Changes in the Volatile Components of Candied Kumquats in Different Processing Methodologies with Headspace-Gas Chromatography-Ion Mobility Spectrometry

Odor Fingerprinting of Chitosan and Source Identification of Commercial Chitosan: HS-GC-IMS, Multivariate Statistical Analysis, and Tracing Path Study

Chitosan samples were prepared from the shells of marine animals (crab and shrimp) and the cell walls of fungi (agaricus bisporus and aspergillus niger). Fourier-transform infrared spectroscopy (FT-IR) was used to detect their molecular structures, while headspace-gas chromatography-ion mobility spectrometry (HS-GC-IMS) was employed to analyze their odor composition. A total of 220 volatile organic compounds (VOCs), including esters, ketones, aldehydes, etc., were identified as the odor fingerprinting components of chitosan for the first time. A principal component analysis (PCA) revealed that chitosan could be effectively identified and classified based on its characteristic VOCs. The sum of the first three principal components explained 87% of the total variance in original information. An orthogonal partial least squares discrimination analysis (OPLS-DA) model was established for tracing and source identification purposes, demonstrating excellent performance with fitting indices R2X = 0.866, R2Y = 0.996, Q2 = 0.989 for independent variable fitting and model prediction accuracy, respectively. By utilizing OPLS-DA modeling along with a heatmap-based tracing path study, it was found that 29 VOCs significantly contributed to marine chitosan at a significance level of VIP > 1.00 (p < 0.05), whereas another set of 20 VOCs specifically associated with fungi chitosan exhibited notable contributions to its odor profile. These findings present a novel method for identifying commercial chitosan sources, which can be applied to ensure biological safety in practical applications.

Integrated HS-GC-IMS and UPLC-Q-Orbitrap HRMS-based metabolomics revealed the characteristics and differential volatile and nonvolatile metabolites of different citrus peels

Citrus is an important genus in the Rutaceae family, and citrus peels can be used in both food and herbal medicine. However, the bulk of citrus peels are discarded as waste by the fruit processing industry, causing environmental pollution. This study aimed to provide guidelines for the rational and effective use of citrus peels by elucidating the volatile and nonvolatile metabolites within them using metabolomics based on headspace-gas chromatography-ion mobility spectrometry and ultra-high-performance liquid chromatography-Q-Orbitrap high-resolution mass spectrometry. In addition, the antioxidant activities of the citrus peels were evaluated using DPPH radical scavenging, ABTS radical scavenging, and ferric reducing antioxidant power. In total, 103 volatile and 53 nonvolatile metabolites were identified and characterized. Alcohols, aldehydes, and terpenes constituted 87.36% of the volatile metabolites, while flavonoids and carboxylic acids accounted for 85.46% of the nonvolatile metabolites. Furthermore, (Z)-2-penten-1-ol, L-pipecolinic acid, and limonin were identified as characteristic components of Citrus reticulata Blanco cv. Ponkan (PK), C. reticulata 'Unshiu' (CLU), and C. reticulata 'Wo Gan' (WG), respectively. Principal component analysis and partial least squares discriminant analysis indicated that C. reticulata Blanco 'Chun Jian' (CJ), PK, CLU, and C. reticulata 'Dahongpao' (DHP) were clustered together. DHP is a traditional Chinese medicine documented in the Chinese Pharmacopoeia, suggesting that the chemical compositions of CJ, PK, and CLU may also have medicinal values similar to those of DHP. Moreover, DHP, PK, C. reticulata 'Ai Yuan 38'(AY38), CJ, C. reticulata 'Gan Ping'(GP), and C. reticulata 'Qing Jian'(QJ) displayed better antioxidant activities, recommending their use as additives in cosmetics and food. Correlation analysis suggested that some polyphenols including tangeritin, nobiletin, skullcapflavone II, genistein, caffeic acid, and isokaempferide were potential antioxidant compounds in citrus peel. The results of this study deepen our understanding of the differences in metabolites and antioxidant activities of different citrus peel varieties and ultimately provide guidance for the full and rational use of citrus peels.

