Of Chickens and Viruses

If you live in the US, you most likely have two egg-color options at your grocery store or farmers' market: white or brown. The color of these eggs doesn't affect flavor or nutritional content of the eggs - it just depends on the breed of chicken that layed them. However, if you have a Araucana, Dongxiang, or Lushi chicken (and if you do, you probably don't live in North America) they will probably lay blue eggs. A recent study in PLoS Genetics has shown that the reason for this is a retrovirus, EAV-HP, that has affected the chicken and turned it's eggs blue. But how can a virus affect eggs color?

The answer lies in how retroviruses work. Retroviruses use RNA as their genetic material (instead of DNA like we do). However, when the virus infects a host cell, it uses an enzyme called Reverse Transcriptase to translate it's RNA genome into DNA. This DNA is then inserted into the host cells' DNA genome, essentially tricking the host cell into using the information in the new DNA to make more retroviruses. The most famous retrovirus that affects humans is probably the Human Immunodeficiency Virus, shown in the image above (green) infecting a human lymphocyte (pink). Sometimes, when a retrovirus inserts a gene into the host DNA, it can change or affect the expression of genes around the insertion point. This is what happened with the blue egg-laying chickens.

In the case of EAV-HP, the virus inserted near a gene for a membrane transporter called SLCO1B3 and turned it on in the chicken uterus. This change allows the developing eggs to take up a bile pigment called biliverden from the chicken's body, turning the egg blue. Because this gene became part of the chicken's DNA, it is able to pass on the trait to it's offspring. Due to preferential breeding of Araucana, Dongxiang, or Lushi chickens that have this trait, most chickens of these breeds now lay blue eggs. The exact DNA sequences near theSLCO1B3 genes in these breeds is different, suggesting that the retrovirus caused the DNA changes that result in blue eggs in independent events in all three breeds. Both the blue pigment and the retrovirus involved are completely harmless to humans, so if you see a blue egg, don't hesitate to fry it up and enjoy!

(via BoingBoing)
(Image: Human Immunodeficiency Virus (HIV-I), a Creative Commons 2.0-licenses image from Microbe World's photostream)

Science of Beating Eggs

My friend Lynn tipped me off to a neat story on the NPR website about the science of beating eggs. Read it if you'd like to get some pro-tips (from a real chef!) on beating egg whites into a foam for use in a souffle (or other whipped-egg-white application, such as meringue).

The first trick is to separate your eggs (that is, separate the yolks from the whites) without letting any of the egg yolks contaminate your whites. This is important because, while the egg white is entirely made of protein, the yolk contains some fat. When you whip the egg whites, you denature some of the proteins, which unfold and expose some hydrophobic areas. These hydrophobic areas would rather stick to each other than to the surrounding water, so the proteins stick together, creating a sort of net that can surround air bubbles, creating a foam. This foam is what makes whipped egg whites fluffy. If you contaminate your whites with the fat from the egg yolks, the hydrophobic areas of the egg white proteins will interact with the fat from the yolks instead of each other, leaving you with no net of denatured protein in which to catch bubbles. No bubbles means no foam.

Another note: if you over-beat the egg whites, continuing to beat them after a proper foam has formed, the egg white proteins will coagulate completely, sticking together so strongly that they force out all of the liquid between them, leaving you with a clumpy, separated, egg white mess.

If you're more of a visual learner and are interested in learning this useful kitchen technique, check out this how-to slideshow from Serious Eats or this excellent segment on souffle from the ever-informative Alton Brown from Good Eats.

Related: The Science Behind Poaching an Egg

(Image: Soufflé, a Creative Commons Attribution 2.0 image from David_Turner's photostream)

Sous-Vide

From BoingBoing, a cool article about how to make yourself a DIY sous-vide waterbath for around $75. Normally, buying one of these puppies would cost a couple thousand.

Sous-vide is a method of cooking things in a water bath, sometimes called an immersion-circulator, in a plastic bag. It literally means "under-vacuum," a reference to the method of vacuum-sealing food in a plastic bag before cooking via this method. It's become quite trendy as of late, especially with the molecular gastronomy set.

In the above post, they point out one great use of the sous-vide method: cooking an egg. Previously on this blog, we've discussed protein denaturation, even specifically as it relates to eggs. That is, the way that proteins unfold when exposed to high heat or another denaturing environment. Egg proteins denature and coagulate at fairly low temperatures, much lower than the boiling point of water, for instance. By boiling or frying an egg, we transfer a lot of heat to the egg very quickly and rapidly denature and coagulate the proteins. By instead using sous-vide, you slowly bring the egg proteins to the point at which they denature and coagulate. The temperature does not exceed this point, so the egg attains a texture unlike that of eggs cooked using any other method. Of course, this takes much longer than frying an egg - cooking anything sous-vide takes longer since the difference in temperature between the food and the surrouding cooking medium is lower. I'm sure Ferran Adria would say it's worth the wait.

Peep-a-palooza 2010!

In honor of the upcoming Easter holiday, Food/Science offers a science-tastic and marshmallow-riffic celebration of Easter candy offerings!

