What is Rennin Definition Function and Uses in Digestion
Rennin is also known as chymosin. Rennin meaning is given as a protein-digesting enzyme that curdles milk by transforming the caseinogen into insoluble casein. It is found only in the cud-chewing animal's fourth stomach, like cows. Its action extends the period where milk is retained in the young animal's stomach. In animals, which lack rennin, milk can be coagulated by the pepsin action, as is the case rennin in humans. Rennet, which is a commercial form of rennin, is used in the manufacturing of preparing junket and cheese.
There are many useful pepsin and rennin actions that may be applied to humans and other living organisms.
Occurrence
The chymosin can be found in a diverse range of tetrapods, although it is one of the best-known ones to be produced by ruminant animals in the abomasum lining. Chymosin can be produced by gastric chief cells in newborn mammals to curdle the milk that they ingest by allowing a longer residence in better absorption and the bowels. Cats, pigs, seals, and chicks are non-ruminant animals that contain chymosin.
A study that is reported finding a chymosin-like enzyme in a few human infants (rennin in infants), but the others have failed to replicate this specific finding. Humans contain a pseudogene for the chymosin, which does not generate a protein found on chromosome 1. Also, humans have other proteins for milk digestion, such as lipase and pepsin.
In addition to the primate lineage leading up to humans, a few other mammals have also lost the chymosin gene.
Enzymatic Reaction
Chymosin can be used to bring about curd formation and extensive precipitation in cheese-making. Chymosin's native substrate is K-casein that is particularly cleaved at the peptide bond between the amino acid residues 105 and 106, methionine, and phenylalanine. Calcium phospho caseinate is the resultant product. When a particular linkage between the hydrophilic (acidic glycopeptide) and hydrophobic (para-casein) groups of casein is broken, the hydrophobic groups get to unite and form a 3D network, which traps the milk's aqueous phase.
Charge interactions between the glutamates and histidines on the kappa-casein and the aspartates of chymosin initiate enzymes, which is binding to the substrate. When chymosin isn't the binding substrate, a beta-hairpin known as "the flap" will hydrogen bond to the active site, covering it and preventing further substrate binding.
Recombinant Chymosin
Due to the imperfections and scarcity of animal and microbial rennets, producers sought replacements. With genetic engineering development, it became possible to extract the rennet-producing genes from the stomach of animals and insert them into certain fungi, yeasts, or bacteria, to make them form chymosin during the fermentation process.
The microorganisms, which are genetically modified, can be killed after the fermentation, and chymosin is isolated from the fermentation broth so that Fermentation-Produced Chymosin (FPC), which is used by the cheese producers, does not contain any ingredient or GM component. FPC has identical chymosin as the animal source but is produced in an efficient way. Also, the FPC products have been on the market since 1990, and they are considered the ideal milk-clotting enzyme.
FPC was given as the first artificially produced enzyme to be registered and allowed by the United States Food and Drug Administration. About 60% of US hard cheese was made in 1999 with FPC, and it has around 80% of the global market share for rennet.
Coagulation of Milk
In order to understand how to coagulate milk by chymosin, one should know something about milk proteins. Casein is the most abundant protein in milk, and it comes in four different types: alpha-s1, alpha-s2, beta, and kappa. Both the alpha and beta caseins are hydrophobic proteins, which are precipitated readily by calcium - the normal calcium concentration in the milk is far more than required to precipitate these proteins.
But, kappa casein is a distinctly varied molecule, and it is not calcium-precipitable. As the caseins get secreted, they self-associate into the aggregates, known as micelles, where the alpha and beta caseins are kept from the precipitating process by their interactions with kappa casein. In essence, kappa casein preserves the bulk of milk protein soluble while also preventing it from coagulating spontaneously.
Enter chymosin. The chymosin then proteolytically cuts and inactivates kappa casein by converting it into para-kappa-casein and a smaller protein known as macropeptide. On the other side, para-kappa-casein does not hold the ability to stabilize the calcium-insoluble caseins precipitate and the micellar structure, forming a curd.
