Application of Sorbent-Based Extraction Techniques in Food Analysis.

This review presents an outline of the application of the most popular sorbent-based methods in food analysis. Solid-phase extraction (SPE) is discussed based on the analyses of lipids, mycotoxins, pesticide residues, processing contaminants and flavor compounds, whereas solid-phase microextraction (SPME) is discussed having volatile and flavor compounds but also processing contaminants in mind. Apart from these two most popular methods, other techniques, such as stir bar sorptive extraction (SBSE), molecularly imprinted polymers (MIPs), high-capacity sorbent extraction (HCSE), and needle-trap devices (NTD), are outlined. Additionally, novel forms of sorbent-based extraction methods such as thin-film solid-phase microextraction (TF-SPME) are presented. The utility and challenges related to these techniques are discussed in this review. Finally, the directions and need for future studies are addressed.

Role of Sulfur Compounds in Vegetable and Mushroom Aroma.

At the base of the food pyramid is vegetables, which should be consumed most often of all food products, especially in raw and unprocessed form. Vegetables and mushrooms are rich sources of bioactive compounds that can fulfill various functions in plants, starting from protection against herbivores and being natural insecticides to pro-health functions in human nutrition. Many of these compounds contain sulfur in their structure. From the point of view of food producers, it is extremely important to know that some of them have flavor properties. Volatile sulfur compounds are often potent odorants, and in many vegetables, belonging mainly to Brassicaeae and Allium (Amaryllidaceae), sulfur compounds determine their specific flavor. Interestingly, some of the pathways that form volatile sulfur compounds in vegetables are also found in selected edible mushrooms. The most important odor-active organosulfur compounds can be divided into isothiocyanates, nitriles, epithionitriles, thiols, sulfides, and polysulfides, as well as others, such as sulfur containing carbonyl compounds and esters, R-L-cysteine sulfoxides, and finally heterocyclic sulfur compounds found in shiitake mushrooms or truffles. This review paper summarizes their precursors and biosynthesis, as well as their sensory properties and changes in selected technological processes.

Chemical Changes in the Broccoli Volatilome Depending on the Tissue Treatment.

The storage of plant samples as well as sample preparation for extraction have a significant impact on the profile of metabolites, however, these factors are often overlooked during experiments on vegetables or fruit. It was hypothesized that parameters such as sample storage (freezing) and sample pre-treatment methods, including the comminution technique or applied enzyme inhibition methods, could significantly influence the extracted volatile metabolome. Significant changes were observed in the volatile profile of broccoli florets frozen in liquid nitrogen at -20 °C. Those differences were mostly related to the concentration of nitriles and aldehydes. Confocal microscopy indicated some tissue deterioration in the case of slow freezing (-20 °C), whereas the structure of tissue, frozen in liquid nitrogen, was practically intact. Myrosinase activity assay proved that the enzyme remains active after freezing. No pH deviation was noted after sample storage - this parameter did not influence the activity of enzymes. Tissue fragmentation and enzyme-inhibition techniques applied prior to the extraction influenced both the qualitative and quantitative composition of the volatile metabolome of broccoli.

Determination of Volatile Terpenes in Coriander Cold Pressed Oil by Vacuum Assisted Sorbent Extraction (VASE).

Cold-pressed plant oils are of high interest to consumers due to their unique and interesting flavors. As they are usually only pressed at low temperatures and filtered, without further processing stages (as refining), they preserve their character that originates from the plant the oil was extracted from. Coriander cold pressed oil is gaining popularity as a novel product, obtained from its fruits/seeds; due to the high amount of terpenes, it has very characteristic flavor. A novel, vacuum-assisted sorbent extraction (VASE) method was used to extract terpenes from coriander cold pressed oil. Optimal parameters were determined. The profile of compounds extracted using VASE was compared with that of classic hydrodistillation method. Moreover, 17 monoterpene hydrocarbons and alcohols were identified with ß-linalool as the main compound, followed by α-pinene, γ-terpinene, camphor, sylvestrene, ß-pinene, and o-cymene. Differences were noted between profiles of terpenes after hydrodistillation and VASE extraction. For 8 out of 17 terpenes, VASE was used for their quantitative analysis. Regarding simplicity of the method, small sample requirement (200 mg) and short extraction time (5 min), VASE combined with GC/MS is well suited for characterization of terpenes in such matrix as plant oils.

Changes in Volatile Compound Profiles in Cold-Pressed Oils Obtained from Various Seeds during Accelerated Storage.

