Effect of Drying Methods on Volatile Compounds of Citrus reticulata Ponkan and Chachi Peels as Characterized by GC-MS and GC-IMS

Comparison of flavor components between normal and gas-producing wasabi based on HS-GC-IMS, HS-GC-MS and electronic sensory technology

Wasabi is a type of sauce made from the plant horseradish. During its production and storage, gas production sometimes occurs, which leads to changes in the flavor quality of wasabi. In this study, an electronic nose, electronic tongue, headspace-gas chromatography-mass spectrometry and headspace-gas chromatography-ion mobility spectrometry combined with multivariate statistical analysis were used to compare the differences in odor, taste and volatile components between normal and gas-producing wasabi. The results showed that normal and gas-producing wasabi samples could be distinguished by the electronic nose and electronic tongue. Furthermore, 72 and 65 volatile components were identified from wasabi by headspace-gas chromatography-mass spectrometry and headspace-gas chromatography-ion mobility spectrometry analysis, respectively. In addition, 33 key volatile components that caused the difference between normal and gas-producing wasabi were identified through variable projection importance index analysis. Therefore, normal and gas-producing wasabi could be effectively distinguished and their differences in odor, taste and volatile components could be clarified by the four flavor analysis techniques combined with multivariate statistical analysis, which provide a scientific basis for the quality control and process optimization of wasabi.

Volatile Profile of Bee Pollens: Optimization of Sampling Conditions for Aroma Analysis, Identification of Potential Floral Markers, and Establishment of the Flavor Wheel

The volatile profile of bee pollen samples from Central and Eastern Europe was investigated by headspace solid phase microextraction (HS-SPME) combined with gas chromatography-mass spectrometry-olfactometry (GC-MS-O). Sampling conditions were optimized for the extraction of volatiles. Pollen odorants were extracted with six different fiber coatings, five various extraction times, three diverse extraction temperatures and three differing desorption times. The most effective combination was the application of divinylbenzene/carboxen/polydimethylsiloxane (DVB/CAR/PDMS) fiber coating used at 60°C for 30 min for extraction and 1 min for desorption. The optimized method was applied to investigate the volatile profile of 14 pollen samples (three rapeseed, musk thistle, rock-rose, traveler's joy, dropwort, honey locust, sunflower, red poppy, phacelia, sweet cherry, wild blackberry, and dandelion). The volatile profiles of bee pollens were different and were crucially depended on botanical origin. The aroma activity of the samples was generated by 31.0%-48.3% of total volatiles. The number of the identified odorants were between 75 and 101 in the pollen samples by GC-MS, of which 26-42 were aroma-active. The volatile organic compounds (VOCs) were classified into 13 different chemical classes. In most pollen, fatty acids were the predominant volatiles (14.87%-50.58%), while in some samples esters were the most abundant odorants (4.09%-45.46%). Panelists confirmed the presence of six main sensory characteristics described as "green/sour", "fruity", "spicy/herbal", "earthy/mushroom", "sweet/baked/caramel/honey", and "floral" compounds. These results establish the flavor wheel suitable for the comprehensive sensory description of pollen pellets from individual plant species. All samples contained characteristic odorants that may help in their botanical identification.

Comparing effects of tangerine-peel (Citrus reticulata Blanco) age and concentration on deep-fried rabbit meat: Impact on heterocyclic aromatic amines, amino acids, and flavor compound formation

Many nutritional experts recommend rabbit meat as a high-protein source. However, the high temperatures used to prepare deep-fried rabbit meat (DFRM) typically produce numerous heterocyclic aromatic amines (HAAs), a class of substances with carcinogenic risks. In this study, we chromatographically evaluate changes in the volatile compounds, amino acids, and HAAs in DFRM while employing tangerine peel (TP) as an additive. A total of 35 volatile organic compounds are detected in the TP, which increase the concentrations of sweet and umami amino acids in the DFRM. Remarkably, the TP substantially inhibits the IQ-type HAAs, particularly MeIQ, MeIQx, 4,8-DiMeIQx, and PhIP, which are produced during deep frying. Correlation analyses reveal that the histidine, aldehydes, and alcohols are strongly and positively correlated (P < 0.001) with the MeIQ, MeIQx, 4,8-DiMeIQx, and PhIP production. This study offers innovative and natural approaches for reducing HAA formation during the frying of rabbit meat.

Accurate Discrimination of Mold-Damaged Citri Reticulatae Pericarpium Using Partial Least-Squares Discriminant Analysis and Selected Wavelengths

Unscrupulous merchants sell the mold-damaged Citri Reticulatae Pericarpium (CRP) after removing the mold. In this study, an accurate and non-destructive strategy was developed for the discrimination of mold-damaged CRPs using portable near-infrared (NIR) spectroscopy and chemometrics. The outer surface and inner surface spectra were obtained without destroying CRPs. The discrimination models were established using partial least squares-discriminant analysis (PLS-DA) and wavelength selection strategy was used to further improve the discrimination ability. The predictive ability of models was assessed using the test set and an independent test set obtained one month later. The results demonstrate that the models of the outer surface outperform those of the inner surface. With multiplicative scatter correction (MSC)-PLS-DA, 100% accuracies were obtained in test and independent test sets. Furthermore, the wavelength selection strategy simplified the models with 100% discrimination accuracy. In addition, the randomization test (RT)-PLS-DA model developed in this study combines both the benefits of high accuracy and robustness, which can be applied for the accurate discrimination of mold-damaged CRPs.

