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 Addiction: Junk Food Edition

Everybody knows that we shouldn't eat so much processed junk food, and everybody also knows that's it's sometimes difficult to control your intake of these foods. However, I don't think that many people have thought about what goes on in your brain when you eat many more potato chips than you had planned to eat. In the NYT this week there  is a very interesting piece addressing just these issues and the research that has contributed to our current understanding of why humans love junk food.

For the past 50 years or so, a great deal of research has gone into what it is that humans like to eat and how to market it to them, beginning with military research into which MREs soldiers prefer and continuing to the modern day with research into how many pounds per square inch of pressure it takes to break the ideal potato chip and how to successfully market baby carrots as snack food. Most of this research has been done by large processed food companies with an eye to idealizing the taste of their snack foods so that people will eat more of them. By most accounts, they have been wildly successful - so successful that in the U.S. today one in three adults is obese and the rate of type II diabetes climbs  every year.

One interesting tidbit from the article is that research shows that, although we like strong or unique tasting foods for a short time, we quickly tire of them if we eat the same one over and over again. Over the long term, we will eat more of relatively bland but tasty foods (like white bread and potato chips). This is great news for the makers of salty, fatty, but unremarkable snack foods (I'm looking at you, Cheetos!) that we know so well.

There is a growing awareness that the types of foods, especially processed foods, that people eat contributes to (or detracts from) their health as much, if not more, than the quantity of that food. As I learned from this article, even people involved with marketing processed foods to the public are acknowledging that what we eat is part of the growing health crisis in our country.

Hopefully in the future we can put all of the research behind marketing and idealizing unhealthy food to work helping people to make better choices about what they eat. The more we understand about why people like certain foods, the more we can make healthy foods that people like to eat, or at least stop making and eating addictive foods that ultimately make us sick. The solution to the problem will have to be a combination of information that consumers can use to make better food choices and more responsible food manufacturing and marketing by the handful of companies that control the majority of processed food in America. Understanding what is going wrong now is the first step in the right direction.

(Image: Junk food, grocery store, Houston, TX, USA, a Creative Commons 2.0 licensed image from Cory Doctorow's Photostream via BoingBoing)

A New Kind of Cooking Class

I'd heard previously about the wildly successful "Kitchen Chemistry" class taught at MIT and how it combined chemistry and kitchen skills into a class about cooking that was based in science (and counted for a science credit). It turns out that this class might be part of a larger trend towards teaching the science behind what's happening in the kitchen. Classes are cropping up at other universities around the country, according to Chemical and Engineering News.

That's good news for several reasons. First, I think any topic that relates science to everyday life helps to engage students with science and results in more overall science literacy, which is important for a well-informed populace. Second, I think educating people about food and cooking helps to make them more enthusiastic and confident cooks. This in turn helps people that eat better, healthier food, increasing health and quality of life in our society. Lastly, it's great for me, since I'm pretty sure I can't think of  job I'd enjoy more than teaching such a class.

(via BoingBoing)

Quick Hit: The Future of Food @ Slate

Slate has an interesting set of articles up on their Future Tense blog about technology and food production. It includes discussions of robotics in small scale agriculture, the future possibilities of genetically engineered foods, large scale agriculture in the face of climate change, and more. If you're interested in high tech food packaging, nanoparticles, genetic engineering, and laboratory-grown meat (and who isn't?!), go check it out.

The Ongoing Quest for In Vitro Meat

For many years, people who think about these things have posited that lab grown meat could replace meat from animals as food, thus eliminating all of the animal cruelty and environmental issues associated with farming animals for meat. "Cultured meat" could be the choice of future carnivores.

However, making this meat is easier said than done. Growing muscle tissues in a laboratory setting is not an easy task, nor, it turns out, is it cheap. Right now, it requires many man hours and expensive supplies and equipment to grow mammalian cells in culture. Muscle cells, the kind that make up the animal meat we eat, also needs to be stretched or exercised in order to develop into tasty muscle. As an additional hurdle, many in vitro mammalian cell culture systems used by scientists use products made from farmed animals. If laboratory meat is going to be made in a way that does not harm animals, components like this are off the table.

