Black Sesame Seeds on Heavy Metal Cleanup

Black sesame seeds: more than just a tasty garnish on sushi rolls and rice. Photo credit: Arnold Gatilao (arndog/Flickr)

Black sesame seeds: more than just a tasty garnish on rice. Photo credit: Arnold Gatilao (arndog/Flickr)

Heavy metals, such as cadmium, lead, and mercury, leach into our food supply through the air and water; these undesirable additives come from industrial processes such as mining, smelting, battery manufacture, electroplating, and pesticide production. Cadmium and lead are the chief contaminants of rice, wheat, and foods containing these cereals [1]. Mercury is often found in seafood, but cadmium and lead can also be present in smaller amounts [2]. Even trace amounts of these heavy metals can be extremely toxic to human health, since they have extremely long biological half-lives, or time required for half the absorbed metals to leave the body: 10 years for cadmium [3], 30 days for lead [4], and 60 days for mercury [5]. Thus, there is an increased risk of chronic poisoning due to heavy metal accumulation in tissues and organs, which can lead to impairment of the immune and central nervous system [6].

Current protective measures against dietary exposure to heavy metals involve chelating agents, which are compounds that can bind to metal ions. Chelating agents include cereal fibers from wheat, rice, and oat bran, as well as polyglutamic acid, which is the main constituent of nattō, Japanese fermented soybeans [7]. Although edible, the efficacy of these particular chelating agents has so far only been evaluated for removing heavy metals from water and soil.

What about the heavy metals we’ve already ingested? In a collaboration among researchers in Italy and Austria, ground black sesame seeds (Sesamum indicum L.) were shown to effectively bind to cadmium, lead, and mercury under simulated physiological conditions.

A major challenge in using chelating agents is that they also bind to many essential ions in the body, such as calcium (Ca2+), zinc (Zn2+), and iron (Fe2+); this can result in deficiencies, which can have negative health effects. Unlike other chelating agents used for heavy metal detoxification, which cannot differentiate between essential metal ions and toxic heavy metal ions (cadmium (Cd2+), lead (Pb2+), and mercury (Hg2+)), black sesame seeds exhibited selectivity towards the heavy metals. In mixtures that contain heavy metals plus essential metal ions, the ground black sesame seeds bound to far more heavy metals than essential metals. Interestingly, low levels of iron increased the amount of cadmium and lead bound to the sesame seeds. While other chelating agents, such as thiamine and becozinc, risk deficiencies in essential metals [8], the preference of black sesame seeds to bind to toxic heavy metals make it a favorable dietary supplement for heavy metal detoxification.

The ability of black sesame seeds to bind to toxic heavy metals may be attributed to lignans, a type of phytochemical commonly found in plants and a major component of sesame seeds. To determine how the heavy metals were binding to the ground black sesame seeds, the study compared the binding abilities of ground black sesame seeds against model phytochemicals, caffeic acid, ferulic acid, and coniferyl acid, which represented sesame seed lignans after digestion in the stomach. Of the three model pigments, caffeic acid was observed to remove the most heavy metals, suggesting that digested sesame seed lignans may have a similar chemical structure to caffeic acid.

Lignans in black sesame seeds are responsible for heavy metal binding. Left: Model pigments representing digested lignans were compared to ground black sesame seeds (BSP) for heavy metal removal. Right: Caffeic acid and the suggested binding sites for cadmum (Cd2+), lead (Pb2+), and mercury (Hg2+)

Lignans in black sesame seeds are responsible for heavy metal binding. Left: Model pigments representing digested lignans were compared to ground black sesame seeds (BSP) for heavy metal removal. Right: Caffeic acid and the suggested binding sites for cadmum (Cd2+), lead (Pb2+), and mercury (Hg2+)

There are additional benefits to lignans in sesame seeds! As a major category of phytoestrogens, lignans are known to be effective antioxidants. Moreover, sesame seeds specifically contain the lignans, sesamin and sesamolin, which studies have shown to also contain pharmacological benefits such as antihypertensive, anti-inflammatory, and anticarcinogenic properties [9].

