Difference between revisions of "Tetrahydropyridine"

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===Brettanomyces===
 
===Brettanomyces===
  
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In ''Brettanomyces'', ATHP and ETHP are produced by metabolizing the amino acids L-Lysine and D-Lysine, along with ethanol and a glucose or fructose molecule. As with other amino acids, lysine is taken up by ''Saccharomyces'' during fermentation, and then released after fermentation.  Levels of lysine fluctuate slightly through fermentation, but are generally high throughout a beer's lifetime <ref>[http://link.springer.com/article/10.1385/CBB:46:1:43 The α-aminoadipate pathway for lysine biosynthesis in fungi.  Hengyu Xu, Babak Andi, Jinghua Qian, Ann H. West , Paul F. Cook.  Sept 2006.]</ref><ref>[http://pubs.acs.org/doi/abs/10.1021/bi9829940 Lysine Biosynthesis in Saccharomyces cerevisiae:  Mechanism of α-Aminoadipate Reductase (Lys2) Involves Posttranslational Phosphopantetheinylation by Lys5.  David E. Ehmann , Amy M. Gehring , and Christopher T. Walsh.  1999.]</ref><ref>[http://onlinelibrary.wiley.com/doi/10.1002/j.2050-0416.2007.tb00249.x/abstract Elucidation of the Role of Nitrogenous Wort Components in Yeast Fermentation.  C. Lekkas, G.G. Stewart, A.E. Hill, B. Taidi and J. Hodgson.  May 2012.]</ref><ref>[http://www.sciencedirect.com/science/article/pii/S0308814699000710 Proteins and amino acids in beers, their contents and relationships with other analytical data.  S. Gorinstein, M. Zemsera, F. Vargas-Albores, J-L. Ochoa, O. Paredes-Lopez, Ch. Scheler, J. Salnikow, O. Martin-Belloso, S. Trakhtenberg.  1999.]</ref>.   
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In ''Brettanomyces'', ATHP and ETHP are produced by metabolizing the amino acids L-Lysine and L-ornithine, along with ethanol and a glucose or fructose molecule <ref name="Snowdon"></ref>. As with other amino acids, lysine is taken up by ''Saccharomyces'' during fermentation, and then released after fermentation.  Levels of lysine fluctuate slightly through fermentation, but are generally high throughout a beer's lifetime <ref>[http://link.springer.com/article/10.1385/CBB:46:1:43 The α-aminoadipate pathway for lysine biosynthesis in fungi.  Hengyu Xu, Babak Andi, Jinghua Qian, Ann H. West , Paul F. Cook.  Sept 2006.]</ref><ref>[http://pubs.acs.org/doi/abs/10.1021/bi9829940 Lysine Biosynthesis in Saccharomyces cerevisiae:  Mechanism of α-Aminoadipate Reductase (Lys2) Involves Posttranslational Phosphopantetheinylation by Lys5.  David E. Ehmann , Amy M. Gehring , and Christopher T. Walsh.  1999.]</ref><ref>[http://onlinelibrary.wiley.com/doi/10.1002/j.2050-0416.2007.tb00249.x/abstract Elucidation of the Role of Nitrogenous Wort Components in Yeast Fermentation.  C. Lekkas, G.G. Stewart, A.E. Hill, B. Taidi and J. Hodgson.  May 2012.]</ref><ref>[http://www.sciencedirect.com/science/article/pii/S0308814699000710 Proteins and amino acids in beers, their contents and relationships with other analytical data.  S. Gorinstein, M. Zemsera, F. Vargas-Albores, J-L. Ochoa, O. Paredes-Lopez, Ch. Scheler, J. Salnikow, O. Martin-Belloso, S. Trakhtenberg.  1999.]</ref>.   
  
