Formation and antioxidant activity of volatile compounds produced by heating glucose with tyrosine/histidine in water-ethanol and water-glycerol media

Unraveling the Enantiomeric Distribution of Glycosidically Bound Linalool in Teas (Camellia sinensis) and Their Acidolysis Characteristics and Pyrolysis Mechanism

Glycosidically bound linalool plays important roles in the formation of excellent tea flavor, while their enantiomeric distribution in teas and the actual transformations with free linalool are still unclear. In this study, a novel chiral ultrahigh performance liquid chromatography-mass spectrometry/mass spectrometry approach to directly analyze linalyl-β-primeveroside and linalyl-β-d-glucopyranoside enantiomers in teas was established and then applied in 30 tea samples. A close transformation relationship existed between the two states of linalool for their consistent dominant configurations (most S-form) and corresponding distribution trend in most teas (r up to 0.81). The acidolysis characterization indicated that free linalool might be slowly released from linalyl-β-primeveroside with stable enantiomeric ratios during long-term withering of white tea in a weakly acidic environment, along with other isomerized products, e.g., geraniol, nerol, α-terpineol, etc. Furthermore, a novel online thermal desorption-gas chromatography-mass spectrometry approach was established to simulate the pyrolysis releasing of linalyl-β-primeveroside during tea processing. Interestingly, free linalool was not the selected pyrolysis product of linalyl-β-primeveroside but rather trans/cis-2,6-dimethyl-2,6-octadiene during the high-fire roasting or baking step of oolong and green teas. The identification of above high-fire chemical marks presented great potential to scientifically evaluate the proper thermal conditions in the practical production of tea.

Effects of moisture content on the enolization products formation in glucose-proline Maillard reaction models

BACKGROUND

2,3-Dihydro-3,5-dihydroxy-6-methyl-4(H)-pyran-4-one (DDMP) and 5-hydroxymethylfurfural (HMF) are two main enolization products in the Maillard reaction and found in some foodstuffs. For many years, whether they are functional or noxious to human health has been a matter of debate. Thus, insight into their formation pathways is important to manage Maillard reaction products. In this study, DDMP and HMF were quantified and compared with regard to their formation and degradation in the d-glucose and l-proline Maillard reaction models using different moisture contents (0, 0.1, 0.5, 1.0, and 4.0 mL) at 150 °C for various heating times.

RESULTS

DDMP was predominantly generated in dry or low water-content heating models along with n increased 1-deoxyglucosone (1-DG) generation via 2,3-enolization. However, increasing moisture content resulted in a decay of reaction intensity, 1-DG, and DDMP due to a change in the reaction mechanism from 2,3-enolization to 1,2-enolization, which facilitated 3-deoxyglucosone (3-DG) and HMF formation.

CONCLUSION

Increased moisture content in glucose-proline models reduced reaction intensity and also inhibited DDMP and facilitated HMF formation by promoting the pathway change from 2,3-enolization to 1,2-enolization to generate more 3-DG. A water content of 1.0 mL was identified as a critical value, from which the 1,2-enolization became a primary pathway occurring in the Maillard reaction. © 2022 Society of Chemical Industry.

Investigations on the Key Odorants Contributing to the Aroma of Children Soy Sauce by Molecular Sensory Science Approaches

To investigate the key odor-active compounds in children’s soy sauce (CSS), volatile components were extracted by means of solvent extraction coupled with solvent-assisted flavor evaporation (SE-SAFE) and solid-phase microextraction (SPME). Using gas chromatography-olfactometry (GC-O) and gas chromatography-mass spectrometry (GC-MS), we identified a total of 55 odor-active compounds in six CSSs by comparing the odor characteristics, MS data, and retention indices with those of authentic compounds. Applying aroma extract dilution analysis (AEDA), we measured flavor dilution (FD) factors in SE-SAFE isolates, ranging from 1 to 4096, and in SPME isolates, ranging from 1 to 800. Twenty-eight odorants with higher FD factors and GC-MS responses were quantitated using the internal standard curve method. According to their quantitated results and thresholds in water, their odor activity values (OAVs) were calculated. On the basis of the OAV results, 27 odorants with OAVs ≥ 1 were determined as key odorants in six CSSs. These had previously been reported as key odorants in general soy sauce (GSS), so it was concluded that the key odorants in CSS are the same as those in GSS.

