, long-term, and large-scale remotely sensed maps on rapeseed cultivation in China. Here this study utilizes multi-source data such as satellite images, GLDAS environmental variables, land cover maps, and terrain data to create the China annual rapeseed maps at 30 m spatial resolution from 2000 to 2022 (CARM30). Our product was validated using independent samples and showed average F1 scores of 0.869 and 0.971 for winter and spring rapeseed. The CARM30 has high spatial consistency with existing 10 m and 20 m rapeseed maps. Additionally, the CARM30-derived rapeseed planted area was significantly correlated with agricultural statistics (R2 = 0.65-0.86; p < 0.001). The obtained rapeseed distribution information can serve as a reference for stakeholders such as farmers, scientific communities, and decision-makers.

Effects of different amino acid enzymatic preparations on the quality and flavor of fragrant rapeseed oil

Enzymatically prepared aromatic oils commonly have high purity and aroma quality. However, amino acid type and content vary greatly according to the type of oil, which impacts overall aroma and quality. In this study, the effects of lysine (Lys), arginine (Arg), proline (Pro), and glutamic (Glu) acid on physicochemical indices, nutrients, hazardous substances, fatty acid composition, and flavor during fragrant rapeseed oil (FRO) enzymatic preparation were investigated using the Maillard reaction (MR). In the lysine-treated group, the unsaturated fatty acids (93.16 %), α-tocopherol (183.06 mg/kg), γ-tocopherol (404.37 mg/kg), and δ-tocopherol (12.69 mg/kg) contents were the highest, whereas the acid value (1.27 mg/g) and moisture (0.10 %) and benzo[a]pyrene (1.45 μg/kg) contents were the lowest. Sensory evaluation showed that lysine effectively enhanced FRO flavor by enhancing the nutty/toasted flavor (4.80 scores). Principle component analysis (PCA) showed that the nutty/toasted flavor correlated mainly with 2,6-dimethylpyrazine, 2,5-dimethyl-pyrazine, 2-methyl-pyrazine, and trimethylpyrazine, nutty/toasted flavor strength increased with pyrazine content, which were the highest in the lysine group (24.02 μg/g). This study provides a guide for FRO preparation by adding external MR prerequisites.

Flavor precursors identification and thermal degradation mechanisms of glucoerucin in fragrant rapeseed oil

The degradation products of glucosinolates endow rapeseed oil with a characteristic aroma, however, the mechanism remains unclear. In this study, 29 individual glucosinolates were identified in six rapeseeds (Brassica napus) using widely targeted metabolism, including 22 aliphatic, 5 aromatic, and 2 indole glucosinolates. Characterization of thermally induced aromas from new precursors-glucoerucin was performed in different pH matrices via headspace-solid phase microextraction and gas chromatography-mass spectrometry. Six glucoerucin degradation were identified including 5-methylthio-pentanenitrile and dimethyl trisulfide et al. The results of thermal model showed that Glucoerucin could generate volatile 5-methylthio-pentanenitrile via dehydration and formed 1-isothiocyanato-4-(methylsulfanyl)butane via (394.9 μg/kg) by the Rosen rearrangement further product pungent odors 4-isothiocyanato-1-butene (5.6 μg/kg) at pH 5. Sulfur-containing compounds included dimethyl disulfide and dimethyl trisulfide can provide pungent and cabbage notes in matrices at pH 7 and 9. The results provide a new understanding in the forming mechanism of characteristic odor in fragrant rapeseed oil.

