X-ray diffraction patterns reveal the orientation of fat crystals. The distribution and directionality of these crystal nanostructures (parallel to the shear field in C, randomly arranged in D) affects the flavor and texture of foods.

From butter in croissants to cocoa solids in chocolate, edible fats pack a flavor punch that delights like no other macronutrient we consume. Fats are the most energy dense macronutrients, providing more than twice as many kilocalories per gram as proteins or carbohydrates, which may be the reason we’ve developed a taste for them. Fats are an efficient method of fueling a surviving species, but what gives them their oh-so-delicious disposition?

The sensory characteristics of fatty foods come largely from the physical makeup of crystals that form within the nanoscale structure of fat molecules. As explained in a review paper by Alejandro Marangoni published in Soft Matter, fats are made up of fractal-like crystalline structures, which give rise to properties such as flavor, texture, meltability, and mouthfeel.

Fats are composites called triglycerides or triacylglycerides (TAGs) made up of one glycerol molecule and three fatty acid chains. The physical properties of these fatty acids and the positions they take on the glycerol molecule give rise to changes in the foods that contain them. For example, the length of fatty acid chains affects a fat’s melting point. Saturated or longer chain fatty acids, like those in milk fat or cocoa butter, will have higher melting points than triglycerides with mostly shorter or unsaturated fatty acid chains, such as olive oil. That’s why at your dinner table, the salad dressing is liquid, but the butter dish holds a solid stick.

Changes in flavor and texture of fats can also come down to which fatty acids sit where on the glycerol molecule. Milk fat contains short-chained butyric acid, which sits in the 3^rd position, while cocoa butter’s 2^nd position is populated almost exclusively by oleic acid.

Depending on how they are heated and cooled, triglycerides can crystallize into several forms. The resulting fractal-like crystalline structures give rise to flavor, texture, and meltability in foods like chocolate bars. Six different forms of crystal structure have been identified for cocoa butter. But only one form will turn out chocolate that tastes and feels good to eat.

The so-called Form V has a tuning fork structure to its crystals, which produces a melting range close to the temperature of the mouth. Chocolate manufacturers devote much effort to producing bars with this specific form of crystallization through the use of tempering, a process which heats and cools the chocolate to get a desired consistency.

If Form V crystals transform to Form VI, the chocolate will have a higher melting point and the cocoa butter will coat the inside of the mouth, leaving a waxy sensation. Form VI crystals can also bloom into  large, visible crystals, transforming a chocolate bar from a silky melt-in-your-mouth treat into a rough, white, waxy snack.

Marangoni and his collaborators have used x-ray diffraction at the National Synchrotron Light Source to categorize the many facets of fat crystals:

“At the mesoscale level (length scales within the micrometer range), we can witness a very diverse assortment of crystal habits – spherulites, needle-like crystals, microplatelets, disordered crystal aggregates, spherical crystal aggregates, fractal-like aggregates, and even some morphologies that defy proper description.

Despite the wide variety of crystal morphologies, they all share some common attributes: (1) the structures are awe-inspiringly beautiful when viewed under a polarized light microscope and (2) the crystalline mass in a network of these crystals is distributed in a fractal fashion.”

The discovery and characterization of these nanoplatelets adds to the knowledge upon which the food industry bases its design and engineering of food materials. Understanding how the physical chemistry of fats affects the way foods taste and feel could also potentially be useful when trying to curb the excessive consumption of fat-rich foods, writes Marangoni.

With close to 35% of the U.S. adult population and 20% of U.S. children identified as clinically obese, and the incidences of Type II diabetes and cardiovascular disease on the rise, the challenge for food engineers is to produce low-calorie foods containing fewer ‘bad fats’ while retaining many of the quality characteristics historically associated with a particular food.

Where I work, we slam together small things to break them into even smaller things until we have the smallest things possible. This is how we know what matter is made of. We gave names to the smallest things in matter like “up”, “down”, “strange”, “top”, and “bottom”. Each of those things can be either matter or not-matter and can have three types. We use the name of a different color, either red, green, or blue for each type. So we can make a red-up small thing and that red-up-thing can come together with a green-up-thing and a blue-down-thing. But those small things can never be alone. They can’t escape their groups. They are held together by a strong force.

