Antioxidant activity of Maillard reaction products (MRPs) in a lipid-rich model system

Synergistic Effect of a Thermal Reaction and Vacuum Dehydration on Improving Xylose-Phenylalanine Conversion to N-(1-Deoxy-d-xylulos-1-yl)-phenylalanine during an Aqueous Maillard Reaction

The synergistic effect of a thermal reaction and vacuum dehydration on the conversion of xylose (Xyl) and phenylalanine (Phe) to a Maillard-reaction intermediate (MRI) was researched. The yield of N-(1-deoxy-α-d-xylulos-1-yl)-phenylalanine was successfully improved and increased from 13.62 to 47.23% through the method combining a thermal reaction and vacuum dehydration. A dynamic process was involved in the transformation of Xyl and Phe (Xyl-Phe) to N-substituted d-xylosamine and in the transformation of N-substituted d-xylosamine to N-(1-deoxy-α-d-xylulos-1-yl)-phenylalanine during the initial stage of dehydration; then, only the transformation of N-substituted d-xylosamine to N-(1-deoxy-α-d-xylulos-1-yl)-phenylalanine occurred during the final stage. Furthermore, the MRI was prepared under optimized conditions (90 °C and pH 7.4), and the obtained MRI was characterized and confirmed by ESI mass spectrometry and NMR.

Antioxidant activity and inhibitory effects of 2-hydroxy-3-methylcyclopent-2-enone isolated from ribose-histidine Maillard reaction products on aldose reductase and tyrosinase

This study aimed to better understand the functional properties of ribose and 20 amino acid Maillard reaction products (MRPs). The ABTS⁺ radical scavenging ability of the ribose-20 amino acid MRPs was evaluated. Among the MRPs, ribose-histidine MRPs (RH-MRPs) showed the highest inhibitory activities on the ABTS⁺ radical scavenging ability, aldose reductase (AR), and tyrosinase compared to other MRPs. Functional compounds with antioxidant and AR inhibitory activities have been recognized as an important strategy in the prevention and treatment of diabetic complications, and the search for tyrosinase inhibitors is important for the treatment of hyperpigmentation, development of skin-whitening agents, and use as preservatives in the food industry. On this basis, we sought to isolate and identify compounds with inhibitory activities against AR and tyrosinase. RH-MRPs were heated at 120 °C for 2 h and fractionated using four solvents: methylene chloride (MC), ethyl acetate, n-butanol, and water. The highest inhibitions were found in the MC fraction. The two compounds from this fraction were purified by silica gel column and preparative thin layer chromatography, and identified as 2-hydroxy-3-methylcyclopent-2-enone and furan-3-carboxylic acid. AR inhibition, tyrosinase inhibition, and ABTS⁺ scavenging (IC₅₀) of 2-hydroxy-3-methylcyclopent-2-enone were 4.47, 721.91 and 9.81 μg mL^-1, respectively. In this study, inhibitory effects of 2-hydroxy-3-methylcyclopent-2-enone isolated from RH-MRP were demonstrated on AR, tyrosinase, and its antioxidant activity for the first time. RH-MRP and its constituents can be developed as beneficial functional food sources and cosmetic materials and should be investigated further as potential functional food sources.

Effects of high-intensity ultrasound and oil type on the Maillard reaction of d-glucose and glycine in oil-in-water systems

This study addresses the effect of high-intensity ultrasonic processing on four oil-in-water systems, using sunflower, peanut, olive and flaxseed oils, respectively, that contained an aqueous d-glucose and glycine Maillard reaction (MR) model system. The MR in the water phase was promoted as observed from higher depletion of reactants and higher amount of MR products (MRPs). A significantly higher amount of pyrazines was generated after ultrasonic processing, particularly in the sunflower and olive oil systems. These promotions were attributed to a well-mixing effect and a localised high temperature and pressure environment generated by the high-intensity ultrasound. However, upon 1 h of ultrasonic processing at 80 °C, a significant increase of oxidation was observed with high peroxide and p-anisidine values in the post-processed oils; meanwhile, the amount of unsaturated fatty acids decreased as well. As a result, some off-flavours were also detected in the post-processed oils, which affected the overall flavour profile of the MR systems.

Ultrasound generates more flavour species in oil-in-water mixtures containing sugar and amino acid than heating, but meanwhile degrades oils. Weibiao Zhou at National University of Singapore and collaborators in China studied the effect of high-intensity ultrasonic processing on model food systems with sugar and amino acid in mixtures of water and different oils. The researchers found that high-intensity ultrasound can speed up the Maillard reaction, a chemical reaction that yields various flavour compounds from amino acids and reducing sugars, because it can induce a temporary condition of high temperature and high pressure and promote the mixing between water and oil. On the other hand, ultrasound is responsible for increased oxidation of unsaturated oils, leading to off-flavours and loss of nutrients. These results may help improve ultrasound-assisted food processing techniques.

Antimicrobial and antioxidant capacity of glucosamine-zinc(II) complex via non-enzymatic browning reaction

Coordination compounds play an important role in the life process, and have been widely used in food, cosmetics and pharmaceutical industry. Herein, we have developed a novel kind of glucosamine-zinc(II) complex (GlcN-ZC) for food additive using non-enzymatic browning reaction. The GlcN-ZC was characterized by FTIR and XRD. Moreover, UV absorbance changes, browning intensity, fluorescence changes, antioxidant activity and antimicrobial assessment of GlcN-ZC were also evaluated. Results showed the GlcN-ZC intermediate compounds were accumulated in non-enzymatic browning while prolonging heating time and melanoidins were produced in the final stage. The fluorescence changes confirmed that fluorophores were formed during the non-enzymatic reaction and fluorescence intensity reached a maximun at 60 min. The highest radical scavenging activity of GlcN-ZC formed after 180 min of heating was 79.2%. Furthermore, GlcN-ZC exhibited excellent antibacterial activity against E. coli and S. aureus. Therefore, GlcN-ZC can be used as a novel promising additive in the food industry.