Additionally, if people are to eat this in vitro meat, it would have to taste something like meat from animals, and would have to be comparably priced. That requires some advancements in the methods and technology currently used to grow tissue in culture. In an effort to promote innovation on this front, currently PETA (People for the Ethical Treatment of Animals) is offering one million dollars to anyone who can produce and affordable lab-grown replacement for chicken before June 30, 2012.

Recently, however, there has been some progress toward the production of cultured meat. Dutch scientists have created lab-grown meat from bovine stem cells harvested from a slaughterhouse. The "meat" consists individually grown sheets of muscle tissue, grown in culture using Velcro tabs to stretch the fibers so that they develop properly. Right now, the cost of a hypothetical burger made out of this meat, consisting of hundreds of thousands of sheets of muscle tissue, is estimated at $345,000. That's still a little steep for consumers, but the scientists say they plan to produce one as proof of principle within a year. Since the tissue is grown without a circulatory system, it lacks blood and is white in color, and it also lacks the associated fat of meat from an animal. Currently, the scientists say that improving the taste and color, possibly by adding laboratory-grown fat or blood, are goals that they are working towards.

Proponents say that this meat could replace or supplement modern factory farming as a more sustainable, cruelty-free meat product. However, challenges include making the meat palatable, ensuring that the product appears appetizing, and producing it at a cost where it can compete with farmed meat.

Until your laboratory-grown burger becomes available commercially, if you'd like an environmentally friendly, affordable, laboratory-grown protein, you'll have to be satisfied with mycoprotein (which, as an omnivore, I find quite tasty, even though it's not meat).

(via BoingBoing)

(Image: ...meat x 250, a Creative Commons Attribution 2.0 image from x ray delta one's photostream)

Probiotics - How Do They Work?

(Image: Yogurt Parfait, a Creative Commons Attribution (2.0) image from mrdestructicity's photostream) 

In the past couple years, there has been a lot of debate (and at least one lawsuit) regarding the effectiveness of yogurt and other foods and supplements that contain "probiotics," or beneficial microorganisms. Various studies have linked the consumption of probiotics to various health benefits, including treatment of gastoenteritis and diarrhea, lowering cholesterol, improving immune function, and reducing inflammation, among other claims. However, most of these studies studied one particular strain of bacteria, so results may not be applicable to all probiotics, and many studies involving humans show correlation with positive health outcomes, but not causation. To date, little is known with scientific certainty about the effectiveness of probiotics, and even less about how they function in the human body.

A recent study has evidence that probiotics may function by altering the expression of genes in your gut bacteria, thereby altering their metabolism of the foods that are present in your gut. After feeding mouse and human subjects probiotics, researchers at Washington University in St. Louis found that, although the composition of gut bacteria were not altered, gene expression of the gut bacteria of the mice were. The effects of the resulting metabolic changes could be observed in the mice's urine.

This study sheds some light on a previously mysterious process. It seems that probiotics may have a real effect on the human digestive system. Hopefully further studies will be able to further elucidate the mechanism of the changes brought about by these organisms and help us to understand which strains may be beneficial and for what purpose.

(via BoingBoing)

Food & Think

I recently discovered a really intelligent and interesting blog about food over at the Smithsonian Magazine website: Food & Think. It's the thinking person's food blog, full of information about the culture and history of food, with great tie-ins to current (non-food) events (see several posts relating to the recent hurricane situation in the Northeast). You should go check it out, right now!

Food Science @ TED

Many of you may be familiar with the TED (Technology Entertainment and Design) conference. It features talks about "ideas worth spreading," and these talks are available free from TED.com. Recently, a post at onlineclasses.org was brought to my attention that has collected many of these talks relating to food science, called 20 Great TED Talks for Total Foodies. Some of them are really interesting, including a talk that I featured earlier on this blog by William Li called "Eating to Starve Cancer." There are also talks by talented and famous food people, including Michael Pollan among others. Go check them out!

