Theory and protocol of dual mode unity solid-phase microextraction.

The solid-phase microextraction (SPME) bias problem limits comprehensive analysis of volatile compounds in real samples. The study introduces dual mode unity solid-phase microextraction (DMU-SPME) as a novel SPME mode to achieve balanced extraction of both volatile and low-volatile compounds. The DMU-SPME method exhibits excellent linearity (R2 ≥ 0.994), low quantitation limits (0.12-240 µg/L), and notable stability (relative standard deviations below 20 % for both intra-day and inter-day analyses). In practical application to soy sauce, the DMU-SPME method identified a total of 107 compounds, encompassing all those detected by both headspace solid-phase microextraction (HS-SPME) and direct immersion solid-phase microextraction (DI-SPME). Theoretical insights indicate that DMU-SPME is less influenced by Kfs0 and Kfs in comparison to HS/DI-SPME, rendering it suitable for complex matrices containing both volatile and low-volatile compounds. In conclusion, DMU-SPME emerges as a highly effective extraction mode for analyzing volatile and low-volatile compounds in food, medical, and environmental samples.

Selection of a Fermentation Strategy for the Preparation of Clam Sauce with Acceptable Flavor Perception.

Flavor, which mainly depends on volatile compounds, is an important index for evaluating the quality of clam sauce. This study investigated the volatile compounds in clam sauce prepared using four different methods and the influence of aroma characteristics. Fermenting a mixture of soybean koji and clam meat improved the flavor of the final product. Solid-phase microextraction (SPME) combined with gas chromatography-mass spectrometry (GC-MS) identified 64 volatile compounds. Nine key flavor compounds, namely, 3-methylthio-1-propanol, 2-methoxy-4-vinylphenol, phenylethyl alcohol, 1-octen-3-ol, α-methylene phenylacetaldehyde, phenyl-oxirane, 3-phenylfuran, phenylacetaldehyde, and 3-octenone, were selected using variable importance in projection (VIP). The results of the electronic nose and tongue detection of the aroma characteristics of the samples prepared by four different fermentation methods were consistent with those of GC-MS analysis. The clam sauce prepared by mixing soybean koji with fresh clam meat possessed better flavor and quality than that prepared via other methods.

Effects of ethanol pretreatment on osteogenic activity and off-flavors in blue mussel (Mytilus edulis L.) enzymatic hydrolysates.

Aquatic protein hydrolysates have many biological activities, but the off-flavor seriously decreases their commercial acceptability. Therefore, it is important to invest in finding an effective deodorization of aquatic hydrolysates that do not affect activities. In this study, ethanol pretreatment of mussel was applied to establish a new method to deodorize the blue mussel (Mytilus edulis L.) hydrolysates. LC-MS and GC-MS analysis results showed that 87.34% of fatty acids, 83.94% of aldehydes, most volatile flavor compounds including aldehydes, ketones, alcohols, acids, and hydrocarbons were decreased after ethanol pretreatment. Besides, it was found that the enzymatic hydrolysates of mussel with or without ethanol pretreatment showed high osteogenic activity, which induced an increase of 33.65 ± 4.36% and 31.77 ± 5.45% in MC3T3-E1 cell growth. These results suggest that ethanol pretreatment has beneficial potential for improving the flavor aspects of blue mussel peptides which may have the potential to stimulate bone regeneration and formation.

Mechanism of Carbon Skeleton Formation of 2,3,5-Trimethylpyrazine via a Conversion Reaction between Methylglyoxal and Glyoxal.

Maillard flavor compounds, such as 2,3,5-trimethylpyrazine, have been frequently identified in thermally processed food products, such as popcorn and peanuts. However, the origin of the carbon atoms in 2,3,5-trimethylpyrazine has not been clearly elucidated. Herein, a model reaction showed that precursor methylglyoxal and intermediates glyoxal and formaldehyde contributed to the formation of 2,3,5-trimethylpyrazine via a conversion reaction between methylglyoxal and glyoxal. In addition, carbon module labeling technology and model response validation experiments indicated that this transformation reaction between methylglyoxal and glyoxal brought formaldehyde into the methyl group carbon atoms of the 2,3,5-trimethylpyrazine ring. The proposed novel route provides a new perspective for approaches to control the formation of flavor compounds, such as 2,3,5-trimethylpyrazine.

