Rennet: Difference between revisions
Content deleted Content added
No edit summary |
|||
| Line 1: | Line 1: | ||
| ⚫ | |||
'''Rennet''' is a natural complex of enzymes produced in any mammalian stomach to digest the mother's milk. Rennet is a [[proteolytic]] enzyme ([[protease]]) that coagulates the milk, causing it to separate into solids ([[curds]]) and liquid ([[whey]]). The active [[enzyme]] in rennet is called ''rennin'' or ''chymosin'' ({{EC number|3.4.23.4}}) but there are also some other important enzymes in it, e. g., [[pepsin]] or [[lipase]]. There are also non-animal sources of rennet. |
|||
---- |
|||
---- |
|||
| ⚫ | |||
---- |
|||
---- |
|||
The most common source for animal-based rennet is the [[abomasum]] (fourth [[stomach]]) of [[Slaughter (livestock)|slaughtered]], milk-fed new-born [[cow]] [[calf|calves]]. But stomachs of other young [[ruminant]]s, such as [[camels]] for camel's milk, [[goats]] for goat's milk, or [[lamb]] for [[ewe]]'s milk, are also used. |
|||
---- |
|||
The chief use of rennet is in the making of [[cheese]] and [[Junket (dessert)|Junket]]. The enzyme reacts specifically with κ-casein, cleaving the protein between the [[amino acid]]s [[phenylalanine]](105) and [[methionine]] (106), producing two fragments. The soluble fragment (residues 106-169) which becomes part of the whey is known as [[glyco macro peptide]] and contains the [[glycosylation]] sites for κ-casein. The other component (residues 1-105) is insoluble. This in the presence of [[calcium]] ions causes the coagulation of the casein micelles to form a curd. |
|||
==Production of natural calf rennet == |
|||
Natural rennet is produced in the inner [[mucosa]] of the fourth stomach of young ruminants. These stomachs are a [[by-product]] of [[veal]] production. |
|||
'''Traditional method''' |
|||
Today this method is only used by some very experienced and traditional cheese-makers in central [[Europe]], e.g. in [[Switzerland]], [[Jura (département)|Jura]] in France, or Alp-Sennereien in [[Austria]]. |
|||
Dried and cleaned stomachs of young calves are sliced into small pieces and then put into saltwater, together with some [[vinegar]] or [[wine]] to get a lower pH. After some time – overnight or several days - this solution has to be filtered. This crude rennet can then be used for coagulation of the milk. 1 gram of this solution should then coagulate 2000 to 4000 grams of milk. |
|||
'''Modern method''' |
|||
Deep-frozen stomachs are milled and put into an extracting solution – in this solution the enzymes are extracted. The crude rennet extract is than activated by adding acid – the enzymes in the stomach are produced in an inactive pre-form and are activated by the stomach acid. After [[neutralisation]] of the acid, the rennet extract is filtered in several stages and concentrated until reaching the required potency - e.g. 1:15.000 (1 kg of rennet would have the ability to coagulate 15,000 litres of milk). |
|||
1 kg of rennet extract contains about 0.7 grams of active enzymes and no other organic material – the rest is water and salt and sometimes some [[sodium benzoate]], [[E211]], |
|||
0.5% - 1% for preservation. 1 kg of cheese contains about 0.0003 grams of rennet enzymes. |
|||
==Alternative coagulants== |
|||
Due to the limited availability of proper stomachs for rennet production, cheese-makers have always looked for other ways to coagulate the milk. Only about 35% of world-wide cheese production can be done by the use of animal rennet; 65% is already done with other coagulants. Artificial coagulants are a useful alternative, especially for cheap or lower-quality cheeses. |
|||
As the proper coagulation is done by enzymatic activity, the task was to find enzymes for cleaving the casein that would result in taste and texture similar to what animal-based rennet produces. |
|||
;[[Vegetable rennet]] |
|||
Many plants have coagulating properties. Some examples include [[fig tree]] bark, [[nettles]], [[thistle]]s, [[mallow]], and [[Creeping Charlie]]. Commercial so called vegetable rennets usually contain rennet from the [[mold]] ''Mucor miehei'' - see microbial rennet. Rennet from thistle or ''[[cynara]]'' is used in some traditional cheese production in the [[Mediterranean]]. |
|||