(Thanks to Jasmine for the tip!)

Cooking Meat: Thermodynamics and Biochemistry

Yesterday I attended Cooking For Geeks: Chemistry From the Kitchen, a talk given by Jeff Potter, at the New York Academy of Sciences. Mr. Potter is the author of Cooking for Geeks, a book about science and cooking. Although I haven't read it, I really enjoyed the talk, so I have every hope that the book will be just as funny and enlightening.

One topic addressed in the talk was the science behind cooking steak. As you may know, meat is mostly composed of muscle tissue from animals. In the case of steak, it's the muscle tissue of a cow. Here is a schematic of the type of muscle (skeletal muscle) that we most like to eat:

Schematic of skeletal muscle - what meat is made of!

As you can see, muscles are made up primarily of fibers made of two proteins called Actin and Myosin. Although opinions vary, most people prefer their steak to be cooked somewhere between rare and well done. In order to figure out why this is the case and what is it people enjoy about steak at the medium temperature (130-155F), we have to look at what is happening to this tissue at theses temperatures. Potter points out that at these temperatures, the Myosin in steaks has reached the temperature at which it denatures, or unfolds. Thea Actin, however, is a more thermostable protein and has not yet denatured. He concludes that, although this is just a correlation, it's too striking to be a coincidence. People, he believes, like the taste of denatured Mysoin and native (non-denatured) Actin.

Mmmm.... denatured Myosin.

However, as someone who is familiar with protein biochemistry, I have an alternative explanation. Could it be, instead, that people like the taste of meat that has been partially denatured because it affects the juiciness of the steak?

When proteins are in their native state, the long chain of amino acids that make up a protein cause it to fold up into a characteristic conformation. Some amino acids are hydrophillic (water-loving) and some are hydrophobic (water-hating). Like oil and water, these residues only get along with others of their kind. Generally, hydrophobic residues are folded into the inside of the protein, where they can interact with each other, while hydrophillic residues are on the outside of the protein, where they can interact with the surrounding liquid. When a protein denatures, this chain unfolds, exposing many hydrophobic residues. If there are other unfolded proteins around, the denatured proteins tend to stick together because their exposed hydrophobic residues interact with those on a neighboring protein. This often causes the proteins to become much less soluble, and they are no longer dissolved in solution, meaning that they no longer interact well with liquids.

If a steak is cooked so that some of the proteins are denatured, it becomes much less "chewy," partially because cells break down and proteins are denatured, allowing the muscle fibers to be more easily broken apart. However, if you cook a steak until it is "well done," people often complain that it is dry and tough. My hypothesis is that this dry, chewy texture occurs because the steak has reached a temperature where all of the proteins are denatured and are insoluble, so they can no longer hold on to moisture within the steak. This, combined with the fact that water evaporates faster at higher temperatures (and will convert to steam above 212F), results in massive moisture loss from the meat. A raw steak is too tough because the muscle is completely intact, but a steak that has been partially denatured (where, perhaps, Mysoin but not Actin proteins are denatured) is broken down somewhat, making it tender. Some of the proteins have been denatured, but there are still a sufficient number of native proteins to hold on to some moisture, resulting in a juicy piece of meat. At least, I think that's one good explanation. At this point, no one knows for sure - this hypothesis is fairly difficult to test, given the number of other variables. If one of my readers can think of a good experiment to test this, I'd love to hear about it in the comments!

What is the take home message of all of this? Don't under or over-cook your meat. Different meats (different cuts and species) have different forms and ratios of Actin and Myosin (and also different potential food borne pathogens) and need to be cooked differently. Chicken needs to be cooked to a higher temperature to be sure that there is no Salmonella contamination, but cooking it too long will also cause it to be dry for the same reason that overcooked steak is also dry - you have denatured all of the proteins and forced out all of the water from the meat.

For more interesting discussion of how to cook meat, also check out this timely post about frying Thanksgiving turkey (spoiler alert: don't do it!) from Food Lab.