Effects of different lactic acid bacteria on the characteristic flavor profiles of Chinese rice wine

BACKGROUND

It has been well accepted that lactic acid bacteria (LAB) are the main bacterial genera present during the brewing of Chinese rice wine (CRW). LAB plays a decisive role in the flavor quality of CRW; however, its application in CRW has previously been overlooked. Therefore, effects of different LAB as co-fermenter on the flavor characteristics of CRW were investigated.

RESULTS

Co-fermentation of LAB increased the utilization rate of reducing sugar, concentration of lactic acid, amino acid nitrogen and total acidity, as well as the content of volatile flavor compounds. Different LAB doses had little effect on the flavor profiles of CRW, but the species of LAB greatly affected the flavor characteristic. The flavor of CRW co-fermented with Lactococcus lactis was characterized by long-chain fatty acid ethyl esters, while co-fermentation with Weissella confusa highlighted the ethyl esters of low molecular weight and short carbon chains in the resultant CRW. Alcohol compounds were dominant in the CRW co-fermented using Pediococcus pentosaceus.

CONCLUSION

The co-fermentation of LAB increased the number of volatile flavor compounds, especially esters. LAB exhibited great potential in the application of CRW industry to enrich the flavor characteristics and enhance the flavor diversity of the final product. © 2023 Society of Chemical Industry.

Gas Chromatographic-Ion Mobility Spectrometry Combined with Chemometrics to Study the Changes in Characteristic Odor Components of Galli gigerii Endothelium Corneum in Different Processing Methods

Galli gigerii endothelium corneum (GGEC) is a traditional Chinese medicine commonly used in clinical practice to treat various conditions such as indigestion, vomiting, spermatorrhea, and enuresis. In this study, the volatile components of different concoctions of GGEC were examined by gas chromatography-ion mobility spectrometry (GC-IMS), and the changes of the components were compared by fingerprinting, combined with principal component analysis (PCA) and orthogonal partial least squares-discriminant analysis (OPLS-DA) to analyze the main volatile components and find out the different markers that can distinguish the different concoctions of GGEC. In the result, the GC-IMS fingerprints of GGEC and its different concoctions showed differences in their volatile components, of which 49 volatiles were clearly characterized, with some components including monomers and dimers. The characteristic volatile components of raw GGEC (SP) were n-nonanal, (E)-2-octenal, beta-ocimene, 2-ethyl-1-hexanol, etc. The characteristic volatile components of stir-fried GGEC (QC) are heptanal, 2-octanol, (E)-2-heptenal, etc. The characteristic volatile components of sand ironing GGEC (ST) are isoamyl acetate, decanal, cyclohexanone, 2-ethyl pyrazine, etc. The characteristic volatile components of stir-fried GGEC with vinegar (CZ) are thiazole, linalool, 2,3,5-trimethylpyrazine, etc. The characteristic volatile components of stir-fried GGEC with milk (FH) are 2-methylbutanoic acid, ethyl acetate, ethyl 2-hydroxypropanoate, butyl acetate, etc. By chemometric analysis, components such as n-nonanal, (E)-2-octenal, 2-pentyl-furan, butanal, 1,4-dioxane, and 2-methylpropanoic acid could be used as difference markers to distinguish different concoction products of GGEC. Furthermore, by analyzing different volatile compounds, we can examine the changes in volatile components during processing of GGEC, which can provide experimental data for the identification and establishment of quality standards.

