|EC Number||EC 126.96.36.199 etc.|
Lipase carries out hydrolysis, synthesis and transfer reaction of triglyceride that is composed of fatty acids and glycerin as its substrate. Due to the diversity of triglycerides that lipases can accept as their substrates, there are a wide variety of lipases with different specificity for the triglycerides they break down. The substrate specificity of lipases can be classified as follows:
1. Positional specificity on ester hydrolysis.
When a lipase acts on a triglyceride to release a fatty acid, the position of the ester the lipase hydrolyzes depends on the type of lipase being applied. There are three types of lipases in which one type acts on the α- and α'-positions. Another acts on the β-position, and the third kind works on all of the α- and α'- and β-positions. Here, the central position of the triglyceride where the fatty acid residue is attached is referred to as the β-position, and the outer positions are referred to as the α- and α'-positions.
2. Specificity for the fatty acid chain length.
The length of the fatty acid chains that are connected to the triglyceride group in terms of the number of carbon atoms covers a wide range from two to 24 atoms. Although lipases can be categorized broadly into those that hydrolyze short-chain fatty acid esters efficiently and those that hydrolyze medium- to long-chain fatty acid esters effectively. However, the boundary is not clear.
Lipase is a digestive enzyme found in the digestive juice, namely gastric juice and pancreatic juice. Its industrial applications include medicinal digestive enzyme preparation, diagnostic reagent, food processing agent and catalyst for chiral chemical synthesis.
One application that takes advantage of the hydrolytic ability of lipase is the production of food-flavoring agents. This application relies on the fact that the fatty acid released from triglyceride upon hydrolysis by lipase gives different flavors depending on the type of fatty acid being released. For example, among the fatty acids obtained by hydrolyzing cow’s milk triglycerides with lipases, short-chain fatty acids give off a cheesy aroma, those fatty acids with longer chain give off a milky smell, and those with even longer chain give off a buttery scent. Thus, lipases are used widely as flavor-intensifying food additive in various food products, such as dairy products, confectioneries, ice cream and industrial-grade cheese. Lipases are also used to remove lipids in food products. For example, lipids from yolk that are mixed in with the egg white can be removed by breaking the lipids down with lipases.
Lipases used in chemical synthesis are employed as enzymes that act on ester linkages, and are used for the formation and exchange of esters. A representative application of lipases in synthetic reactions is the reforming of oil. By attaching a fatty acid to a diglyceride to form a triglyceride using a lipase in diglyceride-rich oil, the quality of the oil can be improved. Similarly, as far as a transfer reaction is concerned, by replacing the fatty acid in certain oil to other fatty acid with lipase, increase in the added value of the oil can be accomplished. By esterifying fatty acid and alcohol with lipase, various types of fragrance can be produced as well.
The superior ability of asymmetric recognition by lipases is exploited for applications in chiral synthesis. To be useful in chiral synthesis, it is important that the enzymes remain stable in organic solvents. However, lipases have many lipophilic amino acid residues on the surface of the enzymes, and are thought to be able to retain their three-dimensional structures even inside organic solvents. Reports on the studies on the lipases from Burkholderia cepacia and Candida antarctica are most prevalent. However, studies on lipases from other strains, such as Candida rugosa, Pseudomonas fluorescens, Aspergillus niger and Bacillus, are currently being conducted.
Lipases can be found in a wide range of microorganisms, plants and animal tissues. They are used as enzyme for food manufacturing industry. Lipases can be found in various sources, including calf sublingual gland extract, pancreas extract, Aspergillus niger, Candida rugosa, Candida lipolytica, Rhizopus oryzae, Penicillium camembertii, Penicillium roqueforti and Mucor javanicus.
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