Titanium Dioxide in Food

Video & guest post by Carolyn Meyers & Edgar Rodriguez

Titanium dioxide isn’t something we usually request as a donut topping from the local bakery. However, most of the sweets we eat on a daily basis contain this chemical.

What is titanium dioxide?

Titanium dioxide has a solid tetragonal crystalline structure and is derived from three main natural minerals: rulite, anatase, and brookite.


Photo credit: Dambournet, D., Belharouak, I., Amine, K. Chem Mat, 2009, 22, 1173-1179.

Where does titanium dioxide come from?

U.S. Companies, such as DuPont, Cristal Global, Louisiana Pigment Co. L.P., and Tronox Ltd. process the mineral into a white powder, which has a refractive index of 2.5837, making it ideal for use as a filler or pigment that adds opacity to things like sunblock, shampoo, chewing gum, chocolate, and powdered donuts. Production of pure titanium dioxide is achieved through a method called the chloride process, wherein the raw minerals are first reduced with carbon and then oxidized with chlorine. Liquid titanium chloride (TiCl4) is then distilled and converted back into titanium dioxide by heating it to high temperatures in a pure oxygen flame.


Photo credit: GreenMedInfo

Titanium dioxide nanoparticles (TiO2) are widely used as a food additive and are consumed by millions of consumers on a daily basis, as manufactures incorporate it into their food products. TiO2 nanoparticles are used as an additive mainly to prevent UV light from penetrating the food, effectively increasing the shelf life. It is also used as a color enhancer to make foods appear white by enhancing the opacity.

How much TiO2 is in your food?

Many popular consumer products such as candies, gum, and baked goods contain 0.01 to 1 mg Ti per serving. The products with the highest titanium contents are sweets or candies [1]. For example, powdered donuts can contain up to 100 mg Ti per serving.


The amount of titanium found in certain popular consumer products. [1]

What are the health effects of ingesting titanium dioxide?

Titanium dioxide is marketed by DuPont as an inert chemical, meaning it shouldn’t react with other chemicals. Given the fact that powdered donuts include 100 mg per serving of titanium dioxide and the lethal dosage, measured as the LD50 or the amount needed for 50% of the population to perish from consuming the chemical, was measured in rats to be 5,000 mg/kg, A 200 lb human (90.7kg) would need to eat 4,535 powdered donuts and have a 50% chance of survival. (5000)X90.7= 453500 mg. Although it is impossible for a human to consume this many donuts at once, Dunkin Donuts recently stopped using titanium dioxide in their powdered sugar donuts after being pressured by the public to do so.

There have been numerous scientific studies done on how titanium dioxide affects the health. Many of these studies are performed using animal models, such as mice. Both positive and negative health effects have been found. One possibly positive health effect of ingesting titanium dioxide is a substantial increase in the levels of dopamine, the happiness hormone [2]. Negative health effects due to the ingestion of TiO2 nanoparticles include damage to the liver, kidneys, testes, brain and heart of mice and rats, as described below [3,4,5]:

  • Mice given doses as low as 50 mg/kg body weight experience hepatic damage in the form of: hepatic cell death, increased levels of reactive oxygen species, and altered antioxidant activity, as well as kidney damage [2,3,6].


    Photo credit: BabyMed

  • Oral exposure to Ti nanoparticles have been shown to produce significant negative effects in the brain such as major degenerative changes in the visual cotex and inflammation in the hippocampus [2, 7, 8, 9].


    Photo credit: UCSF News Center

  • Titanium dioxide particles have been shown to cross the blood-testis barrier in mammals, leading to reproductive toxicity in males, including a decrease in sperm motility percentage, sperm cell concentration, sperm viability and serum testosterone level, as well as a significant increase in sperm abnormalities [7, 10].


    Photo credit: WiseGeek

  • In humans, clinical research shows that patients with ulcerative colitis, a chronic inflammatory disease of the large intestine, have elevated levels of titanium in the blood and an accumulation of the chemical in the spleen [11].


    Photo credit: Turmeric for Health

Given this information, it remains the consumers’ responsibility, as always, to make an informed decision on the foods they eat and follow rules of moderation in everyday life.

