Promoted Formation of Pyrazines and Sulfur-Containing Volatile Compounds through Interaction of Extra-Added Glutathione or Its Constituent Amino Acids and Secondary Products of Thermally Degraded N-(1-Deoxy-d-ribulos-1-yl)-Glutathione

Effect of protease reaction conditions on volatile compounds generated in Maillard reaction products from soy protein hydrolysates

Maillard reaction products (MRPs) produced by heating protease-catalyzed soy protein hydrolysates (SPHs) with cysteine and ribose can generate meat-like flavors. However, the impact of protease reaction conditions on the volatile compound composition of MRPs has not been thoroughly investigated. In this study, seven SPHs were prepared using two proteases, flavourzyme and trypsin, over reaction times of 10, 120, and 1440 min. The volatile compound compositions, including sulfur-containing compounds, aldehydes, pyrazines, and furans, of the seven SPHs and the corresponding seven MRPs varied according to the protease reaction conditions and the Maillard reaction. Differences in pH, free amino acid composition, and peptide composition were responsible for these variations. Notably, soy-derived peptides containing unique cysteine sequences, such as PGCPST, DETICT, ECQIQK, and HCQR, were significantly reduced during the Maillard reaction, suggesting that these sequences may serve as precursors to volatile compounds.

Accelerated Degradation of DiXyl-α,ε-Lys-ARP via Interaction between Extra-Added Xylose and Monosubstituted Lys-ARPs during Maillard Reaction

Lysine (Lys) is capable of forming a di-substituted Amadori rearrangement product (ARP) with xylose (Xyl), designated as diXyl-α,ε-Lys-ARP. DiXyl-α,ε-Lys-ARP degradation was characterized by two steps: Initially, Xyl-α- and Xyl-ε-Lys-ARP were formed through elimination or hydrolysis at specific Nα/Nε positions of the corresponding enol and imine intermediates, which were then further degraded to dicarbonyl compounds and regenerated Lys. Xyl-α- or Xyl-ε-Lys-ARP had a reactive free amino group (ε-NH2 or α-NH2), both of which were still highly reactive and able to undergo further reactions with Xyl. Therefore, the diXyl-α,ε-Lys-ARP/Xyl model system was established to explore the impact of extra-added Xyl on diXyl-α,ε-Lys-ARP degradation behavior. Extra-added Xyl remarkably affected the degradation pathway of diXyl-α,ε-Lys-ARP by capturing the Xyl-α- and Xyl-ε-Lys-ARP to regenerate diXyl-α,ε-Lys-ARP. This interaction between Xyl and mono-substituted Lys-ARPs promoted the shift of chemical equilibrium toward the degradation of diXyl-α,ε-Lys-ARP, thereby accelerating its degradation rate. This degradation was markedly facilitated by the elevated temperature and pH values. Interestingly, the yield of Xyl-α- and Xyl-ε-Lys-ARP was particularly dependent on the pH during diXyl-α,ε-Lys-ARP degradation. Xyl-ε-Lys-ARP was the dominant product at pH 5.5-7.5 while Xyl-α-Lys-ARP possessed a relatively higher content under weak alkaline conditions, which was related to the reactivities of the Nα/Nε positions under various reaction conditions.

Maillard Reaction Process and Characteristic Volatile Compounds Formed During Secondary Thermal Degradation Monitored via the Change of Fluorescent Compounds in the Reaction of Xylose-Corn Protein Hydrolysate

Until now, no effective method has been found to monitor the Maillard reaction process for complex protein hydrolysates. Dynamic changes in the concentration of α-dicarbonyl compounds, fluorescence intensity, and browning degree were investigated during the Maillard reaction of corn protein hydrolysates. When the fluorescence intensity reached the peak, deoxyosones would continue to be increased by ARP's degradation. However, the reaction node with the highest fluorescence intensity coincided with the turning point of the browning reaction, and the subsequent browning rate remarkably increased. Therefore, the change in fluorescence intensity could be used to monitor the degradation of ARP and the formation of browning melanoidin at different stages of the Maillard reaction of complex systems, thus effectively indicating the process of the Maillard reaction. When Maillard reaction intermediates (MRIs) with maximum fluorescent compounds were heated, the most abundant pyrazines were subsequently achieved. However, furan compounds would be progressively increased during the thermal process of MRIs with continuously enhanced browning.

