What’s that you’re eating?
If you enroll in Amy Rowat's class, "Science and food: The physical and molecular origins of what we eat," at UCLA, you get to eat apple pie on the first day. Pretty soon, though, you have to do more than just enjoy pie: You have to ask how to achieve its texture and its flavor, and what will happen if you vary the water content in butter, the protein content in the flour, and other parameters. Next thing you know, you have to do experiments to answer your own questions. By the end of the term, you've participated in a pie bake-off and learned about such things as elasticity, diffusion, and viscosity.
When Rowat arrived at Mount Allison University in Sackville, New Brunswick, she didn't know what her major would be. But, she says, "Pretty quickly, I honed in on physics—largely because my undergraduate physics professor was great. He was really interactive and drew us into the subject in a way that made me think." And through undergraduate research projects, "I realized that science—and physics—was really creative, and that I really liked it." She ended up completing her major in honors physics, and doing a triple minor in math, Asian studies, and French.
Amy Rowat at her lab bench. CREDIT: Todd Cheney
One undergraduate project set the course for her future career. While making thin polymer films, she says, "I kept thinking, 'This would be so fascinating if these were actually living membranes.'" That obsession with biomembranes led her to Ole Mouritsen's lab at the University of Southern Denmark, where she did a PhD in biophysics. She then spent time as a postdoc at Harvard University before joining the faculty in the department of integrative biology and physiology at UCLA in 2011.
Rowat's research is mainly focused on understanding the mechanical properties of cells and nuclei. And it's not unusual for her to see links between her research and food preparation. "What is amazing to me," she says, "is that many of the same molecules that play an important role in physiology are also used and exploited in cuisine."
Over virtual coffee and pastries, Rowat chewed over her teaching and research with Physics Today.
PT: Tell how food and cooking entered the mix of your biophysics research program.
ROWAT: Along the way in my academic career in biophysics, I got increasingly involved with merging food into what I do on a daily basis—at least in teaching and education. It started when I was at Harvard. There was a professor who put on lectures for the holiday season, and he'd never done one on food. I thought this would be a great topic, so we put on a lecture on pizza, and then one on chocolate.
Around the same time, Ferran Adrià [a noted chef and practitioner of molecular gastronomy] came to speak at Harvard. Hundreds of people showed up. Obviously there was demand from the public to learn more about food and science. This was a perfect opportunity for a collaboration, so together with my colleagues at Harvard, we developed a class on science and cooking.
PT: What did you teach in that class?
ROWAT: We based the class around concepts in soft-matter physics that we thought would be important for students to know about cooking, and we included a few other topics that were important for cooking. For example, we taught about exponential growth to understand microbial populations and fermentation. We developed labs and integrated them to go along with the science concepts. The students were doing lab activities and eating the results. When I arrived at UCLA, I modified the class to focus more on biophysics.
PT: Say more about the concepts you want to convey in your science and food course.
ROWAT: Diffusion, elasticity, viscosity, binding affinity, freezing point depression. These are the types of concepts that I would teach in a biophysics course, but that are also important in understanding the foods we eat. The basic theme of the class is to link the macroscopic properties of foods and biological materials to their microscopic properties and molecular compositions.
For example, if you think of the physical properties of membranes, how are they different for creatures that live at great depths under the sea versus those of creatures that live at sea level? Creatures that live deep under the sea contain more unsaturated lipids, because these help to maintain the fluidity of membranes at higher pressures.
Or take molecules such as starches that are important energy stores for plants, such as wheat and corn. Those are really important thickening molecules in making gravies and sauces. And it's because they are such large molecules that they are so effective at increasing viscosity.
PT: How is your course structured?
ROWAT: Typically, each week consists of two science lectures, where I teach a concept and also highlight the role of that concept in food and physiology. The third lecture is by some guest lecture who comes and talks about practical applications of that concept.
For example, in teaching self-assembly, we talk about lipid membranes and then do a demo and the students make cheese. Then I had a cheese maker come and talk about his craft. From the guest lecturer, [the students] get the connections to food, the connections to real life, and how the processes they are learning about are really important in different ways.
Having studied the science of apple pie, Rowat's students make their own pies and compete in a bake-off. CREDIT: Patrick Tran.
PT: Why is cheese a good vehicle for learning about self-assembly?
