Rapid, High-Throughput Quantitation of Odor-Active 2-Acetyl Azaheterocycles in Food Products by UHPLC-MS/MS

Injection artifacts in odorant analysis by gas chromatography

Odor-active compounds are major quality parameters in food and other consumer products. In the analysis of odorants, gas chromatography (GC) plays a dominant role and is particularly indispensable for odorant screening by GC-olfactometry (GC-O). Whereas artifact formation during workup before GC analysis has been widely discussed, artifact formation during GC injection has not been adequately addressed so far. Using a set of 14 test compounds, we evaluated ten different GC injection approaches. Artifact-producing reactions were particularly 1,2-eliminations. Linalyl acetate additionally showed [1,3]-sigmatropic shifts. On-column injection was confirmed as the gold standard, with virtually zero artifact formation observed not only with classic cold on-column injection in the oven, but also with on-column injection in a programmable temperature vaporizing (PTV) injector. Substantial artifact formation was observed when a high fixed injector temperature was combined with splitless injection. This applied to the injection of liquid samples but even more so to headspace solid-phase microextraction (HS-SPME) approaches. In conclusion, we recommend using on-column injection whenever aiming at a representative odorant spectrum, such as in GC-O. In targeted analysis, critical approaches such as SPME should be carefully tested for artifact formation. For the evaluation of the artifact formation potential of different injection approaches, cedryl acetate emerged as an excellent test compound.

Ultrasound-Assisted Extraction of Squalene and 2-Acetyl-1-Pyrroline from Pandan Leaf: The Effects of Drying Methods and Extraction Conditions

Pandan, a tropical crop, is rich in squalene (SQ), known for its antioxidant and hypoglycemic properties, and 2-acetyl-1-pyrroline (2-AP), which imparts a characteristic aroma. This study focuses on the extraction of the two bioactive compounds from Pandan leaves and investigates the effects of drying methods, extraction solvents, and conditions on the yield of SQ and 2-AP. Results show that hot air-dried Pandan leaves when extracted using the binary solvent system of ethanol and n-hexane (EH), yield higher SQ content while maintaining an adequate content of 2-AP. To further optimize the extraction process, a single-factor experiment was followed by optimization using Box-Behnken design (BBD) and response surface methodology (RSM). The optimal extraction conditions were determined as follows: ultrasound time of 60 min, a temperature of 50 °C, power of 300 W, and a solid-to-liquid ratio of 1:5 g/mL. Under these conditions, an SQ yield of 1229.98 ± 13.09 μg/DW 1 g Pandan leaves and a 2-AP yield of 80.72 ± 0.88 μg/DW 1 g Pandan leaves were achieved, representing increases of 3.30% and 9.82% compared to pre-optimization values. Additionally, the antioxidant activities of EH extracts were evaluated through various in vitro assays. The extracts demonstrated significant DPPH and ABTS free radical scavenging activity (12.46 μmol TE/g DW and 22.14 μmol TE/g DW, respectively), along with ferric and cupric ion reducing power (10.629 μmol TE/g DW and 14.275 μmol TE/g DW, respectively). The extracts also exhibited notable inhibitory effects on α-amylase and α-glucosidase. The findings suggest that these extracts are a promising natural source of antioxidants with potential applications in health and nutrition.

Molecular Changes during Germination of Cocoa Beans, Part 1

Some germination is known to occur during the process of fermentation in cocoa beans. The impact of this biological process on the course of cocoa fermentation is not known and was thus investigated. In order to determine the impact of germination at the molecular level as well as on flavor, an untargeted metabolomics approach using Ultra Performance Liquid Chromatography-Electrospray Ionization-Time of Flight-Mass Spectrometry (UPLC-ESI-ToF-MS) with simultaneous acquisition of low- and high-collision energy mass spectra (MSe) was performed. Extracts of raw and germinated cocoa beans of the same origin were measured and compared for characteristic differences by unsupervised principal component analysis. OPLS-DA revealed 12-hydroxyjasmonic acid (HOJA) sulfate, (+)-catechin and (-)-epicatechin as most down-regulated compounds as well as two hydroxymethylglutaryl (HMG) glucosides A and B among others as decisive up-regulated compounds in the germinated material. Additionally, further HMG glucosides and 12-hydroxyjasmonic acid could be identified in cocoa for the first time by coelution with isolated and synthesized reference compounds. HOJA sulfate, which has been postulated in cocoa, and HOJA were revealed to impart bitter and astringent taste qualities.