Cold-pressed oils are highly valuable sources of unsaturated fatty acids which are prone to oxidation processes, resulting in the formation of lipid oxidation products, which may deteriorate the sensory quality of the produced oil. The aim of the study was to determine the main volatile compounds which differentiate examined oils and could be used as the markers of lipid oxidation in various oils. In the experiment, cold-pressed oils-brown flaxseed, golden flaxseed, hempseed, milk thistle, black cumin, pumpkin, white poppy seed, blue poppy seed, white sesame, black sesame and argan oils from raw and roasted kernels-were analyzed. To induce oxidative changes, an accelerate storage test was performed, and oils were kept at 60 °C for 0, 2, 4, 7 and 10 days. Volatile compound profiling was performed using SPME-GC-HRToFMS. Additionally, basic measurements such as fatty acid composition, peroxide value, scavenging activity and phenolic compound contents were carried out. Multivariate statistical analyses with volatile compound profiling allow us to differentiate oils in terms of plant variety, oxidation level and seed treatment before pressing. Comparing black cumin cold-pressed oil with other oils, significant differences in volatile compound profiles and scavenging activity were observed. Compounds that may serve as indicators of undergoing oxidation processes in flaxseed, poppy seed, milk thistle and hemp oils were determined.

Inactivation of Thioglucosidase from Sinapis alba (White Mustard) Seed by Metal Salts.

The glucosinolates which are specialized plant metabolites of Brassica vegetables are prone to hydrolysis catalyzed by an endogenous enzyme myrosinase (thioglycoside hydrolase, thioglucosidase) that exists in Brassica plant tissue causing volatile isothiocyanates release. Currently existing literature data on the inactivation of myrosinase is insufficient in particular for use in the analysis of volatile and odor compounds in vegetables rich in glucosinolates. In this study, the impact of different metal salts in effective inactivation of enzyme activity was investigated by solid-phase microextraction (SPME) and GC/MS system in aqueous samples and kohlrabi matrix. A saturated solution of calcium chloride which is commonly used to stop enzyme activity in plant tissue inactivates the myrosinase-glucosinolate system. However, even without the participation of myrosinase, it changes the reaction pathway towards nitrile formation. The model experiment shows that optimum efficiency in inhibition of the enzyme system shows iron(III) ions, silver ions, and anhydride sodium sulfate resulting in no volatile products derived from glucosinolates. However, in the kohlrabi matrix, the strongest enzyme inhibition effect was observed for silver salt resulting in no volatile products, also both anhydrous Na2SO4 and saturated CaCl2 solution seem to be useful inhibitors in flavor studies.

Identification of Odor Active Compounds in Physalis peruviana L.

The volatiles of cape gooseberry fruit (Physalis peruviana L.) were isolated by solvent-assisted flavor evaporation (SAFE), odor active compounds identified by gas chromatography-olfactometry (GC-O) and gas chromatography-mass spectrometry (GC-MS). Quantitation of compounds was performed by headspace-solid phase microextraction (HS-SPME) for all but one. Aroma extract dilution analysis (AEDA) revealed 18 odor active regions, with the highest flavor dilution values (FD = 512) noted for ethyl butanoate and 4-hydroxy-2,5-dimethylfuran-3-one (furaneol). Odor activity values were determined for all 18 compounds and the highest was noted for ethyl butanoate (OAV = 504), followed by linalool, (E)-non-2-enal, (2E,6Z)-nona-2,6-dienal, hexanal, ethyl octanoate, ethyl hexanoate, butane-2,3-dione, and 2-methylpropanal. The main groups of odor active compounds in Physalis peruviana L. were esters and aldehydes. A recombinant experiment confirmed the identification and quantitative results.

Volatile Compounds of Selected Raw and Cooked Brassica Vegetables.

Brassica vegetables are a significant component of the human diet and their popularity is systematically increasing. The interest in plants from this group is growing because of numerous reports focused on their pro-health properties. However, some consumers are not enthusiastic about these vegetables because of their specific bitter taste and sharp, sulfurous aroma. In this study, the volatile composition of 15 Brassica cultivars (five Brussels sprouts, four kohlrabi, three cauliflower and three broccoli), both raw and cooked, was analyzed by solid phase microextraction and comprehensive two-dimensional gas chromatography with time of flight mass spectrometry (SPME-GC×GC-ToFMS). Differences were found between the analyzed vegetables, as well as different cultivars of the same vegetable. Moreover, the influence of cooking on the composition of volatile compounds was evaluated. All the vegetables were frozen before analyses, which is why the impact of this process on the volatile organic compounds (VOCs) was included. The most abundant groups of compounds were sulfur components (including bioactive isothiocyanates), nitriles, aldehydes and alcohols. Cooking in general caused a decrease in the abundance of main volatiles. However, the amount of bioactive isothiocyanates increased in most cultivars after cooking. The effect of freezing on the volatile fraction was presented based on the Brussels sprout cultivars. Most of the changes were closely related to the activity of the lipoxygenase (LOX) pathway enzymes. These are characterized by a marked reduction in alcohol contents and an increment in aldehyde contents. Moreover, important changes were noted in the concentrations of bioactive components, e.g., isothiocyanates. This research included a large set of samples consisting of many cultivars of each analyzed vegetable, which is why it provides a considerable body of general information concerning volatiles in Brassica vegetables.

