Tag Archive for: biochemistry

Kent Kirshenbaum

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Dr. Kent Kirshenbaum received his PhD in Pharmaceutical Chemistry at UCSF, is an NSF Career Award recipient, and is currently a professor of Chemistry at NYU. His research focuses on the creation of new peptide-based macromolecules that can be used as research tools or therapeutic strategies. In 2012, he filed a patent for a foaming agent which acts as a vegan substitute for egg whites, making vegan meringues a delicious possibility.

See Kent Kirshenbaum March 8, 2016 at “The Impact of What We Eat: From Science & Technology, To Eating Local”

Kent Kirshenbaum

What hooked you on cooking?
Spending time with my mom got me hooked on cooking. She exemplified the “slow food” concept, and she’d take days to make a pasta sauce. I grew up in a drafty house in San Francisco that was cold all year around, and being near her at the stove was the warmest place to be. Once my wife and I had kids, I realized how satisfying it was for me to provide my family with sustenance through cooking and culture through cuisine.
My dad got me hooked on science. He studied metallurgy and worked for a mining company. He would go on business trips and bring me back samples of different minerals to play with. It was kind of like the situation described in the book “Uncle Tungsten” by Oliver Sachs.
The coolest example of science in your food?
Mayonnaise. You take two immiscible liquids – oil and water, and find a way to get them to mix. How do they do that?? Add an emulsifier, provide some energy and voila! It’s just a shame the product itself is so repugnant.
The food you find most fascinating?
Fermented butters. Such as smen, the fermented butter of North Africa and “bog butter” from the British Isles.
What scientific concept–food related or otherwise–do you find most fascinating?
I’m fascinated by the relationship between the sequence, structure and function of proteins.
In the kitchen, transglutaminase — also known as meat glue — is a compelling example of enzymology. Nixtamilization is an amazing concept, and the word “nixtamilization” itself is like a really short poem.
Your best example of a food that is better because of science?
Either Pop Rocks or the clean water that comes out of my home faucet. Although I’m not sure either of them really qualify as a foodstuff.
We love comparing the gluten in bread to a network of springs. Are there any analogies you like to use to explain difficult or counter-intuitive food science concepts?
When explaining specificity in the sensory perception of food, I use the “lock in key” analogy to describe how ligands engage protein receptors. Although the analogy is imperfect, it begins to get the idea across.
How does your scientific knowledge or training impact the way you cook? Do you conduct science experiments in the kitchen?
Because I am trained as a chemist, I am fastidious about following a published protocol (recipe) and I tend to be absurdly precise about volumes. I love experimenting with food – we filed a patent application on new way to make vegan meringues. But when it comes to cooking at home I tend to be a traditionalist.
One kitchen tool you could not live without?
My home water carbonation system. I love sparkling water that I can generate from the New York City public water supply and doesn’t need to be shipped from a European spring.
Five things most likely to be found in your fridge?
Harissa, capers, preserved sour cherries, home-made stock and parmesan cheese. I get anxious if my supply of Reggiano is running low.
Your all-time favorite ingredient? Favorite cookbook?
I’m a spice guy. Right now I’m fixated on sumac and cardamom. My favorite cookbooks is “Where Flavor Was Born” by Andreas Viestad which explores how spices are used across the region of the Indian Ocean. It inspired me to visit a cardamom plantation in Kerala, India.
Other favorites include “In Nonna’s Kitchen” and “Cucina Ebraica”, because these books connect me to the memories of my mother and her mother.
Your standard breakfast?
A cup of black coffee and a baked good that I enjoy on my walk from home to my lab. New Yorkers have a bad habit of walking and eating. On the weekends, bagels and smoked salmon. No doughnuts. Never a doughnut. Maybe a beignet. But only in New Orleans.

