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November 27, 2015

牛磺酸對貓之必要


No Bull, Taurine Is a Must for Kitty
牛磺酸對貓之必要

Last Updated on Saturday, September 26, 2015 06:21 PM
Published on Saturday, December 13, 2014 09:28 PM
Written by Marta Kaspar

最近更新: 2015年9月26日
原始刊出日: 2014年12月13日
作者: Marta Kaspar
原文出處連結: http://feline-nutrition.org/nutrition/no-bull-taurine-is-a-must-for-kitty

 

I am sure that you have all heard about the importance of taurine in a cat's diet. Taurine is a naturally occurring amino acid mostly found in muscle meat and organs like heart, kidney and liver and in seafood. In muscles, taurine gets more concentrated the harder the muscle works. Dark meat has more than light meat because it comes from parts of the body that work harder, legs as opposed to breast. Heart is another great example. Although it is termed an organ, it is really the hardest working muscle in the body and it has one of the highest concentrations of taurine. Shellfish such as mussels and clams also have a lot of taurine. They are constantly filtering and they follow the same "hard-working" scenario, concentrating taurine to a high degree in their tissues. Small amounts of taurine are found in dairy products. Plant products contain either low or undetectable amounts taurine. Despite meat being a good source of taurine, there is a significant amount of variability within meat samples according to a published study.¹ Taurine content of meat was not only affected by diet, breed and environment, but also by the freshness of the meat.

相信你們都聽過牛磺酸在貓食中的重要性. 牛磺酸是一種自然氨基酸, 主要存在於肉和內臟, 例如心臟, 腎臟, 肝和海鮮. 越結實的肌肉含有越多的牛磺酸. 深色肉的牛磺酸比淺色肉多, 因為深色肉通常是身體比較有在活動的部位, 例如腿是深色肉, 胸是淺色肉. 心臟是另一個很好的例子. 雖然心臟是內臟, 但其實是身體中最用力運作的肌肉, 所以含有最多的牛磺酸. 帶殼海鮮, 例如淡菜和蛤蜊, 也含有很多牛磺酸. 帶殼海鮮不斷的過濾所處環境中的水, 努力的運作身體, 所以牛磺酸含量豐富. 乳製品有少量的牛磺酸. 植物的牛磺酸很低, 或甚至低到無法偵測出來. 儘管肉是很好的牛磺酸來源, 但根據一份已出版的報告, 不同部位的肉的牛磺酸含量也會有很大的不同. (註1) 牛磺酸在肉中的含量會受到飲食, 品種, 環境和肉的新鮮度影響.

Cats, unlike some other carnivores and unlike herbivores or omnivores, are not able to synthesize all the taurine they need from other amino acids like methionine and cysteine. In addition, many animal species can use glycine or taurine to conjugate bile acids into bile salts, but cats can only conjugate bile acids with taurine. This low rate of taurine synthesis combined with the loss of taurine in bile contributes to an increased dietary requirement of taurine for cats. With insufficient amounts of this essential amino acid in their diet, cats can develop central retinal degeneration, reproductive failure and impaired fetal development or heart cardiomyopathy. Clinical signs of taurine deficiency will not be apparent right away, it might take couple of months or years in some cases, but once a cat starts exhibiting clinical signs, usually significant damage has already been done.

不同於某些肉食動物, 也不同於雜食和草食動物, 貓是無法從其他氨基酸, 例如甲硫胺酸和半胱胺酸, 來合成所需要的所有牛磺酸. 此外, 許多動物可以使用甘胺酸或牛磺酸去結合膽酸, 使之轉成膽塩, 但貓只能使用牛磺酸來結合膽酸. 低比率的牛磺酸合成率, 加上膽中牛磺酸的流失, 都在提高貓由食物中攝取牛磺酸的需求. 當食物中這種必要氨基酸的份量不足時, 貓會產生一些健康問題, 例如視網膜退化, 不孕, 胎兒發育不全或是心肌肥大. 牛磺酸攝取不足不會立刻反應在臨床症狀上, 可能需要好幾個月或好幾年. 但是一旦症狀出現, 通常實質的傷害已經造成.