 
Oxygen has a stimulatory effect in it's production, but this is probably because ''Brett'' has a higher biomass formation under aerobic conditions <ref>[http://www.brettanomycesproject.com/dissertation/introduction/ Yakobson, Chad.  The Brettanomyces Project; Introduction.  Retrieved 3/10/2015.]</ref><ref>[http://pubs.acs.org/doi/abs/10.1021/jf071243e The Role of Lysine Amino Nitrogen in the Biosynthesis of Mousy Off-Flavor Compounds by Dekkera anomala.  Paul R. Grbin, Markus Herderich, Andrew Markides, Terry H. Lee, and Paul A. Henschke. J. Agric. Food Chem., 2007.]</ref><ref name="Oelofse">[http://scholar.sun.ac.za/handle/10019.1/8437 Significance of Brettanomyces and Dekkera during Winemaking: A Synoptic Review.  A. Oelofse, I.S. Pretorius, and M. du Toit.  2008.]</ref>.  Therefore, limiting oxygen exposure during kegging/force carbonating is recommended for helping to reduce THP production.  The level of THP production varies widely between species and strains of ''Brett'', with some strains not producing it at all and some producing very high amounts above taste threshold.  Additionally, THP production appears to require glucose or fructose, which explains why THP may be seen more often in stuck wine fermentations rather than wine that has finished fermenting.  ATHP production by ''Brett'' was observed in wine with glucose or fructose added, along with synthetic growth media, suggesting that the type of growth substrate does not effect production <ref>[http://www.ncbi.nlm.nih.gov/pubmed/18194246 Growth and volatile compound production by Brettanomyces/Dekkera bruxellensis in red wine.  Romano A, Perello MC, de Revel G, Lonvaud-Funel A.  J Appl Microbiol. 2008 Jun.]</ref>.   
 
Oxygen has a stimulatory effect in it's production, but this is probably because ''Brett'' has a higher biomass formation under aerobic conditions <ref>[http://www.brettanomycesproject.com/dissertation/introduction/ Yakobson, Chad.  The Brettanomyces Project; Introduction.  Retrieved 3/10/2015.]</ref><ref>[http://pubs.acs.org/doi/abs/10.1021/jf071243e The Role of Lysine Amino Nitrogen in the Biosynthesis of Mousy Off-Flavor Compounds by Dekkera anomala.  Paul R. Grbin, Markus Herderich, Andrew Markides, Terry H. Lee, and Paul A. Henschke. J. Agric. Food Chem., 2007.]</ref><ref name="Oelofse">[http://scholar.sun.ac.za/handle/10019.1/8437 Significance of Brettanomyces and Dekkera during Winemaking: A Synoptic Review.  A. Oelofse, I.S. Pretorius, and M. du Toit.  2008.]</ref>.  Therefore, limiting oxygen exposure during kegging/force carbonating is recommended for helping to reduce THP production.  The level of THP production varies widely between species and strains of ''Brett'', with some strains not producing it at all and some producing very high amounts above taste threshold.  Additionally, THP production appears to require glucose or fructose, which explains why THP may be seen more often in stuck wine fermentations rather than wine that has finished fermenting.  ATHP production by ''Brett'' was observed in wine with glucose or fructose added, along with synthetic growth media, suggesting that the type of growth substrate does not effect production <ref>[http://www.ncbi.nlm.nih.gov/pubmed/18194246 Growth and volatile compound production by Brettanomyces/Dekkera bruxellensis in red wine.  Romano A, Perello MC, de Revel G, Lonvaud-Funel A.  J Appl Microbiol. 2008 Jun.]</ref>.   
  
