Enzymes are proteins which catalyse chemical reactions selectively as part of essential life processes such as digestion, respiration and metabolism in organisms. For centuries, human beings have exploited the impressive catalytic efficiency of these ubiquitous biomolecules for food processing, especially in the preparation of beer, wine, cheese and bread. Enzymes are generally extracted from edible plants and the tissues of animals. Certain enzymes also are produced by microorganisms like bacteria, yeasts, and fungi. Rennet, for instance, is a natural enzyme mixture from the stomach of calves and other domestic animals that has been used in the preparation of cheese. The industrial revolution also contributed to the growth of the enzyme industry particularly in applications like baking, beverages, brewing and dairy products. Additionally, enzymes also find applications in detergents, leather, textile pulp, and paper industries. A recent survey on world sales of enzymes ascribes 31% for food enzymes, 6% for feed enzymes and the remaining for technical enzymes.1
Some of the enzymes generally employed in food industry are listed below:
Classes of Enzymes:
Depending on the types of reaction they catalyse, enzymes are broadly classified inot six major categories as shown in Scheme1.
| Class | Chemical Reaction Catalyzed | Example |
| Oxidoreductase | Oxidation-reduction in which oxygen and hydrogen are gained or lost | Cytochrome oxidase |
| Transferase | Transfer of functional groups, such as an amino group, acetyl group, or phosphate group | Acetate kinase |
| Hydrolase | Hydrolysis (addition of water) | Protease |
| Lyase | Removal of groups of atoms without hydrolysis | Oxalate decarboxylase |
| Isomerase | Rearrangement of atoms within a molecule | alanine racemase |
| Ligase | Joining of two molecules (in presence of ATP) | DNA ligase |
Proteases in Food Industry:
Proteases are protein-hydrolysing enzymes which belong to the class “hydrolases”. They are involved in breaking long protein chains into shorter fragments by splitting the peptide bonds that link amino acid residues. Those which break the terminal amino acids from the protein chain are called exopeptidases (Eg: carboxypeptidase A) whereas, those which attack internal peptide bonds of a protein are called endopeptidases (Eg: trypsin). These enzymes are involved in a multitude of physiological reactions from simple digestion of food proteins to highly regulated biological processes like the blood-clotting cascade. Certain proteases have been used in food processing for centuries. Rennet (mainly chymosin), obtained from the fourth stomach (abomasum) of unweaned calves, has been used traditionally in the production of cheese. Similarly, papain from the leaves and unripe fruit of Carica papaya has been used to tenderise meat.
Rennet and Milk Coagulation
The role of rennet in cheese making specifically involves the hydrolysis of a specific peptide linkage, between phenylalanine and methionine residues (-Phe105-Met106-) in the kappa-casein protein present in milk. There are four major types of casein molecules in milk, viz., alpha-s1, alpha-s2, beta and kappa. The alpha and beta caseins are hydrophobic proteins that are readily precipitated by calcium but kappa casein is not calcium-precipitable. The caseins self-associate into micelles in which the alpha and beta caseins are kept from precipitating by their interactions with kappa casein. In essence, kappa casein normally keeps the majority of milk protein soluble and prevents it from spontaneously coagulating. Chymosin proteolytically cuts and inactivates kappa casein. This destabilizes the micellar structure and the calcium-insoluble caseins precipitate, forming a curd (Fig 1).2
Calf rennet, consisting of mainly chymosin with a small but variable proportion of pepsin, is a relatively expensive enzyme and various attempts have been made to find cheaper alternatives from microbial sources. These have ultimately proved to be successful and microbial rennets are used for about 70% of USA cheese and 33% of cheese production world-wide.
In summary, enzymes have been widely employed in various food and related industries for centuries. Their specificity and mild reaction conditions make them ideal candidates for a wide variety of food products like wine, juices, cheese and other dairy products. Of particular importance are the protein-breaking enzymes, viz., proteases, which are employed in cheese making and meat tenderizing applications.
References and Further Reading:
“This article is authored by Dr. R. Prakash Chandran, Department of Chemistry, Mannam Memorial NSS College, Kottiyam, Kollam-691571 “