For those worried about chronic dietary exposure to heavy metals, prevention may be as tasty as black sesame seeds sprinkled on sushi rolls.

 

References cited

  1. Cuadrado C., Kumpulainen J., Carbajal A., Moreiras O. Cereals contribution to the total dietary intake of heavy metals in Madrid, Spain. Journal of Food Composition and Analysis, 2013; 13: 495-503.
  2. Falcó G., Llobet J., Bocio A., Domingo J. Daily intake of arsenic, cadmium, mercury, and lead by consumption of edible marine species. Journal of Agricultural and Food Chemistry, 2006; 54: 6106-6112.
  3. Godt J., Scheidig F., Grosse-Siestrup C., Esche, V., Bradenburg P., Reich A., Groneberg D. A. The toxicity of cadmium and resulting hazards for human health. Journal of Occupational Medicine and Toxicology, 2006; 1: 22.
  4. Gulson B., Stable lead isotopes in environmental health with emphasis on human investigations. Science of the Total Environment, 2008; 400: 75-92.
  5. Yaginuma-Sakurai K., Murata K., Iwai-Shimada M., Kurokawa N., Tatsuta N., Satoh H. Hair-to-blood ratio and biological half-life of mercury: experimental study of methylmercury exposure through fish consumption in humans. Journal of Toxicological Sciences, Feb 2012; 37(1): 123-130.
  6. Woimant F. Trocello J. M., Disorders of heavy metals. Handbook of Clinical Neurology, 2014; 120: 851-864.
  7. Siao, F. Y., Lu J. F., Wang J. S., Inbaraj B. S. Chen B. H. In vitro binding of heavy metals by an edible biopolymer poly(γ-glutamic acid). Journal of Agricultural and Food Chemistry, 2009; 57: 777-784.
  8. Tandon S. K., Singh S. Role of Vitamins in Treatment of Lead Intoxication. The Journal of Trace Elements in Experimental Medicine, 2000; 13: 305-315.
  9. Kim J. H., Seo W. D., Lee Y. B., Park C. H., Ryu H. W., Lee J. H. Comparative assessment of compositional components, antioxidant effects, and lignan extractions from Korean white and black sesame (Sesamum indicum L.) seeds for different crop years. Journal of Functional Foods, 2014; 7: 495-505.

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.

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The Keys to Cheese: Does This Cheese Melt?

Melted Cheese [Photo Credit: Pittaya Sroilong]

Melted Cheese Frize [Photo Credit: Pittaya Sroilong]

Whether you are making cheese fries, grilled cheese sandwiches, quesadillas, baked cheese bites, or homemade mac and cheese, choosing the right type of cheese can make or break these comfort foods. The key to all of these dishes is cheese that produces an even and homogenous melt. Cheeses like Cheddar, Mozzarella, and Gruyere are used often. If you aren’t feeling adventurous, you could just memorize the names of these greatest hits. However, if you want to experiment and change the melty cheese game, you’re going to have to understand why these cheeses work.

Let’s first examine what happens to cheese as it melts. The interactions of casein (milk proteins) and calcium help define its solid structure. When solid, caseins are bound together in large branching porous protein networks that entrap milkfat and water. Calcium (as calcium phosphate) acts as a bridge to stabilize these networks. When you apply heat to a cheese, melting occurs in two stages. First, at around 90 ˚F, milkfat is released1. This is because hydrophobic (water-repulsive) interactions between casein molecules increase under heat2. These interactions force out water molecules and the space between casein molecules increases allowing milkfat, which melts at this temperature, to escape. If you’ve put cheese on a burger that’s being grilled, you may see little sweat beads of liquid form on the cheese in the early stages of melting. The second stage happens at about 40 to 90 degrees higher, at around 130 – 180˚F3. At this point, the casein proteins do not break down, but rather, the increased movement of the proteins, resulting from the heat, allows for the proteins to act more fluid-like and the cheese melts.

There are many factors that control melting and explain why melting temperatures vary by as much as 50 degrees. No one factor defines a cheese’s melting properties as these factors can interact.