References cited

  1. Weir, Alex, Paul Westerhoff, Lars Fabricius, Kiril Hristovski, and Natalie Von Goetz. “Titanium Dioxide Nanoparticles in Food and Personal Care Products.” Environmental Science & Technology Environ. Sci. Technol. 46.4 (2012): 2242-250. Web.
  2. Shrivastava R, Raza S, Yadav A, Kushwaha P, Flora SJS (2014) Effects of sub-acute exposure to TiO2, ZnO and Al2O3 nanopar- ticles on oxidative stress and histological changes in mouse liver and brain. Drug Chem Toxicol 37(3):336–347. doi:10.3109/ 01480545.2013.866134
  3. El-Sharkawy NI, Hamza SM, Abou-Zeid EH (2010) Toxic impact of titanium dioxide (TiO2) in male albino rats with special refer- ence to its effect on reproductive system. J Am Sci 6(11):865–872
  4. WangJ,ZhouG,ChenC,YuH,WangT,MaY,JiaG,GaoY,Li B, Sun J, Li Y, Jiao F, Zhao Y, Chai Z (2007) Acute toxicity and biodistribution of different sized titanium dioxide particles in mice after oral administration. Toxicol Lett 168(2):176–185. doi:10. 1016/j.toxlet.2006.12.001
  5. BuQ,YanG,DengP,PengF,LinH,XuY,CaoZ,ZhouT,XueA, Wang Y, Cen X, Zhao YL (2010) NMR-based metabonomic study of the sub-acute toxicity of titanium dioxide nanoparticles in rats after oral administration. Nanotechnol 21(12):125105. doi:10. 1088/0957-4484/21/12/125105
  6. Vasantharaja D, Ramalingam V, Aadinaath Reddy G (2015) Oral toxic exposure of titanium dioxide nanoparticles on serum bio- chemical changes in adult male Wistar rats. Nanomedicine J 2(1):46–53
  7. Elbastawisy YM, Saied HA (2013) Effects of exposure to titanium dioxide nanoparticles on albino rat visual cortex Belectron micro- scopic study. J Am Sci 9(5):432–439
  8. ZeY,ShengL,ZhaoX,HongJ,ZeX,YuX,PanX,LinA,Zhao Y, Zhang C, Zhou Q, Wang L, Hong F (induced hippocampal neuroinflammation in mice. PLoS ONE 9(3), e92230. doi:10.1371/journal.pone.0092230
  9. Mohammadipour A, Hosseini M, Fazel A, Haghir H, Rafatpanah H, Pourganji M, Ebrahimzadeh Bideskan A (2013) The effects of exposure to titanium dioxide nanoparticles during lactation period on learning and memory of rat offspring. Toxicol Ind Health. doi: 10.1177/0748233713498440
  10. Hong, F., Y. Wang, Y. Zhou, W. Zhang, Y. Ge, M. Chen, J. Hone, and L. Wang. “Exposure to TiO2 Nanoparticles Induces Immunological Dysfunction in Mouse Testitis.” PubMed. – Journal of Agricultural and Food Chemistry (ACS Publications), 13 Jan. 2016. Web. 22 Feb. 2016.
  11. Ruiz, PA, B. Moron, HM Becker, S. Lang, K. Atrott, MR Spalinger, M. Scharl, KA. Wojtal, A. Fishbeck-Terhalle, I. Frey-Wagner, M. Hausmann, T. Kraemer, and G. Rogler. “Titanium Dioxide Nanoparticles Exacerbate DSS-induced Colitis: Role of the NLRP3 Inflammasome.” PubMed. BJM, 4 Feb. 2016. Web.

Kent Kirshenbaum

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.

Anatomy of a hot chocolate

Photo credit: Flickr/louish

Hot chocolate: it’s a winter staple. Amidst falling temperatures and dreary skies, there’s nothing quite like taking a swig of this sumptuous beverage and seeking warm refuge in the delights of a steaming mug. Hot chocolate is as straightforward as drinks go: at its core, it’s milk, cocoa powder, and sugar. Despite its simplicity, this cold-weather classic is swirling with science.

The backbone of any decent hot chocolate is milk. Beyond water, milk is perhaps the most basic and familiar substance to humans. We’re all born drinking some form of it, but how often do we stop and think about its underlying science?  Milk is an emulsion, which is a mixture of two immiscible liquids—in this case, water and fat.   The water-based component of milk is loaded with vitamins, minerals, and protein and contains immiscible fat globules suspended throughout. How do water and fat coexist peacefully in solution together? The answer lies in emulsifiers, which are molecules that are both water- and fat-soluble. Milk contains proteins, namely casein, that attract and unite the fluids that would otherwise separate. Rich, silky, and chemically intriguing, this dairy product serves as the perfect vehicle for chocolate (1).