ROWAT: The basic concept is that when you denature proteins in the milk by heating it up, they will now have hydrophobic and hydrophilic bits exposed. By minimizing the exposure of the hydrophobic parts of the water, all of the water molecules can maximize their entropy. That drives the denatured milk proteins to spontaneously assemble into aggregates. That assembly is in fact curd. Then you strain out the whey, and you have cheese.
PT: How do you teach the concept of elastic moduli?
ROWAT: That ties in with the texture of meat. The elastic modulus relates to the underlying structure of a protein network, which depends on the density of crosslinks between molecules. The example I give is to look at how different cuts of meat have different textures, depending where they come from in the animal. They have been subject to different amounts of mechanical load over the lifetime of the animal, and the animal responds by adjusting the density of collagen networks in its muscles.
For this topic, I brought in a chef to talk about the different ways he prepares different cuts of meat to optimize the texture. Chefs may not have thought about the crosslinking of molecules, but they know that different cuts of meat have different amounts of collagen. If a cut of meat has more collagen, it's better to cook it slowly for a longer time at a lower temperature to break down the collagen. The collagen degrades into small pieces, including gelatin, and that is important for perfecting the mouth feel and tenderness of meat.
PT: Do you have a food-grade lab?
ROWAT: That's a bit of a challenge, but luckily we have a newly renovated building where we can conduct the labs. And some of the lab exercises are portable enough that students can do them anywhere.
PT: What have you learned about food from pursuing this avenue of teaching?
ROWAT: A lot! One concrete example this year is about pie. For final projects, the students had to ask a scientific question about apple pie, and then do experiments and generate data about apple pie. Some students focused on the filling, and looked at the role of different thickening molecules. Others looked at the different types of fat in the crust, and devised a way to measure the force under which a piece of pie crust will break.
PT: What stands out in terms of physics and food?
ROWAT: One thing I realized is how much phase transitions play a role in baking pie.
PT: Describe your research.
ROWAT: In my lab, we work with different cell systems—including cancer cells and also plant cells. The nucleus is one of the largest organelles of cells, so it plays a major role in how deformable a cell is, or how a cell would respond to mechanical stress. Ultimately, all these things will have implications for gene expression and, fundamentally, how cells regulate their response to the environment.
We make measurements using microfabricated devices. Basically, we somehow deform or torture cells, and then measure the resulting deformations.
With one of our tools, that is already existing, we apply a pressure to force cells to deform through narrow, micron-scale pores. We count the number of cells that get through to the other side. This provides us with a relative measure of deformability. It's not very precise, but it is helpful if we need to look at large numbers of samples.
The other tool we are building is a tiny cell poker. You take a microfluidic channel and embed a force probe on one side and a sensor on the other. These are connected to teeny tiny parallel-plate capacitors, so we can drive displacements of the force probe by applying a voltage to the capacitor.
PT: So your existing tool gives you the deformability for a sample of cells, and with the new one you will be able to make measurements on individual cells?
ROWAT: Yes. We'll be able to look at both populations of cells and individual cells.
PT: Does your class on food feed back into your research?
ROWAT: Yes. The whole question about plant nuclei arose as I was developing curriculum on pressure. I was using plants as a system that relates to food and cooking to teach about pressure. In that context I began to wonder about the nuclei of plant cells.
Another example is that we found that a whipped cream canister—a pressurized nitrous oxide canister—can actually be really helpful for extracting nuclei from plant cells.
PT: What are the overarching goals in your research?
ROWAT: On a very basic level, we hope to learn more about the origins of the mechanical properties of cells. What are the physical origins and what are the different molecules that are involved in regulating these properties?
We are also addressing some more applied questions, such as, "Can we use these technologies for cancer prognosis?" There is increasing evidence that during the malignant transformation of cancer cells, they become softer, so can we use this mechanical phenotyping to look at a sample of tumor cells and predict what stage of disease they are at? There are also different mechanical responses when you treat tumors with drugs. So can we use this [mechanical phenotyping] as a complementary way to assay different treatment strategies? Those are much longer term potential applications, but they illustrate the sorts of things we are doing for both basic research and applications in health and disease.
PT: Did you know when you went to university that you would go into science?
ROWAT: Oh no, not at all. Although now, looking back, it does seem sort of obvious. I didn't have any of the stereotypical toys and games that kids play with when they are destined to be scientists—like I didn't have a chemistry set or a microscope. But I loved cooking, and building model houses, and experimenting in the kitchen—which in a way is like doing soft-matter physics experiments.
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