Effects of Different Probiotics on the Volatile Components of Fermented Coffee Were Analyzed Based on Headspace-Gas Chromatography-Ion Mobility Spectrometry

Headspace-gas chromatography-ion mobility spectrometry (HS-GC-IMS) was used to study the effects of four kinds of probiotics on the volatile components of fermented coffee. The fingerprints showed that 51 compounds were confirmed and quantified, including 13 esters, 11 aldehydes, 9 alcohols, 6 ketones, 3 furans, 5 terpenes (hydrocarbons), 2 organic acids, 1 pyrazine, and 1 sulfur-containing compound. After fermenting, the aroma of the green beans increases while that of the roasted beans decreases. After roasting, the total amount of aroma components in coffee beans increased by 4.48-5.49 times. The aroma differences between fermented and untreated roasted beans were more significant than those between fermented and untreated green beans. HS-GC-IMS can distinguish the difference in coffee aroma, and each probiotic has a unique influence on the coffee aroma. Using probiotics to ferment coffee can significantly improve the aroma of coffee and provide certain application prospects for improving the quality of commercial coffee beans.

Characteristic Volatile Organic Compound Analysis of Different Cistanches Based on HS-GC-IMS

Cistanche is a medicinal and food homologous substance with a long history of consumption and medicinal use in China. In order to further understand the volatile organic compound differences between different cistanches, this study selected oil cistanche, blood cistanche and cistanche tubulosa in Xinjiang for HS-GC-IMS volatile organic compounds, and established the characteristic fingerprints of different cistanches for organic content and characteristic organic compound analysis. PCA and cluster analysis were used to study the similarity between different cistanches. After qualitative analysis, a total of 32 volatile organic compounds were identified, covering aldehydes (17), ketones (5), furans (1), alcohols (5), lactones (1) and esters (3), and the volatile organic compounds between samples a, b and c could be significantly distinguished, affecting the flavor of cistanche itself. It provides a basic theoretical basis for the study of cistanche flavor.

Insight into the Characterization of Volatile Compounds in Smoke-Flavored Sea Bass (Lateolabrax maculatus) during Processing via HS-SPME-GC-MS and HS-GC-IMS

The present study aimed to ascertain how the volatile compounds changed throughout various processing steps when producing a smoke-flavored sea bass (Lateolabrax maculatus). The volatile compounds in different production steps were characterized by headspace-solid phase microextraction-gas chromatography-mass spectrometry (HS-SPME-GC-MS) and headspace-gas chromatography-ion mobility spectrometry (HS-GC-IMS). A total of 85 compounds were identified, and 25 compounds that may be considered as potential key compounds were screened by principal component analysis (PCA) and partial least squares discriminant analysis (PLS-DA). Results indicated that aldehydes were the major volatile compounds throughout the processing. The characteristic volatile compound in fresh samples was hexanol, and curing was an effective method to remove the fishy flavor. The concentration of volatile compounds was significantly higher in dried, smoked, and heated samples than in fresh and salted samples. Aldehydes accumulated because of the drying process, especially heptanal and hexanal. Smoke flavoring was an important stage in imparting smoked flavor, where phenols, furans and ketones were enriched, and heating leads to the breakdown of aldehydes and alcohols. This study will provide a theoretical basis for improving the quality of smoke-flavored sea bass products in the future.

Application of gas chromatography-ion mobility spectrometry in the analysis of food volatile components

Gas chromatography-ion mobility spectrometry (GC-IMS) is an emerging analytical technique that has the advantages of fast response, high sensitivity, simple operation, and low cost. The combination of the fast speed and resolution of GC with the high sensitivity of IMS makes GC-IMS play an important role in the detection of food volatile substances. This paper focuses on the basic principles and future development trend, and the comparative analysis of the functions, similarities and differences of GC-IMS, GC-MS and electronic nose in the detection of common volatile compounds. A comprehensive introduction to the main application of GC-IMS in food volatile components: fingerprint identification of sample differences and detection of characteristic compounds. On the basis of perfecting the spectral library, GC-IMS will have broad development prospects in food authentication, origin identification, process optimization and product classification, especially in the analysis and identification of trace volatile food flavor substances.

