Characteristics and antioxidative activity of Maillard reaction products from a porcine plasma protein–glucose model system as influenced by pH

Preface Introduction The Chemistry of Non-Enzymic Browning Recent Advances Colour Formation in Non-Enzymic Browning Flavour and Off-Flavour Formation in Non-Enzymic Browning Toxicological Aspects Nutritional Aspects Other Physiological Aspects Other Consequences of Technological Significance Implications for Other Fields Non-Enzymic Browning Due Mainly to Ascorbic Acid Caramelisation Inhibition of Non-Enzymic Browning in Foods Inhibition of the Maillard Reaction in Vivo Subject Index

The Maillard reaction : chemistry, biochemistry and implications

A kinetic model for the glucose/glycine Maillard reaction pathways

Analysis and biological properties of amino acid derivates formed by Maillard reaction in foods

Two new types of unsymmetrical bis(thiosemicarbazone) proligands and their neutral zinc(II) and copper(II) complexes have been synthesized. These bifunctional ligands both chelate the metal ions and provide pendent amino groups that can be readily functionalized with biologically active molecules. Functionalization has been demonstrated by the synthesis of three water-soluble glucose conjugates of the new zinc(II) bis(thiosemicarbazonato) complexes, and their copper(II) analogues have been prepared in aqueous solution via transmetalation. A range of techniques including NMR, electron paramagnetic resonance, cyclic voltammetry, high-performance liquid chromatography (HPLC), UV/vis, and fluorescence emission spectroscopy have been used to characterize the complexes. Four compounds, including two zinc(II) complexes, have been characterized by X-ray crystallography. The connectivity and conformation of the glucose conjugates have been assigned by NMR spectroscopy. Time-dependent density functional theory calculations have been used to assign the electronic transitions of the copper(II) bis(thiosemicarbazonato) chromophore. Two copper-64-radiolabeled complexes, including one glucose conjugate, have been prepared and characterized using radio-HPLC, and transmetalation is shown to be a viable method for radiolabeling compounds with copper radionuclides. Preliminary cell washout studies have been performed under normoxic conditions, and the uptake and intracellular distribution have been studied using confocal fluorescence microscopy.

Functionalized bis(thiosemicarbazonato) complexes of zinc and copper: synthetic platforms toward site-specific radiopharmaceuticals.

The fate of the Amadori compound N-(1-deoxy-D-fructos-1-yl)glycine (DFG) was studied in aqueous model systems as a function of time and pH. The samples were reacted at 90 degrees C for up to 7 h while maintaining the pH constant at 5, 6, 7, or 8. Special attention was paid to the effect of phosphate on the formation of glycine and the parent sugars glucose and mannose, as well as formic and acetic acid. These compounds and DFG were quantified by high-performance anion-exchange chromatography. The rate of DFG degradation increased with pH. Addition of phosphate accelerated this reaction, particularly at pH 5-7. The rate of glycine formation increased with pH in both the absence and presence of phosphate. High glycine concentrations (60-70 mol %) were obtained, preferably at pH 6-8 with phosphate. However, the yield of glycine formed from DFG decreased at the advanced reaction stage for all pH values studied, both in water and in phosphate buffer. The rate of parent sugar formation increased from pH 5 to pH 7 in the absence of phosphate, leading to glucose and mannose in a constant ratio of 7:3. Addition of phosphate accelerated this reaction, yielding up to 18% parent sugars, most likely formed by reverse Amadori rearrangement. The formation rate of acetic and formic acid increased with increasing pH. The sum of both acids attained 76 mol %. However, the acetic acid concentrations were much higher than those of formic acid.

Sandra Aubin

Papers

Degradation of the Amadori Compound N-(1-Deoxy-d-fructos-1-yl)glycine in Aqueous Model Systems