Moisture and Fat

Cheese with higher moisture and fat content tends to have lower melting points. For example, high moisture cheeses like Mozzarella melt around 130 ˚F and low moisture cheeses like Swiss melt at 150 ˚F 2. First, as previously highlighted, the milkfat and water portion of the cheese react to heat at lower temperatures than the proteins. Accordingly, with more moisture and fat present in a cheese, greater proportions of the cheese are susceptible to melting at lower temperatures. When the fat becomes liquid, it can no long provide support for the protein networks. Secondly, increased moisture and fat means that the casein proteins are more spread out and the mesh size (gap between proteins) is larger. This means there are fewer connections (bound calcium bridges) between proteins networks making melting more likely to occur at lower temperatures.

You may not know the exact moisture and fat content of every cheese variety without looking at a label, but intuitively, softer cheeses have more moisture and fat. Additionally, younger cheeses generally have more moisture so they also tend to melt more uniformly and evenly.

Acid Content

Chesses typically melt homogenously and evenly around a pH of 5.0 – 5.44. This is related to the calcium bridges. At too high a pH (pH > 6), too much calcium is present as bound calcium phosphate and the protein is too tightly bound to melt. With lowered pH, the calcium phosphate bound to the casein is replaced by hydrogen (H+), allowing for more movement among proteins.2 At around a pH of 5.0 – 5.4, there is a sufficient number of calcium present as bridges to allow for melting. At too low a pH (pH < 4.6), too many calcium bridges are lost and proteins aggregate and are unable to flow and melt evenly.

Lastly as a caveat, the factors being highlighted are specific to rennet-set cheeses, and not acid-set cheeses. Acid-set cheeses like queso fresco, paneer, and ricotta are not generally used, as they don’t produce even melts4. This results from the way they were made. In cheese making, you have two options for separating the solid curds (primarily casein proteins) and the liquid whey; Use rennet (an enzyme derived from the intestines or baby goats and cows) or use an acid (like vinegar or lemon juice).

When they are free floating in liquid milk, casein proteins have a slightly different molecular structure than when they are in cheese. In milk, caseins stick together in small clusters (micelles) that have negative charges on their surface. Since negative charges repel each other, these micelles won’t combine. Adding acid to heated milk lowers the pH, which neutralizes the negative charges on the micelles; therefore the casein micelles can aggregate. In contrast, using rennet to set cheese is a more targeted approach. In this process, an enzyme contained in rennet called chymosin, selectively removes negatively charged portions of the casein micelles and allows the micelles to clump.

In an acid-set cheese, calcium bridges are never formed as a result of the acidic environment used to generate the cheese5. These cheeses are only held together in protein aggregates rather than protein networks with calcium bridges and don’t produce the even melt desired.

Bottom Line:

Rennet-set cheeses with high moisture and fat are the best cheeses for melting as they melt evenly and consistently.

But don’t fret if you still want to harness the flavor of other cheeses (especially older or drier cheeses)! You have options: Try using a cheese blend with a higher proportion of the better melting cheeses and a small proportion of the other cheeses. For example, this recipe uses a 1:4 ratio. Experiment! You now know the keys for melty cheese!

References cited

  1. Schloss, Andrew and David Joachim. “The Science of Melting Cheese” http://www.finecooking.com/item/64019/the-science-of-melting-cheese
  2. Johnson, Mark. “The Melt and Stretch of Cheese” https://www.cdr.wisc.edu/sites/default/files/pipelines/2000/pipeline_2000_vol12_01.pdf
  3. Mcgee, Harold. On Food and Cooking. 2004 “Cheese” (57 – 67).
  4. Tunick, Michael. The Science of Cheese. 2013 “Stretched Curd Cheeses, Alcohols, and Melting” (82 – 91).
  5. Sargento Food Service. “Cheese Melt Meter” http://www.sargentofoodservice.com/trends-innovation/cheese-melt-meter/
  6. Achitoff-Grey, Niki. “The Science of Melting Cheese” http://www.seriouseats.com/2015/08/the-science-of-melting-cheese.html