Effects of Silica Hydrogel on Degumming of Fragrant Rapeseed Oil

Hot-pressed rapeseed oils with pleasant flavor, i.e., fragrant rapeseed oils, are favored by consumers, especially people from the southwest provinces of China. Although degumming is an important section in producing edible rapeseed oils, conventional degumming techniques are generally suffered from disadvantages such as moisture control, and large losses of micronutrients and flavors. In the present paper, hot-pressed rapeseed oils were treated with silica hydrogel to remove their gums, and changes in phospholipids, acid values, peroxide values, tocopherols, total phenols, and flavor compounds were analyzed to compare the silica hydrogel-degumming with conventional methods. The optimized conditions were suggested to be carried out at 45°C for 15 min, and the silica hydrogel dosage was 1.10%. More than 97.00% of phospholipids were removed after the degumming, and more than 85.00% of micronutrients, were retained in the treated oils. The degumming efficiency was therefore significantly higher than those operated by conventional acid degumming and soft degumming techniques. It was found that the dosage of the silica hydrogel significantly affected the removal rate of phospholipids compared with degumming time and temperature. There were nearly typical volatile compounds found in the rapeseed oils, while most of them kept almost stable after the silica hydrogel-degumming. In this regard, silica hydrogel adsorption exhibited little effect on volatile compounds, making it more suitable for the production of fragrant rapeseed oils.

Indication of the color change on the oxidation properties of fragrant rapeseed oil during shelf storage

The cause and trend of color change and their links to oxidative properties were investigated by simulating shelf storage conditions for fragrant rapeseed oils (FROs). Under illumination, the L* value gradually increased with the storage time. The a* and b* values showed different trends depending on brands. The photodegradation rates of chlorophylls were 8.6 ∼ 15 times higher than those of carotenoids. The change in color of FROs was mainly caused by the light-induced photodegradation of chlorophyll. Compared with the hydroperoxides, the contents of some secondary oxidation products [i.e., 2-butenal, octane, (Z)-2-octene, 2,4-octadiene, (Z)-2-heptenal, (E, E)-2,4-heptadienal, and (E)-2-decenal] were more closely associated with the color variation with correlation coefficients of 0.6 ∼ 0.94. Significant negative correlation was found between α-tocopherol content and oil color difference. Therefore, illumination was the main reason for the color degradation of the FROs. The varying degree of color difference was strongly linked to the quality deterioration caused by oxidation.

Widely targeted metabolomics reveal the glucosinolate profile and odor-active compounds in flowering Chinese cabbage powder

Widely targeted metabolomics were performed to explore the differences in glucosinolate and odor-active compound levels between flowering Chinese cabbage powder (FCCP) under vacuum-drying and oven-drying conditions. Twenty-three aliphatic, five indole, and three aromatic glucosinolates were identified in two pretreated FCCP. Higher aliphatic glucosinolate levels were retained in vacuum-dried cabbage powder compared to oven-dried samples, and they were negatively correlated with treated temperatures. A total of 36 major odor contributing compounds were detected, including 5 sulfur compounds, 10 aldehydes, 9 heterocyclic compounds, 7 nitriles, 3 acids, and 2 others. 5-Hexenenitrile and (methyldisulfanyl)methan, provide typical pungent, sulfous, and vegetable notes in FCCP. Four major GSLs, namely 2(R)-hydroxy-3-butenyl glucosinolate, (2S)-2-hydroxy-4-pentenyl glucosinolate, 5-(methylthio)pentyl glucosinolate and 2-phenylethyl glucosinolate were the key precursors to form odor-active compounds. Higher temperatures in thermal effects promotes the formation of sulfur-containing and nitrile compounds compared to the vacuum-dried ones. This work can provide a guide for flavor and nutrition retention in FCCP process.

Glucosinolates or erucic acid, which one contributes more to volatile flavor of fragrant rapeseed oil?

This study aims to investigate the effect of three rapeseed varieties with different erucic acid (EA) and glucosinolates (GLSs) content, and different degumming methods on the volatile flavor profiles of fragrant rapeseed oil (FRO). A total of 171 volatile compounds were identified by headspace solid-phase microextraction combine with gas chromatography-mass spectrometry (HS-SPME/GC-MS), and 87 compounds were identified as key odorants owing to their relative odor activity values (ROAV) ≥ 1. Methyl furfuryl disulfide was identified in rapeseed oil for the first time, with highest ROAVs (up to 26805.46). The volatile flavor profile of rapeseed oil was affected by GLSs content to a certain extent rather than EA content. Rapeseed varieties with low-EA and high-GLSs are suitable to produce FRO. Silicon dioxide adsorbing was an effective alternative method to water degumming in FRO. This work provided a new idea for selection of raw materials and degumming methods in FRO production.