Bitter taste of Brassica vegetables: The role of genetic factors, receptors, isothiocyanates, glucosinolates, and flavor context.

It is well known that consumption of Brassica vegetables has beneficial effect on human's health. The greatest interest is focused on glucosinolates and their hydrolysis products isothiocyanates, due to their potential as cancer preventing compounds. Brassica vegetables are also rich in flavor compounds belonging to many chemical groups. The main sensory sensation related to these vegetable is their characteristic sharp and bitter taste, and unique aroma. Because of these features this group of vegetables is often rejected by consumers. Interestingly, for some people unpleasant sensations are not perceived, suggesting a potential role of inter-individual variability in bitter taste perception and sensibility. Receptors responsible for bitter sensation with the emphasis on Brassica are reviewed, as well as genetic predisposition for bitterness perception by consumers. Also the role of glucosinolates and isothiocyanates as compounds responsible for bitter taste is discussed based on data from the field of food science and molecular biology. Isothiocyanates are shown in broaded context of flavor compounds also contributing to the aroma of Brassica vegetables.

In-tube extraction for the determination of the main volatile compounds in Physalis peruviana L.

An analytical procedure based on in-tube extraction followed by gas chromatography with mass spectrometry has been developed for the analysis of 24 of the main volatile components in cape gooseberry (Physalis peruviana L.) samples. According to their chemical structure, the compounds were organized into different groups: one hydrocarbon, one aldehyde, four alcohols, four esters, and 14 monoterpenes. By single-factor experiments, incubation temperature, incubation time, extraction volume, extraction strokes, extraction speed, desorption temperature, and desorption speed were determined as 60°C, 20 min, 1000 µL, 20, 50:50 µL/s, 280°C, 100 µL/s, respectively. Quantitative analysis using authentic standards and external calibration curves was performed. The limit of detection and limit of quantification for the analytical procedure were calculated. Results shown the benzaldehyde, ethyl butanoate, 2-methyl-1-butanol, 1-hexanol, 1-butanol, α-terpineol, and terpinen-4-ol were the most abundant volatile compounds in analyzed fruits (68.6-585 µg/kg). The obtained data may contribute to qualify cape gooseberry to the group of superfruits and, therefore, increase its popularity.

Unravelling the importance of seed roasting for oil quality by the non-targeted volatilomics and targeted metabolomics of cold-pressed false flax (Camelina sativa L.) oil and press cakes.

False flax (Camelina sativa L.), known as camelina, is an ancient oil plant that has gathered renewed interest. In this study, a comprehensive analysis encompassing nontargeted volatilomics and targeted, quantitative metabolomics performed for cold-pressed oil and press cake and was integrated with sensory analysis of cold-pressed camelina oil and the effect of seed roasting was evaluated. Roasting in general resulted in the formation of 22 new volatile organic compounds (VOCs) in oil, while roasting at 140 and 180 °C resulted in the formation of 12 and 124 unique VOCs, respectively. Roasting notably influenced the profile of primary and secondary metabolites in both oil and press cakes, as well as volatilome and aroma of cold-pressed camelina oil. Many VOCs can be attributed to thermal degradation of primary and secondary metabolites. Roasting intensified the flavour of cold-pressed camelina oil, enhancing the perception of notes formed through the Maillard reaction.

Automated sequential SPME addressing the displacement effect in food samples.

The displacement effect can be an issue for the quantitation of analytes with low affinity towards the extraction phase in solid-phase microextraction (SPME) for food samples that have low level of binding matrix or high level of hydrophobic compounds. In this communication, automated sequential SPME-GC-MS strategy was developed for addressing the displacement issue. The SPME thin film with PDMS coating was firstly used for the extraction of hydrophobic components in the sample which cause displacement and then SPME fiber with DVB/CAR/PDMS coating was applied in the second step for the extraction of the remain compounds. This new strategy was investigated by using 10 key food odorants as target analytes and tested in commercial beer samples. The results suggested that sequential SPME can decrease the displacement effect and improve the extraction efficiency for polar analytes.