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ATHP is further metabolized into 2-ethyltetrahydropyridine (ETHP/ETPY) by Brettanomyces, although not much is known about this metabolic process <ref>[http://ucce.ucdavis.edu/files/repositoryfiles/Joseph_5_Aromatic_Diverswity_of_Brettanomyces-82350.ppt Joseph, C.M. Lucy.  ''Aromatic Diversity of Brettanomyces''.  U.C. Davis.  Retrieved 3/10/2015.]</ref>.  ETHP has a significantly higher taste threshold, and is often not detected in contaminated wine <ref name="Oelofse"></ref>.   
+
As ''Brett'' continues through it's growth cycle, ATHP is produced as a secondary metabolite <ref name="Snowdon"></ref>.  ATHP is further metabolized into 2-ethyltetrahydropyridine (ETHP/ETPY) by ''Brettanomyces'', although not much is known about this metabolic process <ref>[http://ucce.ucdavis.edu/files/repositoryfiles/Joseph_5_Aromatic_Diverswity_of_Brettanomyces-82350.ppt Joseph, C.M. Lucy.  ''Aromatic Diversity of Brettanomyces''.  U.C. Davis.  Retrieved 3/10/2015.]</ref>.  ETHP has a significantly higher taste threshold, and is often not detected in contaminated wine <ref name="Oelofse"></ref>.   
  
 
The presence of the "mousy off-flavor" caused by THP appears to be temporary in beer.  Although not much is known about the degradation or metabolic break down of ATHP/ETHP, it tends to age out of beer after 2-6 months.  Another unknown is why ''Brett'' produces THP shortly after kegging and force carbonating a beer that has reached final gravity.  Pitching fresh ''Saccharomyces'' for bottle conditioning a beer with ''Brett'' in it has reportedly reduced THP production, perhaps through the quicker metabolism of both the oxygen and sugar that is introduced during packaging time.   
 
The presence of the "mousy off-flavor" caused by THP appears to be temporary in beer.  Although not much is known about the degradation or metabolic break down of ATHP/ETHP, it tends to age out of beer after 2-6 months.  Another unknown is why ''Brett'' produces THP shortly after kegging and force carbonating a beer that has reached final gravity.  Pitching fresh ''Saccharomyces'' for bottle conditioning a beer with ''Brett'' in it has reportedly reduced THP production, perhaps through the quicker metabolism of both the oxygen and sugar that is introduced during packaging time.   
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===LAB===
 
