Enzymes - continued digestive

For some foods, incomplete extraction of color is obtained, probably due to the high binding affinity of dyes to the bulk of the food matrix, especially to proteins, lipids, and carbohydrates (156,161,162). This problem can be overcome by the use of selected solvents or enzymes to digest the food prior to extraction. Petroleum ether can be used to extract lipids (163). Acetone can be used to remove lipids and coagulate protein (164). Enzymes, such as amyloglucosidase (165,166), papain (167), lipase, pectinase, cellulase, and phospholipase, added to the sample and incubated under optimum pH and temperature conditions release synthetic colors bound to or associated with the food matrix. Furthermore, enzyme digestion can solubilize some foods, enabling analysis to be continued (156). 

Note that even human tissues fixed immediately after their removal from the body may undergo cellular changes because usually the vascular supply is terminated before the tissue is surgically removed. During this duration ( 1 hr) the tissue remains at body temperature, at which the activity of digestive enzymes continues, damaging the cellular structures (Grizzle et al., 2001). 

An example of a type I reaction is the use of enzymes such as proteases or amylases in laundry detergents however, this enzyme reaction has caused some controversy in relation to water pollution. Once in solution, the soluble enzyme may digest (i.e., break down) an insoluble substrate such as a blood stain, A major research effort is currently being directed at type II reactions. By attaching active enzyme groups to solid surfaces, continuous processing units similar to the packed catalytic bed reactor discussed in Chapter 10 can be developed. 

By contrast, in necrosis, severe physical, chemical, or bacterial damage causes a cell membrane to burst, releasing apoptotic mediators (Sect. 13.4.3) and proinflammatory cytokines into the stroma (Sect. 13.2.2). The cytosolic enzymes continue to make lactic acid in the absence of mitochondrial function, making the necrotic environment strongly acidic and activating lysosomal enzymes (Sect. 13.2.1) to digest the released cytosolic contents. Necrosis is discussed in relation to aggressive periodontitis (Chap. 14). 

When you eat starchy foods, they are broken down into glucose by enzymes. The process starts in your mouth with the enzyme amylase found in saliva. This explains why, if you chew a piece of bread long enough, it starts to taste sweet The breakdown of starch molecules continues in other parts of the digestive system. Within 1 to 4 hours after eating, all the starch in food is converted into glucose. 

After the food is swallowed, the digestive process continues in the stomach where the food is attacked by stomach acid. In fact, stomach acid is concentrated hydrochloric acid. The hydrochloric acid, along with an enzyme called pepsin, breaks down proteins in the food. Pepsin can only function in the low pH environment of the stomach. The hydrochloric acid is needed to maintain the low pH that pepsin needs to function. 

Effect of substrate concentration. In the following experiments the cholinesterase activities were measured by a continuous titration method. The digest of acetylcholine and horse-serum cholinesterase (total vol. 10 ml.), containing bromothymol blue and 0-0002 m phosphate, was titrated with 0-01 n NaOH to maintain the pH at 7-4. The titrations, which were carried out at 20°, were linear over a period of 10-15 min. The velocity was expressed as ml. 0-01 n NaOH/5 min. under the conditions used, it was proportional to the enzyme concentration. When an inhibitor was added, this was equilibrated with the enzyme, etc., for 5 min. at 20° before adding the substrate contained in a volume of 1 ml. 

The enzyme amylase is present in the small intestines, too, so the digestion of carbohydrates can continue there. The carbohydrates eventually are broken down into their simplest form— glucose—which cells can use during respiration to produce the energy the body needs to function. 

Protein digestion starts in the mouth and continues in your stomach and small intestines. This is due to pepsin, which is secreted in the saliva and obviously the gastric juice, followed by pancreatic enzymes, then absorbed by the mucosal cells in the small intestines. In short, the digestive system breaks down protein into its peptide amino acid structures so they can be absorbed in the small intestine via the... 

---