Toward Unified Flavor Quantitation in Cocoa-Based Products

Because food flavor is perceived through a combination of odor and taste, an analytical method that covers both dimensions would be very beneficial for mapping the consistent product quality over the entirety of a manufacturing process. Such a method, so-called "unified flavor quantitation", has been successfully applied to several different food products in recent years. The simultaneous detection of aroma and taste compounds by means of ultra-high-performance liquid chromatography tandem mass spectrometry (UHPLC-MS/MS) enables the analysis and quantification of an enormously large number of compounds in a single run. To evaluate the limits of this method, chocolate, a high-fat, complex matrix, was selected. In 38 distinct commercial chocolate samples, 20 flavor-active acids, aldehydes, and sugars were analyzed after a simple, rapid extraction step followed by derivatization with 3-nitrophenylhydrazine using a single UHPLC-MS/MS method. The results obtained highlight the great potential of the "unified flavor quantitation" approach and demonstrate the possibility of high-throughput quantitation of key aroma- and taste-active molecules in a single assay.

Thermal/Redox-triggered release of pyrazinic functional molecules by coordination polymers with luminescence monitoring ability

Storage of volatile active molecules, along with the prolongation of their specific functions, requires the use of regulatable carriers. Pyrazine derivatives are highly volatile compounds with a broad application owing to their flavoring, pharmaceutical, antimicrobial, antiseptic, and insecticidal properties. In this study, pyrazines were stored by coordinating them with cuprous iodide to easily generate a series of luminescent coordination polymer (CP)-based carriers. The CPs could respond to thermal-redox stimuli and manipulate pyrazine release by breaking the labile Cu-N bonds when triggered by the two stimuli. Moreover, the release process could be visualized by decreased luminescence caused by the gradual decomposition of CP structures. The loading efficiencies ranged from 31% to 38%, and the controlled release behaviors accord with the zero-order kinetics. This work is the first to prove that CPs could function as dual stimuli-mediated delivery systems, which hold the potential to control the release and strengthen the usability of functional molecules.

Flavor perception and health benefits of tea

As one of the most consumed non-alcoholic beverages in the world, tea is acclaimed for its pleasant flavor and various health benefits. Different types of tea present a distinctive flavor and bioactivity due to the changes in the composition and proportion of respective compounds. This article aimed to provide a more comprehensive understanding of tea flavor (including aroma and taste) and the character of tea in preventing and alleviating diseases. The recent advanced modern analytical techniques for revealing flavor components in tea, including enrichment, identification, quantitation, statistics, and sensory evaluation methodologies, were summarized in the following content. Besides, the role of tea in anti-cancer, preventing cardiovascular disease and metabolic syndrome, anti-aging and neuroprotection, and regulating gut microbiota was also listed in this article. Moreover, questions and outlooks were mentioned to objectify tea products' flavor quality and health benefits on a molecular level and significantly promote our understanding of the comprehensive value of tea as a satisfactory health beverage in the future.

Toward High-Throughput Analysis of Aroma Compounds Using Ultrahigh-Performance Liquid Chromatography-Tandem Mass Spectrometry: Screening of Key Food Odorants in Various Foods

Recent studies show the immense capacities of the unified quantitation of aroma and taste compounds using liquid chromatography-mass spectrometry (LC-MS). The goal of this study was to highlight the broad application of this unified method. Thus, a stable isotope dilution analysis quantification method of the most important key food odorants in various food categories by LC-MS was developed. Using the well-known derivatization agent 3-nitrophenylhydrazine for carbonyl derivatization and a newly developed approach for alcohol and thiol derivatization, a method for the quantitation of 20 key food odorants was established. Intraday precision was determined to be ≤26%, and interday precision was between 24 and 31%. Limits of quantitation were determined between 0.014 and 283 μg/kg. The work shows that a wide array of aroma compounds can be analyzed accurately by LC-MS.

Highly sensitive and selective Sb2WO6 microspheres in detecting VOC biomarkers in cooked rice: Experimental and density functional theory study

The palatability of cooked rice is susceptible to the flavor and effective detection of volatile organic compounds (VOCs) can avoid deterioration and improve the taste quality. Herein, hierarchical antimony tungstate (Sb₂WO₆) microspheres are synthesized through a solvothermal process and the effect of solvothermal temperature on the room temperature gas-sensing properties of gas sensors is investigated. Outstanding sensitivity towards VOC biomarkers (nonanal, 1-octanol, geranyl acetone and 2-pentylfuran) in cooked rice is achieved and the sensors exhibit remarkable stability and reproducibility, which are contributed to the formation of the hierarchical microsphere structure, larger specific surface area, narrower band gap and increased oxygen vacancy content. The kinetic parameters combined with principal component analysis (PCA) effectively distinguish the four VOCs while the enhanced sensing mechanism was substantiated through density functional theory (DFT) calculation. This work provides a strategy for fabricating high performance Sb₂WO₆ gas sensors which can be practically applied to food industry.