===LAB===
  
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Heterofermentative [[Lactobacillus]] spp., particularly ''L. hilgardii'' and ''L. brevis'', can also produce ATHP and ETHP from Lysine and ethanol <ref name="Costello">[http://pubs.acs.org/doi/abs/10.1021/jf020341r Mousy Off-Flavor of Wine:  Precursors and Biosynthesis of the Causative N-Heterocycles 2-Ethyltetrahydropyridine, 2-Acetyltetrahydropyridine, and 2-Acetyl-1-pyrroline by Lactobacillus hilgardii DSM 20176.  Peter J. Costello and Paul A. Henschke.  2002.]</ref><ref>[http://www.ajevonline.org/content/37/2/127.abstract Formation of Substituted Tetrahydropyridines by Species of Brettanomyces and Lactobacillus Isolated from Mousy Wines.  Tamila Heresztyn.  1986.]</ref><ref>[http://onlinelibrary.wiley.com/doi/10.1111/j.1755-0238.2001.tb00205.x/abstract Ability of lactic acid bacteria to produce N-heterocycles causing mousy off-flavour in wine.  PETER J. COSTELLO1, TERRY H. LEE1, and PAULA. HENSCHKE.  2008.]</ref><ref>Sparrows, Jeff.  ''Wild Brews''.  Brewers Publications.  2005.  Pg. 112.</ref><ref>[https://books.google.com/books?id=tFjsAuo5WocC&pg=PA348&lpg=PA348&dq=lactobacillus+Tetrahydropyridine&source=bl&ots=QUVyoFtIwK&sig=h1cdjB0r1pIRX2Bms8wVA0UiLk4&hl=en&sa=X&ei=4DX_VPz5CsH6oQSAzoGgBA&ved=0CEwQ6AEwCQ#v=onepage&q=lactobacillus%20Tetrahydropyridine&f=false Lahtinen, Ouwehand, Salminen, von Wright. Lactic Acid Bacteria: Microbiological and Functional Aspects, Fourth Edition.  Pg 348.]</ref><ref>[http://ajevonline.org/content/37/2/127.short Heresztyn, Tamila.  Formation of Substituted Tetrahydropyridines by Species of Brettanomyces and Lactobacillus Isolated from Mousy Wines.]</ref>.  Most species of [[Pediococcus]] do not create THP, although a few species do.  In particular, these include ''P. pentosaceus'' <ref>[http://www.uniprot.org/uniprot/Q03HT0 UniProt article.  Retrieved 3/10/2015.]</ref><ref>[http://www.uniprot.org/uniprot/U5ZF76 UniProt article.  Retrieved 3/10/2015.]</ref>, and ''P. clausenii'' <ref>[http://www.uniprot.org/uniprot/G8PEU4 UniProt article.  Retrieved 3/10/2015.]</ref> (note that commercial cultures of [[Pediococcus]] are normally ''P. damnosus'').  ''Oenococcus oeni'' and ''Leuconostoc mesenteroides'' have also been associated with creating THP <ref name="Costello"></ref>.
+
Heterofermentative [[Lactobacillus]] spp., particularly ''L. hilgardii'' and ''L. brevis'', can also produce high levels of ATHP, ETHP, and APY from L-lysine/L-ornithine and ethanol <ref name="Costello">[http://pubs.acs.org/doi/abs/10.1021/jf020341r Mousy Off-Flavor of Wine:  Precursors and Biosynthesis of the Causative N-Heterocycles 2-Ethyltetrahydropyridine, 2-Acetyltetrahydropyridine, and 2-Acetyl-1-pyrroline by Lactobacillus hilgardii DSM 20176.  Peter J. Costello and Paul A. Henschke.  2002.]</ref><ref>[http://www.ajevonline.org/content/37/2/127.abstract Formation of Substituted Tetrahydropyridines by Species of Brettanomyces and Lactobacillus Isolated from Mousy Wines.  Tamila Heresztyn.  1986.]</ref><ref>[http://onlinelibrary.wiley.com/doi/10.1111/j.1755-0238.2001.tb00205.x/abstract Ability of lactic acid bacteria to produce N-heterocycles causing mousy off-flavour in wine.  PETER J. COSTELLO1, TERRY H. LEE1, and PAULA. HENSCHKE.  2008.]</ref><ref>Sparrows, Jeff.  ''Wild Brews''.  Brewers Publications.  2005.  Pg. 112.</ref><ref>[https://books.google.com/books?id=tFjsAuo5WocC&pg=PA348&lpg=PA348&dq=lactobacillus+Tetrahydropyridine&source=bl&ots=QUVyoFtIwK&sig=h1cdjB0r1pIRX2Bms8wVA0UiLk4&hl=en&sa=X&ei=4DX_VPz5CsH6oQSAzoGgBA&ved=0CEwQ6AEwCQ#v=onepage&q=lactobacillus%20Tetrahydropyridine&f=false Lahtinen, Ouwehand, Salminen, von Wright. Lactic Acid Bacteria: Microbiological and Functional Aspects, Fourth Edition.  Pg 348.]</ref><ref>[http://ajevonline.org/content/37/2/127.short Heresztyn, Tamila.  Formation of Substituted Tetrahydropyridines by Species of Brettanomyces and Lactobacillus Isolated from Mousy Wines.]</ref>.  Most species of [[Pediococcus]] do not create THP, although a few species do.  In particular, these include ''P. pentosaceus'' <ref>[http://www.uniprot.org/uniprot/Q03HT0 UniProt article.  Retrieved 3/10/2015.]</ref><ref>[http://www.uniprot.org/uniprot/U5ZF76 UniProt article.  Retrieved 3/10/2015.]</ref>, and ''P. clausenii'' <ref>[http://www.uniprot.org/uniprot/G8PEU4 UniProt article.  Retrieved 3/10/2015.]</ref> (note that commercial cultures of [[Pediococcus]] are normally ''P. damnosus'').  ''Oenococcus oeni'' and ''Leuconostoc mesenteroides'' have also been associated with creating THP.  Since only heterofermentative species produce significant amounts of THP, it is thought that it's production is linked to the heterolactic pathway, and thus the metabolism of sugars in LAB <ref name="Costello"></ref>.
 +
 
 +
===AAB===
 +
Although research is limited, acetic acid bacteria have been shown to occasionally produce forms of THP <ref name="Snowdon"></ref>.
  