The small things come in groups of two or of three. The groups of three have to have all three colors, like a red-up with a blue-up, and a green-down. The groups of two have to be matter with not-matter like a red-up and a not-red not-up. Sometimes the small things can change groups and new ones can come and go in pairs: a small matter thing and its small not-matter friend thing can pop out of space.

We are made of lots of groups of either up-things, up-things and down-things, or up-things, down-things, and down-things. That’s up, up, and down grouped together, or up, down, and down grouped together. These two little groups are at the heart of almost all the matter we see.

What we really like to do is make big groups of these small things and make them as hot as we can. Really hot. More than ten hundred hundred times hotter than the sun. We do this by slamming four hundred up, up, down, and up, down, down things together all at the same time. When we do this, they all become very hot and new small matter and not-matter things are made out of this thick hot stuff. The new small things are the same number of matter and not-matter. Light comes out of the thick hot stuff too and we can tell how hot the stuff is from the color of the light.

Usually, the little up and down things can’t escape their groups. The field that keeps them together is very strong. But when the thick hot stuff is hot enough, then the little up and down things escape from their groups and become free for a little time. Eventually the thick hot stuff grows and cools until the little things start to stick together again into groups. Those groups fly away until the thick hot stuff is gone. We catch the light and the little groups as they come from the thick hot stuff. By studying how they came out of the thick hot stuff, we learn what the thick hot stuff was like. We also learn about the strong force that holds the groups together.

We found that the thick hot stuff is so thick it makes all the little things move together, dragging on the faster ones, and pulling on the slower ones. It’s a lot like water but not like air. The thick hot stuff we make where I work is the same as what was in all of space one hundred, hundred, hundred, hundred, hundred years ago when time had just begun.

I think I have a cool job! Please tell the people with money to keep letting me do it and I’ll keep telling you about it and using what I know to help everyone as much as I can.

You can also check out Paul talking about his research at RHIC in this video, where he isn’t limited to just those thousand most common words.

Understanding change at the top of the world so we’ll know what is going to happen later

When we drive cars and warm our homes we give out bad stuff that ends up in the air. The bad stuff in the air makes our world warmer, which is not good. Every year there is more bad stuff in the air, and our world gets a little bit warmer. Some people pretend this is not happening, they are wrong.

The green things that live outside suck up the bad stuff in the air that we give out when we drive our cars and use it to grow bigger.  This is good because the green things are slowing down the warming of our world. When the green things die, tiny life forms in the ground eat them and return the bad stuff back to the air, this is normal.

Up near the top of the world it is really cold and lots of old dead green things have been stuck in ice in the ground for a very long time.  When the dead green things are stuck in ice the tiny life forms can’t eat them and the bad stuff is stuck where it can’t make the world hotter. When ice gets warmed up it starts to go away and when it does the tiny life forms in the ground can eat the old dead green things and give out the bad stuff that makes our world warmer. When the world gets warmer more ice goes away, more dead green stuff gets eaten and more bad stuff ends up in the air which makes the world get warmer, and so on. This could make the world get hotter very quickly, and we need to know more about it.

To help work out what might happen at the top of the world years from now we are trying to understand as much as we can about the way the ice goes away, the green things that grow outside and the tiny life forms that eat them.  When we know some more about this stuff we can put what we have learnt in a big thinking box (a bit like the one you are using to read this) and use it to tell us what will happen years from now.

Now, a team of scientists has peered into floating water bridges with high-energy x-rays using the Advanced Photon Source (APS) at Argonne National Laboratory. Their work, “Floating water bridges and the structure of water in an electric field,” was published recently in the Proceedings of the National Academy of Sciences. I spoke with Brookhaven National Laboratory chemist John Parise, who worked with the team at APS to explore this unexplained phenomenon. 