Photo credit: Flickr/chocolatereviews

Chocolate serves as the heart of the beverage. Some recipes call for it in the form of cocoa powder. Cocoa powder mixed in with your milk is a colloid—a type of mixture in which solid particles are dispersed throughout a fluid. Another popular culinary colloid you may recognize is coffee, which contains small coffee particles dispersed in water.


Photo credit: Flickr/csb13

A glass of hot chocolate simply isn’t complete with a dollop of whipped cream plopped on top. Lauded for its decadent mouthfeel, cream is an emulsion of butterfat and water, similar to milk but with a higher fat content. Fresh milk left undisturbed will separate into two layers; the top becomes enriched with fat globules that can be skimmed off as cream, leaving behind a relatively fat-free layer—skim milk. Cream and milk have remarkably different fat contents, as cream is required to have at least 30% milk fat compared to whole milk which is a mere 3%.

With some simple agitation, willpower, and a whisk, we can transform heavy cream into whipped cream, a culinary foam. Similar to emulsions, foams combine two immiscible substances, but instead of water and fat, air or gas is entrapped within a fluid or solid. Whisking incorporates air into the cream, and the newly introduced bubbles are held captive by the structure of the foam. Fluids and gases have very different properties, so how does agitation keep them together?  Agitation disorients the fat globules and strips away their protective membranes, forcing them to cling to other fat molecules or aggregate around air bubbles—anything to avoid having to be in contact with water. Agitate your cream enough and you’ll wind up with stiff peaks when these fat-encapsulated air bubbles begin to form a stable network (2).


Photo credit: Flickr/knitsteel

Whether they’re being roasted over a campfire or floating lazily on the surface of your hot chocolate, marshmallows are a surefire way to please and are another way to enhance your chocolate-drinking experience. Marshmallows were originally made as a meringue (yet another culinary foam!) consisting of whipped eggs and sugar flavored with the juice from roots of the marsh mallow plant. The making of marshmallows has since evolved so that now they are created by aerating a mixture of simple sugar syrup and gelatin to form a foam that stabilizes once the gelatin sets. Whipping incorporates air bubbles that are trapped in the solid matrix, forming these springy and sugary confections that pair exceptionally well with chocolate (1).

Hot chocolate is the ultimate winter beverage. It’s creamy, decadent and versatile. Drink it plain or spice it up with some chili powder, orange, or peppermint and you’ll surely find a style that will leave you positively foaming at the mouth.

References cited

    1. McGee, Harold. On Food and Cooking: The Science and Lore of the Kitchen. New York: Scribner, 2004. Print.
    2. Lower, Claire. Cream Science: On Whipping, Butter, and Beyond. Serious Eats. 2014.

Mai NguyenAbout the author: Mai Nguyen is an aspiring food scientist who received her B.S. in biochemistry from the University of Virginia.

Read more by Mai Nguyen

Caffeine vs. Chocolate: A Mighty Methyl Group

Guest post by Christina Jayson

Photo credit: Lisa Townley (left); Pyogenes Gruffer (right), Flickr.

Photo credit: Lisa Townley (left); Pyogenes Gruffer (right), Flickr.

When my organic chemistry professor told me that the main molecular component of chocolate, theobromine, differs from caffeine only by the absence of one methyl group I was delighted: I could skip an entire step in caffeine metabolism, avoid the bitter taste of coffee, and increase my chocolate consumption. It seemed to make sense that as the caffeine I drank was metabolized by removing the methyl group, caffeine would convert to theobromine (the main compound of chocolate) (Figure 1). At the molecular level, a methyl group is a carbon with three hydrogens attached. It may seem simple, but a methyl group is an integral part of chemistry, biology, and biochemistry. For example, additional methyl groups can help a molecule to cross the blood-brain barrier and enter our brain – this barrier protects our brain from foreign molecules traveling in the blood that can be harmful [1, 2]. In the case of caffeine, it turns out that the extra methyl group on the molecule is what makes coffee active on our central nervous systems and an “energy stimulator,” while chocolate functions as a sweet treat and smooth muscle stimulator.