Full Workflows for the Analysis of Gas Chromatography-Ion Mobility Spectrometry in Foodomics: Application to the Analysis of Iberian Ham Aroma

Gas chromatography—ion mobility spectrometry (GC-IMS) allows the fast, reliable, and inexpensive chemical composition analysis of volatile mixtures. This sensing technology has been successfully employed in food science to determine food origin, freshness and preventing alimentary fraud. However, GC-IMS data is highly dimensional, complex, and suffers from strong non-linearities, baseline problems, misalignments, peak overlaps, long peak tails, etc., all of which must be corrected to properly extract the relevant features from samples. In this work, a pipeline for signal pre-processing, followed by four different approaches for feature extraction in GC-IMS data, is presented. More precisely, these approaches consist of extracting data features from: (1) the total area of the reactant ion peak chromatogram (RIC); (2) the full RIC response; (3) the unfolded sample matrix; and (4) the ion peak volumes. The resulting pipelines for data processing were applied to a dataset consisting of two different quality class Iberian ham samples, based on their feeding regime. The ability to infer chemical information from samples was tested by comparing the classification results obtained from partial least-squares discriminant analysis (PLS-DA) and the samples’ variable importance for projection (VIP) scores. The choice of a feature extraction strategy is a trade-off between the amount of chemical information that is preserved, and the computational effort required to generate the data models.

Different distillation stages Baijiu classification by temperature-programmed headspace-gas chromatography-ion mobility spectrometry and gas chromatography-olfactometry-mass spectrometry combined with chemometric strategies

Liquid-liquid microextraction (LLME) combined with gas chromatography-olfactometry-mass spectrometry (GC-O-MS) was used to detect the variations in volatile compounds during the distillation process (head, heart, and tail) of raw Baijiu produced by different layers of fermented grains; 47 aroma compounds were sniffed and identified. Moreover, temperature-programmed headspace gas chromatography-ion mobility spectrometry (TP-HS-GC-IMS) was applied to characterize the Baijiu distillation process for the first time. The 3D fingerprint spectrum clearly showed a variation in volatile compounds from different distillation stages, and most compounds showed a downward trend. In addition, multivariate statistical analysis, including principal component analysis (PCA), partial least squares discriminant analysis (PLS-DA), etc., confirmed ten aroma active markers related to classification, indicating that these markers had a great influence on the flavor of raw Baijiu.

Analysis of volatile compounds and flavor fingerprint in Jingyuan lamb of different ages using gas chromatography-ion mobility spectrometry (GC-IMS)

In this study, gas chromatography coupled to an ion mobility spectrometry (GC-IMS) was used for analyzing some volatile components and flavor fingerprint in samples from Jingyuan lambs of different ages (2, 6, and 12 months). The data obtained from ion mobility were processed using laboratory analysis view processing software for fingerprint recognition, and the principal component analysis (PCA) was performed. GC-IMS provided information on the characteristics and strength of 66 volatile flavor compounds (monomers and dimers). The differences in flavoring substances between lambs of different ages were observed. The compounds with higher intensity peaks in the lamb meat samples were alcohols (1-octen-3-ol, ethanol, (E)-2-hexen-1-ol, 1-pentanol, and 2-propanol), ketones (2-pentanone, 2-heptanone, 3-hydroxy-2-butanone, 2-hexanone, 2-butanone, 2-propanone, and 4-methyl-2-pentanone), aldehydes (n-nonanal, octanal, heptanal, 3-methylbutanal, hexanal, pentanal, 2-methylbutanal, (E)-2-octenal, (E)-2-nonenal, methional, and phenylacetaldehyde), esters (methyl benzoate), furan (2-pentylfuran), and thiazole (trimethylthiazole). The results showed that the flavor fingerprint in samples from Jingyuan lambs of different ages (2, 6, and 12 months) can be established by GC-IMS and PCA based on the identified volatile compounds. This method might be used for the rapid and comprehensive analysis of volatile components in lamb meat.