Efficient Formation of N-(1-Deoxy-d-ribulos-1-yl)-Glutathione via Limited Oxidation and Degradation of Glutathione during the Atmospheric-Vacuum Thermal Reaction

The efficient preparation of the ribose-glutathione (Rib-GSH) Amadori rearrangement product (RG-ARP) as a potent precursor of meaty flavor was studied through the atmospheric-vacuum thermal reaction. Liquid chromatography-mass spectrometry (LC-MS) analysis revealed that the oxidation and degradation of GSH occurred during the preparation of RG-ARP via the atmospheric thermal reaction, especially at a low molar ratio of Rib to GSH and high reaction temperature. The RG-ARP and the ARPs derived from the products of GSH oxidation and degradation with the participation of Rib were identified by MS/MS as N-(1-deoxy-d-ribulos-1-yl)-glutathione, N-(1-deoxy-d-ribulos-1-yl)-cysteinylglycine, and N-(1-deoxy-d-ribulos-1-yl)-glutathione disulfide. The selective formation of RG-ARP was disrupted due to the multiple consumption pathways of GSH and Rib. The removal of water and the reduction of oxygen content during vacuum dehydration exhibited an obvious inhibitory effect on the oxidation of cysteinyl and the cleavage of glutamyl, limiting the oxidation and degradation of GSH. Meanwhile, the rapid evaporation of water promoted the molecular collision between the reactants, which allowed the glycation reaction of GSH to be advanced and fragmentation of RG-ARP to be inhibited at a mild dehydration temperature. Accordingly, the atmospheric-vacuum thermal reaction was proposed to limit the generation of secondary byproducts and enhance the yield of RG-ARP, enabling the RG-ARP yield to reach 49.23% at 80 °C and a molar ratio of 2:1 (Rib/GSH) for 20 min.

Exogenous Threonine-Induced Conversion of Threonine-Xylose Amadori Compound to Heyns Compound for Efficiently Promoting the Formation of Pyrazines

The involvement of exogenous threonine during the degradation of l-threonine-d-xylose Amadori rearrangement product (Thr-ARP) was found to promote the formation of pyrazines. A model including Thr-ARP and ¹⁵N-labeled l-threonine was applied to reveal the role of free threonine in Thr-ARP conversion to pyrazines. Quantitative analyses of pyrazines in the model of Thr-ARP/¹⁵N-labeled threonine showed a precedence of the endogenous threonine (formed by the degradation of Thr-ARP) over the exogenous threonine in pyrazines formation, and the ratio of ¹⁵N to ¹⁴N content in pyrazines increased significantly over time. According to the observed occurrence of the Heyns rearrangement products (HRP) derived from ¹⁵N-threonine, as well as the sharp decrease of ¹⁵N-threonine content and a rapid increase of ¹⁴N endogenous threonine at the initial stage of heat treatment, it was proposed that aldimine condensation between exogenous threonine and Thr-ARP followed by the hydrolysis led to the endogenous threonine and the generation of HRP. Then, the HRP underwent dehydration followed by hydrolysis to form exogenous threonine and deoxyxyosones, and the dehydration and hydrolysis of deoxyxyosones to form organic acids was inhibited, but the retro-aldolization of deoxyxyosones was promoted, facilitating the generation of reactive α-dicarbonyl compounds. In this way, exogenous threonine accelerated the release of endogenous threonine and α-dicarbonyl compounds and the pH decline was slowed down, which was favorable for the formation of pyrazines.

Potential biomarkers analysis and protein internal mechanisms by cold plasma treatment: Is proteomics effective to elucidate protein-protein interaction network and biochemical pathway?

New market trends of meat flavor, tenderness, and color quality indicators have prompted the research on meat preservation as a crucial topic to received attention. Present research about the effects of irradiation, cold plasma technology on meat is incomplete. There are strongly recommended that proteomics techniques be jointly to enhance the coverage of internal meat molecules for meat research. By identifying meat proteins, detecting biological functions, and quantifying the protein segments of specific meat biomarkers, which can be provided for the information of diagnostic components in preservative technologies. The current review provides scientific findings on various control strategies: (i) combine the data-independent acquisition to provide a reference for the meat molecular mechanism and rapid identification; (ii) design molecular networks biological functions assessment model; (iii) molecular investigations of cold plasma techniques and underlying mechanisms; (iv) explore the X-rays and γ-rays treatment in meat preservation and myoglobin change mechanism more comprehensively.

Mechanism of Pyrazine Formation Intervened by Oxidized Methionines during Thermal Degradation of the Methionine-Glucose Amadori Compound

Methionine (Met) oxidation was observed during thermal degradation of methionine/glucose-derived Amadori rearrangement product (MG-ARP). The effects of oxidized methionine products, methionine sulfoxide (MetSO) and methionine sulfone (MetSO₂), on pyrazine yields of the MG-ARP model were investigated. The pyrazine contents in the MG-ARP/Met and MG-ARP/MetSO models were found lower compared to those in the MG-ARP/MetSO₂ model, and the inefficiency of pyrazine formation in the MG-ARP/Met model was proposed due to the fact that Met oxidation competitively inhibited the oxidation of dihydropyrazines for pyrazine formation in spite of relatively high methylglyoxal (MGO) content. The models of MGO mixed with Met, MetSO, or MetSO₂ were established for further investigation of the mechanism for the involvement of Met oxidation in pyrazine formation. It was observed that the aldolization or carbonyl-amine reaction of MetSO with MGO was another important reason for the inhibition of pyrazine formation, except for the competitive inhibition of oxidative formation of MetSO on dihydropyrazine oxidation, and the adduct of MGO-MetSO was identified by MS/MS. These results also accounted for the phenomenon of low pyrazine yields but high yields of long-chain substituted pyrazines, which were converted from dihydropyrazines with the aldehyde involvement.