Cranberry

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Cranberries are harvested in late autumn, just in time to celebrate the holidays. Whether you prefer to enjoy cranberries in a jam, as a sauce from the can, juiced, dried, or fresh, there’s no denying that cranberries are festive. They’re tart, dark red, and pair really well with a turkey dinner (according to science). Read more

Meat: where physiology meets flavor

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A charcuterie board is the perfect accompaniment to any gathering and rivals a cheese plate as a crowd-pleaser. It’s low maintenance, delicious, and will almost certainly have a taste or texture to appeal to the pickiest of palates. Meat comes in an array of textures, fat content, and flavors, which vary species to species and even within the same animal. Flavor profiles of meat can vary wildly and subtleties between different cuts of meat can all be largely explained by chemistry.

meat

Photo credit: willmacdonald18 (Flickr)

What is meat exactly? Meat can loosely mean any type of edible tissue originating from an animal – including everything from chicken feet to cow tongue. The majority of meat we consume, however, is skeletal muscle tissue, comprising roughly 75% water, 20% protein, and 3% fat. While the function of muscle tissue—which is to generate movement—is simple, muscle tissue is a complex system of biochemical machinery.

Muscle tissue consists white and red fibers, which each generate contrasting types of movement. The major differences between the two types of muscle fibers are summarized in the table below.

red muscle fibers white muscle fibers
alternate names slow-twitch fibers fast-twitch fibers
relative size thin thick
movement type prolonged, deliberate short, high-powered bursts
fueled by fat + oxygen glycogen
Requires oxygen? absolutely yes, but can run anaerobically
taste/nutrtion fattier, more flavorful higher in protein, relatively bland
appearance dark/red white

The main distinction between these types of tissue is in their function and metabolic demands. Red muscle fibers are designed for endurance—think long distance running—or sustained motion. Red tissue runs on fat and oxygen and absolutely requires oxygen to function properly. Since red muscle tissue demands oxygen, it contains an abundance of a pigmented protein called myoglobin. Myoglobin binds and stores oxygen from the then passes it along to a fat-oxidizing cytochrome that generates ATP to fuel the cell. The more exercise a muscle receives, the higher its demand for oxygen, and the more myoglobin and cytochromes it will contain, leading to a darker appearance.

duck meat

Photo credit: Harlanh (Flickr) Duck breast – an example of dark meat

White muscle fibers, on the other hand, are specialized for more sporadic and brief energetic demands. These tissues use oxygen to burn glycogen, but can also produce energy anaerobically if needed. However, anaerobic metabolism results in the buildup of lactic acid and limits the endurance of these tissues, which is why they can only be used for short periods. White muscle fibers, unsurprisingly, are what comprise white meat—chicken breast, turkey breast, frog legs, and rabbit meat.

whitemeat

Photo credit: allthingschill (Flickr) Turkey breast

The link between structure, function, and taste can be used to answer the question of why chickens and turkeys have a combination of dark and white meat, but why ducks and geese are all dark meat. They’re all birds, after all, so it’s rather surprising that there’s such a drastic difference in their breast meat, until you consider their habits. Chickens and turkeys are relatively flightless birds. They stand, walk, or run, and use their legs to bear their weight. Their constantly used legs are mainly dark meat and their infrequently used breasts are composed of white meat. Duck and geese, however, are migratory birds whose flight patterns enlist the use of breast muscles to help them stay airborne for extended periods. To aid them in sustained flights, their chests muscles require increased stores of oxygen and myoglobin, making their breast meat dark, in stark contrast to a chicken or turkey’s breast.

The dichotomy of metabolic demands between red and white meat clearly impacts their physiology, but how does this translate into taste? The complexity of the biochemical equipment needed to store fat and oxygen and metabolize fat in red muscle tissue equates to a higher number of enzymes present in the cell that can break down and produce more flavorful compounds when cooked. A piece of dark or red meat is fattier, boasts richer and more complex flavors, and retains moisture far better than white meat.

How else can chemistry explain the different tastes of meat, ranging from the beefy flavors of cow to the gamey flavors of duck breast? It’s a common saying in the culinary world that where there’s fat, there’s flavor. While fat serves as storage for energy, it doubles as storage for flavor. With fat distributed throughout the meat, any fat-soluble flavor or aroma compounds can end up in them providing meat with its unique flavor profile. What winds up in the fat is heavily influenced by diet – cows taste “beefy” as a result of flavor compounds metabolized from grass and forage. Lamb and sheep’s distinctive flavors come from compounds produced by the liver, and the gamey flavors of duck meat are likely derived from intestinal microbes.