上圖左半部翻譯如下:
Eyes: deficiency can lead to blindness
眼睛: 牛磺酸攝取不足可能會導致眼盲

Brain & nerves: taurine plays many roles in nerve and cell function. Taurine crosses the blood-brain barrier
腦和神經: 牛磺酸在神經和細胞功能扮演許多角色. 牛磺酸跨越血腦障壁.(白話:牛磺酸可以藉由血液進入腦部.)

譯註: Blood-brain barrier 血腦障壁的解釋: 百年前,曾發現若將藍色染劑注入動物的血管內,除了腦以及脊髓以外的組織,身體其他部位通通都變成藍色。為了解釋這個現象,科學家認為避免物質由血液進入腦部的「血腦障壁」(Blood-Brain-Barrier,BBB)應是存在的。近來,科學家對於血腦障壁的結構與功能已有更多的發現。 如果想對血腦障壁有更多的了解可以點以下連結: http://www.dls.ym.edu.tw/neuroscience/bbb_c.htm

Heart: deficiency can cause cardiomyopathy and death
心臟: 牛磺酸攝取不足會導致心肌肥大及死亡

Digestion: combines with bile acides for proper digestion
消化: 牛磺酸與膽酸結合才能有適當的消化

Immune function: taurine affects immune system responsiveness
免疫功能: 牛磺酸影響免疫系統的反應力

Fetal development: deficiency can cause stillbirths, low birth weights and birth defects in kittens
胎兒發育不全: 牛磺酸不足可能造成死胎, 體重不足以及畸胎.

譯註: 上圖右半部沒有翻譯, 因為文章中都有提到.

One very important property of taurine is its high solubility in water. The final amount of taurine in the food will depend on the food preparation and storage techniques. To minimize the loss, one should always try to retain all of the liquids coming from the meat. For example, if the meat is cooked, it should be done in a small amount of water so that it can all be incorporated back into the food. Cooking meat at temperatures used for normal food preparation by itself does not change the amino acid in any way. It just leeches the taurine out from the meat into the water. I have been asked many times if taurine loses its potency during food storage in the freezer. The answer is yes and no. Freezing does not affect taurine potency, but, during the thawing process a lot of liquid is released. Since taurine is highly water soluble, that liquid will be taking a lot of the meat's taurine with it. For example, if you buy raw ground meat/bone/organ packages, the liquid that comes out as it thaws – which is not blood despite its red color – is full of dissolved taurine. If this broth is discarded, the meat ends up with a lower taurine content than before freezing.

牛磺酸一個非常重要的特質是可以溶於水. 食物中牛磺酸的最終份量取決於食物的準備過程以及貯存技巧. 保留肉所流出的水分, 才能把牛磺酸的流失降到最低. 例如, 如果肉是有經過烹煮, 那麼應該用少量的水進行烹煮, 以儘可能的把養分留在食物中. 用平常煮食物的溫度來煮肉並不會改變牛磺酸的本質. 烹煮時肉會流出水份, 牛磺酸便跟著水排出來. 曾經有很多人問我, 在冷凍貯存的過程中, 肉中的牛磺酸會不會流失. 答案是會以及不會. 冷凍並不會影響牛磺酸的效力, 但是, 在解凍的過程中水會從肉中被釋出. 因為牛磺酸高度溶於水, 所以肉中流出的水份便夾帶很多牛磺酸. 例如買現成絞好的肉/骨/內臟生肉餐, 解凍時流出來的水並不是血水, 雖然是紅色, 而是充滿溶解在水中的牛磺酸. 如果把這個水倒掉, 那麼牛磺酸的含量會比冷凍前低很多.