 
==Thresholds==
 
==Thresholds==

Revision as of 15:17, 22 September 2015

Forms of Tetrahydropyridines (THP), specifically 6-Acetyl-2,3,4,5-tetrahydropyridine (ATHP or ACTPY), 2-ethyltetrahydropyridine (ETHP), and 2-acetyl-1-pyrroline (ACPY or APY) [1], which are classified as ketones [2], are commonly attributed to the "mousy", "urine" (in high amounts) "cheerios" or "Captain Crunch" (in low amounts), "breakfast cereal", or more generically, "cracker biscuit" flavor in sour beers. The flavor is detected towards the end of the swallow, and the aftertaste can remain for a few minutes. Not all people are able to detect this flavor [3]. Diacetyl is sometimes mistakenly indicated as a potential cause of this flavor in sour beers. However, Tetrahydropyridines are the accepted cause. The flavor tends to age out of sour beers after 2-6 months (it is unknown whether cold or room temperature storage speeds this up), although the exact mechanism for this is not fully understood [4]. Many brewers have noticed that pitching rehydrated wine yeast at bottling reduces the amount/duration of this flavor [5].

In food, Tetrahydropyridines are associated with the aroma of baked goods such as white bread, popcorn, and tortillas, and is formed by Maillard reactions during heating. ATHP and APY have an odor threshold of 0.06ng/l [1].

Traditionally, the mousy/cheerios flavor from THP is considered an off flavor in both wine and sour beer. There is some debate and differing opinions as to whether or not a small amount of THP flavor is allowable (or even enjoyable) in sour beers, however most consider any level to be an off flavor.

Types of THP

ETHP

ETHP was first identified in wine in 1973, but until recently further studies weren't able to confirm it's presence in wine. It's odor threshold is quite high (see Thresholds), and so it was not considered a major source of mousy off-flavors in wine. Consequently, research on ETHP has been limited. More recently, it was shown that Lactic Acid Bacteria (LAB) can produce above threshold levels of ETHP, making it important to wine researchers [3].

It has been speculated by scientists studying mousy off-flavors in wine that it's production is the result of slow metabolism of ATHP into ETHP by Brettanomyces. ETHP was observed to form much slower than ATHP, and coincided with a decrease in ATHP. This slow production of ETHP may be another reason it has been underestimated by researchers until recently [3].

ATHP

ATHP has a much lower flavor threshold than ETHP (see Thresholds). In wine, its aroma cannot be detected, only the flavor. It is easier to detect in higher pH wines. ATHP is the form of THP that is the major contributor to the aroma of freshly baked bread, corn tortilla chips, and crackers. How different foods/wines/beers interact with ATHP on the palate may explain the different flavors that are detected by people, as well differing concentrations and peoples' ability to detect ATHP [3].

APY

APY is a more volatile form of THP, and has a stronger odor than ATHP. It can also be found in damp pearl millet, bread, and more aromatic rice such as Indian Basmati [3].

Production

Proposed pathway for THP production by Brett [6]

(This section is in progress)

All species of Brettanomyces can produce forms of Tetrahydropyridine. Additionally, Lactic Acid Bacteria (LAB) including Lactobacillus and Pediococcus can produce forms of THP. Acetic Acid Bactera (AAB) has also been demonstrated to produce forms of THP [3].

Brettanomyces

In Brettanomyces, ATHP and ETHP are produced by metabolizing the amino acids L-Lysine and L-ornithine, along with ethanol and a glucose or fructose molecule [3]. As with other amino acids, lysine is taken up by Saccharomyces during fermentation, and then released after fermentation. Levels of lysine fluctuate slightly through fermentation, but are generally high throughout a beer's lifetime [7][8][9][10].