Examining meat through a scientific lens allows us to relate some common mantras of biology, chemistry, and cooking: structure and function go hand in hand, fat is where the flavor is, and you are (and you also taste like) what you eat. In the context of meat, physiology and flavor are intertwined and whether you’re a fan of dark or white meat, you can surely appreciate the fascinating connection between animal physiology and flavor.

References Cited:

  1. McGee, Harold. On food and cooking: the science and lore of the kitchen. New York: Simon & Schuster, 1997. Print.

Mai NguyenAbout the author: Mai Nguyen is an aspiring food scientist who received her B.S. in biochemistry from the University of Virginia. She hopes to soon escape the bench in pursuit of a more creative and fulfilling career.

Read more by Mai Nguyen

Food, Wine, and Biochemistry

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Photo Credit: Kirti Poddar (22598380@N07/Flickr)

Photo Credit: Kirti Poddar (22598380@N07/Flickr)

Wine and food pairing may seem like a refined art form, cultivated through trial and error to best suit the individual, but what if we told you there was also a science to it?

When it comes to wines, the word “tannin” is thrown around a lot. In broad terms, tannins are a type of flavonoid molecule, which reside in the bark, leaves, and unripe fruits of a wide variety of plants. The three major classes of tannins are hydrolyzable, condensed, and phlorotannins. Where wine is concerned, phlorotannins are nonexistent (only found in brown algae); hydrolyzable tannins leach from the oak barrel that wines have fermented and aged in; and condensed tannins come from the grapes [1]. While hydrolyzable tannins may be present in all wines, since winemaking traditions necessitate oak barrels, these offer little towards wine taste, mouthfeel, and color. Viniculture favors condensed tannins. Originating from the grape skins, seeds, and stems that go into winemaking, condensed tannins play a key role in wine-tasting.

Red wines are made using the entire wine grape, obtaining their color from anthocyanin, another type of flavonoid molecule found alongside tannins in grape skins. By contrast, white wines are produced from just the grape pulp. Since the tannin-containing parts of the grape do not go into white wine production, white wines are often lower in tannin levels and generally lack condensed tannins.

So how is all this discussion about tannins relevant in choosing which wine to serve alongside a steak dinner?

Tannins contribute to two wine-tasting characteristics: bitterness and astringency [1,3]. Anyone who has ever eaten an under-ripe grape has experienced an exaggerated sensation of astringency, as under-ripe grape skins contain high tannin concentrations. However, astringency should not be confused with bitterness or sourness; these tastes are perceived on the tongue through bitter and sour taste receptors. Conversely, astringency is a physical sensation, frequently described as a dryness or roughness on the tongue.

A sip of wine is just the beginning of the biochemical process behind astringency. Our saliva contains proteins that are able to organize water molecules about themselves, which increases saliva viscosity to above water viscosity, giving rise to “mouth lubrication” [2]. Tannins in wine readily bind to saliva proteins. This causes a snowball effect: tannin-bound proteins end up clumping together with other tannin-bound proteins, creating an aggregate [3]. This aggregate inevitably precipitates out of our saliva. With fewer free, unbound saliva proteins, there is a decrease in saliva viscosity, subsequently leading to a decrease in mouth lubrication [3]. In short, tannins physically dry out the tongue.

In this respect, high-tannic red wines pair well with high-protein foods. With more tannins binding to food proteins, saliva proteins are spared and the wine doesn’t feel as astringent in the mouth. Tried-and-true pairings include Cabernet Sauvignon with a rack of lamb, Pinot Noir with pork roast, and Chianti with grilled salmon.

Besides the protein interactions, tannins have also been shown to favorably bind to fats [4]. Fats are polar molecules by nature (they don’t like to interact with water). On the other hand, saliva is mostly water. By attaching to tannins, fats hinder tannins from mixing with saliva and binding to proteins. Essentially, fats wash the tannins away. For this reason, wine paired with cheese is a great treat, as is a gourmet burger with a glass of Zinfandel.