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

Read more by Vince Reyes


Structural Changes in Chocolate Blooming

Is there anything more disappointing than finding a chocolate bar in the back of the desk drawer, anticipating a tasty treat, then unwrapping the bar only to find a dull, grey haze has overtaken your dear candy? Seeing as bloomed chocolate is still edible, yes, there are many things more disappointing than that. But surely you’re curious about how chocolate that was once shiny and perfect came to be filmy and rough. Chocolate blooming, the process that produces the white-grey film that appears on the surface of an old chocolate, is due to molecular migration. More specifically, this imperfection is caused by the movement of fats to the surface of the chocolate followed by a subsequent recrystallization. In a paper published by Applied Materials & Interfaces, a team of researchers dedicated to keeping our chocolates blemish-free has clarified the precise mechanisms that cause chocolate blooming.

The main fat in chocolate is cocoa butter, which is solid at room temperature and melts at 37 degrees Celsius. The proportion of solid to liquid cocoa butter depends on the lipid composition, which depends on which specific triglycerides are present. The solid to liquid proportion also varies with the storage conditions of the chocolate.

As proposed by Aguilera et al, scientists who study this chocolate blooming, consider chocolate as a particulate medium of fat-coated particles such as cocoa solids, sucrose, and milk powder, all suspended in a fat phase with the aid of an emulsifier, which helps to mix fats and oils with water, which usually repel each other. There are six crystallographic polymorphs of cocoa butter molecules, that is, there are six ways the molecules can organize themselves. The structural stability of these polymorphs increases from 1- 6; form 1 is the best at forming solid butter at room temperature, while form 6 tends to arrange in the loose bonds of a liquid. Form 5 is the main form in chocolate, as it possesses the most aesthetically desirable properties. While the phenomenon of blooming is well known to result from melting and recrystallization of chocolate into a less desirable polymorph, it has been unclear how fat moves through the chocolate particle network: Does it move along the fat-particle interface? Does it diffuse through the fat phase (cocoa butter), or through the matrix of assorted particles?

Possible lipid migration pathways in chocolate - Reinke et al

Possible lipid migration pathways in chocolate – Reinke et al

In this experiment, researchers used synchrotron microfocus small-angle X-ray scattering to determine the preferential migration pathway of the cocoa butter molecules surrounded by three different soild components (cocoa solids, skim milk, and sucrose). This technique allows researchers to record the scattering of x-rays through a sample with defects in the nanometer range. They can then extrapolate information about the material’s macromolecules, their shapes and sizes up to 125 nanometers, and distances between partially ordered materials, such as pore sizes. For this experiment, this method is better than more traditional macroscopic techniques as the sample does not need to be dissected in order to examine it, therefore the same sample can be continually analyzed.

Sketch of the experimental setup - Reink et al

Sketch of the experimental setup – Reink et al

The researchers prepared and tempered four different chocolate samples. An initial scattering of x-rays and data collection was performed before the addition of sunflower oil, then 10 uL of oil was pipetted onto the chocolate surface, and a second scan was performed. Images of the droplet were captured through a high-speed camera. These scans were repeated at 5, 10, and 30 minutes after oil addition, and again after 1, 2, 5, and 24 hours.

The results obtained suggest that oil is migrating through pores and cracks in the solid structure driven by capillarity within seconds. This means that the oil can flow in narrow spaces in opposition to gravity. Then chemical migration through the fat phase occurs. The oil doesn’t traverse the fat-particle interface, nor does it move through the matrix of solid particles. This migration disrupts the crystalline cocoa butter, which induces softening.

Because the most immediate migration of oils occurs through the material porous structure, the formation of chocolate bloom could be prevented by minimizing pores and defects in the chocolate matrix. To prevent the longer-term effects of chemical migration of lipids, one must minimize the content of non-crystallized liquid cocoa butter. Tempering chocolate lends to crystalline structures that resist migration, as will reducing the liquid fat content. However, to ensure that you never encounter a sad hazy chocolate again, we recommend eating all chocolate goods expeditiously.

