266 The nutrition handbook for food processors Denaturation of proteins, with the important consequence of the deactivation of enzymes that destabilise foods or decrease their digestibility, such as lipases, lipoxygenases, hydrolases, and trypsin inhibitors. Lipid autoxidation Transformations of minor compounds, for example vitamins Reactions involving free or protein-bound amino acids The last reactions belong essentially to four categories breaking and/or recombination of intramolecular or intermolecular disulfide reactions of the basic and acidic side chains of amino acids to give isopep- tides(for example Lys Asp) reactions involving the side chains of amino acids and reducing sugars in a very complex process generally named as "Maillard reaction(MR) reactions involving the side chains of amino acids through leaving group elimination to give reactive dehydro intermediates, which can produce cross-linked amino acids The Maillard reaction is described in this chapter and some information given on those reactions involving the side chains of amino acids. The Maillard reaction, or non-enzymatic browning, is one of the most important processes involving on one hand amino acids, peptides and proteins, and on the other reducing sugars (Ledl and Schleicher, 1990; Friedman, 1996). The MR is a complex mixture of competitive organic reactions, such as tautomerisations, eliminations, aldol con- densations, retroaldol fragmentations, oxidations and reductions. Their interpre- tation and control is difficult because they occur simultaneously and give rise to many reactive intermediates Soon after the discovery of the MR it became clear that it influences the nutritive value of foods. The loss in nutritional quality and, potentially, in safety is attributed to the destruction of essential amino acids, interaction with metal ions, decrease in digestibility, inhibition of enzymes, deactivation of vitamins and formation of anti-nutritional or toxic compounds. However, while the reaction has its negative effects, the positive effects are considerably eater 11.2 The maillard reaction About 90 years ago Maillard(1912)observed a rapid browning and CO2 devel opment while reacting amino acids and sugars: he had discovered a new reaction that became known as the"Maillard reaction or non-enzymatic browning. Nine teen years later Amadori (1931) detected the formation of rearranged stable products from aldoses and amino acids that became known as the Amadori rearrangement products(ARPs). The development of industrial food processing, especially after World War Il, gave a large impulse to research in this field and• Denaturation of proteins, with the important consequence of the deactivation of enzymes that destabilise foods or decrease their digestibility, such as lipases, lipoxygenases, hydrolases, and trypsin inhibitors. • Lipid autoxidation. • Transformations of minor compounds, for example vitamins. • Reactions involving free or protein-bound amino acids. The last reactions belong essentially to four categories: • breaking and/or recombination of intramolecular or intermolecular disulfide bridges; • reactions of the basic and acidic side chains of amino acids to give isopep￾tides (for example Lys + Asp); • reactions involving the side chains of amino acids and reducing sugars in a very complex process generally named as ‘Maillard reaction’ (MR); • reactions involving the side chains of amino acids through leaving group elimination to give reactive dehydro intermediates, which can produce cross-linked amino acids. The Maillard reaction is described in this chapter and some information given on those reactions involving the side chains of amino acids. The Maillard reaction, or non-enzymatic browning, is one of the most important processes involving on one hand amino acids, peptides and proteins, and on the other reducing sugars (Ledl and Schleicher, 1990; Friedman, 1996). The MR is a complex mixture of competitive organic reactions, such as tautomerisations, eliminations, aldol con￾densations, retroaldol fragmentations, oxidations and reductions. Their interpre￾tation and control is difficult because they occur simultaneously and give rise to many reactive intermediates. Soon after the discovery of the MR it became clear that it influences the nutritive value of foods. The loss in nutritional quality and, potentially, in safety is attributed to the destruction of essential amino acids, interaction with metal ions, decrease in digestibility, inhibition of enzymes, deactivation of vitamins and formation of anti-nutritional or toxic compounds. However, while the reaction has its negative effects, the positive effects are considerably greater. 11.2 The Maillard reaction About 90 years ago Maillard (1912) observed a rapid browning and CO2 devel￾opment while reacting amino acids and sugars: he had discovered a new reaction that became known as the ‘Maillard reaction’ or non-enzymatic browning. Nine￾teen years later Amadori (1931) detected the formation of rearranged stable products from aldoses and amino acids that became known as the Amadori rearrangement products (ARPs). The development of industrial food processing, especially after World War II, gave a large impulse to research in this field and 266 The nutrition handbook for food processors