Armed with this knowledge, why not begin your own wine and food adventure? May we suggest a Cabernet with mac and cheese with spam?

Photo Credit: Jose Tagarao (lidocaineus/Flickr)

References cited

  1. Goode, Jamie. “Tannins in Wine.”Wine Anorak.
  2. Hatton M, et al. Lubrication and viscosity features of human saliva and commercially available saliva substitutes. Journal of Oral and Maxillofacial Surgery. June 1987;45(6):96-99.
  3. Cala O, et al. NMR and molecular modeling of wine tannins binding to saliva proteins: revisiting astringency from molecular and colloidal prospects. The FASEB Journal. November 2010;24(11):81-90.
  4. Furlan, A, et al. Red wine tannins fluidify and precipitate lipid liposomes and bicelles. A role for lipids in wine tasting? Langmuir. May 2014;30(19):18-26.

Alice PhungAbout the author: Alice Phung once had her sights set on an English degree, but eventually switched over to chemistry and hasn’t looked back since.

Read more by Alice Phung

A Matter of Taste: Full-Fat Versus Reduced-Fat Cheese

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Photo credit: Wikimedia Commons

Photo credit: Wikimedia Commons

Given the popularity of cheese and the seeming ubiquitous goal towards eating less fat, it is no surprise that reduced- and low-fat cheeses have great market potential. Though as many cheese companies have discovered, reducing the amount of fat for the sake of fewer calories sacrifices that rich, bold, creamy flavor of cheese. Fat is a major contributor to taste and mouthfeel of foods, and many cheeses are considered high-fat foods. But how exactly does fat content influence cheese taste and texture?

In cheesemaking, the process of converting milk to cheese alters the structure and composition of milk, essentially reducing it to a concentrated form of milk fat and casein, a major milk protein. Casein forms a protein matrix that traps fat and water, giving cheese that soft, moist texture we expect [1]. Full-fat cheeses typically have a casein-to-fat ratio of less than one, meaning there is a higher concentration of fat compared to casein in the cheese. Because fat is a nonpolar biomolecule, the greater fat content, locked within the casein network, gives rise to a predominantly nonpolar cheese matrix.

By definition, reduced-fat cheeses have at least 25% less fat than their full-fat counterparts and low-fat cheeses have 3g of fat or less per serving (21 Code of Federal Regulations [101.62b]), which is roughly around an 80% reduction or greater, depending on the type of cheese. To accomplish this, lower fat milks, such as skim milk, are used to produce the lower fat variants, which have a casein-to-fat ratio greater than one [1,2]. With less fat, the casein networks form a tighter matrix that gives rise to firmer cheese [1]. To replace the fats removed from the cheese matrix and to soften the texture, water is typically added back into the cheeses [2]. Water is a polar molecule, so by increasing the moisture this way, the cheese matrices of reduced- and low-fat cheeses are more polar, unlike the nonpolar matrices of the full-fat cheeses.

Comparing the casein-to-fat ratios of different cheeses gives insight into more than simply cheese composition—the ratios signify how we taste the cheese. When a piece of cheese is ingested, it increases in temperature in our mouth and dissolves with saliva, transforming from a semisolid to a liquid. In addition to textural changes, aromatic flavor compounds are also released during this phase change [3]. The rate at which these compounds are released is determined by their partition coefficient, which is the concentration of the aromatic compound in its gas form compared to its concentration in its liquid form [3]. Whether the flavor compound is in a polar versus a nonpolar matrix can influence the partition coefficient, altering the timing of their release and ultimately, our sensory perception of the flavor [3]. Many flavor compounds found in cheeses happen to be fat-soluble, meaning they can mix with other nonpolar substances without separating into two layers. Considering that lower fat cheeses have prevalently polar matrices, the way the flavor compounds interact with the cheese matrices differs significantly enough to change flavor-release patterns. This is what causes some reduced- and low-fat cheeses to taste “off” compared to full-fat cheeses.

