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Vinylpyrazine compounds are widely present in foods, especially in hot-processed foods, as a class of flavor compounds; however, their formation mechanism in food systems is still unclear. Therefore, in this study, 2-vinylpyrazine and 2-vinyl-6-methylpyrazine were identified in the Maillard model reaction of D-glucose and glycine. The Maillard model reaction of glucose–glycine was constructed to explore the effects of reaction parameters on vinylpyrazines and the related products. The Maillard reaction of [U-13C6] glucose and glycine was established, and alkylpyrazines and formaldehyde were determined via isotope tracing technique as the precursors of vinylpyrazines. The formation of vinylpyrazines was verified by building a model reaction between alkylpyrazines and formaldehyde. The H/D exchange experiment confirmed that the active site of alkylpyrazines was on the methyl group, which was the reaction site for the condensation reaction of alkylpyrazines with formaldehyde. Results suggest that vinylpyrazines are formed by the condensation reaction of alkylpyrazines and formaldehyde.

2-Acetylthiazole possesses a nutty, cereal-like and popcorn-like aroma and a low odor threshold, and this compound has been identified in some processed foods, while the formation pathway of 2-acetylthiazole has not been clearly elucidated. Here, a model reaction of d-glucose and l-cysteine was constructed to investigate the formation pathway of 2-acetylthiazole. l-Cysteine, d-glucose and the corresponding intermediates, namely, dicarbonyl compounds (DCs), were involved in the formation of 2-acetylthiazole and detected by high-performance liquid chromatography with tandem mass spectrometry (HPLC-MS/MS), high-performance ion chromatography (HPIC) and HPLC, respectively. The carbon module labeling (CAMOLA) technique revealed that the C-4 and C-5 of 2-acetylthiazole were derived from the carbons of glucose. The potential of glyoxal, which is degraded by glucose, to form 2-acetylthiazole was revealed for the first time. A novel route to form 2-acetylthiazole by the reaction of glyoxal and methylglyoxal produced by d-glucose with H2S and NH3 produced by l-cysteine was proposed.

The flavor release mechanism related to the interaction of aroma compounds with proteins is still unclear. In this study, the interaction of protein with pyrazine homologues, such as 2-methylpyrazine (MP), 2,5-dimethylpyrazine (DP), 2,3,5-trimethylpyrazine (TRP) and 2,3,5,6-tetramethylpyrazine (TEP), was investigated to elucidate the effect of alkyl distribution in a pyrazine ring on its flavor release in bovine serum albumin (BSA) solution (pH 7.4). The results of SPME-GC-MS indicated that methyl distribution in a pyrazine ring significantly affected its release from BSA solution. The pyrazines released from BSA solution with an increasing order of MP, DP, TRP and TEP. The inhibition mechanism of alkyl-pyrazine release was further elucidated by the interaction between alkyl-pyrazines and BSA using multiple spectroscopic methods. The non-covalent interaction between alkyl-pyrazines and BSA was confirmed as the main interaction force by the value of the bimolecular quenching constant (Kq > 2 × 1010 L mol−1 s−1). A decrease in the hydrophobicity of the microenvironment between the alkyl-pyrazine and BSA was detected by synchronous fluorescence spectra, which revealed that alkyl-pyrazines were mainly bound on the sites of tyrosine and tryptophan in BSA. The UV-vis absorption spectra and circular dichromatic (CD) spectrum revealed that alkyl-pyrazines could induce polarity and conformation change of BSA. The above results indicated that the structure of the flavor homologues can affect their release in food matrices.

The dispersion solid-phase microextraction (DSPE) combined with dispersion liquid–liquid microextraction (DLLME) was developed as a rapid, simple and effective pretreatment method for the determination of flavor enhancers (maltol, ethyl maltol, vanillin, methyl vanillin, ethyl vanillin) of ready-to-eat seafood products (dried squid, baked squid, fried fish, steamed abalone). Under the optimized DSPE–DLLME method, the developed method exhibited low limits of quantitation (0.20–0.50 μg g−1) and excellent linearity (R2 ≥ 0.995). The recoveries of flavor enhancers in the actual samples were 83.7%–114.9%. Compared with traditional pretreatment methods, the developed DSPE–DLLME method was rapid (17 min) and easy to determine the flavor enhancers by high performance liquid chromatography with photodiode array detector (HPLC-PDA). In the actual samples, creamy compounds such as vanillin, methyl vanillin and ethyl vanillin were hardly found. However, the flavor compounds produced by thermal reactions such as maltol (except for dried squid 3) and ethyl maltol were present in all samples.

The current study developed a cheap and effective method for the simultaneous extraction of 14 heterocyclic aromatic amines (HAAs) in food matrix. Core-shell Fe3O4@PDA nanoparticles were constructed and acted as the magnetic solid-phase extraction adsorbent to separate and purify HAAs from meat products for the first time. Then, UPLC-MS/MS technique was employed to identify and quantify the HAAs easily. Fe3O4@PDA nanoparticles were synthesized and characterized successfully. Totally 14 HAAs were completely separated in 19.99 min with good regression coefficients. LODs and LOQs were in the range of 0.013–0.247 ng/g and 0.056–0.803 ng/g, respectively. The intra-day precisions and inter-day precisions were below 9%. Except for IQ[4,5-b], Phe-p-1, PhIP, other 11 types of HAAs (DMIP, 1,5,6-TMIP, IQ, IQx, MeIQ, MeIQx, 7,8-DiMeIQx, AαC, MeAαC, Harman, Norharman) could acquire relatively high recoveries (71.06%–108.49%). The proposed method was successfully devoted to the evaluation of HAAs levels in 8 commercial meat products to verify the adaptability.

Dried Lentinus edodes (Berk.) sing stipe (LES) is mostly discarded owing to its high fibre content and bad palatability, causing significant waste of resources. The aim of this study is to sustainably use LES for the production of flavour soybean oil using the supercritical CO2 fluid extraction (SFE) method. The quality properties of the obtained soybean oil flavoured by LES (OFLS) were evaluated in this study. Profiles obtained with an electronic nose and gas chromatography results obtained by quadrupole time-of-flight mass spectrometry and with a mass-selective detector indicated that mushroom-like aroma compounds were mainly concentrated into the OFLSs from separation kettle A (9 MPa). Interestingly, off-flavour compounds from soybean oil, such as o-xylene and trans-2-nonenal, were mostly distilled into separation kettle B (4 MPa). More importantly, the developed SFE method effectively improved the colour quality of the OFLSs. Additionally, the decrease of the viscosity of the OFLSs indicated that the thermal stability of the edible oil could be improved. In summary, the OFLSs prepared by the green and sustainable SFE method significantly improved the quality of the edible oil.