Figure 1: During the metabolism of caffeine in the body, the methyl group (highlighted by the yellow box) is removed from caffeine and it is converted to theobromine (Modified from Wolf LK, 2013) [9].

Figure 1: During the metabolism of caffeine in the body, the methyl group (highlighted by the yellow box) is removed from caffeine and it is converted to theobromine (Modified from Wolf LK, 2013) [9].

So how do these two molecules act on different parts of the body, making coffee the substance of choice over chocolate bars when midterm season hits?

Caffeine is mostly derived from Coffea Arabica, or coffee beans, and seeds [3]. It is predominantly a central nervous stimulant, though it also stimulates cardiac and skeletal muscles and relaxes smooth muscles. Chocolate, or theobromine, is found in products of Theobroma cacao, or cocoa plant seeds (Figure 2). Much like caffeine, theobromine is a diuretic; however it mainly acts as a smooth muscle relaxant and cardiac stimulant [3]. While these two compounds have similar effects, the key difference is that caffeine has an effect on the central nervous system and theobromine most significantly affects smooth muscle [4]. In behavioral studies, caffeine intake improves self-reported alertness and mood over a period of 24 hours [5]. Theobromine produces mild positive effects in pleasure, but does not affect attention or alertness in moderate doses compared to caffeine [6].

Figure 2: Chocolate (left) is made from Theobroma cacao, or cacao plant seeds and contains theobromine (PC: Nic Charalambous). Coffee (right) is made from Coffea Arabica, or coffee beans, and seeds and contains caffeine (Photo credit: JIhopgood/Flickr).

Figure 2: Chocolate (left) is made from Theobroma cacao, or cacao plant seeds and contains theobromine (PC: Nic Charalambous). Coffee (right) is made from Coffea Arabica, or coffee beans, and seeds and contains caffeine (Photo credit: JIhopgood/Flickr).

But the true difference in the compounds lies at the molecular level. Both caffeine and theobromine belong to the methylxanthine chemical family. These chemicals act as stimulants of the nervous system, most notably by binding to adenosine receptors in the brain and thereby blocking adenosine from binding to the receptors [7]. Adenosine binding to adenosine receptors normally reduces neural activity, so the antagonistic action of caffeine and theobromine prevents this activity reduction (Figure 3). The increased energy and alertness that we connect to massive coffee consumption is due to the caffeine preventing your body from responding to signals that tell it to slow down or de-stimulate. Ever felt your hands jitter uncontrollably after too many shots of espresso?

Figure 3: Caffeine molecules (C) compete with adenosine molecules (A) to bind to the adenosine receptors in the brain (Schardt, 2012) [10].

Figure 3: Caffeine molecules (C) compete with adenosine molecules (A) to bind to the adenosine receptors in the brain (Schardt, 2012) [10].

Experiments show the activity of caffeine on the nervous system is stronger than theobromine [7]. Caffeine and theobromine compete with adenosine to bind to the same adenosine receptor. Studies have shown that caffeine molecules are better able to compete with adenosine to bind adenosine receptors than theobromine – caffeine binds these receptors with two to three times higher affinity than theobromine [8].

To gain access to the different locations of the adenosine receptors throughout the body, the extra methyl group on caffeine ends up coming in handy. Because caffeine has three methyl groups instead of two like theobromine, it more easily crosses the blood-brain barrier. In crossing the blood-brain barrier, caffeine can act on the central nervous system. So while theobromine can act as a heart stimulant and smooth muscle relaxant, caffeine – boasting its extra methyl group – has access to the neurons of the central nervous system and can consequently enhance physical performance and increase alertness.

Photo credit: Chris Swift, Rogers Family Co [11]

Photo credit: Chris Swift, Rogers Family Co [11]

This means my master plan to forego coffee for chocolate won’t actually improve my alertness and energy to the same extent. However, indulging in chocolate flavored coffee may provide me with all the caffeine derivatives I need for a stimulating day.