Fat reduction also modifies the cheese biochemistry. Through analysis of full-fat cheese versus 75% reduced-fat cheese, it was found that different sets of flavor compounds are critical for the cheesy flavor of the two types of cheese [3]. When certain flavor compounds characteristic of full-fat aged cheddar were added to reduced-fat young cheddar, tasters scored the two cheeses similarly [3]. So take heart, cheese-lovers. Reduced-fat cheeses certainly do have the potential to be healthy and delicious.

References Cited

  1. Banks, J. M. (2004). The Technology of Low-Fat Cheese Manufacture. International Journal of Dairy Technology, 57(4), 199-207. doi:10.1111/j.1471-0307.2004.00136.x
  2. Impact of Fat Reduction on Flavor and Flavor Chemistry of Cheddar Cheeses. (2010). Journal of Dairy Science, 93(11), 5069-5081. doi:10.3168/jds.2010-3346
  3. Kim, M. K., Drake, S. L., & Drake, M. A. (2011). Evaluation of Key Flavor Compounds in Reduced- and Full-Fat Cheddar Cheeses Using Sensory Studies on Model Systems. Journal of Sensory Studies, 26(4), 278-290. doi:10.1111/j.1745-459X.2011.00343.x

Alice PhungAbout the author: Alice Phung once had her sights set on an English degree, but eventually switched over to chemistry and hasn’t looked back since.

Read more by Alice Phung

Prehistoric Cheese & Acid Whey

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prehistoriccheese

Biochemists discover the remains of prehistoric cheese, while Modern Farmer looks at Chobani’s acid whey problem. Read more

Thanksgiving, Turkeys, and Tryptophan

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Photo credit: Tim Sackton (timsackton/Flickr)

Photo credit: Tim Sackton (timsackton/Flickr)

Turkey is the star of the most famous dinner of the year; it is also the victim of a myth that persists every holiday season. At the end of Thanksgiving dinner, there’s a good chance that someone will mention that a molecule called tryptophan is the culprit for the post-feast drowsiness. The science seems sound enough. Turkey contains tryptophan, which is a precursor for serotonin, a neurotransmitter. In turn, serotonin produces melatonin, a hormone that helps regulate sleep. This myth perpetuates, like many others, because it is based on a huge oversimplification of the truth.

On the most fundamental level, tryptophan is an essential amino acid required to make many different proteins in the body. Our bodies can’t produce tryptophan, so we have to get it from the foods we eat. Considering amino acids are used to make proteins, we get them by consuming other proteins such as meats, poultry, eggs, dairy, rice, and beans.

Chemically, tryptophan is the same whether it’s in a test tube or in our bloodstream, meaning there’s really nothing special about the tryptophan found in turkey versus other protein sources, like chicken. Turkey actually contains less tryptophan per gram than chicken, and half as much as in soybeans [1], but would anyone ever blame a tryptophan-induced food coma on a Thanksgiving chicken or tofurkey?

Tryptophan can directly cause drowsiness—if taken in pill form on an empty stomach [2]. Before tryptophan can be converted to serotonin, it must first cross the blood-brain barrier to enter the brain. This would be simple enough if tryptophan was the only amino acid capable of crossing the blood-brain barrier. However, after a meal―especially a high-protein meal like a turkey dinner―there will be many different amino acids floating around the bloodstream, many of which can also enter the brain. Despite this barrage at the gates, the brain can only take up a limited amount of amino acids. As tryptophan makes up only a small fraction of all the amino acids we consume, the other amino acids directly compete with tryptophan to cross the blood-brain barrier, ultimately decreasing tryptophan’s chances of entering the brain. Even if you stuffed yourself on nothing but tofurkey, only small amounts of tryptophan would ever enter the brain to make you sleepy.