A comparative study on flavor trapping techniques from the viewpoint of odorants of hot-pressed rapeseed oil

Rapeseed oil, as one of the three major vegetable oils in the world, its matrix effect makes the decoding flavor a challenge. Solid-phase microextraction (SPME), SPME-Arrow, headspace stir bar sorptive extraction (HSSE), direct thermal desorption (DTD), and solvent-assisted flavor evaporation (SAFE) were compared based on the odorants in hot-pressed rapeseed oil. Besides, methodological validation for 31 aroma standards was conducted to compare reliability and robustness of these approaches. DTD showed the largest proportion of acids, while the other techniques extracted a majority of nitriles. The highest number of odorants was detected by SAFE (31), followed by HSSE (30), SPME-Arrow (30), SPME (24), and DTD (14). SPME-Arrow showed the best performance in linearity, recovery, and reproducibility followed by SPME, HSSE, DTD, and SAFE. Results reveal the advantages and limitations of diverse methodologies and provide valuable insights for the selection of extraction methods in an oil matrix and flavor decoding.

Effects of High-Canolol Phenolic Extracts on Fragrant Rapeseed Oil Quality and Flavor Compounds during Frying

Fragrant rapeseed oil (FRO) is a frying oil widely loved by consumers, but its quality deteriorates with increasing frying time. In this study, the effect of high-canolol phenolic extracts (HCP) on the physicochemical properties and flavor of FRO during frying was investigated. During frying, HCP significantly inhibited the increase in peroxide, acid, p-anisidine, and carbonyl values, as well as total polar compounds and degradation of unsaturated fatty acids. A total of 16 volatile flavor compounds that significantly contributed to the overall flavor of FRO were identified. HCP was effective in reducing the generation of off-flavors (hexanoic acid, nonanoic acid, etc.) and increased the level of pleasant deep-fried flavors (such as (E,E)-2,4-decadienal). Therefore, the application of HCP has a positive effect on protecting the quality and prolonging the usability of FRO.

Sensory Wheel and Lexicon for the Description of Cold-Pressed Hemp Seed Oil

Cold-pressed hemp seed oil (CP-HSO) has become available on the market and is gaining popularity mainly for its appeal and nutritional profile. The sensory quality largely depends on seed quality and processing as well as oil storage conditions. Given the "native" nature of the product, obtained by cold-pressing, the development of a standardized methodology to evaluate and describe the sensory quality of HSOs is of the utmost importance. To this aim, 16 commercial HSOs were evaluated, covering the main differences in brands and sales channels. A trained panel developed a vocabulary to describe the HSO profile consisting of 44 attributes, and a practical sensory wheel was proposed to classify attributes in different clusters and according to sensory modality. A sensory profile sheet was developed including two color descriptors (yellow, green), seven main positive (sunflower/pumpkin seeds, nutty, toasted nutty, hay, sweet, bitter, and pungent), several secondary positive (herbs, coffee, tobacco, etc.), four main defects (rancid, paint, burnt, and fish), and other secondary negative descriptors (boiled vegetables, cucumber, etc.). Subsequently, specific training of the panelists was carried out, and a satisfactory performance level was reached. This study represents the first attempt to standardize the sensory quality and terminology of HSO.

Comparative characterization of key odorants and aroma profiles of fragrant rapeseed oil under different roasting conditions

Fragrant rapeseed oil (FRO) produced by typical roasting process is popular for its characteristic aroma. Accordingly, key aroma-active compounds were characterized in FRO by the Sensomics approach and then correlated to the crucial roasting parameters revealed by aroma profile analysis and hierarchical cluster analysis. Nineteen key odorants in FRO were identified and quantified, among which dimethyl trisulfide (OAV, odor active value, 323, cabbage-like, sulfury) and 4-isothiocyanato-1-butene (OAV, 88, pungent) were the most important aroma-active compounds in FRO and showed first rising and then decline trends as the increased roasting temperature and time. The oil under high-temperature-short time and low-temperature-long time conditions imparted similar aroma profiles. On the basis of sensory evaluation, roasting at 160, 170, 180, 190, and 200 °C should not exceed 50, 40, 30, 30, and 30 min, respectively to satisfy consumer preference. All findings provide a reference on industrial FRO production in terms of not only aroma but also sustainability.