Can Volatiles Fingerprints be an Alternative to Isotope Ratio Mass Spectrometry in the Botanical Origin Determination of Spirits?

Mass spectrometry based quasi-electronic nose using solid-phase microextraction to introduce volatiles directly to mass spectrometer without chromatographic separation (HS-SPME-MS) was used to discriminate 45 raw spirits produced from C3 (potato, rye, wheat) and C4 (corn, sorghum) plants. The samples were also subjected to isotope ratio mass spectrometry (IRMS), which unequivocally distinguished C3 from C4 samples; however, no clear differentiation was observed for C3 samples. On the contrary, HS-SPME-MS, which uses unresolved volatile compounds "fingerprints" in a form of ions of a given m/z range and various intensities provided excellent sample classification and prediction after OPLS-DA data processing verified also by the artificial neural network (ANN).

Differentiation of raw spirits of rye, corn and potato using chromatographic profiles of volatile compounds.

BACKGROUND: The origin of the raw spirits influences the sensory quality of rectified spirits that are subsequently used for the production of vodka. The aim of this research was to evaluate the effectiveness of two methods based on the comparison of profiles of volatile compounds [solid phase microextraction-gas chromatography-mass spectrometry (SPME-GC-MS) and gas chromatography with flame ionisation detection (GC-FID)] for the determination of origin of raw spirits obtained from rye, corn (maize) and potato. RESULTS: Profiles obtained for the volatile compounds by using these methods were different and were influenced by the sample introduction method. The main groups of volatiles obtained using SPME-GC-MS method were fatty acid ethyl esters, while in the case of GC-FID fusel alcohols and ethyl acetate dominated. Data obtained from these methods were treated using principal component analysis and linear discriminant analysis to test the possibility of sample differentiation and classification. It was relatively easy to differentiate potato spirits from the remainder; however, it was not possible to fully distinguish the corn samples from rye samples. The classification ability of the SPME-GC-MS method was 95% but the prediction ability was 97.4%. For the GC-FID method the classification ability was 90.1%, whereas the prediction ability was 94.27%. CONCLUSIONS: The methods presented can be used for reliable differentiation of potato spirits from corn and rye spirits.

Changes in volatile, sensory and microbial profiles during preparation of smoked ewe cheese.

BACKGROUND: Oscypek is a special type of Polish smoked ewe cheese with a unique flavour described as slightly sour, piquant, salted and smoked. In this study the volatile, sensory and microbial profiles of Oscypek cheese were analysed during its various preparation stages of curding, scalding, brining and smoking. RESULTS: The smoked ewe cheese was characterised by 54 volatile compounds belonging to nine different chemical groups (free fatty acids, esters, ketones, alcohols, aldehydes, furans/furanones, phenols, sulfur compounds, terpenes). The sensory aroma profile analysis of unsmoked and smoked cheese showed an important correlation with the analysis of volatile compounds. The microbial profile data indicated that in smoked cheese such as Oscypek the levels of selected bacteria diminished after the curding stage as a result of the subsequent scalding, brining and smoking stages. CONCLUSION: From the results it can be concluded that, although the analysed smoked cheese consisted of three groups of compounds, the first derived from biochemical reactions (free fatty acids, esters, ketones, alcohols, aldehydes, sulfur compounds), the second from smoking (furans and furanones, phenols) and the third from milk flavour (terpenes), it is the smoking process that mainly influences its typical flavour.

Comprehensive two-dimensional gas chromatography-time of flight mass spectrometry (GC×GC-TOFMS) in conventional and reversed column configuration for the investigation of Baijiu aroma types and regional origin.

Baijiu is a traditional Chinese spirit with an extraordinarily rich pattern of volatile compounds resulting from the microflora involved in fermentation, as well as the complexity of technological process. Comprehensive two-dimensional gas chromatography in the conventional and reversed column setups (non-polar - polar and polar - non-polar columns) was tested for its ability to differentiate Baijiu samples in terms of their aroma and origin (region). A total of 65 Baijiu samples were used for the study and volatile compounds were extracted by SPME with a subsequent analysis by GC×GC-TOFMS. Orthogonality of both setups was compared, so was the number of compounds identified using each setup. Repeatability of compound groups for the conventional and reversed column setups was compared; moreover, multiblock orthogonal component analysis (MOCA) was used to visualize data sets. OPLS-DA was used for Baijiu classification. Both column setups provided excellent discrimination of the Light, Soy sauce, Feng and Herbal aromas. A better classification result for the Strong and Jian aromas was recorded for the conventional column setup. Within the Strong aroma using OPLS-DA both column setups provided perfect abilities to discriminate Baijiu from the Sichuan, Heilongjiang and Jiangsu regions. Two validation methods were applied in the classification models - all the predictive abilities evaluated by the internal validation were further confirmed by the external validation.