References cited

  1. Vauzour D, Vafeiadou K, Rodriguez-Mateos A, Rendeiro C, and Spencer JPE. The neuroprotective potential of flavonoids:a multiplicity of effects. Genes Nutr. 2008 3(3-4): 115–126.
  2. Svenningsson P, Nomikos GG, Fredholm BB. The stimulatory action and the development of tolerance to caffeine is associated with alterations in gene expression in specific brain regions. J Neurosci 1999. 19(10):4011–4022.
  3. Barile FA. Clinical toxicology: Principles and mechanisms. 2nd ed. Informa Healthcare Press. 2010. Ch 15, Sypathomimetics. 174-177.
  4. Coleman W. Chocolate: Theobromine and Caffeine. J Chem Educ. 2004. 81(8): 1232
  5. Ruxton C. The impact of caffeine on mood, cognitive function, performance and hydration: a review of benefits and risks. Nutr Bull 2008. 33:15–25.
  6. Baggot MJ, Childs E, Hart AB, de Bruin E, Palmer AA, Wilkinson JE, de Wit, H. Psychopharmacology of theobromine in healthy volunteers. Psychopharma. 2013. 228(1): 109-118.
  7. Kuribara H, Asahi T, Tadokoro S. Behavioral evaluation of psycho-pharmacological and psychotoxic actions of methylxanthines by ambulatory activity and discrete avoidance in mice. J Toxicol Sci. 1992;17:81-90.
  8. Daly JW, Butts-Lamb P, and Padgett W. Subclasses of adenosine receptors in the central nervous system: Interaction with caffeine and related methylxanthines. Cell Mol Neurobiol. 1983. 1: 69-80.
  9. Wolf LK. Caffeine Jitters. Chem & Eng News. 2013. 91(5): 9-12.
  10. Schardt, D. Caffeine! Nutrition Action Healthletter. 2012.
  11. Swift, C. (2014, June 2). Which is better for your brain? Beer or Coffee? You’ll never guess. [Web log post].

Christina Jayson is a recent UCLA Biochemistry graduate and currently a Ph.D. student in the Biological and Biomedical Sciences program at Harvard.

Freezer Burnt Meat

Photo credit: flickr/Steven Depolo

Photo credit: flickr/Steven Depolo

Freezing is an indispensable tool in modern cooking and eating. The biochemical processes that typically occur in meats cause decay, fat oxidation, and rancidity; the higher the temperature, the faster these reactions occur. Thus, we can largely thwart off these undesirable processes by keeping meat chilled. But tossing meat into the freezer rarely results in rainbows, sunshine, or perfect burger patties, because strangely enough we can also accelerate meat decay with cold. Freezer burn can take a beautiful filet mignon and turn its surface into a leathered, unappetizing slab.

Freezer burn is caused by water sublimation from ice crystals at the meat’s surface into the dry freezer air. Sublimation occurs when a solid substance undergoes a phase change and becomes a vapor without first passing through the liquid phase. The ice crystals on the meat surface sublimate, and leave behind tiny cavities. These tiny yet numerous cavities increase the surface area of the meat and expose more tissue to the air. This accelerates oxidation of fats, which causes the rancid flavors of old spoiled meat. We usually describe oxidized fats as simply tasting “off,” which is a vague term but seems apt if you’ve ever tasted lipids past their prime, perhaps by using shortening that has been in the pantry since you were a toddler.

Photo Credit: flickr/Marcus Ward

Here, solid ice crystals directly vaporize without first passing through the liquid phase. Photo Credit: flickr/Marcus Ward

In addition to the surface area increase caused by sublimation, the freezing process itself lends itself to fat oxidation. When the liquid water in meats crystallize in the cold, the concentrations of oxidizing salts and trace metals in the tissues increases. Unfortunately, oxidation can occur over time even in wrapped and frozen meats. Some oxygen will inevitably remain in contact with the meat, unless we create a vacuum seal.

Once meat has been damaged by the cold, there’s no undoing the oxidation. So either we plan our meals so that meats are cooked immediately after purchase, or we learn to prevent the sublimation that ruins both our pork chops and our days. We simply need to keep water crystals inside the meat and keep oxygen out. Using a vacuum sealer is our best bet for avoiding freezer burn, but for cheapskates like me who won’t shell out the $30 for the sealing device, a water-impermeable plastic wrapped tightly around the meat works well enough for most home chefs.

Thus meat is sealed away happily in plastic, free from villainous oxygen. Photo credits: flickr/Mike

Thus meat is sealed away happily in plastic, free from villainous oxygen. Photo credits: flickr/Mike

References cited

  1. McGee, Harold. “Meats.” McGee on Food & Cooking: An Encyclopedia of Kitchen Science, History and Culture. London: Hodder & Stoughton, 2004. N. pag. Print.
  2. “Sublimation.” The Columbia Electronic Encyclopedia. Columbia University Press, 2012. Web. 20 July 2015.


