The formation of 2-alkylfurans from the corresponding lipid-derived α,β-unsaturated aldehydes under dry-roasting conditions was investigated in detail. The addition of an amino acid to an α,β-unsaturated aldehyde drastically increased 2-alkylfuran formation. Peptides and proteins as well were able to catalyze 2-alkylfuran formation from the corresponding α,β-unsaturated aldehydes. Further investigation of 2-alkylfuran formation showed the need of oxidizing conditions and the involvement of radicals in the reaction. This way, the formation of 2-methylfuran from 2-pentenal, 2-ethylfuran from 2-hexenal, 2-propylfuran from 2-heptenal, 2-butylfuran from 2-octenal, 2-pentylfuran from 2-nonenal, and 2-hexylfuran from 2-decenal was shown. The impact of amino acids on 2-alkylfuran formation from lipid-derived α,β-unsaturated aldehydes represents an interesting example of the complex role of amino acids in the multitude of chemical reactions occurring during thermal processing of lipid-rich foods.

Whereas most studies concerning the Maillard reaction have focused on free amino acids, little information is available on the impact of peptides and proteins on this important reaction in food chemistry. Therefore, the formation of flavor compounds from the model reactions of glucose, methylglyoxal, or glyoxal with eight dipeptides with lysine at the N-terminus was studied in comparison with the corresponding free amino acids by means of stir bar sorptive extraction (SBSE) followed by GC-MS analysis. The reaction mixtures of the dipeptides containing glucose, methylglyoxal, and glyoxal produced 27, 18, and 2 different pyrazines, respectively. Generally, the pyrazines were produced more in the case of dipeptides as compared to free amino acids. For reactions with glucose and methylglyoxal, this difference was mainly caused by the large amounts of 2,5(6)-dimethylpyrazine and trimethylpyrazine produced from the reactions with dipeptides. For reactions with glyoxal, the difference in pyrazine production was rather small and mostly unsubstituted pyrazine was formed. A reaction mechanism for pyrazine formation from dipeptides was proposed and evaluated. This study clearly illustrates the capability of peptides to produce flavor compounds that can differ from those obtained from the corresponding reactions with free amino acids.

Introduction 7876 2. Importance of Peptides in Food 7877 3. Degradation of Peptides without the Intervention of Other Reactive Species 7877 3.1. Peptide Chain Cleavage 7879 3.1.1. Peptide Hydrolysis 7879 3.1.2. Intramolecular Cyclizations in the Peptide Chain 7879 3.2. Peptide Backbone Modifications 7881 3.3. Peptide Side-Chain Modifications 7882 3.4. Peptide Cross-Linking 7883 3.5. Peptide Breakdown 7884 4. Reactions of Peptides with Carbonyl Compounds 7885 4.1. Reactions between Peptides and Carbohydrates 7885 4.1.1. Introduction 7885 4.1.2. Initial Stage of the Maillard Reaction 7885 4.1.3. Advanced Stages of the Maillard Reaction 7887 4.1.3.1. Formation of Color 7888 4.1.3.2. Formation of Taste 7888 4.1.3.3. Formation of Aroma 7888 4.1.3.4. Formation of Biological Activity 7889 4.1.3.5. Formation of Peptide Side-Chain Modifications and Cross-Links 7890 4.2. Reactions between Peptides and Lipids 7893 4.3. Reactions between Peptides and Glyoxal or Methylglyoxal 7896 4.4.

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