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.

Rapid analysis of Baijiu volatile compounds fingerprint for their aroma and regional origin authenticity assessment.

Solid-phase microextraction - mass spectrometry (SPME-MS) and fast gas chromatography based electronic nose (GC-E-Nose) were used and compared for their suitability to distinguish Baijiu of various aroma types and geographical origin. Baijiu is a traditional Chinese distilled spirit produced with complex consortia of microorganisms, which results in very complex aroma compounds profiles. A total of 65 Baijiu samples representing 6 aromas were investigated. Strong aroma types from 3 regions were examined for their origin. Data acquired on two analytical systems were processed using uniform statistical approach. Data were pre-processed for multi-classification (OPLS-DA) models as well as for binary classification (PLS-DA) ones. Aroma and regional classification performed using OPLS-DA indicated that the approach based on SPME-MS had better fitness and prediction ability compared with GC-E-Nose. The total correct classification rate for SPME-MS was 94.44% for aroma and 100% for region, whereas for GC-E-Nose these values were 91.53% and 93.94% respectively.

Metabolic syndrome in postmenopausal women is associated with lower erythrocyte PUFA/MUFA and n-3/n-6 ratio: A case-control study.

The aim of this study was to compare fatty acid (FA) intake and status in postmenopausal women with or without metabolic syndrome (MetS). 131 women were recruited to a case-control study in 2016-2018 in Poznan, Poland. Dietary intake, anthropometric and biochemical measurements, FA level in red blood cells (RBCs), and FADS1 (rs174546) and FADS2 (rs3834458) genotypes were determined. Compared to women without MetS, those with MetS had lower levels of EPA, n-3, EPA/α-linolenic acid (ALA), EPA/AA, DHA/AA, EPA+DHA/AA, PUFA/saturated FA, PUFA/monounsaturated FA, and n-3/n-6 ratios in RBCs. Participants with at least one minor allele of each polymorphism had lower levels of EPA, and EPA/AA, and a higher level of DHA/EPA in RBCs than did women with major alleles. MetS is associated with lower levels FAs that have a protective effect on cardiometabolic health. FADS1 and FADS2 polymorphisms are associated with unfavorable FA and status EPA/AA in RBC contributes to MetS.

Formation of Key Aroma Compounds during Preparation of Pumpernickel Bread.

Application of gas chromatography-olfactometry (GC-O) analysis to pumpernickel bread and its intermediate products obtained during the fermentative process allowed for the recognition of 32 key aroma compounds with specific odor notes. Subsequent quantitation using the stable isotope dilution assay (SIDA) and calculation of odor activity values (OAVs) revealed 22 compounds with OAV > 1, with the highest OAV for 3-methylbutanal with a malty odor (6660), 2-methylbutanal with a malty odor (4560), 3-(methylthio)propanal with a boiled potato odor (2047), 3-hydroxy-4,5-dimethyl-2(5H)-furanone with a lovage-like odor (1233), dimethyl trisulfide with a cabbage-like odor (475), 2-phenylethanol with a rosy odor (414), ß-damascenone with a boiled apple odor (200), 4-hydroxy-3-methoxybenzaldehyde with a vanilla-like odor (184), 4-hydroxy-2,5-dimethyl-3(2H)-furanone with a caramel odor (172), and phenylacetladehyde with a honey odor (100). The results showed that aroma of pumpernickel bread is mostly formed during baking; however, the fermentation process influences the formation of several compounds, such as ethyl acetate, 2,3-butanedione, acetic acid, 3-methyl-1-butanol, ethyl butyrate, ethyl lactate, ethyl-3-methyl butyrate, ethyl hexanoate, phenylacetaldehyde, and 2-phenylethanol. Furthermore, the addition of functional components, such as malt and wheat fiber, affects the concentration of several key odorants in the final product, such as 2- and 3-methylbutanals, 3-hydroxy-2-methyl-4H-pyran-4-one, and 4-hydroxy-3-methoxybenzaldehyde.