Andy Montoya
Proteolytic enzymes have been used in cheesemaking for thousands of years, with the earliest indication of cheese-making descending from cave paintings around 5000 BC. The process of milk coagulation is the main step in producing cheese, and proteolytic enzymes are used to separate milk into solid curds and liquid whey. The most common source of these enzymes is rennet, which is traditionally derived from the stomachs of ruminant mammals, specifically calves. However, due to the limited availability and high price of rennet, alternative sources such as microbial, recombinant, and plant-based enzymes have been explored. These substitutes have proven to be suitable replacements for animal rennet and are commonly used in cheese production today.
| Characteristics | Values |
|---|---|
| Name | Rennet |
| Description | A complex set of enzymes produced in the stomachs of ruminant mammals |
| Key Component | Chymosin, a proteolytic enzyme that curdles the casein in milk |
| Other Components | Pepsin, lipase, and other enzymes |
| Traditional Use | Separation of milk into solid curds and liquid whey for cheese production |
| Modern Use | Most cheese now uses chymosin from bacterial sources; less than 5% of cheese in the US is made with animal rennet |
| Alternatives | Vegetable rennet, microbial rennet, fermentation-produced chymosin (FPC), plant proteases, microbial coagulants |
| Function in Cheese Making | Milk coagulation, proteolysis during ripening, flavour and texture development |
| EMC (Enzyme-Modified Cheese) | A concentrated cheese flavour ingredient produced by treating cheese or its ingredients with proteases, lipases, and esterases |
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What You'll Learn
- Rennet is a complex set of enzymes produced in the stomachs of ruminant mammals
- Rennet contains chymosin, a protease enzyme that curdles the casein in milk
- Plant proteases have been used as milk coagulants in cheesemaking for centuries
- Enzyme-modified cheese (EMC) is a concentrated cheese flavour ingredient
- Proteolysis is a crucial biochemical event during the ripening of most cheese varieties
Rennet is a complex set of enzymes produced in the stomachs of ruminant mammals
In addition to chymosin, rennet contains other enzymes such as pepsin and a lipase. The type and concentration of these enzymes can vary depending on the age and diet of the ruminant. For example, rennet extracted from older calves may contain less or no chymosin but higher levels of pepsin, making it suitable only for specific types of milk and cheeses.
The use of rennet in cheese-making has a long history, with evidence suggesting that it has been used for thousands of years. Traditionally, rennet was obtained from the stomachs of ruminants, especially calves. However, due to the limited availability and high price of rennet from animal sources, as well as religious factors and bans on recombinant calf rennet in some countries, alternative sources have been explored.
These alternatives include microbial, recombinant, and plant-based enzymes. Plant proteases, such as those found in fig juice, have been used as milk coagulants in cheesemaking for centuries. However, the excessive proteolytic nature of most plant coagulants has limited their use due to lower cheese yields, bitter flavours, and texture defects. Microbial coagulants, on the other hand, have improved greatly over time due to the characterisation and purification of secondary enzymes, allowing for the production of high-quality cheeses with microbial rennet.
Today, most cheese is made using chymosin derived from bacterial sources, as it is less expensive than animal rennet. The use of rennet substitutes, such as microbial and vegetable coagulants, also makes cheese suitable for vegetarians and those adhering to religious dietary restrictions.
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Rennet contains chymosin, a protease enzyme that curdles the casein in milk
Rennet is a complex set of enzymes produced in the stomachs of ruminant mammals. It is used to separate milk into solid curds and liquid whey, which is useful in the production of cheese. Rennet contains chymosin, a protease enzyme that curdles the casein in milk.
Chymosin is the key component of rennet and is responsible for curdling the milk, which is the first stage in cheese production. It does this by breaking down kappa casein, which normally keeps milk proteins soluble and prevents them from coagulating. Chymosin breaks the peptide bond between amino acid residues 105 and 106, phenylalanine and methionine, in kappa casein. This cleavage removes the negatively charged glycomacropeptide (GMP) from the surface of the casein micelle. As negative charges repel each other, the removal of GMP allows the casein micelles to adhere to each other, resulting in milk coagulation.
The traditional method of obtaining chymosin was by extracting it from the stomachs of slaughtered calves. However, this source of rennet has become less common, with less than 5% of cheese in the United States being made using animal rennet today. This is due to the limited availability of mammalian stomachs, as well as the imperfections and scarcity of animal rennet.
To overcome these limitations, producers have sought alternative sources of chymosin. With the development of genetic engineering, it became possible to extract rennet-producing genes from animal stomachs and insert them into bacteria, fungi, or yeasts. This process allows these microorganisms to produce chymosin during fermentation. The genetically modified microorganism is then killed, and the chymosin is isolated from the fermentation broth. This type of chymosin, known as fermentation-produced chymosin (FPC), has been on the market since 1990 and is considered the ideal milk-clotting enzyme. FPC is widely used in industrial cheesemaking in North America and Europe due to its lower cost compared to animal rennet.