Quality Change of Citri Reticulatae Pericarpium (Pericarps of Citrus reticulata 'Chachi') During Storage and Its Sex-Based In Vitro Digestive Performance

Citri Reticulatae Pericarpium (CRP), particularly including the pericarp of Citrus reticulata 'Chachi' (GCP), has been widely used as a food, a dietary supplement, and traditional Chinese medicine. Despite the widespread use of traditional foods, there is limited evidence regarding the precise relationships between storage conditions, aging duration, and the digestive performance of CRP. In this study, the aim was to investigate the impact of the storage conditions on the quality of aged GCP during shelf life and to evaluate the subsequent digestive performance of corresponding GCP decoctions. Respiration in GCP was monitored by measuring oxygen (O2), carbon dioxide (CO2), and methane (CH4) gases throughout the storage simulation, with O2 and CO2 validated as prospective safety measures. Five flavonoids (hesperidin, didymin, nobiletin, tangeretin, and 3,5,6,7,8,3',4'-heptamethoxyflavone) were determined as quality indicators, and their contents were significantly affected by the duration of the storage simulation and the aging periods of GCP. Our study also found that temperature and humidity significantly affected the volatile organic compounds (VOCs) emission from GCP. Eighteen compounds were proposed to show potential as descriptive measures of aging periods while eight compounds were proposed as potential indicators to discriminate among the spoilage level. Furthermore, the bioaccessibility of hesperidin ranged from ~30% to ~50% and was not significantly affected by the GCP's aging time nor the consumer's sex (p < 0.05). This study presents evidence for the future control of the quality of GCP and its digestive performance in males and females.

Recent advances in the authentication (geographical origins, varieties and aging time) of tangerine peel (Citri reticulatae pericarpium): A review

The consumption of tangerine peel (Citri reticulatae pericarpium, CRP) has been steadily increasing worldwide due to its proven health benefits and sensory characteristics. However, the price of CRP varies widely based on its origin, variety, and aging time, which has led many manufacturers to offer inferior products by exploiting the sensory similarity of CRP, seriously undermining consumers' interests. Therefore, it is essential to identify the authenticity of the CRP. In this study, the research progress on the authenticity of CRP from different origins, years and varieties over the past 10 years and the application and prospects of the main technologies and techniques were reviewed. The advantages and disadvantages of the commonly used methods were also summarized and compared. Mass spectrometry-based and spectroscopy-based techniques are the most commonly used methods for analyzing CRP authenticity. However, designing fast, non-destructive and green methods for identifying CRP authenticity would be the future trend.

Influence of electrohydrodynamics on the drying characteristics and volatile components of iron stick yam

The drying characteristics, rehydration capacity, color, infrared spectra and volatile components of iron stick yam slices were investigated under different alternating current (AC) voltages (13, 17, 21 kV), hot air drying (HAD) (60 °C) and natural drying (AD) by electrohydrodynamic (EHD) drying and HAD experimental devices. The results showed that slices of iron stick yam dried the quickest with HAD, which also had the fastest drying rate; while drying the slices of iron stick yam with EHD led to a better rehydration capacity, higher brightness L* and whiteness, a more stable protein secondary structure, and a greater variety and content of volatile components compared with AD and HAD. These finding indicated that EHD is a more promising method for drying iron stick yam.

Mass Spectrometry Rearrangement Ions and Metabolic Pathway-Based Discovery of Indole Derivatives during the Aging Process in Citrus reticulata 'Chachi'

The rapid analysis and characterization of compounds using mass spectrometry (MS) may overlook trace compounds. Although targeted analysis methods can significantly improve detection sensitivity, it is hard to discover novel scaffold compounds in the trace. This study developed a strategy for discovering trace compounds in the aging process of traditional Chinese medicine based on MS fragmentation and known metabolic pathways. Specifically, we found that the characteristic component of C. reticulata 'Chachi', methyl N-methyl anthranilate (MMA), fragmented in electrospray ionization coupled with collision-induced dissociation (CID) to produce the rearrangement ion 3-hydroxyindole, which was proven to exist in trace amounts in C. reticulata 'Chachi' based on comparison with the reference substance using liquid chromatography-tandem mass spectrometry (LC-MS/MS). Combining the known metabolic pathways of 3-hydroxyindole and the possible methylation reactions that may occur during aging, a total of 10 possible indole derivatives were untargeted predicted. These compounds were confirmed to originate from MMA using purchased or synthesized reference substances, all of which were detected in C. reticulata 'Chachi' through LC-MS/MS, achieving trace compound analysis from untargeted to targeted. These results may contribute to explaining the aging mechanism of C. reticulata 'Chachi', and the strategy of using the CID-induced special rearrangement ion-binding metabolic pathway has potential application value for discovering trace compounds.