The culprits behind the Thanksgiving dinner food coma are thus largely the high-carbohydrate dishes (and alcoholic beverages) surrounding the turkey: potatoes, yams, pies, bread, and stuffing. Eating carbohydrate-rich meals stimulates the production and release of insulin into the bloodstream [3]. Insulin then signals the uptake of amino acids into the muscles. Unlike most amino acids, tryptophan has a rather large and bulky structure that prevents it from entering muscles, so it is left behind in the bloodstream. With fewer of the other amino acids in the blood, tryptophan has less competition and is more likely to cross the blood-brain barrier, where it can be converted into serotonin and melatonin, the brain chemicals attributed to happiness and sleepiness [4].

At this point you might be thinking, “So turkey does make you sleepy! It just needs help from carbs!” Yes, but on that level, Thanksgiving dinner wouldn’t be any different from, say, a bacon and biscuits binge, or any other high-protein, high-carb meal.

And some of you might still adamantly insist, “I even eat turkey outside of Thanksgiving, and I still get super sleepy! It must be the turkey!” But remember: the sugar pill works for a reason. Never underestimate the power of the mind.

Still, don’t let any of this stop you from enjoying this holiday and stuffing your face to your heart’s content.


References Cited

  1. Foods Highest in Tryptophan. Nutrition Data.
  2. Hartmann E (1982). “Effects of L-tryptophan on sleepiness and on sleep”. Journal of Psychiatric Research 17 (2): 107–13.
  3. Wurtman RJ, Wurtman JJ, Regan MM, McDermott JM, Tsay RH, Breu JJ (2003). “Effects of normal meals rich in carbohydrates or proteins on plasma tryptophan and tyrosine ratios”. Am. J. Clin. Nutr. 77 (1): 128–32.
  4. Lyons PM, Truswell AS (1988). “Serotonin precursor influenced by type of carbohydrate meal in healthy adults”. Am. J. Clin. Nutr. 47 (3): 433–9.

Alice PhungAbout the author: Alice Phung once had her sights set on an English degree, but eventually switched over to chemistry and hasn’t looked back since.

Read more by Alice Phung

Jeff Potter

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A science and food geek, Jeff Potter is the author of Cooking for Geeks: Real Science, Great Hacks, and Good Food, which the Washington Post called “one of the most useful books on understanding cooking.” He can be seen on TV engineering the world’s largest donut and is currently obsessed with the science of beverages. Check out more of Jeff’s food geekery at www.jeffpotter.org.