Recent applications of ion mobility spectrometry in natural product research

Ion mobility spectrometry (IMS) is a rapid separation technique capable of extracting complementary structural information to chromatography and mass spectrometry (MS). IMS, especially in combination with MS, has experienced inordinate growth in recent years as an analytical technique, and elicited intense interest in many research fields. In natural product analysis, IMS shows promise as an additional tool to enhance the performance of analytical methods used to identify promising drug candidates. Potential benefits of the incorporation of IMS into analytical workflows currently used in natural product analysis include the discrimination of structurally similar secondary metabolites, improving the quality of mass spectral data, and the use of mobility-derived collision cross-section (CCS) values as an additional identification criterion in targeted and untargeted analyses. This review aims to provide an overview of the application of IMS to natural product analysis over the last six years. Instrumental aspects and the fundamental background of IMS will be briefly covered, and recent applications of the technique for natural product analysis will be discussed to demonstrate the utility of the technique in this field.

Variations of volatile flavour compounds in finger citron (Citrus medica L. var. sarcodactylis) pickling process revealed by E-nose, HS-SPME-GC-MS and HS-GC-IMS

The pickled products of finger citron are famous in southern China for their unique taste and flavor. Although pickling process involves complex treatments including salting, desalting, sugaring, cooking and drying, extended shelf-life up to ten years after pickling can be achieved. In this study, the variations of volatile flavour components in the pickling process of finger citron were investigated by electronic nose (E-nose), headspace solid phase microextraction-gas chromatography-mass spectrometry (HS-SPME-GC-MS) and headspace-gas chromatography-ion mobility spectrometry (HS-GC-IMS). HS-SPME-GC-MS identified 85 substances, and HS-GC-IMS identified 81 substances, including terpenoids (21), aromatic hydrocarbons (11), alcohols (11), aldehydes (10), esters (7), phenols (6), acids (5), ethers (2), ketones (2), and other species (10). Linalool, limonene, (E)-3,7-dimethyl-1,3,6-octatriene, myrcene, 3-carene, β-pinene, α-pinene, terpinolene, 1-methyl-4-(1-methylethyl)-1,4-cyclohexadiene, α-terpinene, (S)-β-bisabolene, 1-isopropyl-2-methylbenzene and 1-methyl-4-(1-methylethenyl)-benzene were the stable substances at relatively high contents in finger citron at different pickling process. Salting and drying steps in the pickling process exerted greatest influence on the volatile components of finger citron. Salting promoted the generation of aldehydes, esters and acids, but led to the disappearance of alcohols, while drying promoted the generation of alcohols, phenols, aldehydes and acids at the expense of reduction in terpenoids. Our study revealed that the characteristic volatile compounds of finger citron pickled products was mainly formed by the biological reactions in the salting stage and thermal chemical transformations in the drying stage. This study also validated the suitability of E-nose combined with HS-SPME-GC-MS and HS-GC-IMS in tracking the changes of volatile components in finger citron during the pickling process.

Characterization of Volatile Organic Compounds of Healthy and Huanglongbing-Infected Navel Orange and Pomelo Leaves by HS-GC-IMS

The Asian citrus psyllid (ACP), Diaphorina citri Kuwayama, is the only natural vector of bacteria responsible for Huanglongbing (HLB), a worldwide destructive disease of citrus. ACP reproduces and develops only on the young leaves of its rutaceous host plants. Olfactory stimuli emitted by young leaves may play an important role in ACP control and HLB detection. In this study, volatile organic compounds (VOCs) from healthy and HLB-infected young leaves of navel orange and pomelo were analyzed by headspace-gas chromatography-ion mobility spectrometry (HS-GC-IMS). A total of 36 compounds (including dimers or polymers) were identified and quantified from orange and 10 from pomelo leaves. Some compounds showed significant differences in signal intensity between healthy and HLB-infected leaves and may constitute possible indicators for HLB infection. Principal component analysis (PCA) clearly discriminated healthy and HLB-infected leaves in both orange and pomelo. HS-GC-IMS was an effective method to identify VOCs from leaves. This study may help develop new methods for detection of HLB or find new attractants or repellents of ACP for prevention of HLB.

