老人常說，紅皮雞蛋比白皮雞蛋有營養，這是真的嗎？不同顏色的雞蛋之間有區別嗎？為什么雞蛋殼會有不同顏色？來看看美國專家怎么說。

截圖來自Howstuffworks網站?

Peruse the egg section of a grocery store or farmers market, and you'll notice cartons of eggs separated into white and brown, sometimes even green or blue eggs. But once they arrive scrambled on a plate, perhaps, or baked into a cake, it's tough to tell the difference. In fact, what is the difference between eggs with shells of different colors?
去超市或農產品市場仔細觀察成箱的雞蛋，你可能會注意到雞蛋既有白的，也有褐色的，有時候甚至是綠色或藍色的。可是變成炒蛋或蛋糕之后，又基本看不出區別了。那么，這些雞蛋除了蛋殼顏色不一樣，還有什么不同呢？

This isn't a flour or rice situation. Brown eggs are not more "natural," and white eggs have not been decolored with bleach. Both varieties occur completely naturally, as do bluish-green chicken eggs. But really, all chicken eggs are the same on the inside. So what causes different egg colors among the same type of bird?
這跟面粉或大米不一樣。褐色的雞蛋不一定更“純天然”，而白色雞蛋也不是被漂白了。相反，它們生來就是那樣的，包括藍綠色的雞蛋也是。但不管蛋殼顏色如何，它們的內在實際上都是一樣的。那為什么這些雞蛋都是母雞生的，“膚色”卻各有不同呢？

Dr. Justin Fowler, a professor in the University of Georgia's poultry science department, shines a light on things. "The different colors, or the presence of spots or speckling, come down to the genetics of the bird," he says.
喬治亞大學家禽學系的賈斯汀·福勒教授對此作出了闡釋：“雞蛋顏色不同，或者有些帶有斑點，是母雞基因不同導致的。”

"Leghorn chickens (which make up most of the commercial egg industry in the US) lay white eggs, while Orphingtons or Plymouth Rocks will lay brown eggs," explains Fowler. "The Ameraucana breed has a pigment that is able to permeate the whole egg shell and make blue-colored eggs that are colored on both the inside and outside of the shell."
“來亨雞是美國最主要的商品蛋雞，它們會下白色的蛋；奧爾平頓雞和洛克雞下的蛋則是褐色的；而阿美饒卡納雞身上會產生一種色素，能夠滲透到整個蛋殼里，讓蛋殼里里外外都變成藍色。”

Want to know whether a specific chicken will pop out a white egg or a colored egg? Examine the chicken's earlobe. (Surprise, birds have earlobes!) "Breeds with white earlobes will typically be those that do not put extra pigment on the egg shell before laying," says Fowler. And more often than not, chickens with lighter earlobes tend to have white feathers, and thus white eggs, while those with colored feathers and earlobes tend to produce colored eggs.
想要知道某只雞下什么顏色的蛋，可以看看它的耳垂是什么顏色（沒錯，人家雞也是有耳垂的！）福勒說道，“白色耳垂的雞產蛋時通常不會分泌色素，所以下的蛋通常是白色的。”一般來說，耳垂顏色較淺的雞羽毛都是白色的，下的蛋也是白色的，而羽毛和耳垂有色的雞則會下有色的蛋。

Where does this color come from? Here's where understanding how an egg comes to be is important. Chicken yolks, or ova, form in the chicken's ovaries. A fully formed ovum will leave the ovary and be deposited into the oviduct. This part of the chicken's reproductive system has five distinct sequential segments which the yolk passes through on its way to the outside world, but it's the fourth one — the shell gland — that affects the color of the egg. This is where the shell forms around the ovum.
這些顏色是怎么來的？這就要從雞蛋的形成過程說起了。母雞的卵巢里會首先孕育出蛋黃（也就是卵子）。成熟的卵子會離開卵巢來到輸卵管。在輸卵管中，卵子會按順序經過五個部分，然后才到達體外；其中第四個部分是卵殼腺，蛋殼就是在這里形成的，這個部分影響了雞蛋的顏色。

"The shell of all chicken eggs are made of calcium carbonate, a crystal that is white in color," says Fowler. "So all eggs are, at least at the start, white. Any that we then see that are other colors have had a pigment deposited on them as they were moving through the oviduct, after the white egg shell had been deposited. You can see this if you open up a brown egg and look at the inside of the shell, it'll be white."
福勒稱，“所有蛋殼都是由碳酸鈣組成的，碳酸鈣是一種白色晶體。所以所有雞蛋至少最初都是白色的。有色的蛋殼都是在經過輸卵管時被染了色。不信你可以敲開一個褐色的雞蛋，看看蛋殼內部的顏色，那一定是白色的。”

Two pigments are responsible for the spectrum of chicken egg color. Shades of greens and blues are caused by the pigment biliverdin, while protoporphyrin is responsible for reddish-brown hues.
決定雞蛋顏色的主要有兩種色素。膽綠素會讓雞蛋變成藍色或綠色，而原卟啉則會把雞蛋染成紅褐色。

The same egg-coloring process holds true for all birds with colorful eggs. American robin (Turdus migratorius) eggs, for instance, are famously blue. The pear-shaped eggs of a common murre (Uria aalge) can sport a blue hue, be speckled or feature brown streaks.
其它鳥類的蛋殼顏色也是一樣的道理。例如，眾所周知，美洲知更鳥下的蛋就是藍色的，而崖海鴉的梨形蛋不僅是藍色的，通常還帶有斑點或褐色條紋。

****小知識****

Should chicken eggs be kept refrigerated or at room temperature? It depends on whether you live in a country (Australia, Japan and the United States, for instance) that requires eggs produced for commercial sale be washed. This process protects against salmonella, but also removes a waxy shell coating that naturally defends eggs against microorganisms, thereby necessitating refrigeration.
雞蛋應該放冰箱里還是常溫儲存？這取決于你生活在哪個國家。澳大利亞、日本和美國等一些國家要求用于銷售的雞蛋必須經過清洗。清洗程序能夠清除沙門氏菌，但同時也洗去了蛋殼上防御微生物的蠟狀保護層，所以需要放冰箱里面。

至于咱們國內的雞蛋，因為不清洗外殼，所以常溫存放即可。

如果你在敲開雞蛋后看見有血絲或黑色褐色的小點，不用擔心，和蛋殼顏色一樣，這是輸卵管的“功勞”。“血斑”源自母雞卵巢或輸卵管的輕微出血。血液滲到卵黃上，被包裹到蛋中，就形成了“血斑蛋”。黑色褐色的斑點是母雞輸卵管脫落的上皮組織或其他異物，在形成蛋清的時候被包裹到雞蛋中而形成，俗稱“肉斑蛋”。

無論是紅蛋、白蛋、綠蛋、褐蛋、血斑蛋、肉斑蛋，只要是新鮮雞蛋，煮熟了都可以放心食用，營養價值也差不多。

來源：Howstuffworks、百度經驗、煎蛋網
編審：丹妮