Kinetics of α‑dicarbonyl compounds formation in glucose-glutamic acid model of Maillard reaction

The kinetic study of 2-acetyl-1-pyrroline accumulation in the model system: An insight into enhancing rice flavor through the Maillard reaction

Controlling the Maillard reaction may affect the generation of 2-acetyl-1-pyrroline, the key aroma compound in rice. In this study, the kinetics of 2-acetyl-1-pyrroline accumulation in the glucose/proline model system was comprehensively investigated and extra methylglyoxal or glyoxal was added to enhance 2-acetyl-1-pyrroline concentrations during rice cooking. Using the multi-response kinetic modeling to derive kinetic parameters, the formation of glyoxal, as the reactive intermediate, was rate-determining for the overall generation rate of 2-acetyl-1-pyrroline. Besides, although 2-acetyl-1-pyrroline generation was easier to occur with lower activation energy, much higher depletion rates of 2-acetyl-1-pyrrroline at 120 °C and 140 °C led to maximal 2-acetyl-1-pyrroline accumulation at the lower temperature of 100 °C. Furthermore, the inclusion of 0.05 μmol/kg additional methylglyoxal in cooked rice significantly enhanced 2-acetyl-1-pyrroline generation. The work suggested that the development of rice products with superior flavor quality may be achieved by the slight accumulation of intermediates prior to thermal processing.

Simultaneous determination of six α-dicarbonyl compounds in traditional Chinese medicines using high-performance liquid chromatography-fluorescence detector with pre-column derivatization

A reliable method for determination of six α-dicarbonyl compounds in traditional Chinese medicines was first developed and validated by high-performance liquid chromatography-fluorescence detector with pre-column derivatization. α-Dicarbonyl compounds in traditional Chinese medicines were extracted and derivatized with 2,3-diaminaphthalene. The derivatization procedure of six α-dicarbonyl compounds was confirmed by high-resolution mass spectrometry. The limits of quantitation for six α-dicarbonyl compounds ranged from 3.70 × 10-3 to 2.21 × 10-2  μM. The established method showed good linearity (regression coefficient > 0.9990), precision (relative standard deviation < 3.37%), and high recovery (97.8%∼113.1%). The developed method was successfully applied to detect the six α-dicarbonyl compounds in traditional Chinese medicines. The result exhibited six α-dicarbonyl compounds was found in the 15 kinds of traditional Chinese medicines, which suggested us that the determination of α-dicarbonyl compounds should be paid more attention in the quality control of traditional Chinese medicines.

Dynamic changes and formation of key contributing odorants with amino acids and reducing sugars as precursors in shiitake mushrooms during hot air drying

The dynamic variations in key contributing odorants, amino acids and reducing sugars in shiitake mushrooms during hot-air drying were determined by gas chromatography-mass spectrometry (GC-MS), high performance liquid chromatography-tandem mass (HPLC-MS/MS) and ion chromatography (IC). The potential precursors were explored by the partial least squares-discriminant analysis and Pearson correlation analysis, and Met, Cys, and ribose were considered as the possible precursors of dimethyl trisulfide and lenthionine. The verification experiments in the absence and presence of shiitake mushroom matrix further confirmed that Met and its interaction with ribose both contributed to generating dimethyl trisulfide. The polynomial nonlinear fitting curve could better represent the dose-effect relationships of Met and Met-ribose to produce dimethyl trisulfide with R² of 0.9579 and 0.9957. Conversely, ribose, Cys or Cys-ribose were verified to be unable to form the key contributing odorants. Collectively, the results provided a method to reveal precursors and generation pathway of odorants.