Elsbeth SitesAbout the author: Elsbeth Sites received her B.S. in Biology at UCLA. Her addiction to the Food Network has developed into a love of learning about the science behind food.

Read more by Elsbeth Sites

Chemical Literacy & Hot Cocoa


In an age where our food supply system grows increasingly complex, chemical literacy is the key to knowing the difference between foods that contain riboflavin versus vitamin B2. With that in mind, let’s take a look at cocoa powder, which is bitter-tasting and impossible to dissolve. To create a sweet, frothy hot cocoa mix from cocoa powder requires some sweeteners, emulsifiers, and…sodium alluminosilicate?
Read more

Flavor-Changing Chewing Gum

Growing up as a chubby kid who tried to convince her parents that candy belonged at every meal (a real life Augustus Gloop, if I may), one of my favorite books was Charlie and the Chocolate Factory. And though I’d dream for a mug of the chocolate river, my favorite of Willy Wonka’s creations was the three-course chewing gum. Tomato soup, roast beef, and blueberry pie in one piece of gum? The possibilities! While you can find some commercial versions of flavor-changing gum at the supermarket today, my fingers are crossed for a three-course meal sometime in the near future.

Image Credit: (stevendepolo/flickr)

Image Credit: (stevendepolo/flickr)

To get any sort of flavor in a chewing gum in the first place, a process called microencapsulation is used, in which a core of tiny flavor particles is surrounded by a shell coating to produce minuscule spherical capsules – we’re talking diameters of roughly a couple hundred micrometers in size [1]. Chewing gums contain these little flavor microcapsules; the core of each microcapsule is usually some sort of liquid flavoring, and the shell is made of crosslinked proteins which stabilize the core material, isolate the core from the chewing gum base, and will break apart in response to the shear forces of chewing to release the core flavoring [1].

So let’s say you have a stick of strawberry-flavored chewing gum. The gum will be studded and mixed with microcapsules filled with strawberry flavoring oils; those are the beady dots you sometimes see on the chewing gum surface. The fruity flavor is released once you chew on the gum and break open the shells of the strawberry capsules to release the flavoring oils in your mouth.

microencapsulated flavor droplet

While there are various methods for flavor encapsulation, the technique which is used to make the capsules in chewing gum is the chemical process called complex coacervation. [4] This process involves an aqueous solution with two or more oppositely charged polymers – one with positive charge (such as gelatin or agar), and another with negative charge (such as carboxymethylcellulose or gum arabic) [2]. These two polymers are diluted into water and then controlled for both pH and temperature, so that when an oily substance (such as a flavoring oil) is mixed into the solution, the molecules form a chemically crosslinked, shell-like film around each of the oil particles, resulting in the encapsulated flavor beads present in chewing gum!

The coacervation solution then separates into two liquid phases – one called a “coacervate” that contains the many tiny oily droplets that contain the polymers and the other is called the “equilibrium liquid”, which serves as the solvent. Once the shells around the oil droplets are formed, the rest of the solution is washed out and the entire capsules are dried so that they can be incorporated into the chewing gum base [3].


The Coacervation Process: (a) The oily flavor droplets float around in an emulsion of the shell polymer solution, (b) The coacervation solution separates into the coacvervate and the solvent (c) The coacervate surrounds the outside of the flavor core, (d) And forms a continuous crosslinked polymer shell around the core.

So how does the flavor-changing gum work? The secret lies in the fact that the tiny flavor capsules in a chewing gum can be engineered to release at different times. By creating microcapsules with different dissolution times, the release of several different flavor capsules can be staggered to make a chewing gum that “changes flavors”. The first flavor composition in a flavor-changing gum is usually the unencapsulated liquid flavor or a starch sugar coating on the surface of the gum, so that the first flavor can be released on contact with saliva [4].