Oxygen has a stimulatory effect in it's production, but this is probably because Brett has a higher biomass formation under aerobic conditions [11][12][13]. Therefore, limiting oxygen exposure during kegging/force carbonating is recommended for helping to reduce THP production. The level of THP production varies widely between species and strains of Brett, with some strains not producing it at all and some producing very high amounts above taste threshold. Additionally, THP production appears to require glucose or fructose, which explains why THP may be seen more often in stuck wine fermentations rather than wine that has finished fermenting. ATHP production by Brett was observed in wine with glucose or fructose added, along with synthetic growth media, suggesting that the type of growth substrate does not effect production [14].

As Brett continues through it's growth cycle, ATHP is produced as a secondary metabolite [3]. ATHP is further metabolized into 2-ethyltetrahydropyridine (ETHP/ETPY) by Brettanomyces, although not much is known about this metabolic process [15]. ETHP has a significantly higher taste threshold, and is often not detected in contaminated wine [13].

The presence of the "mousy off-flavor" caused by THP appears to be temporary in beer. Although not much is known about the degradation or metabolic break down of ATHP/ETHP, it tends to age out of beer after 2-6 months. Another unknown is why Brett produces THP shortly after kegging and force carbonating a beer that has reached final gravity. Pitching fresh Saccharomyces for bottle conditioning a beer with Brett in it has reportedly reduced THP production, perhaps through the quicker metabolism of both the oxygen and sugar that is introduced during packaging time.

LAB

Heterofermentative Lactobacillus spp., particularly L. hilgardii and L. brevis, can also produce high levels of ATHP, ETHP, and APY from L-lysine/L-ornithine and ethanol [16][17][18][19][20][21]. Most species of Pediococcus do not create THP, although a few species do. In particular, these include P. pentosaceus [22][23], and P. clausenii [24] (note that commercial cultures of Pediococcus are normally P. damnosus). Oenococcus oeni and Leuconostoc mesenteroides have also been associated with creating THP. Since only heterofermentative species produce significant amounts of THP, it is thought that it's production is linked to the heterolactic pathway, and thus the metabolism of sugars in LAB [16].

AAB

Although research is limited, acetic acid bacteria have been shown to occasionally produce forms of THP [3].

Thresholds

Editor's note: the following thresholds are from a study on wine, and may not hold true for beer.

  • 2-ethyltetrahydropyridine (ETHP/ETPY)
    • Taste threshold (wine): 150 µg/L
    • Concentration reported in wines exhibiting mousy off-flavour: 2.7-18.7 µg/L
  • 2-acetyltetrahydropyridine (/ATHP/ACTPY) -
    • Odor threshold (water): 1.6 µg/L
    • Concentration reported in wines exhibiting mousy off-flavour: 4.8-106 µg/L
  • 2-acetyl-1-pyrroline (ACPY)
    • Odor threshold (water): 0.1 µg/L
    • Concentration reported in wines exhibiting mousy off-flavour: Tr-7.8 µg/L [25]

Discussions

Below is a list of discussions on internet forum threads that may shed light on specific strains and individual experiences. Keep in mind that many of the opinions and experiences are anecdotal, although commonalities and shared experiences may prove to be useful and accurate.