Exploring the roles of microorganisms and metabolites in the 30-year aging process of the dried pericarps of Citrus reticulata 'Chachi' based on high-throughput sequencing and comparative metabolomics

GuangChenpi (GCP), the dried pericarps of Citrus reticulata 'Chachi', has been consumed daily as a food and dietary supplement in China for centuries. Its health benefits are generally recognized to be dependent on storage time. However, the specific roles of microorganisms and metabolites during long-term storage are still unclear. In this study, comparative metabolomics and high-throughput sequencing techniques were used to investigate the effects of co-existing microorganisms on the metabolites in GCP stored from 1 to 30 years. In total, 386 metabolites were identified and characterized. Most compounds were flavonoids (37%), followed by phenolic acids (20%). Seventeen differentially upregulated metabolites were identified as potential key metabolites in GCP, and 8 of them were screened out as key active ingredients by Venn diagram comparative analyses and verified by network pharmacology and molecular docking. In addition, long-term storage could promote the accumulation of secondary metabolites. Regarding the GCP microbiota, Xeromyces dominated the whole 30-year aging process.Moreover, Spearman correlation analysis indicated that Bacillus thuringiensis and Xeromyces bisporus, the dominant bacterial and fungal species, were strongly associated with the key active metabolites. Our results suggested that the change of active ingredients caused by the dominant microbial is one of the mechanisms affecting the GCP aging process. Our study provides novel functional insights and research perspectives on microorganism-associated metabolite changes that may improve the GCP aging process.

Electronic Nose and Head Space GC-IMS Provide Insights into the Dynamic Changes and Regularity of Volatile Compounds in Zangju (Citrus reticulata cv. Manau Gan) Peel at Different Maturation Stages

Zangju (Citrus reticulata cv. Manau Gan) is the main citrus cultivar in Derong County, China, with unique aroma and flavour characteristics, but the use of Zangju peel (CRZP) is limited due to a lack of research on its peel. In this study, electronic nose, headspace-gas chromatography-ion mobility spectrometry (HS-GC-IMS), and partial least squares-discriminant analysis (PLS-DA) methods were used to rapidly and comprehensively evaluate the volatile compounds of dried CRZP and to analyse the role of dynamic changes at different maturation stages. The results showed that seventy-eight volatile compounds, mainly aldehydes (25.27%) and monoterpenes (55.88%), were found in the samples at four maturity stages. The contents of alcohols and aldehydes that produce unripe fruit aromas are relatively high in the immature stage (October to November), while the contents of monoterpenoids, ketones and esters in ripe fruit aromas are relatively high in the full ripening stage (January to February). The PLS-DA model results showed that the samples collected at different maturity stages could be effectively discriminated. The VIP method identified 12 key volatile compounds that could be used as flavour markers for CRZP samples collected at different maturity stages. Specifically, the relative volatile organic compounds (VOCs) content of CRZP harvested in October is the highest. This study provides a basis for a comprehensive understanding of the flavour characteristics of CRZP in the ripening process, the application of CRZP as a byproduct in industrial production (food, cosmetics, flavour and fragrance), and a reference for similar research on other C. reticulata varieties.

Effects of Drying Methods on Taste Components and Flavor Characterization of Cordyceps militaris

The influences of four drying methods (hot air drying (HAD), vacuum freeze drying (VFD), vacuum drying (VD) and intermittent microwave combined with hot air drying (MW-HAD)) on the taste profile and flavor characteristic of Cordyceps militaris were investigated. MW-HAD samples had the highest levels of umami taste 5'-nucleotides, bitter taste amino acids, and equivalent umami concentration (EUC) value. The aroma fingerprints and differences of dried Cordyceps militaris were established by GC-MS with odor activity values (OAVs) and GC-IMS with principal component analysis (PCA). GC-MS data showed that the predominant volatiles of dried samples were aldehydes, alcohols, and ketones. VFD samples had the highest amount of total aroma compounds and C8 compounds. Moreover, 21 aroma-active components (OAVs ≥ 1) were the main contributors to the flavor of dried Cordyceps militaris. The OAVs of 1-octen-3-one and 3-octanone associated with mushroom-like odor in VFD were significantly higher than other samples. Furthermore, a significant difference in flavor compounds of four dried samples was also clearly demonstrated by GC-IMS analysis with PCA. GC-IMS analysis revealed that VFD samples had the most abundant flavor compounds. Overall, MW-HAD was an effective drying method to promote umami taste, and VFD could superiorly preserve volatiles and characteristic aroma compounds in dried Cordyceps militaris.