After the initial flavor perception, the second, third, fourth, and any subsequent flavors will be encapsulated, but with varying materials in the cores and shells, so that each flavor is released at a different time during the gum-chewing experience. The goal for a flavor-changing chewing gum is to have its flavors release quickly and intensely, preferably 15 to 45 seconds after the release of the previous flavor [5]. The release times of the microcapsules can depend on a variety of factors involving both the core flavoring substance and the encapsulating materials:

  • Solubility of Flavoring Substance
    Water-soluble flavoring substances are more soluble in our saliva, so they are released in chewing gum before the oil-soluble flavoring substances. Water-soluble flavors include vanilla, synthetic fruit flavors like cherry and lemon, and plant extracts such as coffee and licorice. Oil-soluble flavors include cinnamon oil, peppermint oil, peanut butter flavor, chocolate, and eucalyptus oil [5].

  • Hydrophobicity of Capsule Shell
    Microcapsule shells made of highly hydrophobic proteins, meaning they have low water-absorption properties, take longer to release the core flavor. Meanwhile, shells that are made with less hydrophobic material, which can absorb more water, release the flavor components earlier and more quickly. For example, if we use ethylene-vinyl acetate as the shell material, the release rate can be controlled with a few adjustments. A higher ratio of ethylene to vinyl acetate creates a more hydrophobic shell, which results in a slower release of flavor. On the other hand, using lower ratio of ethylene would create a less hydrophobic shell and a quicker release of flavors [5].

  • Tensile Strength in Microcapsules
    The maximum amount of stress that the encapsulation shell can withstand from chewing before it breaks and releases the core flavor is called the tensile strength. Changing the tensile strength of each flavor’s shell can determine the order in which the flavors are perceived. Materials that lower the shell’s tensile strength are fats, plasticizers, waxes, and emulsifiers, so adding these materials into the shell of a flavor capsule causes it to break more easily and release flavors more quickly [5]. Meanwhile polymers with high molecular weight tend to increase the tensile strength of the shell, so these flavors are released later, since they require more vigorous chewing.

A combination of these factors from hydrophobicity to tensile strength can be used to determine the order of the flavors released for an entire three-course meal (or more!) in just a stick of gum. Tomato soup, roast beef, and blueberry pie, here I come!

Image Credit: (pinkiepielover63/deviantart)

Image Credit: (pinkiepielover63/deviantart)

References Cited:

  1. J. Sris, A. Seethadevi, K. Suria Prabha, P. Muthuprasanna, and P. Pavitra. (2012). Microencapsulation: a review. International Journal of Pharma and Bio Sciences. 3: 509–521.
  2. Feng T., Xiao Z., Tian H. (2009). Recent Patents in Flavor Microencapsulation. Recent Patents on Food, Nutrition, & Agriculture. 1:193–202.
  3. Xiao Z., Liu W., Zhu G., Zhou R., Niu Y. (2014). A review of the preparation and application of flavour and essential oils microcapsules based on complex coacervation technology. Journal of the Science of Food and Agriculture. 94: 1482-1494.
  4. Gaonkar A.G., Vasisht N., Khare A.R., Sobel R. (2014). Microencapsultion in the Food Industry: A Practical Implementation Guide. Academic Press. 421-453.
  5. Lenzi S., Kar S., Michaelidou T.A., and Harvey J.E. (2012). Chewing Gum Compositions Providing Flavor Release Profiles. Kraft Foods Global Brands LLC, assignee. Patent WO2012034012.

Eunice LiuAbout the author: Eunice Liu is studying Linguistics at UCLA. She attributes her love of food science to an obsession with watching bread rise in the oven.

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Sour Beers & Skunky Beers


“Fermenting yeasts produce more than just ethanol and carbon dioxide. They make flavorful, aromatic molecules: acids and esters. But which ones make which ones?” wonders William Bostwick as he attempts to recreate a sour beer in his kitchen in San Francisco’s Mission District. If you’re more interested in preventing your beer from getting skunky than making your own, we found some chemistry to help you out.
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Photo Credits (flickr/veganbaking,net)

Photo Credits (flickr/veganbaking,net)

For the health-conscious members of society, there are several food fiats: thou shalt avoid high fructose corn syrup, steer clear of ingredients that sound like they could be found in jet fuel, and fear partially hydrogenated oils. Oil in and of itself is not inherently bad; how does adding hydrogen to transform it into the bane of all processed foods?

The general term “hydrogenation” refers to the “reaction of hydrogen with an organic compound.” The term organic compound refers to any molecular compound that contains carbon atoms. The process used to modify oils is technically known as “catalytic hydrogenation,” since it takes place in the presence of a catalyst, which helps speed up the reaction.

