Browning reaction nutritive value

While the determination of total lysine is rather straightforward, the determination of free or available lysine is more problematic. In this situation, the term free is meant to imply that the e-amine of the lysine side chain has not reacted with various components of the sample matrix (most commonly carbohydrates via Maillard browning). This is important because reaction of the e-amine can render lysine nutritionally unavailable and the nutritive value for that protein is then diminished if lysine is the limiting amino acid (which is often the situation with soy proteins). While enzymatic digestion in the human gut may not release the modified lysine in a nutritionally available state, often these lysine adducts are labile to the standard acid hydrolysis in 6N HC1 at 110°C. This results in total lysine values that overestimate the amount of nutritionally available lysine. 

Effect of the Maillard Browning Reaction on the Nutritive Value of Breads and Pizza Crusts... 

In another study by Tsen et al (14), a substantial PER difference was observed between diets with bread crust (0.36) and bread crumb (1.35). Palamidis and Markakis (12) also found that the PERs of their bread and its crumb were 0.46 and 0.91, respectively, while the crust showed a negative PER, -0.23. Hansen, et al.(18) reported that bread crumb and crust had respective PERs of"T.36 and 0.62. The difference in PERs for bread crumb or crust reported by the three groups of investigators is largely due to different raw materials and processing conditions for the breads. Nevertheless, the marked difference in PER between bread crumb and crust indicates clearly that the browning reaction can reduce the nutritive value of bread (Table IV). 

The Maillard reaction appears to be the one to occur most commonly, accompanied not only by browning but also by change of aroma, loss of nutritional value, and development of antioxidative ac-... 

These nonenzymatic reactions are responsible for numerous changes on food properties and may impair food safety. Although these reactions are of great importance in the production of aroma, taste and color, they are often accompanied by a reduction of the nutritive value of different foods and by the formation of toxic compounds harmful for human health (Ledl and Schleicher, 1990). Results of nonenzymatic browning can be either desirable or undesirable. The brown crust formation on bread is desirable the brown discoloration of evaporated and sterilized milk is undesirable. For products in which the browning reaction is favorable, the resulting color and flavor characteristics are generally experienced as pleasant. In other products, color and flavor may become quite unpleasant. 

The reaction velocity and pattern are influenced by the nature of the reacting amino acid or protein and the carbohydrate. This means that each kind of food may show a different browning pattern. Generally, lysine is the most reactive amino acid because of the free e-amino group. Since lysine is the limiting essential amino acid in many food proteins, its destruction can substantially reduce the nutritional value of the protein. Foods that are rich in reducing sugars are very reactive, and this explains why lysine in milk is destroyed more easily than in other... 

Transformations Affecting Product Quality Drying, as with any other unit operation, has both productive and harmful transformations that occur. The primary productive transformation is water removal of course, but there are many harmful transformations that can occur and adversely affect product quality. The most common of these harmful transformations includes product shrinkage attrition or agglomeration loss of flavor, aroma, and nutritional value browning reactions discoloration stickiness and flowability problems. These were discussed briefly above, but are worth a more in-depth review. 

Tyrosinase inhibition may be a potential approach to prevent and control the enzymatic browning reactions and improve the quality and nutritional value of food products [20]. Tyrosinase also plays a major key role in the developmental and defensive functions of insects. Tyrosinase is involved in melanogenesis, wound healing, parasite encapsulation, and sclerotization in insects [21-23]. For these reasons, in recent years the development of tyrosinase inhibitors has become an active alternative approach to control insect pests [20]. Additionally, it is now well-recognized that tyrosinase inhibitors are important for their potential applications in medical and cosmetic products [24-26]. 

In addition to the nutritional and physiological effects of Maillard browned protein as described in the previous section, it has been shown that the reduced nutritional value of the brown products does not seem to be limited to the loss of amino acids, since supplementation of the diet with those amino acids could not completely restore its biological value (15). This suggests the possible formation of some inhibitory or anti-nutritional compounds during the Maillard reaction, the presence of which cannot be detected with short-term nutritional feeding assays. Moreover, the short-term feeding effects reported in the literature (30) seem to be due in part to nutritional deficiency and not specifically the browning compounds. 

The major chemical reactions that take place during food processing, as would be expected, occur between the main food components—the carbohydrates, proteins, fats and vitamins. These components can react with each other and with various food additives such as nitrites, sulphite, aldehydes and alkali to give food products of lower nutritional value to produce desirable and undesirable browning and flavours and very occasionally to produce toxic materials. 

Following the formation of the deoxyketosyl derivative, the reactions leading to the formation of the brown pigments or melanoidins (Fig. 3) are not well defined. These reactions, however, are responsible for numerous flavours and odours, possibly for toxicity, and for a further reduction in protein nutritive value via destruction of amino acids and reduced digestibility. There are thought to be three main pathways in the advanced Maillard reaction. 

We have recently begun to investigate the nutritional consequences of the enzymic browning reactions that occur between phenolic acids, such as chlorogenic acid (Fig. 8), and proteins. This type of reaction has been reported to be responsible for the low nutritional value and off-colours of leaf protein and sunflower protein concentrates. The... 

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