References

  1. ↑ 1.0 1.1 6-Acetyl-2,3,4,5-tetrahydropyridine. Wikipedia. Retrieved 3/210/2015.
  2. ↑ Humbard, Matt. Milk The funk Discussion. 3/10/2015.
  3. ↑ 3.0 3.1 3.2 3.3 3.4 3.5 3.6 3.7 3.8 Mousy Off-Flavor: A Review. Eleanor M. Snowdon, Michael C. Bowyer, Paul R. Grbin, and Paul K. Bowyer. 2006.
  4. ↑ Tonsmeire, Michael. Homebrewtalk.com post 1. 11/21/2014. Retrieved 3/10/2015.
  5. ↑ Tonsmeire, Michael. Homebrewtalk.com post 2. 11/21/2014. Retrieved 3/10/2015.
  6. ↑ Managing Wine Quality: Oenology and Wine Quality. A Reynolds Elsevier, Sep 30, 2010. Pg 359.
  7. ↑ The α-aminoadipate pathway for lysine biosynthesis in fungi. Hengyu Xu, Babak Andi, Jinghua Qian, Ann H. West , Paul F. Cook. Sept 2006.
  8. ↑ Lysine Biosynthesis in Saccharomyces cerevisiae:  Mechanism of α-Aminoadipate Reductase (Lys2) Involves Posttranslational Phosphopantetheinylation by Lys5. David E. Ehmann , Amy M. Gehring , and Christopher T. Walsh. 1999.
  9. ↑ Elucidation of the Role of Nitrogenous Wort Components in Yeast Fermentation. C. Lekkas, G.G. Stewart, A.E. Hill, B. Taidi and J. Hodgson. May 2012.
  10. ↑ Proteins and amino acids in beers, their contents and relationships with other analytical data. S. Gorinstein, M. Zemsera, F. Vargas-Albores, J-L. Ochoa, O. Paredes-Lopez, Ch. Scheler, J. Salnikow, O. Martin-Belloso, S. Trakhtenberg. 1999.
  11. ↑ Yakobson, Chad. The Brettanomyces Project; Introduction. Retrieved 3/10/2015.
  12. ↑ The Role of Lysine Amino Nitrogen in the Biosynthesis of Mousy Off-Flavor Compounds by Dekkera anomala. Paul R. Grbin, Markus Herderich, Andrew Markides, Terry H. Lee, and Paul A. Henschke. J. Agric. Food Chem., 2007.
  13. ↑ 13.0 13.1 Significance of Brettanomyces and Dekkera during Winemaking: A Synoptic Review. A. Oelofse, I.S. Pretorius, and M. du Toit. 2008.
  14. ↑ Growth and volatile compound production by Brettanomyces/Dekkera bruxellensis in red wine. Romano A, Perello MC, de Revel G, Lonvaud-Funel A. J Appl Microbiol. 2008 Jun.
  15. ↑ Joseph, C.M. Lucy. Aromatic Diversity of Brettanomyces. U.C. Davis. Retrieved 3/10/2015.
  16. ↑ 16.0 16.1 Mousy Off-Flavor of Wine:  Precursors and Biosynthesis of the Causative N-Heterocycles 2-Ethyltetrahydropyridine, 2-Acetyltetrahydropyridine, and 2-Acetyl-1-pyrroline by Lactobacillus hilgardii DSM 20176. Peter J. Costello and Paul A. Henschke. 2002.
  17. ↑ Formation of Substituted Tetrahydropyridines by Species of Brettanomyces and Lactobacillus Isolated from Mousy Wines. Tamila Heresztyn. 1986.
  18. ↑ Ability of lactic acid bacteria to produce N-heterocycles causing mousy off-flavour in wine. PETER J. COSTELLO1, TERRY H. LEE1, and PAULA. HENSCHKE. 2008.
  19. ↑ Sparrows, Jeff. Wild Brews. Brewers Publications. 2005. Pg. 112.
  20. ↑ Lahtinen, Ouwehand, Salminen, von Wright. Lactic Acid Bacteria: Microbiological and Functional Aspects, Fourth Edition. Pg 348.
  21. ↑ Heresztyn, Tamila. Formation of Substituted Tetrahydropyridines by Species of Brettanomyces and Lactobacillus Isolated from Mousy Wines.
  22. ↑ UniProt article. Retrieved 3/10/2015.
  23. ↑ UniProt article. Retrieved 3/10/2015.
  24. ↑ UniProt article. Retrieved 3/10/2015.
  25. ↑ Malolactic Fermentation 2005. Geneva on the Lake. Feb 2005. Retrieved 3/10/2015.
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