Hydrogenation is typically used to improve the flavor stability and keeping qualities of oil. An unhydrogenated oil can turn rancid because its unsaturated carbon atoms are free to bond to oxygen atoms from the air, forming peroxides, which give rancid fats their “off” flavor. Sometimes oils, particularly vegetable oils, are only partially hydrogenated. Complete hydrogenation creates a product containing only saturated fats, which typically has a solid and waxy consistency that is not appropriate for cooking, baking, or eating. Fully hydrogenated vegetable oils would resemble candle wax and have a melting point above 60°C [1].

So how is oil hydrogenated? Typically, a mixture of refined oil and finely powdered nickel (the catalyst) is pumped into a large capacity cylindrical pressure reactor. Heating coils heat the oil to 120-188°C (248-370°F) at 1-6 atmospheres pressure [1]. Hydrogen gas is pumped into the bottom of the reactor, and everything is continuously stirred to distribute the rising gas bubbles throughout the liquid oil. The high temperature, pressure, and the presence of the catalyst ensure that any carbons in the oil that are not at their full hydrogen bond capacity (the “unsaturated” carbons), form new chemical bonds with the hydrogen atoms, thus becoming more and more “saturated” with hydrogen. As they become fully hydrogenated, the oil molecules begin to straighten out and stick to one another, causing the liquid oil to solidify [2].

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What could be so bad about adding hydrogen atoms to oil molecules? With each hydrogen that is added to the molecule, one of the fat’s carbon-carbon double bonds is replaced with two new bonds, each to a hydrogen atom. If we continue this process until there are no more double bonds left, we would have a completely saturated fat. Because saturated fats are more linear, they stack up upon each other all too well, and can increase body cholesterol levels.  If during hydrogenation the fat molecule is left with one or a few double bonds, the molecule takes up either a trans or cis configuration. As you might have guessed, this is how the infamous trans fat comes to be. Both hydrogen atoms occupy the same side of the double bond, forcing the molecule to kink at the bond. In a trans fat, the hydrogens transverse the double bond, and no kink forms. It is a microscopic difference, but one that has profound effects on their biological roles. Several studies have demonstrated that consuming specifically more trans fats increases risk of cardiovascular disease. [5]

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But hydrogenation is not restricted to humans with access to pressure vats. Microorganisms that live in the rumen of cows and other ruminants can “biohydrogenate” fats without any fancy pressure vats or catalysts [3].

Photo Credits (Flickr/Ruud Cuypers)

Photo Credits (Flickr/Ruud Cuypers)

Scientists who study fats have long known that fats in the tissues of ruminants are more saturated than those of nonruminants [3]. Grass and other typical ruminant feedstuffs are rich in unsaturated fatty acids, yet these fats are only present at low concentrations in meat and milk.

When food enters the rumen (essentially a large fermentation vat intended to break down the animal’s fibrous meals), gut microbes catalyze a range of chemical transformations. For example, ruminal microbes transform lipids through both lipolysis and biohydrogenation.

Through lypolysis, microbes break the bonds of long fat molecules, thus producing simpler fatty acids. Unsaturated fatty acids are also biohydrogenized, a process very similar to industrial hydrogenation, but catalyzed by microbes instead of metal [3].

Because of this biohydrogenation, dairy products typically contain 5-10% trans fatty acids [2], which are consumed by anyone who drinks milk or eats butter, tallow, or beef. It is important to note, however, that the predominant trans fatty acid in ruminant fat (vaccenic acid) is not the same as the predominant trans fatty acid produced by hydrogenation of vegetable oil [2]. High consumption of trans fats from industrial hydrogenation are well documented as being linked to cardiovascular disease, while clinical and rodent studies of vaccenic acid have not documented such a strong correlation. [4] These ruminant fats may even protect our hearts from these diseases, but further research is necessary.[5]




Elsbeth SitesAbout the author: Elsbeth Sites is pursuing her B.S. in Biology at UCLA. Her addiction to the Food Network has developed into a love of learning about the science behind food.

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5 Things About Taste

At our 2014 public lecture How We Taste, Chef Wylie Dufresne, Dr. Dana Small, and Peter Meehan explored the tantalizingly complex concept of flavor. The evening was full of scientific discovery, childhood memories, and culinary innovation. In honor of this enlightening event, here are 5 things you might not know about our sense of taste:

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