Publisher Summary This chapter provides an overview of the 13 Carbon-nuclear magnetic resonance ( 13 C-NMR) spectroscopy of monosaccharides. The 13 C-NMR spectroscopy has become increasingly important as a tool for the characterization and structural elucidation of sugars and their derivatives. Although 13 C-NMR is closely related to 1 H-NMR spectroscopy, especially when both types of spectra are recorded with Fourier-transform instruments, the two techniques are sufficiently different to be valuable complements to each other. In many cases, in particular when dealing with complex molecules such as polysaccharides, the amount of information obtainable from 1 H-NMR spectra is limited as compared to that revealed by 13 C- NMR spectra. This chapter provides an almost complete collection of 13 C- NMR chemical shifts of monosaccharides, their methyl glycosides, and acetates, along with the examples of shift data for as many different types of monosaccharide derivative as possible. It also provides details on sampling techniques and assignment techniques, and discusses the identity of monosaccharides, their structure determination, and conformational analysis .

Carbon-13 Nuclear Magnetic Resonance Spectroscopy of Monosaccharides

Enzymatic and nonenzymatic browning reactions of amino acids and proteins with carbohydrates, oxidized lipids, and oxidized phenols cause deterioration of food during storage and processing. The loss in nutritional quality and potentially in safety is attributed to destruction of essential amino acids, decrease in digestibility, inhibition of proteolytic and glycolytic enzymes, interaction with metal ions, and formation of antinutritional and toxic compounds. Studies in this area include influence of damage to essential amino acids on nutrition and food safety, nutritional damage as a function of processing conditions, and simultaneous formation of deleterious and beneficial compounds. These compounds include kidney-damaging Maillard reaction products, mutagens, carcinogens, antimutagens, antioxidants, antibiotics, and antiallergens. This overview covers the formation, nutrition, and safety of glycated proteins, characterized browning products, and heterocyclic amines. Possible approaches to inhibiting browning reactions and preventing adverse effects of browning during food processing and food consumption, including protection against adverse effects of heterocyclic amines by N-acetylcysteine, caffeine, chlorophyll, conjugated linoleic acid, lignin, and tea extracts, are also described. This research subject covers a complex relationship of the chemistry, biology, and pathology of browning products and the impact on human nutrition and health. Future study should differentiate antinutritional and toxicological relationships, define individual and combined potencies of browning products, and develop means to prevent the formation and to minimize the adverse manifestations of the most antinutritional and toxic compounds. Such studies should lead to better and safer foods and improved human health.

http://nfscfaculty.tamu.edu/talcott/courses/FSTC605/Papers%20Reviewed/Food%20Browning.pdf

Food browning and its prevention: an overview

Fructosamine: A new approach to the estimation of serum glycosylprotein. An index of diabetic control

Nonenzymatically glycosylated proteins gradually form fluorescent cross-linked protein adducts--a process termed "browning." The rate of this reaction increases with the glucose concentration. Assaying for the presence of browning products in long-lived proteins should therefore provide information on long-term metabolic control. We measured collagen-linked fluorescence typical for nonenzymatic browning in skin-biopsy specimens from 41 subjects with longstanding Type I diabetes and from 25 controls. Fluorescence correlated with age and (weakly) with the duration of diabetes. Mean age-adjusted fluorescence values were twice as high in diabetic subjects as in control subjects (P less than 0.0001) and increased with the severity of retinopathy, nephropathy, and arterial and joint stiffness. The correlation was significant for retinopathy (r = 0.42; P less than 0.01), arterial stiffness (r = 0.41; P less than 0.01), joint stiffness (r = 0.34; P less than 0.05), and the sum of all complications (r = 0.47; P less than 0.01). Fluorescence also correlated with systolic (r = 0.42; P less than 0.01) and diastolic (r = 0.36; P less than 0.05) blood pressures. If one can assume that the fluorescence results from a browning product of glucose, our data suggest that there is an overall correlation between the severity of diabetic complications and cumulative glycemia over many years.