Chemical Composition and Sensory Profiles of Fermented Cocoa Beans Obtained from Various Regions of Indonesia

The chemical composition and sensory profile of cocoa beans are essential factors determining the quality of cocoa-based products. In this study, cocoa bean samples were collected from various regions of Indonesia, including Aceh, Banten, Bali, East Java, West Sumatra, West Sulawesi, East Kalimantan, and Yogyakarta. The cocoa beans were fermented and sun-dried according to the producers' protocols and local practices. The sensory profile, fat content, total phenolic content, and the composition of sugars, organic acids, and amino acids of the cocoa bean samples were analyzed. The results revealed that the chemical composition and sensory profiles of the samples were diverse. The sensory profiles of cocoa liquor samples were described by low intensities of cocoa notes with the occurrence of fruity, floral, spicy, and sweet notes. The concentration of acetic acid, lactic acid, and some amino acids (glutamic acid, proline, and methionine) was associated with fresh fruit, browned fruit, and roasted note of the cocoa liquor, respectively. The variation in the environmental conditions and postharvest practices contributed to the diversity of cocoa beans' chemical and sensory characteristics.

Reduction of 3-Deoxyglucosone by Epigallocatechin Gallate Results Partially from an Addition Reaction: The Possible Mechanism of Decreased 5-Hydroxymethylfurfural in Epigallocatechin Gallate-Treated Black Garlic

5-Hydroxymethylfurfural (5-HMF) is a harmful substance generated during the processing of black garlic. Our previous research demonstrated that impregnation of black garlic with epigallocatechin gallate (EGCG) could reduce the formation of 5-HMF. However, there is still a lack of relevant research on the mechanism and structural identification of EGCG inhibiting the production of 5-HMF. In this study, an intermediate product of 5-HMF, 3-deoxyglucosone (3-DG), was found to be decreased in black garlic during the aging process, and impregnation with EGCG for 24 h further reduced the formation of 3-DG by approximately 60% in black garlic compared with that in the untreated control. The aging-mimicking reaction system of 3-DG + EGCG was employed to determine whether the reduction of 3-DG was the underlying mechanism of decreased 5-HMF formation in EGCG-treated black garlic. The results showed that EGCG accelerated the decrease of 3-DG and further attenuated 5-HMF formation, which may be caused by an additional reaction with 3-DG, as evidenced by LC-MS/MS analysis. In conclusion, this study provides new insights regarding the role of EGCG in blocking 5-HMF formation.

Formation of Pyrazines in Maillard Model Systems: Effects of Structures of Lysine-Containing Dipeptides/Tripeptides

At present, most investigations involving the Maillard reaction models have focused on free amino acids (FAAs), whereas the effects of peptides on volatile products are poorly understood. In our study, the formation mechanism of pyrazines, which were detected as characteristic volatiles in sunflower seed oil, from the reaction system of glucose and lysine-containing dipeptides and tripeptides was studied. The effect of the amino acid sequences of the dipeptides and tripeptides on pyrazine formation was further highlighted. Four different dipeptides and six tripeptides were selected. The results showed that the production of pyrazines in the lysine-containing dipeptide models was higher than that in the tripeptide and control models. Compounds 2,5(6)-Dimethylpyrazine and 2,3,5-trimethylpyrazine were the main pyrazine compounds in the dipeptide models. Furthermore, the C- or N-terminal amino acids of lysine-containing dipeptides can exert an important effect on the formation of pyrazines. In dipeptide models with lysine at the C-terminus, the content of total pyrazines followed the order of Arg−Lys > His−Lys; the order of the total pyrazine content was Lys−His > Lys−Arg in dipeptide models with N-terminal lysine. Additionally, for the tripeptide models with different amino acid sequences, more pyrazines and a greater variety of pyrazines were detected in the tripeptide models with N-terminal lysine/arginine than in the tripeptide models with N-terminal histidine. However, the total pyrazine content and the percentage of pyrazines in the total volatiles were similar in the tripeptide models with the same amino acids at the N-terminus. This study clearly illustrates the ability of dipeptides and tripeptides containing lysine, arginine and histidine to form pyrazines, improving volatile formation during sunflower seed oil processing.