Besides its physiologic role, chymosin is also a more important industrial enzyme because it can be widely used in cheesemaking. Chymosin was extracted from dried calf stomachs in days gone by; for this purpose, however, the cheesemaking industry has expanded beyond the supply of available calf stomachs (note that these have to be from the young calves).
Also, it turns out that several proteases are able to coagulate milk by converting the casein to paracasein and alternatives to chymosin are available readily. "Rennet" is the term given to any enzymatic preparation that clots milk.
FAQs on Rennin in Chemistry Structure Source and Biological Role
1. What is rennin in chemistry?
Rennin, also known as chymosin, is a proteolytic enzyme that coagulates milk by specifically breaking down the milk protein casein. In biochemical terms, it is an enzyme that hydrolyses peptide bonds in κ-casein, leading to milk clotting.
- It is naturally found in the stomach of young mammals.
- It plays a key role in the digestion of milk proteins.
- It is widely used in the cheese-making industry.
2. Is rennin the same as rennet?
Rennin is the active enzyme (chymosin), while rennet is the crude extract containing rennin and other enzymes used to coagulate milk.
- Rennin (chymosin) is a specific protease enzyme.
- Rennet is obtained from the stomach lining of calves or produced microbially.
- Rennet may contain additional enzymes such as pepsin.
3. What is the function of rennin in milk digestion?
The main function of rennin is to coagulate milk by converting soluble casein into insoluble paracasein, facilitating digestion.
- Rennin acts on κ-casein in milk.
- It hydrolyses a specific peptide bond in casein.
- This forms a curd (coagulated protein), slowing milk passage in the stomach.
4. How does rennin coagulate milk?
Rennin coagulates milk by enzymatically cleaving κ-casein, destabilizing casein micelles and causing them to aggregate.
- Step 1: Rennin hydrolyses a specific peptide bond in κ-casein.
- Step 2: This forms insoluble paracasein.
- Step 3: In the presence of Ca2+ ions, paracasein forms calcium paracaseinate (curd).
5. Where is rennin produced in the body?
Rennin is produced in the stomach of young mammals, particularly in the gastric glands.
- It is secreted as an inactive precursor called prochymosin.
- Prochymosin is activated in the acidic environment of the stomach.
- It is most abundant in infants who consume milk as their primary diet.
6. What type of enzyme is rennin?
Rennin is a proteolytic enzyme (protease) that specifically hydrolyses peptide bonds in proteins.
- It belongs to the class of aspartic proteases.
- It acts mainly on milk protein casein.
- Its action is highly specific compared to general proteases like pepsin.
7. What is the difference between rennin and pepsin?
The key difference is that rennin specifically coagulates milk casein, while pepsin digests a wide range of proteins.
- Rennin acts mainly on κ-casein in milk.
- Pepsin hydrolyses many different peptide bonds in dietary proteins.
- Rennin is prominent in infants; pepsin is active in both children and adults.
8. Why is rennin important in cheese making?
Rennin is important in cheese making because it coagulates milk to form curd, the solid base of cheese.
- It converts soluble casein into insoluble paracasein.
- The curd traps fats and proteins.
- The remaining liquid (whey) is separated.
9. What is microbial rennin?
Microbial rennin is chymosin produced by genetically engineered microorganisms for industrial cheese production.
- It is made using recombinant DNA technology.
- Microbes such as bacteria, yeast, or fungi produce chymosin.
- It has the same enzymatic activity as animal-derived rennin.
10. Does rennin work best at a specific pH and temperature?
Rennin works best in a slightly acidic medium with an optimum pH around 4–5 and at body temperature (about 37°C).
- Acidic conditions activate prochymosin into active rennin.
- Too high a temperature denatures the enzyme.
- Too low or high pH reduces its enzymatic activity.