photo by John Zich, courtesy of www.zrimages.comwww.jeffpotter.org

photo by John Zich, courtesy of www.zrimages.com | www.jeffpotter.org

What hooked you on cooking? On science?
I find it intensely gratifying to understand how things are made, and science really is about understanding how systems work and behave. Everyone eats, and almost everyone cooks, and the science behind both fascinates me. Plus, every time one steps foot into a kitchen, it’s inherently a science experiment, even if you don’t think about it that way. The amount of science that goes into the morning cup of coffee alone would shock most people. Plus knowing some science behind what you’re doing in the kitchen is one of the best instructors.
Five things most likely to be found in your fridge?
Eggs, yogurt, kale, hot sauce, beans.
One kitchen tool you could not live without?
A good sauté pan. Even a non-stick one. Really, you can get by without much at all, but one decent pan changes everything.
Favorite cookbook?
I was given a dessert cookbook years ago that was an anthology of sorts: one recipe from each of the top pastry chefs in the country. No pictures, not glossy, just a few lines on the chef and then the recipe. Every single recipe I made from that book came out amazing, and every single recipe managed to teach a new concept or idea. I don’t know if it’d stand up very well against all the food porn books that have now come out, but that book (given to me by a chef friend) was amazing for me.
The scientific concept—food related or otherwise—you find most fascinating?
That only a few basic building blocks—hydrogen, carbon, oxygen, nitrogen, and ok, fine, sulfur—are responsible for everything from bars of chocolate to a toucan flying around a rainforest in South America. The difference in complexity just one level up (molecules) from what seems so simple (atoms) is staggering; and then to consider that there are multiple layers up above that until we get to your brain understanding these words… mind-blowing.
The coolest example of science in your food?
You can tell where a tomato was grown—well, at least the latitude—by the ratio of various isotopes in it. It sounds crazy, but rainwater is not “pure” H2O; or more precisely, there are different isotopes of the “O” in “H2O” and the lighter one, 16O, is more likely to evaporate then the heavier one (takes less energy for it to take off). As you go toward the equator, evaporation rates in rainfall go up (it’s warmer, after all), so tomatoes grown toward the equator have higher concentrations of the heavier isotope 18O. The neat thing is that that ratio sticks with the food all the way down to the jar of fancy imported Italian pasta sauce, so you can semi-reliably tell where in Italy the tomatoes were grown if you look at enough of the various isotopes and minerals in it.
Your all-time favorite food ingredient?
I don’t really have a favorite food ingredient, but nothing beats fresh fruit at the peak of its season.
The food you find most fascinating?
Can I go with “beverages” as a general category? Everything from green tea to beer is amazingly complicated. Most food ingredients—apples to flour—are relatively unchanged from their “as-grown” state, but drinks are an entirely different category, as they’re entirely constructed.
Are there any analogies you like to use to explain difficult or counter-intuitive food science concepts?
Breaking of secondary and tertiary bonds in protein denaturation can be a bit confusing, as the “simple” model people have for molecules is that they’re made up of such-and-such atoms, without regard to the shape that the molecule takes impacts how it functions. I’ll sometimes describe the molecule as like an old-fashioned telephone cord (did I just date myself?), where the cord can twist up, kink, and tangle on itself.
Your best example of a food that is better because of science?
The egg. The amount of agricultural science and gains in productivity that have gone into chicken eggs in the past 100 years is just amazing. If the same “gains” had been made in humans, Olympic sprinters would be running at 65 miles per hour…
Your standard breakfast?
Depends on the time of year and where I am. Right now, in New England’s winter, yogurt with muesli, and then sautéed red onion, kale, garlic, two eggs, and a squeeze of lemon juice on top. If I feel like spending more than the two minutes it takes to make it, maybe some grated cheese on top.
How does your scientific knowledge or training impact the way you cook? Do you conduct science experiments in the kitchen?
I only cook on an amateur level, for myself and my friends; so for me cooking is a very ad-hoc thing, without too much fuss or worry about taking good, exact notes—but this is only because, generally speaking, I don’t need reproducibility of an entire dish! But I do perform little mini-experiments each time I cook. Take tonight (it’s after dinner as I write this)—I’ve been wondering why the tofu I’ve been cooking keeps sticking to the pan. It’s a stainless steel pan, and I put some oil in it—but it always seems to stick after it gets up above a certain temperature. I’m guessing it’s steam from the tofu pushing the oil away from the surface of the pan; and then the proteins in the tofu stick to the pan (and do not seem to release even when browned). I’ll probably kick myself later for writing this, as I’m guessing the “why” is simple here, but I was wondering if low heat versus high heat makes a difference… so I tried changing just that. Nope; still sticks. That’s the type of “mini” experimentation I love to encourage in the kitchen, because it doesn’t take any extra work to do it, beyond thinking about it.

Homemade Butter

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ButterBigger

Despite the misconception among certain pop culture icons that butter is a carb, butter, like other fats and oils, is a lipid. Broadly defined, lipids are any molecules that have hydrophobic, or water repelling, characteristics.  In contrast to simple molecules like water (H20) or sugar (C6H12O6), butter does not have one molecular formula; rather, it is a mixture of triglycerides. Here is what a triglyceride looks like [1]:

triglyceride

Triglycerides are molecules made of three fatty acids bound to glycerol, a sugar alcohol. Fatty acids are long hydrophobic chains of hydrogen and carbons that repel water. Triglycerides do not have to be the same three fatty acids, but can be mixed and matched. For example in butter, oleic acid (32%), myristic acid (20%), palmitic acid (15%) and searic acid (15%) make up the greatest percentage of the fatty acids [2].

buttercontent

In addition to all these lipids, surprisingly, butter contains water. While oil and water don’t normally mix, in butter, tiny microscopic water droplets are dispersed within the fat.  This is commonly known as a water-in-oil emulsion. An emulsion is any mixture of two liquids that don’t usually mix. The opposite of a water-in-oil emulsion would be an oil-in-water emulsion in which oil droplets are entrapped within water.

