Temperature Maillard reactions

Another disadvantage of heat sterilising the fresh brown juice is the formation of Maillard reaction products between amino acids and carbohydrates when they are heated to these temperatures. Maillard reactions products are growth inhibitors and reduce the amount of available amino acids and carbohydrates, again, reducing the value of the brown juice as a universal fermentation media. Furthermore, heat sterilisation significantly adds expenses to the low-price end product. 

The rate of aspartame degradation in dry mixes is more dependent on the water activity than on the temperature (23). In dry mixes, aspartame may also engage ia Maillard reactions with the aldehyde moieties of flavoting agents, resulting ia the loss of sweetness and flavor. Use of the corresponding acetals of the flavor compounds to avoid this reaction has been reported (24). 

SEVERINI c and lerici c r (1995) Interaction between Maillard reaction and lipid oxidation in model systems during high temperature treatment , Ital J Food Sci, 1 (2) 189-96. 

Figures 4.2.1 and 4.2.2 [4.9] show sorption isotherms 1, for such products which become less hygroscopic with increased temperature, or 2, for glucose, fats and oils which become more hygroscopic with increased temperature. Since freeze drying lowers aw values, the growth of bacteria, fungus and yeast below aw = 0.8 is reduced, or impossible. On the other hand, the Maillard reaction increases with decreasing aw up to a maximum at aw 0,6-0,7,...

The factors affecting the Maillard reaction include temperature, time, moisture content, concentration, pH, and nature of the reactants. - It has been shown that, out of 21 amino acids, glycine, lysine, tryptophan, and tyrosine provide the most intense browning when exposed to five saccharides, especially a-lactose. The Maillard reaction is also responsible for the decreased availability of lysine in proteinaceous foods. 

The reaction of dextrose with a nitrogen-containing compound, eg, amino acids or proteins, yields a series of intermediates which form pigments of varied molecular weight (Maillard reaction). The type of pigments produced is dependent on reaction conditions such as pH, temperature, and concentration of reactants. 

If food is heated over 300°F (154°C), it turns brown. This is why food that is boiled never browns. When food is boiled, its temperature never gets above 212°F (100°C), the boiling point of water. Food fried in oil gets brown, though, because oil boils at a temperature that is higher than 300°F. This browning is called the Maillard reaction and is caused by a chemical reaction that takes place between the amino acids and the sugars present in food when food is heated above this temperature. The Maillard reaction is named after the French chemist Louis Camille Maillard, who discovered it in 1912. 

Physical preservation methods for foods, such as sterilization and drying, are associated with the application of heat. In these cases, because of its high temperature coefficient, the Maillard reaction becomes the dominant deteriorative reaction (1 2, 3). 

---