Relation between Complications of Type I Diabetes Mellitus and Collagen-Linked Fluorescence

Publisher Summary This chapter discusses the Maillard reaction. Results of the many investigations into the mechanism of the Maillard reaction support one of two main theories. The first assumes the formation of glycosylamines that undergo the Amadori (or, for ketoses, the Heyns) rearrangement. The 1-amino-l-deoxyketose derivative (or 2-amino-2-de- oxyaldose derivative) formed may be dehydrated and cyclized to form furan derivatives, or it may enolize. In either case, intermediates that are readily transformed into brown compounds are formed. A third possibility is for the deoxy sugar derivative to react with more amino acid to form colored products. The many workers who have supported this mechanism found also that optimum conditions for occurrence of the Maillard reaction are (1) fairly low water content, (2) a pH of 7 to 10, and (3) a high temperature. Nevertheless, some reaction occurs under conditions far removed from these, but in the absence of moisture there is no reaction. The formation of an acyclic Schiff base as an initial step is not very likely, since replacement of the aldose by salicylaldehyde caused only a very small loss of amino groups. The second theory of the mechanism of the browning reaction is of recent origin and maintains that the browning reaction and the Maillard reaction are separate and distinct. Browning, according to this school of thought, is due to the effect of pH on the sugar and can occur over a wide range of pH, whereas the Maillard reaction proceeds only in alkaline media.

The Maillard reaction.

Publisher Summary This chapter discusses the reaction that is the isomerization of an aldosylamine to a 1-amino-1-deoxy-2-ketose. This rearrangement was named after Amadori by Kuhn and Weygand, for Amadori was the first to demonstrate that condensation of D-glucose with an aromatic amine ( p -phenetidine, p -anisidine, or p -toluidine) would yield, according to experimental conditions, two structurally different isomers, which are not members of an α, β anomeric pair. Amadori did not realize that an isomerization (“rearrangement”) from an aldose to a ketose configuration had occurred. However, he did discern (by change of optical rotation in acid solution) that one isomer is much more labile than the other toward hydrolysis and more susceptible to decomposition on standing in the solid state in air. He recognized correctly that the labile isomer is the N -substituted glucosylamine, but he mistakenly thought that the stable isomer was a compound of the Schiff-base type. Authentic crystalline products of the Amadori rearrangement have so far been obtained only from D-glucose, D-mannose, and 5- O -trityl-D-xylose as the sugar components. Occurrence of the rearrangement (or at least 1, 2-enolization of the N -substituted glycosylamine) was demonstrated indirectly, however, by isolation and characterization of crystalline epimeric hydrogenation products derived from D- and L-arabinose and also from D-xylose.

The Amadori Rearrangement

Amadori compounds: vacuum thermolysis of 1-deoxy-1-l-prolino-d-fructose

An intensely sweet analog of phyllodulcin: 2-(3-hydroxy-4-methoxyphenyl)-1,3-benzodioxan

Amadori compounds, derived from the condensation of amino acids with reducing sugars in the Mainard reaction, have been isolated from browned, dehydrated fruits and vegetables, bakery products, cane and beet molasses. and cured tobacco. The nonvolatile compounds' in their enolic forms are precursors of flavor compounds, particularly those with burnt and caramel-like aromas. A model basic Amadori compound, I-deoxY-l-piperidino-Dfructose, was pyrolyzed and the volatile products were isolated. These products, high boiling liquids and sublimable solids, consisted mainly of 4-carbon methyl reductones, a-piperidino-')'-butyrolactone, and piperidine amides of carbonic, formic, acetic, butyric, glycolic, and lactic acids. Only a trace of N-lactylpiperidine was found, indicating a predominance of 4:2 over 3:3 splitting of the hexose moiety. A reaction course through the 4-carbon reductones to the 2and I-carbon acid amides is suggested.

Amadori compounds as nonvolatile flavor precursors in processed foods

Preparation of bicyclic hexitol anhydrides by using acidic cation-exchange resin in a binary solvent. p13C-N.m.r. spectroscopy confirms configurational inversion in chloride displacement of methanesulfonate in isomannide and isosorbide derivatives

John E. Hodge

Papers

The Amadori Rearrangement

Amadori compounds: vacuum thermolysis of 1-deoxy-1-l-prolino-d-fructose

An intensely sweet analog of phyllodulcin: 2-(3-hydroxy-4-methoxyphenyl)-1,3-benzodioxan

Amadori compounds as nonvolatile flavor precursors in processed foods

Preparation of bicyclic hexitol anhydrides by using acidic cation-exchange resin in a binary solvent. p13C-N.m.r. spectroscopy confirms configurational inversion in chloride displacement of methanesulfonate in isomannide and isosorbide derivatives