Identification and quantification of organic molecules Lab # 4 Bio 201 Medgar Evers College

Aim Testing for the presence of sugars, Starch, protein, and fat in several food samples using an indicator. The food we eat contains several nutrients that our body needs. These include starch, glucose, fat and protein.

Starch Starch is a polysaccharide that consists of glucose molecules put together by dehydration synthesis. There exist two forms; amylase and amylopectin. They both can be detected in food by a simple test involving Iodine. Iodine is an amber colored solution that will turn blue-black in the presence of starch.

Monosaccharides and disaccharides Mono and disaccharides can be detected by a reagent called Benedict’s reagent. It is a blue reagent that will turn orange in the presence of sugars. A green color indicates the presence of a small amount of glucose. Benedict reagent reacts with the aldehyde or ketone group of the linear form of monosaccharides. Any disaccharide that can open its ring form and assume the linear form can also react with benedict. Sucrose can’t! Most mono and disaccharides caused reduction and are called reducing sugars.

Protein Proteins are needed by our body for proper growth and maintenance. Proteins in food can be detected by a reagent called biuret. It is a light blue colored solution that will turn purple/lilac in the presence of protein.

Fat Fat is a source of energy and insulation. Fatty acids are broken down in a process called beta oxidation to yield molecules of acetyl CoA that enter the process of respiration. Fat can be detected by rubbing a food into a brown paper bag and checking for a translucent spot or using Sudan IV (a lipid soluble dye). Sudan IV is a red dye that is taken in by lipids turning it bright red!