To understand the secret of how butter can be made of two immiscible liquids, we need to delve back into the molecular structure.  Butter is made from the cream, which has a higher fat content (15-25%) than milk (5 – 10%) [3].  In milk and cream, which are oil-in-water emulsions, the fatty triglycerides stay suspended in liquid because they are encapsulated in tiny fatty spheres or globules. Each globule is surrounded by a nanoscopically thin layer of phospolipids and stabilizing proteins. Phospholipds have hydrophobic lipid tails that love to repel water; they also have hydrophilic, or water loving, heads that contain a phosphate group (thus the name, phospho-lipid). Here is a picture of a phospholipid [1]:

phospholipid

The phospholipids organize themselves in a thin layer so that the water repelling hydrophobic portions are aligned with the fatty acid chains while the water loving hydrophilic heads interact with the milk liquid.  This allows the fats to remain dissolved in the milk and float around like little water balloons.

Milk Fat globule. (A) Diagram of the phosopholipid layer surrounding a fat globule [3]. (B) Cryo-electron microscopy image of a fat globule [4]. The scale bars are 0.1 μm.

Now, that we have talked about the structure of butter, how to get from cream to butter?  (Remember: milk and cream are oil-in-water emulsions and butter is a water-in-oil emulsion.) The oil-in-water emulsion of the cream is reversed into a water-in-oil emulsion in butter. During the churning or mixing process of butter making, the fatty globules in the cream break open to release the entrapped fat molecules. The hydrophobic fat molecules clump together and mix to form larger fat globules that coalesce into larger solid fat droplets. This processes pushes out the liquid portion and the solid portion becomes the butter.  Since these types of fat molecules typically melt at temperatures of 30 to 41°C (86 to 106°F), this means that at cool temperatures below approximately 39°F (4°C), the remaining liquid gets trapped within the solid fat matrix and is unable to separate out of the butter [5].

milktobutter

Below is a recipe for making your own homemade butter. You don’t need fancy equipment or churners like your ancestors used; a well-sealed glass jar works wonders.  The shear forces generated by rigorous shaking are sufficient to convert your cream into butter.

Ingredients

Heavy whipping cream (6 cups makes about 1lb of butter)
Salt, to taste
Jar with lid, any size

Procedure

1. Fill the jar about ¾ of the way to the top with the heavy whipping cream and close the lid.

2. Shake the jar for about 4-5 minutes until the cream begins to thicken. Shake longer if you wish for a thicker consistency.

The shaking motion breaks down the fat globules. The membranes surrounding each fat globule break, releasing the hydrophobic triglycerides. The triglycerides clump together and push away the hydrophilic liquid, the buttermilk.

3. Drain off the buttermilk and place butter in a small bowl. Knead the butter under cold running water to remove any remaining buttermilk.

4. Salt to taste. Form butter into a ball or log. Serve immediately or refrigerate.

Recipe Adapted From:

Online Resources

  1. General Chemistry Online: What is the chemical structure of butter?
  2. “Overview of the Buttermaking Process” from University of Guelph

References Cited

  1. K562. Overweight & obesity. http://www.indiana.edu/~k562/ob.html
  2. Fatty acids in butter. Percentage composition from Practical Physiological Chemistry, P. B. Hawk, O. Bergeim, Blakiston:Philadelphia, 1943.
  3. Gallier, S. et al. 2012. Structural changes of bovine milk fat globules during in vitro digestion. J Dairy Sci. 95(7): 3579- 3592.
  4. Robenek, H. et al 2006. Butyrophilin controls milk fat globule secretion. PNAS. 103 (27): 10385-10390.
  5. Butter: Some Technology and Chemistry. http://drinc.ucdavis.edu/dfoods1_new.htm

Vince ReyesAbout the author: Vince C Reyes earned his Ph.D. in Civil Engineering at UCLA. Vince loves to explore the deliciousness of all things edible.

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