Infrared thermal images of the floating water bridge setup at the Advanced Photon Source at Argonne National Laboratory. The color scale goes from 24°C (dark purple) to 50°C (bright yellow). The four quadrants show the water bridges with different thicknesses and temperatures. The bottom left image shows a water bridge immediately before collapse, due to reduced voltage.

Q: For this experiment, you set up a floating water bridge and used the APS to shine a beam of x-rays through the water. What exactly were you looking for? 

A: We were looking specifically for alignments in the water molecules that were different from alignments of the molecules in liquid water. We’ve recently finished a study where we’d gathered some of the best data ever taken on liquid water, so we had those data to compare with directly. That’s one of the things this paper on floating water bridges does—it looks for small differences between liquid water and the water in this water bridge.

Q: What were you expecting to find?

A: We started out thinking, gosh, there’s got to be some structure in this. If it’s not collapsing under the influence of gravity, there must be some alignment of the molecules. When you fire a beam of high energy x-rays through it, you’ll get a diffuse ring of x-rays on the other side, and you can detect these using an x-ray sensitive detector. But you should see modulation of the intensity around the ring that tells you that instead of the water molecules being randomly oriented that there’s a predominant orientation. Theoretical calculations tell us that the alignment, if it exists, should be along the bridge direction.

Q: How did the APS help you test for that alignment?

A: One of the powerful things about high-energy x-ray scattering is that you can take a lot of images vertically across the floating bridge or horizontally along the bridge very rapidly. Synchrotron radiation is so bright that you can take large numbers of images while the bridge is still stable. Plus, you can image the temperature—so you can take images of the part of the bridge that’s hot, the part that’s cold, the skin, and that type of thing.

Q: So, what did you find?

A: As soon as we took our first shot, I said, “That looks awfully even. It just shouldn’t be like that.” The result is that there’s just no quantitative difference between the liquid water and the water in this floating bridge. I was very surprised.

It turns out that you need an awful lot of high voltage to align a significant number of water molecules, and that’s not happening with these water bridges. But we only know that now, after we’ve done the experiment.

The conclusion is that this water bridge must be stabilized by a very thin layer of water, and it’s basically surface tension holding it together—the surface tension across the top and bottom of that bridge.

Q: Did you think your findings were wrong?

A: Well yeah! But we did many, many tests and they all revealed the same thing. Of course, then we started to think that this was a sheath, that in fact the voltage was affecting only the molecules at the surface.

Q: What does this experiment and your research into the nature of water tell us?

A: Well, we wouldn’t be able to exist without water having the properties that it has. Life on Earth wouldn’t exist. And it’s all up to something as simple as the fact that water is a very peculiar sort of liquid, in many ways. These water bridges are a result of the geometry of the molecules and hydrogen bonding. It’s fascinating behavior and understanding the phenomenon at a deep level tells us something fundamental about liquid water.

One aim of our research is to look at things under extreme conditions and see whether extreme conditions can be used to manipulate those materials. Anything that tells you about how you can manipulate matter, especially liquid matter, and how you can direct it to go in this direction rather than that direction is potentially useful fundamental knowledge.

Q: What more do you hope to learn about floating water bridges?

The next thing to do is to look very carefully at the surface and try to use more surface-sensitive techniques. That would be potentially a great thing to look at with the National Synchrotron Light Source II at Brookhaven National Laboratory, which will have much finer beams than the APS. At APS and especially at NSLS-II, we can do some small angle x-ray scattering studies to see if there’s any organization in the skin.

Water is a quantum liquid, the universal solvent, and it is essential to biology. The arrangement of water molecules in electric fields and at charged surfaces has important implications in electrochemistry, mineralogy and biology.

And once we understand this phenomenon in water, the obvious thing is to move on to other solvents. You can form bridges with other materials that are quite different from water and have much lower surface tension–the most likely explanation of the water bridge stability at this stage–but they all seem to have one thing in common: hydrogen bonding.

Water’s many unusual properties depend on its unique molecular interactions, and its structure has long been a matter of debate. Understanding the “how” of the water bridge stability may allow us to manipulate liquids, including water, with electric fields.