Aqueous Preparation of Maillard Reaction Intermediate from Glutathione and Xylose and its Volatile Formation During Thermal Treatment

Maillard reaction intermediate (MGX) generated from glutathione and xylose in aqueous medium was prepared via the Maillard reaction performed under a two-stage temperature increase process. The purified MGX was identified by Fourier-transform infrared spectroscopy, mass spectrometry, and nuclear magnetic resonance as N-(1-deoxy-d-xylulos-1-yl)-glutathione (Amadori compound, C₁₅ H₂₅ O₁₀ N₃ S) with five main isomers. The method of Maillard reaction performed under a two-stage temperature increase process was further verified by high-performance liquid chromatography. The optimal reaction time and temperature for the preparation of MGX was determined as 60 min at 90 °C. The yield of MGX was increased from 8.60% to 55.52% through thermal reaction coupled with vacuum dehydration. In addition, rapid and more Maillard-type volatile compounds were formed in MGX during thermal treatment than that in Maillard reaction products or glutathione-xylose mixture. Beside, MGX possessed more pleasing meat-like volatile profile compared with the Amadori compound of glutamic acid-xylose (AAX), cysteine-xylose (ACX), and glycine-xylose (AGX). Therefore, it suggested that the MGX had the potential to achieve a better flavor formation during thermal treatment. PRACTICAL APPLICATION: Maillard reaction intermediates, such as Amadori or Heyns rearrangement products (ARP or HRP), are important flavor precursors, which possess stable physicochemical properties, but tend to degrade into flavor compounds at high temperatures. Maillard reaction intermediate from glutathione and xylose acts as primary flavor enhancers to complete Maillard reaction to produce flavors in the subsequent thermal processing, which can significantly improve and stabilize the flavor quality of the meaty food, and deserves a very broad application prospects. The new developed method will be a significant theoretical basis on research preparation and properties of Maillard reaction intermediates in complex food systems.

Insights into the Regulation Effects of Certain Phenolic Acids on 2,3-Dihydro-3,5-dihydroxy-6-methyl-4(H)-pyran-4-one Formation in a Microaqueous Glucose-Proline System

The control of 2,3-dihydro-3,5-dihydroxy-6-methyl-4(H)-pyran-4-one (DDMP) formation in the Maillard reaction is important to improve the thermally treated food quality as a result of its intense bitterness and potential toxicity. In this work, phenolic acids, such as gallic, protocatechuic, caffeic, and ferulic acids, were applied to modulate DDMP formation in a microaqueous glucose-proline model. The formation of DDMP was inhibited at low concentrations (from 0.1 to 5.0 mM) while enhanced at 10.0 mM gallic, protocatechuic, and caffeic acids. Ferulic acid always inhibited DDMP formation as a result of the absence of catechol groups on its benzene ring. The result indicated that the control of DDMP formation depended upon the concentration and chemical structures of phenolic acids, such as the number of hydroxyl groups. Further studies indicated that the hydroxyl distribution of phenolic acids regulated the peroxide formation in the model reaction system and further changed the development of the oxidation reaction, which affected the degradation of glucose via caramel or Maillard reaction, Amadori rearrangement product oxidation, and 1-deoxyglucosone degradation to form the intermediates.

Sodium sulfite pH-buffering effect for improved xylose-phenylalanine conversion to N-(1-deoxy-d-xylulos-1-yl)-phenylalanine during an aqueous Maillard reaction

The yield of the Maillard reaction intermediate (MRI), prepared in aqueous medium, is usually unsatisfactory. However, the addition of sodium sulfite could improve the conversion of xylose-phenylalanine (Xyl-Phe) to the MRI (N-(1-deoxy-d-xylulos-1-yl)-phenylalanine) in aqueous medium. Sodium sulfite (Na₂SO₃) showed a significant pH-buffering effect during the Maillard reaction, which accounted for its facilitation of the N-(1-deoxy-d-xylulos-1-yl)-phenylalanine yield. The results revealed that the pH could be maintained at a relatively high level (above 7.0) for an optimized pH-buffering effect when Na₂SO₃ (4.0%) was added before the reaction of Xyl-Phe. Thus, the conversion of Xyl-Phe to N-(1-deoxy-d-xylulos-1-yl)-phenylalanine increased from 47.23% to 74.86%. Furthermore, the addition moment of Na₂SO₃ and corresponding solution pH were crucial factors in regulating the pH-buffering effect of Na₂SO₃ on N-(1-deoxy-d-xylulos-1-yl)-phenylalanine yield. Based on the pH-buffering effect of Na₂SO₃ and maintaining the optimal pH 7.4 relatively stable, the conversion of Xyl-Phe to N-(1-deoxy-d-xylulos-1-yl)-phenylalanine was successfully improved.

Controlled formation of flavor compounds by preparation and application of Maillard reaction intermediate (MRI) derived from xylose and phenylalanine

An effective method for preparing Maillard reaction intermediate (MRI) derived from xylose (Xyl) and phenylalanine (Phe) in aqueous medium was proposed in this study.