First, let's start off with a handful of Peepy-links:

• Peep Research - science approved!
• Serious Eats' Street Vendor Peep Diorama
• Peep Microwave Disaster
• WaPo's Annual Peep Diorama Contest
• Peeps Krispies Treats (recipe)
• Peep Sushi (Peepshi)
• DIY Peeps 

Furthermore, here are some Easter recipes for all of your Easter cooking needs:

• Easter Egg Layer Cake
• Chipotle deviled eggs (for dyeing leftovers!)
• For a Polish Easter, you might like Easter Babka and kielbasa
• My favorite as a kid: Roast Leg of Lamb

 And, for those of you who love to dye eggs, did you know that all you need is white vinegar and food coloring? It's true - DIY Easter Egg Dye instructions to the rescue! You can also dye Easter eggs with Natural Egg Dyes that you can find at the grocery store. Vinegar is often used when dyeing eggs because it helps to achieve a deeper color. Egg shells are about 95% calcium carbonate. This mineral is dissolved by the acidic vinegar and water solution, removing the outer surface of the eggshell and allowing the dye to adhere to the egg. In fact, if you leave an egg in pure vinegar long enough, you can dissolve the entire eggshell, leaving you with a "naked egg".

Finally, if you still have room after your brunch, Easter meats, and tons of colored eggs, I will gift you with this recipe for the Ultimate Easter Sammitch:

The Peepernutter S'more Sandwich:

Materials:
1 hollow chocolate bunny
2-3 marshmallow Peeps
2 slices of white bread
peanut butter (or other nut butter)

Protocol:

1. Cut Peeps in half lengthwise and arrange in a single layer on one slice of bread.
2. Spread peanut butter on other slice of bread.
3. Chop or crush chocolate bunny into small chunks and sprinkle evenly over peanut butter. Gently press them into the peanut butter so they stick.
4. Assemble the sandwich by placing the peanut butter and chocolate topped bread over the Peep topped bread.
5. Heat in toaster oven, sandwich press, or George Foreman grill until bread is golden brown and peeps and chocolate are soft. Alternatively, you can melt a little butter in a nonstick skillet and heat the sandwich for 1-2 minutes per side (a la grilled cheese) for a similar result.
6. Enjoy your sugar rush!

Happy Easter!

The Science Behind Poaching an Egg

(via Tastespotting)

Poached eggs are delicious – at least I think so. I suspect that a number of other people do, as well, yet they remain relatively unpopular when compared to other methods of egg preparation. This may be because oftentimes the result of boiling an egg without its shell resembles Egg-drop soup more than Eggs Benedict.

Science to the rescue! Actually, poaching an egg is not that difficult, especially if you think a little bit about what’s going on inside your pot. With a little bit of know-how behind you, preparing perfect poached eggs, without space-hogging and expensive unitaskers, is no problem.

What’s going on when you cook an egg? The answer is all about proteins. Egg whites are made of proteins and water. Proteins themselves are large (macro) molecules that consist of long chains of smaller molecules called amino acids folded up into complex structures. When proteins are subjected to heat, they denature, that is, the chains unfold and lose their structure. This often causes the proteins to lose solubility (they can no longer be dissolved in liquid). In the case of ovalbumin, the main protein component of egg whites, this causes the egg white to solidify and look white and cooked. The key to perfect poached eggs is to have this happen as fast as possible when cooking the egg, before the egg white has a chance dissipate into the water in the pot.

How to do this? Well, it has been shown that ovalbumin is more easily denatured at acidic pH¹. This is the science behind why vinegar is often added to egg poaching water. This recipe outlines the basic approach I take. A simple experiment shows that adding 1 tsp. (4.9 mL) of white vinegar (5% acetic acid v/v) in 2 quarts of NYC tap water (1.9L) changes the pH from 6.75 to 3.43 at room temperature (25C) (Remember that pH 7 is neutral, lower pH is acidic, and higher pH is basic or alkaline). At a simmer (95C), the pH of tap water is changed from 6.84 to 3.87. This more acidic pH, combined with the heat of simmering water, rapidly denatures the ovalbumin in the egg whites, creating a coating of cooked egg that the interior of the egg is trapped in while cooking. This prevents the egg from falling apart and the result is a perfectly poached egg.

Poached Egg Protocol:

Materials: 1-4 fresh eggs (egg white proteins break down over time, resulting in a runnier white that spreads out more in the pot), 2qt or larger pot, small bowl, white vinegar, slotted spoon, paper towel

• Bring ~2qt. water to a low simmer (NOT a vigorous boil) and add 1 tsp. white vinegar.


• Crack one egg into a small bowl before sliding it into the simmering water so as not to break up the egg on it’s way into the water.


• Repeat for subsequent eggs, spacing eggs out from each other so that they heat quickly and evenly and don’t stick together.


• Cook eggs 2-3 minutes (or until desired done-ness level). Eggs will continue to cook as long as they are hot, so expect them to cook a little more after they have been removed from the pot.


• Evacuate eggs to a paper towel on a plate using a slotted spoon.


• Bon Appetit!

¹Koseki et al. Conformational Changes in Ovalbumin at Acid pH. J Biochem.1988; 103: 425-430