In addition to FPC, chymosin can also be derived from bacterial sources and plants. For example, in India, where cows are revered for religious reasons, fruit trees were used as a source of chymosin for coagulating milk. However, it is important to note that plant-based coagulants may lead to bitter and undesirable flavors in cow's milk cheeses.
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Plant proteases have been used as milk coagulants in cheesemaking for centuries
Plant proteases used in cheesemaking primarily belong to the group of aspartic proteases, which have the ability to clot milk under the right conditions. However, enzymes from other groups, such as cysteine and serine proteases, have also been shown to effectively clot milk. The use of plant proteases in cheesemaking results in cheeses with a characteristic soft texture and a slightly bitter flavour.
The process of milk coagulation is crucial in cheesemaking, as it directly influences the cheese yield, texture, and flavour. The widely used milk-clotting enzyme, chymosin, is an aspartic protease that selectively hydrolyses the Phe105-Met106 bond in κ-casein, initiating the coagulation process. Other plant proteases, such as those extracted from Solanum dubium, Actinidia chinensis, Zingiber officinale, and Cynanchum otophyllum Schneid, have also been found to effectively hydrolyse different sites in κ-casein, contributing to milk coagulation.
The search for alternatives to animal rennet has led to the discovery of various plant-based coagulants that can be used in cheesemaking. These include enzymes extracted from plants like Pergularia tomentosa, Carica papaya, and Cynara (artichokes and cardoons). The use of these plant-based coagulants allows for the production of cheeses that cater to specific dietary and religious preferences, such as vegetarian, kosher, and halal requirements.
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Enzyme-modified cheese (EMC) is a concentrated cheese flavour ingredient
EMC is created through an incubation period under controlled conditions, which is necessary for the proper development of flavour. These enzymes are added during cheesemaking, after the cheese curds have been pressed, or even after the cheese has been naturally aged. The resulting flavour depends on the curds and the specific enzyme composition used. For example, a cheddar-type EMC derives most of its lactate and acetate from the natural cheddar curd it is based on.
EMCs are typically added to foods in dosages of around 0.1-2%, sometimes up to 5%, to impart a cheesy flavour. They have an intense flavour that is 10-30 times stronger than natural cheeses but have a different and much more exaggerated taste profile. By manipulating the parent cheese, enzyme mixtures, or aging times, a variety of EMC flavours have been created, including mild, medium, and sharp cheddar, Colby, Swiss, Provolone, and Parmesan, among others.
The creation of EMCs involves the use of proteolytic enzymes, which play a crucial role in the ripening and flavour development of cheese. Proteolytic enzymes act on proteins, breaking them down into smaller peptides and free amino acids, which contribute to the desired cheese texture and flavour. Deviations from the precise balance of this process can lead to undesirable deviations in texture and flavour, such as the development of a bitter taste in the cheese.
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Proteolysis is a crucial biochemical event during the ripening of most cheese varieties
Enzymes play a vital role in proteolysis during cheese ripening. Traditionally, rennet, a complex set of enzymes derived from the stomachs of ruminant mammals, has been used to coagulate milk for cheese production. Chymosin, the key component of rennet, curdles the casein in milk, initiating the proteolysis process. However, due to limited availability and high costs, alternative sources of enzymes have been explored, including microbial, recombinant, and plant-based enzymes.
Plant proteases, such as those derived from figs, thistles, and artichokes, have been used as milk coagulants for centuries. While they can effectively clot milk, their excessive proteolytic nature has limited their use due to lower cheese yields, bitter flavours, and texture defects. On the other hand, microbial coagulants have improved significantly over time, leading to the production of high-quality cheeses with better flavour and texture profiles.
The use of enzymes in cheese ripening goes beyond coagulation. Enzyme-modified cheese (EMC) is a concentrated cheese flavour ingredient produced by treating cheese or its upstream ingredients with proteases, lipases, and esterases. EMCs accelerate and intensify the ripening process, creating a more intense flavour profile than natural cheeses. The development of EMC flavours involves analysing flavouring compounds such as amino acids and fatty acids to mimic the target cheese variety.
In summary, proteolysis is indeed a crucial biochemical event during cheese ripening, influencing the final characteristics of the cheese. The careful selection and application of enzymes throughout the process are essential to achieving the desired flavour, texture, and overall quality of the cheese.
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Frequently asked questions
Rennet is a complex set of enzymes produced in the stomachs of ruminant mammals. It has traditionally been used to separate milk into curds and whey for the production of cheese.
Chymosin is the key component of rennet. It is a proteolytic enzyme that curdles the casein in milk.
Some substitutes for animal rennet include microbial, recombinant, and plant-based enzymes. Many plants have coagulating properties, such as fig juice, which was used by the ancient Greeks.