Lipid oxidation in fragrant rapeseed oil: Impact of seed roasting on the generation of key volatile compounds

This work sought to identify the influence of roasting on lipid oxidation-derived volatile compounds in fragrant rapeseed oils (FROs) via gas chromatography–mass spectrometry and gas chromatography–ion mobility spectrometry. Seven volatiles could be regard as aroma-active compounds by application of odor activity value (OAV ≥ 1) calculation, and caused fatty-like, nutty-like, and green-like notes. After 60 min of roasting, the OAVs of hexanal, octanal, (E,E)-2,4-heptadienal, and nonanal in FROs were greater than 3. The same compounds, including hexanal, (E,E)-2,4-heptadienal, nonanal, 1-octanol, and nonanoic acid were also detected in the model systems of lipid oxidation. Notably, the values of p-anisidine, conjugated dienes, and conjugated trienes increased significantly (p < 0.05). Furthermore, correlation analysis showed that hexanal, (E,E)-2,4-heptadienal, and nonanal have a significant positive correlation with the oxidative degree of FROs (R = 0.70–0.94, p < 0.05). Thus, the three above-mentioned aldehydes could serve as important markers for FRO quality during roasting.

Citrus juice off-flavor during different processing and storage: Review of odorants, formation pathways, and analytical techniques

As the most widespread juice produced and consumed globally, citrus juice (mandarin juice, orange juice, and grapefruit juice) is appreciated for its attractive and distinct aroma. While the decrease of characteristic aroma-active compounds and the formation of off-flavor compounds are easy to occur in processing and storage conditions. This review provides a comprehensive literature of recent research and discovery on citrus juice off-flavor, primarily focusing on off-flavor compounds induced during processing and storage (i.e., thermal, storage, light, oxygen, package, fruit maturity, diseases, centrifugal pretreatment, and debittering process), formation pathways (i.e., terpene acid-catalyzed hydration, caramelization reaction, Maillard reaction, Strecker degradation, and other oxidative degradation) of the off-flavor compounds, effective inhibitor pathway to off-flavor (i.e., electrical treatments, high pressure processing, microwave processing, ultrasound processing, and chemical treatment), as well as odor assessment techniques based on molecular sensory science. The possible precursors (terpenes, sulfur-containing amino acids, carbohydrates, carotenoids, vitamins, and phenolic acids) of citrus juice off-flavor are listed and are also proposed. This review intends to unravel the regularities of aroma variations and even off-flavor formation of citrus juice during processing and storage. Future aroma analysis techniques will evolve toward a colorimetric sensor array for odor visualization to obtain a "marker" of off-flavor in citrus juice.

Exploring Lignans, a Class of Health Promoting Compounds, in a Variety of Edible Oils from Brazil

Lignans, a group of polyphenols, have been identified in eight cold pressed oils from fruits, nuts, and seeds, retrieved from the Brazilian market. The oils under investigation were avocado, Brazilian nut, canola, coconut, grapeseed, macadamia, palm, and pequi. Olive oil was selected as a reference oil, since numerous data on its lignan content are available in literature. The qualitative and quantitative profiles were obtained, after extraction, by means of UFLC-ESI-MS/MS analyses. The total lignan content showed a high variability, ranging from 0.69 mg·Kg-1 (pequi) to 7.12 mg·Kg-1 (grapeseed), with the highest content registered for olive oil. Seven lignans were quantified, matairesinol and pinoresinol being the most abundant. The LC-MS/MS method was validated, showing linearity in the range of 12.5-212.5 mg·Kg-1, LOD in the range of 0.18-11.37 mg·Kg-1, and LOQ in the range of 0.53-34.45 mg·Kg-1. Additionally, part of the study was focused on the evaluation of the flavor profile, this being a key element in consumers' evaluations, by means of HS-SPME-GC. In total, 150 volatile compounds were determined in the eight oils, with identified fractions ranging from 91.85% (avocado) to 96.31% (canola), with an average value of 94.1%. Groups of components contributed characteristically to the flavour of each oil.

