Study of maillard reaction products in model aqueous and water/ethanol systems containing glucose and glycine, diglycine, and triglycine

Simultaneously Enhanced Formation of Pyrazines and Furans during Thermal Degradation of the Glycyl-l-glutamine Amadori Compound by Selected Exogenous Amino Acids and Appropriate Elevated Temperatures

The Amadori compound of glucose and glycyl-l-glutamine (Gly-Gln-ARP) was prepared and characterized by UPLC-MS/MS and NMR. Gly-Gln-ARP could be thermally degraded into Gly-Gln and other secondary reaction products like glycyl-l-glutamic acid and its ARP via deamidation. The thermal processing temperature exerted a tremendous influence on the flavor formation of ARP. Furans were mainly formed at 100 °C, while an elevated temperature of 120 °C facilitated the massive accumulation of α-dicarbonyl compounds through the retro-aldolization of deoxyglucosone, and then increased the formation of pyrazines. The extra-added amino acids further promoted the formation of pyrazines at 120 °C, especially Glu, Lys, and His, further increasing the total concentration of pyrazines to 457 ± 6.26, 563 ± 65.5, and 411 ± 59.2 μg/L, respectively, exceeding the pure heated control at 140 °C (296 ± 6.67 μg/L). The total concentration of furans was enhanced to (20.7 × 10³) ± 8.17 μg/L by extra-added Gln. Different increasing effects were observed on the type and flavor intensity of formed pyrazines and furans from different extra-added amino acids.

Glycine, Diglycine, and Triglycine Exhibit Different Reactivities in the Formation and Degradation of Amadori Compounds

A series of Amadori compounds of glucose were prepared from glycine (G-ARP), diglycine (DiG-ARP), and triglycine (TriG-ARP), and identified by UPLC-MS/MS and NMR. The formation rate of ARPs was TriG-ARP > DiG-ARP > G-ARP, and their activation energies were 63.48 kJ/mol (TriG-ARP), 72.84 kJ/mol (DiG-ARP), and 84.76 kJ/mol (G-ARP), respectively, suggesting that ARP was formed more easily from small peptides than from amino acid. Although 1-DG was formed much more difficultly than 3-DG, the same order of the formation of 1-DG, 3-DG, and browning was DiGly > TriGly > Gly. It was also confirmed that more methylglyoxal and glyoxal would be formed from small peptides than equimolar amino acids. Compared with free amino acid, ARP, deoxyglycosones, and their secondary degradation products were more easily formed from dipeptide and tripeptide, thereby stronger browning occurred and higher reactivity was exhibited in Maillard reaction of di- or tripeptide.

Polymer-based controlled-release fed-batch microtiter plate - diminishing the gap between early process development and production conditions

BACKGROUND

Fed-batch conditions are advantageous for industrial cultivations as they avoid unfavorable phenomena appearing in batch cultivations. Those are for example the formation of overflow metabolites, catabolite repression, oxygen limitation or inhibition due to elevated osmotic concentrations. For both, the early bioprocess development and the optimization of existing bioprocesses, small-scale reaction vessels are applied to ensure high throughput, low costs and prompt results. However, most conventional small-scale procedures work in batch operation mode, which stands in contrast to fed-batch conditions in large-scale bioprocesses. Extensive expenditure for installations and operation accompany almost all cultivation systems in the market allowing fed-batch conditions in small-scale. An alternative, more cost efficient enzymatic glucose release system is strongly influenced by environmental conditions. To overcome these issues, this study investigates a polymer-based fed-batch system for controlled substrate release in microtiter plates.

RESULTS

Immobilizing a solid silicone matrix with embedded glucose crystals at the bottom of each well of a microtiter plate is a suitable technique for implementing fed-batch conditions in microtiter plates. The results showed that the glucose release rate depends on the osmotic concentration, the pH and the temperature of the medium. Moreover, the applied nitrogen source proved to influence the glucose release rate. A new developed mathematical tool predicts the glucose release for various media conditions. The two model organisms E. coli and H. polymorpha were cultivated in the fed-batch microtiter plate to investigate the general applicability for microbial systems. Online monitoring of the oxygen transfer rate and offline analysis of substrate, product, biomass and pH confirmed that fed-batch conditions are comparable to large-scale cultivations. Furthermore, due to fed-batch conditions in microtiter plates, product formation could be enhanced by the factor 245 compared to batch cultivations.

CONCLUSIONS

The polymer-based fed-batch microtiter plate represents a sophisticated and cost efficient system to mimic typical industrial fed-batch conditions in small-scale. Thus, a more reliable strain screening and early process development can be performed. A systematical scale-down with low expenditure of work, time and money is possible.

Effects of Maillard reaction products in a glucose-glycine alcoholic solution on antioxidative and antimutagenic activities

BACKGROUND

Marinating meat with alcohol, such as wine and beer, is a common culinary practice in cultures worldwide. In this study we use a model marination solution comprising 0.2  mol L^-1 glucose-0.2  mol L^-1 glycine buffered to pH 4.3 containing either 0 or 50% ethanol and mimicked the cooking process by heating for 12 h. Antioxidative and antimutagenic characteristics of Maillard reaction products (MRPs) were investigated. Reducing power, antioxidant activity (ferrous ion chelating ability), and free radical neutralization ability generated from 1,1-diphenyl-2-pichrylhydrazyl and 2,2'-azino-bis(3-ethylbenzthiazoline-6-sulfonic acid) were determined. Ames testing was performed.

RESULTS

Results indicate that MRPs from aqueous and alcoholic solution exhibit four antioxidative assays in a dose-dependent manner from 0.16 to 10.00 mg mL^-1 . However, MRPs from the alcoholic model were superior. In Ames testing, MRPs from both models are neither toxic nor mutagenic at the test concentrations of 0.63-10.00 mg/plate. However, MRPs from the alcoholic model exhibited a higher inhibitory effect on the direct-acting mutagen 4-nitroquinoline-N-oxide compared with the aqueous model. This result is consistent with the observation that MRPs with higher antioxidative capacity exhibit superior antimutagenic activity, suggesting that there are more different products in the alcoholic model.

CONCLUSION

Our results add to the current knowledge about the antioxidative and antimutagenic properties of MRPs arising when food is cooked in the presence of ethanol. © 2018 Society of Chemical Industry.

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.