Carbohydrates
Carbohydrates come in a variet of froms but the major differences in chemicai properties and functions divide them into sugrs and polysaccharides While some molecular aspects are in common to both groups,the sugars and the phlysaccharides have uasyly different functional properties[1]
3.1  sugars
Sugars commonly found in foods are the monosaccharides glucose and fructose and the disaccharides sucrose, lactose, and maltose .All are found naturally and are frequently added as ingredients either in relatively pure form or as a part of some other ingredient. The most obvious contribution of sugars to foods is sweetness although they are not uniformly sweet. Sucrose is used as the reference point for sweetness and is assigned a relative sweetness of 1.0. On an equal weight basis , fructose is 1.1 to 1.5 times more sweet, glucose is 0.7, maltose is 0.5 and lactose is 0.3. One sugar may be used as a substitute for another when formulating to a given level of sweetness, but different amounts of sugar are re
quired.
Sugars, particularly those other than sucrose, can be hygroscopic (water attracting). This means sugary foods tend to retain moisture and are difficult to take to dryness by evaporation. Sugars vary in their solubility and tendency to form crystals when cooled or concentrated. IN confectionery products sugars form crystals or amorphous structures resulting in hard and soft candies. Concentrated sugar solutions are viscous and provide some body to sweetened soft drinks compared to water or soft drinks sweetened with high intensity sweeteners.
Glucose and fructose are widely occurring in natural products like honey, fruits, and fruit juices. When used as more refined ingredients, glucose and fructose are derived from corn and typically used in the liquid syrup form. Maltose, composed of two glucose units, is found in products where there has been starch degradation. Sucrose is glucose and fructose combined into a nonreactive nonreducing sugar, When used as a refined ingredient, sucrose is obtained from sugar beets or sugar cane.
Lactose, composed of glucose and galactose , is found only in milk and dairy products. Lactose intolerant individuals are unable to digest lactose and therefore may experience digestive discomfort when large quantities of lactose are consumed. This is because the lactose splitting enzyme is missing or not active in their digestive systems. In dairy fermentations lactose is converted by bacteria to lactic acid.
Sugar alcohols are sugar derivatives that are found naturally but are more commonly manufactured from sugars and added as pure ingredients. S ugar alcohols provide sweetness but are not fermented by oral bacteria and therefore do not contribute to tooth decay. Examples of these sugar alcohols are sorbitol, mannitol, and xylitol. Compared to sugars, sugar alcohols are chemically less reactive and digested more slowly. If consumed in high levels they may cause digestive discomfort. Sugar alcohols are used as sweeteners in sugarless gum and candy although they contain a caloric density of 4cal/g, the same as sugars.
3.2 Sugar reactions
A key feature for sugar reactivity is the availability of a ketone or aldehyde group making it a reducing sugar. Most sugars are reducing sugars except sucrose and sugar alcohols. Even then, sucrose can hydrolyze to its component sugars glucose and fructose. The hydrolysis of disaccharides to monosaccharides occurs with heat and acid or enzyme. The acid environment in a soft drink can convert sucrose to glucose and fructose during storage. The effects of sucrose hydrolysis on sweet taste are not great because the two component sugars result in a similar overall level of sweetness. However, the reactivity of the component sugars is much greater because both are reducing sugars. When lactose hydrolyzes to galactose and glucose there is an overall increase in sweetness.
When heated to high temperatures, sugars, whether reducing or not, degrade by caramelization. The series of reactions involved leads to the formation of flavor compounds, brown colors, and polymers with limited water solubility.
reaction between pvp and amino
3.3 Maillard Browning
The Maillard browning reaction occurs between a carbonyl (aldehyde or ketone group) foun
d in a reducing sugar and an amine found in proteins and amino acids. The results of the reaction are the flavor and color development of bread crust, cooked meats, coffee, and cocoa. While the products of Maillard reaction are often desirable, they may be undesirable or over produced leading to negative attributes in the products. Maillard browning includes a series of reactions where development of the color is the last step of the process.
The Maillard reaction usually occurs during thermal processing and is common at low moisture levels such as during baking and toasting. The surfaces of products baked in a microwave oven do not show the surface Maillard browning that their conventional oven counterparts do. This is because the surface of products heated in the microwave tends to be more moist and at temperatures not exceeding 100℃.

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