Key volatile compound formation of rapeseed oil induced via the Maillard reaction during seed roasting

This study was designed to investigate the influence of roasting (150 °C for 0-60 min) on key volatile compounds, sensory evaluation, free amino acids, sugars, and Maillard reaction products (MRPs) of five rapeseed varieties and their oils. During the roasting process, key volatile MRPs of fragrant rapeseed oils (FROs) that increased obviously in concentration were mainly pyrazines. After 60 min of roasting, the stronger nutty-like odor in oil from QH was possibly caused by the high levels of 2,5-dimethylpyrazine (21.72 mg/kg) and 3-ethyl-2,5-dimethylpyrazine (5.06 mg/kg). The 5-hydroxymethylfurfural contents and browning indices increased significantly, whereas reducing sugar and free amino acid contents decreased significantly (p < 0.05). This suggested the extent of the Maillard reaction increased with roasting time. Furthermore, the results of Maillard reaction model system demonstrated glycine, lysine, and histidine could react with glucose to generate 2,5-dimethylpyrazine. Hence, 2,5-dimethylpyrazine is identified as one of the important aroma-active MRPs for FRO.

Investigation of volatile thiol contributions to rapeseed oil by odor active value measurement and perceptual interactions

Volatile thiols are important aroma components of rapeseed oil. This study established an identification and quantification method of volatile thiols via headspace solid-phase microextraction and gas chromatography-sulfur chemiluminescence detection. Four thiols (phenylmethanthiol, 3-sulfanyl-1-hexanol, 2-methyl-3-furanthiol, and 2-furylmethanthiol) were newly identified in microwaved rapeseed oil, and cause sesame, roasted meat, and garlic odors. The total concentration of the four thiols in rapeseed oil obtained from 13 rapeseed varieties ranged from 11.47 to 153.72 μg/kg. Determination of the threshold revealed that 3-sulfanyl-1-hexanol possessed the highest odor active value (7565), followed by phenylmethanthiol (3589), 2-furylmethanthiol (626), and 2-methyl-3-furanthiol (28). Further, perceptual interactions between volatile thiols and characteristic odor (3-butenyl isothiocyanate) of rapeseed oil were evaluated by Feller's addition model and S-curve method, which revealed that 2-methyl-3-furanthiol, 2-furylmethanthiol, phenylmethanthiol, and 3-sulfanyl-1-hexanol present a positive effect with 3-butenyl isothiocyanate. This study provides deep insights into the impact of sulfur-containing compounds on the aroma of rapeseed oil.

Key Odorants of Raw and Cooked Green Kohlrabi (Brassica oleracea var. gongylodes L.)

Volatile compounds of raw and cooked green kohlrabi were investigated using a sensomics approach. A total of 55 odor-active compounds were detected and identified in raw and cooked green kohlrabi using GC-O. Twenty-eight odor-active compounds with high flavor dilution (FD) factors ranging from 64 to 1024 were quantitated, and odor activity values (OAVs) were determined. Eight compounds showed high OAVs in raw and cooked kohlrabi: five sulfur compounds (dimethyl trisulfide, methyl 2-methyl-3-furyl disulfide, and three isothiocyanates (1-isothiocyanato-3-(methylsulfanyl)propane, benzyl isothiocyanate, and 1-isothiocyanato-4-(methylsulfanyl)butane)), two lipid oxidation products (1-octen-3-one and trans-4,5-epoxy-(2E)-dec-2-enal), and 2-isopropyl-3-methoxypyrazine. Among these, the sulfur compounds contributed most to the overall smell of the raw and cooked vegetables. The quantitation analysis indicates that the eight odorants are the backbone compounds for raw and cooked kohlrabi. The OAVs for the backbone compounds and also for minor odorants are clearly higher in raw kohlrabi than in the cooked one. Differences can be explained by the influence of the cooking process.