Balanced extraction of volatile and semi-volatile compounds by dynamic linked position unity solid-phase microextraction.

Although the compound profiles in extracts are linked to the solid-phase microextraction (SPME) position (headspace or liquid), a theoretical interpretation of this scenario has not yet been provided. In this study, the dynamic linked position unity (DLPU)-SPME is proposed as a method that allows balanced extraction of volatile and semi-volatile compounds. Furthermore, the pH, temperature, and salt were confirmed as the key factors affecting the extraction efficiency of DLPU-SPME. Theoretical calculations indicated that Kfs0Kfs is a key factor directly indicating the SPME extraction position (Kfs0Kfs > 1, headspace; Kfs0Kfs = 1, any position; Kfs0Kfs < 1, in liquid), while the target analytes determined that VhKhs+VsVeKfhKhs regulates the effect of the extraction position on the extracted amount. The proposed DLPU-SPME method containing both extraction positions (i.e., headspace and liquid) can simultaneously extract volatile and semi-volatile compounds, thus avoiding extraction bias.

A Debittered Complex of Glucose-Phenylalanine Amadori Rearrangement Products with ß-Cyclodextrin: Structure, Molecular Docking and Thermal Degradation Kinetic Study.

Non-volatile flavor precursors could be used to overcome the flavor loss problems of volatile flavor enhancers during long-term storage. Glu- and Phe-derived Amadori rearrangement products (ARPs) produce pleasant aroma tones thermally but are bitter. We used ß-cyclodextrin (ß-CD) for debittering Glu-Phe ARPs. ITC analysis indicated that CD-ARP complexes with 1:1 stoichiometry were obtained. NMR analysis indicated that the aromatic ring of Glu-Phe ARPs was embedded in the ß-CD cavity. Molecular docking simulations of the bitter taste receptor hT2R1 showed that CD-ARP complex was inactive compared to Glu-Phe ARPs. Complexation with ß-CD resulted in the thermal stabilization of Glu-Phe ARPs and a decrease in the degradation rate constant. Compared to Glu-Phe ARPs, the CD-ARP complex in the thermally treated food system slowed down the formation of browning compounds but didn't inhibit flavor compound formation. The CD-ARP complex is a promising flavor enhancer for applications in flavored and heated foods.

Model studies on the formation of 2-vinylpyrazine and 2-vinyl-6-methylpyrazine in Maillard-type reactions.

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.

A novel magnetic solid-phase extraction method for detection of 14 heterocyclic aromatic amines by UPLC-MS/MS in meat products.

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.

Reinvestigation of 2-acetylthiazole formation pathways in the Maillard reaction.

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.

High Internal Phase Emulsion for Food-Grade 3D Printing Materials.

Three-dimensional printing (3DP) has attracted significant attention for its use in additive manufacturing techniques because it provides customizability and flexibility for fabricating structures with arbitrary shapes. Certain applications in the food and medicine industries require 3D printable materials that are both biocompatible and biodegradable. Consequently, this study reports 3D printable materials constructed from food-grade high internal phase emulsions (HIPEs). The studied HIPEs (phase ratio 85%) were stabilized by the efficient adsorption behavior of cod proteins (concentration range, 10-50 mg mL-1) at the oil-water interface. The stability of the oil-in-water HIPEs was improved by the formation of a concentration-dependent percentage of adsorbed proteins and cross-linking networks, and homogeneous and self-supporting structures were generated after 7 days of storage at 4 °C. The gel-like shear thinning rheological behavior induced by the cross-linking networks in the studied HIPEs can be tuned to obtain the desired printability and extrudability during 3DP. In the present study, the HIPEs stabilized with 50 mg mL-1 of cod proteins exhibited the highest printing resolution, gel strength, hardness, adhesiveness, and chewiness during 3DP. These food-grade HIPE inks have the potential to diversify the applications of 3DP in foods, cosmetics, drug delivery systems, and packaging materials.

Dispersive solid-phase extraction and dispersive liquid-liquid microextraction for the determination of flavor enhancers in ready-to-eat seafood by HPLC-PDA.

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.

Effect of alkyl distribution in pyrazine on pyrazine flavor release in bovine serum albumin solution.

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 (K q > 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.