These real vegetable rennets are also suitable for [[vegetarian]]s. |
|||
;Microbial rennet |
|||
There are some [[moulds]] like [[mucor]] [[miehei]] that have the capability to produce proteolytic enzymes. These moulds are produced in a [[fermenter]] and than especially concentrated and purified to avoid contamination with unpleasant side products of the mould growth. |
|||
The flavour and taste of cheeses produced with microbial rennets tend towards some bitterness, especially if longer maturation is wanted. These so-called "microbial rennets" are suitable for vegetarians if there was no animal-based alimentation used during the production in the fermenter. |
|||
;Genetic rennet |
|||
Because of the above imperfections of microbial rennets, some big companies sought further replacements of natural rennet. With the development of genetic engineering, it suddenly became possible to use calf-genes to modify some [[bacteria]], [[fungus]] or [[yeast]] to make them produce [[Chymosin]]. [[Chymosin]] produced by genetically modified enzymes was the first artificially produced enzyme to be registered and allowed by the [[FDA]] in the USA. In [[1999]], about 60% of U.S. hard cheese was made with genetically engineered Chymosin.<ref name="60%"> {{cite web |url=http://fpc.state.gov/6176.htm|title="Food Biotechnology in the United States: Science, Regulation, and Issues"|publisher=U.S. Department of State|accessdate=2006-08-14}}</ref> |
|||
Today the most widely-used genetic rennet is produced by the fungus [[Aspergillus niger]]. The problems of destroying the [[aflatoxins]] or the [[antibiotic resistant]] [[marker gene]]s seem to be solved. |
|||
Cheese production with genetic rennet is similar to production with natural calf rennet. Genetic rennet only contains one of the known main chymosin types – either type A or type B. Some of the other chymosin types found in genetic rennet do not exist in natural rennet. This is also the reason why special analysis can determine what kind of coagulant has been used. |
|||
Often a mixture of genetic Chymosin and natural pepsin is used to imitate the complexity of natural rennet and to get the same results in coagulation and in development of flavour and taste. |
|||
The so-called "genetic rennets" are suitable for vegetarians if there was no animal based alimentation used during the production in the fermenter. |
|||
;Acid coagulation |
|||
Milk can also be coagulated by adding some [[acid]], e.g. [[citric acid]]. This form of coagulation is sometimes used in cheap [[mozzarella]] production without maturation of the cheese. [[Paneer]] is also made this way. The acidification can also come from bacteria as happens in [[soured milk]]. |
|||
==See also== |
|||
* [[Pepsin]] |
|||
==External links== |
|||
*[http://www.inchem.org/documents/jecfa/jecmono/v28je08.htm FDA-registration of recombinat chymosin] |
|||
*[http://dwb.unl.edu/Teacher/NSF/C08/C08Links/www.fst.rdg.ac.uk/courses/fs560/topic1/t1g/t1g.htm Recombinant Chymosin] |
|||
*[http://jds.fass.org/cgi/content/abstract/73/8/2028 Cheese Yield Experiments and Proteolysis by Milk-Clotting Enzymes] |
|||
*[http://lib.bioinfo.pl/pmid:15969502 Validation of recombinant and bovine chymosin by mass spectrometry] |
|||
==References== |
|||
<div class="references-small"> |
|||
<references /> |
|||
</div> |
|||
Carroll, Ricki. ''Making Cheese, Butter, & Yogurt''. Storey Publishing 2003. |
|||
"Biotechnology and Food: Leader and Participant Guide," publication no. 569, produced by North Central Regional Extension. Printed by Cooperative Extension Publications, University of Wisconsin-Extension, Madison, WI, 1994. Publication date: 1994. |
|||
Tom Zinnen, biotechnology specialist, University of Wisconsin-Extension and UW Biotechnology Center, UW-Madison; and Jane Voichick, professor, Nutritional Sciences, UW-Madison and UW- Extension. |
|||
[[Category:Animal products]] |
|||
[[Category:EC 3.4.23]] |
|||
[[Category:Food industry]] |
|||
[[de:Lab]] |
|||
[[fr:Présure]] |
|||
[[ja:レンネット]] |
|||
[[nl:Stremsel]] |
|||
[[pl:Podpuszczka]] |
|||
Revision as of 17:36, 9 September 2006
Thousands of years ago, people discovered that milk stored in a dried stomach – especially the fourth stomach of a young calf – will become hard and remain fit to eat for long time