Volatile Organic Compounds, Evaluation Methods and Processing Properties for Cooked Rice Flavor

Rice (Oryza sativa L.), as the main refined grain in China, has attracted much attention in terms of quality. Rice is usually consumed after cooking, and it is a commonly staple food. Nowdays, people's requirements for cooked rice focus more on the taste characteristics and quality. Furthermore, aroma is one of the primary sensory reference points, which is the most intuitive way for people to judge cooked rice. By integrating and analyzing the researches of cooked rice aroma identification in recent five years, this paper expounds the extraction and identification methods (sensory evaluation method, GC-MS, SPME, MOS sensors, electronic nose, etc.) of the flavor substances in cooked rice, as the processing methods and properties of cooked rice, and the volatile organic compounds of cooked rice under different conditions are summarized as well.

Flavor of tea (Camellia sinensis): A review on odorants and analytical techniques

Tea is among the most consumed nonalcoholic beverages worldwide. Understanding tea flavor, in terms of both sensory aspects and chemical properties, is essential for manufacturers and consumers to maintain high quality of tea products and to correctly distinguish acceptable or unacceptable products. This article gives a comprehensive review on the aroma and off-flavor characteristics associated with 184 odorants. Although many efforts have been made toward the characterization of flavor compounds in different types of tea, modern flavor analytical techniques that affect the results of flavor analysis have not been compared and summarized systematically up to now. Thus, the overview mainly provides the instrumental flavor analytical techniques for both aroma and taste of tea (i.e., extraction and enrichment, qualitative, quantitative, and chemometric approaches) as well as descriptive sensory analytical methodologies for tea, which is helpful for tea flavor researchers. Flavor developments of tea evolved toward time-saving, portability, real-time monitoring, and visualization are also prospected to get a deeper insight into the influences of different processing techniques on the formation and changes of flavor compounds, especially desired flavor compounds and off-flavor substances present at (ultra)trace amounts in tea and tea products.

Isotope-Coding Derivatization for Quantitative Profiling of Reactive α-Dicarbonyl Species in Processed Botanicals by Liquid Chromatography-Tandem Mass Spectrometry

α-Dicarbonyls (α-DCs) are key reactive Maillard intermediates with structural diversity and are widely found in foods and in vivo, but little is known regarding the complete molecular profiles of these potentially harmful electrophiles. Herein, we reported a novel isotope-coding derivatization (ICD) strategy for the broad-spectrum, quantitative profiling of (non)target α-DC species in natural foodstuffs. It utilized differential isotope labeling (DIOL) with a reagent pair o-phenylenediamine (OPD)/OPD-d₄ (deuterated) to form stable quinoxalines for class-specific fragmentation-dependent acquisition using liquid chromatography-hybrid quadrupole linear ion trap mass spectrometry (LC-QqLIT). A combination of facile one-pot quantitative labeling and convenient cleanup protocol afforded satisfactory sensitivity, linearity, accuracy (81-116%), and process recovery (86-109% with RSDs < 10%) by matrix-matched ICD-internal standard calibration, without significant matrix interference (-9 to 5%), isotopic effect (<0.5%), and cocktail effect. A more generic DIOL-based LC-QqLIT algorithm integrated double precursor ion and neutral loss scan to trigger enhanced product ions with the unique isobaric doublet tags (4 Da shift), enabling simultaneous screening and relative quantitation of nontarget α-DC analogues in a single analysis. This study has widened the vision on complex α-DC profiles in traditional botanicals, which revealed a wide occurrence of α-DCs in such processed sugar-rich products, yet their abundance varied greatly among different samples.

A high throughput toolbox for comprehensive flavor compound mapping in mint

Essential oils of the genus Mentha are extensively used as flavor ingredients in the industry. To overcome the time consuming and laborious traditional flavor analysis, a new quick, high-throughput toolbox based on a bead-beater homogenization followed by a UHPLC-MS/MS analysis has been developed and validated. While terpenes could be directly detected using atmospheric pressure chemical ionization (APCI), carbonyl compounds and alcohols required derivatization by 3-nitrophenylhydrazine (3-NPH) and glycidyltrimethylammonium chloride (GTMA) to ensure sufficient sensitivity for analysis of a single leaf. Using this approach, in total, 59 flavor-active metabolites representing the characteristic flavor of mint were quantified in leaves as well as in distilled oils using fast and robust UHPLC-MS/MS methods. The application of this toolbox enables a mapping of key pathways of mint flavor biosynthesis and can therefore support extensive breeding studies and the monitoring of chemosensate changes, depending on factors such as growth stages and environmental conditions.