Hi, my name is Mattina and I’m addicted to summer.
As much as I’d like to vent my annoyance at the now-necessary need for many layers of clothing and mittens I’m bound to lose at some point during my daily commute, this year I’m shifting my perspective. Summer was great, albeit full of work, but now it’s over. The bikinis have long since been pushed to the back of my dresser drawers and my general concern for semi-presentable painted toenails has been thrown out the frosty window. That’s totally okay though, because I have a killer boot collection and an awesome new ‘70s style fringed suede jacket. But there’s one thing that often gets dumped into the “summer only” category that I simply cannot, and will not, label as such: ice cream. We’ll get back to that later, so stay with me.
So yeah, it’s cold. But not that cold.
Here I am sitting in Chicago within my temperature-controlled apartment held at a constant 68 degrees Fahrenheit, bundled up like I’m being forced to withstand frigid conditions of the icy tundra. It’s almost embarrassing because in reality, I have no idea what cold is. No. Idea. But we humans, we’re pretty wimpy. Our bodies, while incredible at times, are actually quite limited in what they can physiologically endure when we consider the extreme range of conditions that other species have adapted to. Perhaps the most beautiful part of scientific research, and arguably the basis of every graduate student’s mid-science-life crisis, is the overwhelming opportunity given to us by nature: to study the diverse collection of organisms on this planet.
Ah, the beauty of comparative physiology.
Late Professor of zoophysiology, August Krogh, addressed the International Physiological Congress in 1929 with a talk titled “The Progress of Physiology”. In the midst of this, he stated:
“For a large number of problems, there will be some animal of choice or a few such animals in which it can be most conveniently studied.”
This concept suggests that researchers compare biological processes in the “ideal” organism (well-adapted to a specific challenge they may be interested in) to that in other animals in an attempt to reveal the biological basis for why certain species are able to succeed in extreme conditions while others cannot. Small and often subtle differences between animals’ biology often lead to great advantages (or disadvantages) in nature and common obstacles often have a variety of evolutionarily derived solutions. Simply put, if you’re interested in how animals can survive in the freezing cold, then you better take a close look at the physiology of species that naturally do and see what they’ve got that others (like me) don’t.
Notorious AFPs and why they are so damn COOL. (bad pun intended)
As stellar as it would be to bounce back from having icicle insides, and some amazing animals can do just this, it is not the route that every organism has evolved to take and would certainly pose a problem for species that live in sub-zero temperatures 365 days a year. Think Antarctica.
It all started when a man named Dr. Arthur DeVries began studying fishes from Polar regions around the ‘70s. These fish are an interesting group of species because the water they inhabit stays around 28.6 °F (-1.9 °C). Seriously cold. If you’re wondering how the oceans can still ebb and flow below the ever-memorized 32 °F (0 °C) freezing point of H2O, just remember we’re talking about the ocean. Salt water. The presence of salts in water depresses the freezing point such that it takes even colder temperatures to initiate the transition to ice. So what happens to the fish species that live in this frigid water? They don’t freeze!
Part of the reason for this phenomenon is that these fish have a lot of sodium (Na+) and chloride (Cl-) ions floating around in their blood. For marine fishes living at “comfortable” temperatures, the presence of NaCl in their blood is almost entirely responsible for the reduction in freezing temperature of their internal body fluids, but when we’re talking about the extremely low temperatures reached near the Earth’s poles, salt isn’t the only major player. Freezing temperature can also be reduced by a group of large glycoproteins (proteins with sugars attached) called antifreeze proteins (AFPs). Antarctic fishes, such as various species of the icefish, were the first animals found to have AFPs. These molecules exist in high concentrations in the blood of extreme-cold-enduring animals and are required for the survival of many species of fish that live in the icy waters of the High Antarctic Zone. They work by lowering their internal freezing point below that of seawater (that’s 28 °F!). More recent work looking at AFPs classifies the protein as a subset of a larger class of “ice-binding proteins” (IBPs). This emphasizes the variety of ways ice formation and growth can be inhibited and since their discovery, many different proteins have been identified across a range of species including insects and fungi. Scientists are continuing to work on describing the efficiency and mechanism of many of these proteins.
How do AFPs work their magic you ask? In general, their shape allows them to affect ice formation. Some are able to stick to ice crystals that are already beginning to form in a way that alters ice crystal shape and slowing or completely stopping the rate of ice growth. This phenomenon is called adsorption. Some prevent recrystallization of ice into large chunks, preserving small and less obstructive ice crystals. For Antarctic fish, AFPs cause thermal hysteresis (making the temperatures at which ice melts and that at which ice freezes different). Mind blown, right? This prevents the initial formation of any ice crystals which would otherwise be lethal to the animal.
Anyone in the mood for dessert?
In the mid-2000s, antifreeze proteins really started to get attention in the biotechnology, food, and biomedical industries. In the world of the frozen food aisle, a major concern for manufacturers is the damaging effects of ice formation which can break open delicate cells, losing important vitamins and minerals; an issue especially important for preservation of meats. On the biomedical side of things, there is risk involved in the thawing process of tissue or blood samples used in research or medicine. The recrystallization of ice may occur as the temperature changes, further deteriorating those delicate cells, ruining the integrity of their membranes. This leads to loss of intracellular water and compounds essential for their original function. In reducing the formation and size of ice crystals, you preserve the structure and contents of the cells keeping your hamburgers full of flavor and beneficial nutrients. And what is the best thing to follow a juicy hamburger? Ice cream!
So now we come back full circle.
Texture is especially important in the production of ice cream. We all know how much of a bummer it is to open a quart of our favorite flavor and find it covered with tiny ice crystals. It’s just never the same after that. Derivatives of the same types of AFPs found in Antarctic fishes have been incorporated into their recipes by many major ice cream companies like Breyer’s, Haagan Dazs, and Edy’s. Are your ice cream bars going to taste a little different now? If yes, don’t hate. Appreciate! Know that their presence is serving to inhibit recrystallization as well as control ice crystal size. This results in the manufacturing of an ice cream with the perfect hardness while also preserving the smooth, creamy deliciousness. Of course this is assuming that your pints of ice cream hang out next to your ice cube trays longer than 24 hours.
In my experience, this is rarely the case.
- Mattina M. Alonge received a M.S. in Biology from DePaul University under supervision of Dr. Jason Bystriansky where she explored expression of Na+/K+-ATPase isoforms in rainbow trout muscle during swimming challenges. She is currently working at University of Chicago Dept. of Medicine in a translational research lab while also finding time to practice yoga, put her figure skates on, look forward to summer flying trapeze classes, and read stacks of books supported by her membership in a hipster book club.