Changes in volatile compounds of fermented minced pepper during natural and inoculated fermentation process based on headspace-gas chromatography-ion mobility spectrometry

Changes in volatile compounds of fermented minced pepper (FMP) during natural fermentation (NF) and inoculated fermentation (IF) process were analyzed by the headspace-gas chromatography-ion mobility spectrometry (HS-GC-IMS). A total of 53 volatile compounds were identified, including 12 esters, 17 aldehydes, 13 alcohols, four ketones, three furans, two acids, one pyrazine, and one ether. Generally, fermentation time played an important role in volatile compounds of FMP. It was found that most esters, aldehydes, and alcohols obviously decreased with the increase in fermentation time, including isoamyl hexanoate, methyl octanoate, gamma-butyrolactone, phenylacetaldehyde, methional, and E-2-hexenol. Only a few volatile compounds increased, especially for 2-methylbutanoic acid, 2-methylpropionic acid, linalool, ethanol, and ethyl acetate. However, no significant difference in volatile compounds was found between NF and IF samples at the same fermentation time. In addition, the fermentation process in all samples was well discriminated as three stages (0 days; 6 day; and 12, 18, and 24 days), and all volatile compounds were divided into two categories (increase and decrease) based on principal component analysis and heat map.

Characterization and Biological Activities of Seed Oil Extracted from Berberis dasystachya Maxim. by the Supercritical Carbon Dioxide Extraction Method

Characterization of the structure and pharmacological activity of Berberis dasystachya Maxim., a traditional Tibetan medicinal and edible fruit, has not yet been reported. In this study, central composite design (CCD) combined with response surface methodology (RSM) was applied to optimize the extraction conditions of B. dasystachya oil (BDSO) using the supercritical carbon dioxide (SC-CO₂) extraction method, and the results were compared with those obtained by the petroleum ether extraction (PEE) method. The chemical characteristics of BDSO were analyzed, and its antioxidant activity and in vitro cellular viability were studied by DPPH, ABTS, reducing power assay, and MTT assay. The results showed that the maximum yield of 12.54 ± 0.56 g/100 g was obtained at the optimal extraction conditions, which were: pressure, 25.00 MPa; temperature 59.03 °C; and CO₂ flow rate, 2.25 SL/min. The Gas chromatography (GC) analysis results showed that BDSO extracted by the SC-CO₂ method had higher contents of unsaturated fatty acids (85.62%) and polyunsaturated fatty acids (57.90%) than that extracted by the PEE method. The gas chromatography used in conjunction with ion mobility spectrometry (GC-IMS) results showed that the main volatile compounds in BDSO were aldehydes and esters. BDSO also exhibited antioxidant ability in a dose-dependent manner. Moreover, normal and cancer cells incubated with BDSO had survival rates of more than 85%, which indicates that BDSO is not cytotoxic. Based on these results, the BDSO extracted by the SC-CO₂ method could potentially be used in other applications, e.g., those that involve using berries of B. dasystachya.

Untargeted and Targeted Discrimination of Honey Collected by Apis cerana and Apis mellifera Based on Volatiles Using HS-GC-IMS and HS-SPME-GC-MS

Fraudulent acts regarding honey authenticity that use Apis mellifera honey as a substitute for Apis cerana honey have garnered considerable concern in China and triggered a trust crisis from consumers. In this study, untargeted metabolomics analysis was carried out based on volatile fractions in honey from A. cerana and A. mellifera using headspace gas chromatography-ion mobility spectrometry (HS-GC-IMS). Honey from A. cerana and A. mellifera was discriminated by HS-GC-IMS profiling, principal component analysis, and orthogonal partial least-squares discrimination analysis. Tentative markers were identified from p-values and the variable importance in projection analysis and confirmed using the retention index, mass fragments, and reference standards by gas chromatography-mass spectrometry (GC-MS). A targeted method was established using the headspace solid phase coupled with microextraction GC-MS (HS-SPME-GC-MS) to quantitate the markers. The results demonstrated that the developed untargeted and targeted metabolomics approach performed well when discriminating honey from A. cerana and A. mellifera.