The Association of American Feed Control Officials, or AAFCO, recommends the minimum allowance of taurine for wet food to be 0.2% on a dry matter basis. The chance is that this amount might be covered by the natural taurine in meat alone, but due to a significant amount of variability of taurine concentrations in meat, high taurine solubility in water, danger of delay in exhibiting clinical signs of taurine deficiency and the fact that taurine supplementation is relatively safe with no reports of any issues associated with taurine overdose, it might be beneficial to always have a small amount of taurine excess in your cat's diet. So what would be a reasonable amount to add? It is approximately 250 mg of taurine per 1lb of meat. I intentionally use "mg" because all taurine supplements are sold as "mg per capsule." Since the smallest amount available is 500 mg per capsule, you can either add one of these capsules to two pounds of meat or 1/2 capsule per one pound of meat.

AAFCO建議的濕食中牛磺酸含量是0.2%乾物比. 有可能食物本身的天然牛磺酸就有達到這個量, 但是因為牛磺酸的含量會因不同部位的肉而有很大的差別, 再加上可以高度溶於水, 有鑑於牛磺酸攝取不足的臨床症狀往往都很晚才出現, 而且目前沒有看到攝取過量牛磺酸可能有害的相關報告, 在貓食中補充加入一些牛磺酸可能是一個有利的作法. 那麼補充的量要多少呢? 一磅的肉(約480公克)大約補充250mg的牛磺酸. 我用mg為單位是因為大部份市售牛磺酸膠囊都是以mg為單位. 目前市面最小包裝是每一膠囊500mg, 你可以在二磅的肉中加入一個500mg的膠囊, 或是一磅的肉中加入半個500mg的膠囊.

A lot of you might not like the fact that supplemental taurine is always synthetic. While I would also prefer a natural product over synthetic, in this case unfortunately, there is currently no other choice. It is important to keep in mind, however, that chemically there is no difference between synthetic or natural taurine because both structures are exactly the same. Taurine, unlike many other amino acids, does not polarize light so there is no left or right rotation which can differentiate natural or synthetic types. Some companies use this exact reasoning to justify their claim for a natural taurine, but I can assure you that it is only a marketing strategy. Taurine can be extracted from natural sources – there is a company in New Zealand that extracts it from ox bile – but this method is commercially unappealing and significantly more expensive. Nevertheless, I am hopeful that one day, a truly natural taurine will be available to consumers.

很多人可能會對牛磺酸營養補充品都是合成感到不甚滿意. 我本人當然也覺得天然的好過合成, 但很不幸的目前牛磺酸補充品除了合成沒有其他選擇. 在化學上, 合成和天然牛磺酸沒有任何不同, 因為兩者的化學結構完全一樣. 不同於許多其他必要氨基酸, 牛磺酸並沒有極化光的特質, 沒有左旋和右旋之分, 所以不會因為是天然或合成而有所不同. 但有些公司以此做為他們天然牛磺酸產品的訴求, 我可以跟你們保證那只是一個市場行銷策略. 牛磺酸可以從天然來源中取得 – 有一家紐西蘭公司提煉牛膽的牛磺酸 – 但這種做法不但達不到商業訴求而且貴很多. 無論如何, 我還是希望有一天所有消費者都可以買到真正天然的牛磺酸.

Marta Kaspar holds a master's degree in chemistry from the University of Pardubice in the Czech Republic. She is a research scientist, and a formulation and analytical chemist in both industrial and academic fields. Marta became interested in feline nutrition when her cats developed health problems. When she decided to prepare their food herself, the effect of the homemade raw meat diet on her cats was so impressive that she created the line of Alnutrin® supplements to help others transition their cats to better diets. You can find her at knowwhatyoufeed.com.

本文作者 Marta Kaspar 擁有捷克 the University of Pardubice 的化學碩士學位. 她本身既是一位從事研究的科學家, 同時也是業界和學界的程式和分析化學家. Marta 是在她的貓健康出現問題才開始對貓科營養產生興趣. 她開始自製貓食後, 在貓身上看到令人印象深刻的轉變, 促使她創立 Alnutrin 品牌預拌粉, 幫助其他的貓轉換食物. 你可以在以下連結找到她: knowwhatyoufeed.com

註1: AR Spitze, DL Wong, QR Rogers and AJ Fascett, "Taurine Concentrations in Animal Feed Ingredients; Cooking Influences Taurine Content," Journal of Animal Physiology and Animal Nutrition 87, 2003, 251-262.


 


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