Works Cited

  1. Tracking Structural Changes in Lipid-based Multicomponent Food Materials due to Oil Migration by Microfocus Small-Angle X-ray Scattering. Svenja K. Reinke, Stephan V. Roth, Gonzalo Santoro, Josélio Vieira, Stefan Heinrich, and Stefan Palzer. ACS Applied Materials & Interfaces 2015 7 (18), 9929-9936. DOI:10.1021/acsami.5b02092
  2. Aguilera, J. M.; Michel, M.; Mayor, G.Fat Migration in Chocolate: Diffusion or Capillary Flow in a Particulate Solid?—A Hypothesis PaperJ. Food Sci. 2004, 69, 167–174

 


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.

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Could Making Beer From Sewage Save Us From The Drought?

[Photo Credit: Vince C Reyes]

[Photo Credit: Vince C Reyes]

The historic drought in California and other U.S. states challenges us to rethink the way food production and consumption shapes our available water supply. To that end, one adventurous brewing club, The Oregon Brew Crew, collaborated with Oregon’s water utility, Clean Water Services, to brew beer from waste water. This comes as part of the water utility’s initiative to make better use of recycled water. As beer is 95% water, we could potentially save significant volumes of water through this less glamorous route.1

To be clear, the brewers did not make beer straight from water entering out of the toilets and sewers of Oregon. Clean Water Services provided the brewers with “ultrapure water” for making their beer. Ultrapure water is made from water that is purified using the most advanced water treatment methods available. Ultrapure water is not new, but is normally not used for brewing. It is traditionally used for generating water for electronics and pharmaceuticals production, scientific research, or any other application where water must be free from as many contaminants as possible.

To generate ultrapure water, Clean Water Services combines traditional wastewater treatment with more advanced methods. For this process, sewage is first cleaned using traditional wastewater treatment, which includes screening, sedimentation, biological treatment, and disinfection. After this step, the sewage is fit to be released to lakes and rivers, but gets a deeper cleaning through more advanced methods. In the case of the water used by the brewers, Clean Water Services uses a three-step process of Ultrafiltration, Reverse Osmosis, and Enhanced Oxidation to produce their ultrapure water.

The water is first subject to Ultrafiltration and Reverse Osmosis. These processes work like a kitchen sieve as they push water through small pores in a barrier to separate water from different molecules. While both Ultrafiltration and Reverse Osmosis use similar physical separation mechanisms, they vary in the products they can remove from water because of their differing pore sizes. Ultra-filtration can be used to remove particles as small as viruses and bacteria (0.005 – 0.5 μm), while Reverse Osmosis uses finer pores, which can remove even smaller molecules like herbicides, pesticides, salts, and metal ions (0.0001 – 0.001 μm) (Figure 1).

Figure 1: The size of materials that can be removed by Ultrafiltration and Reverse osmosis. Figure Credit: Designerwater.co

Figure 1: The size of materials that can be removed by Ultrafiltration and Reverse osmosis. [Figure Credit: Designerwater.co]

In contrast to Ultrafiltration and Reverse Osmosis, the final step, Enhanced Oxidation, uses chemical methods to eliminate any remaining unwanted products in water. Specifically, Enhanced Oxidation uses ultraviolet (UV) light in combination with chemicals like hydrogen peroxide (H2O2) and ozone (O3) to generate hydroxyl radicals. The high energy from the UV light breaks down chemical bonds to form hydroxyl radicals (·OH). For example, here is the break down of hydrogen peroxide by UV light:

H2O2  + UV -> 2·OH

A hydroxyl radical is just a hydrogen atom bonded to an oxygen atom with an extra electron. Having an extra electron makes hydroxyl radicals very reactive and can break down undesirable molecules in water. This final step removes any remaining contaminants that were not eliminated by Ultrafiltration and Reverse Osmosis.

Figure 2: Ultrapure water (high purity water) compared to river water, cleaned sewage water, and tap water. [Image Credit: huffingtonpost.com]

Figure 2: Ultrapure water (high purity water) compared to river water, cleaned sewage water, and tap water. [Image Credit: huffingtonpost.com]

After these three treatments, the ultrapure water was ready to be used for brewing. In regards to taste, this process produced bland tasting water that results from the absence of minerals and salts that are normally found in water from groundwater, reservoirs, lakes, rivers, and the tap2. These atoms and molecules can be challenging for brewers, as they impart a natural flavor to waters that may not be congruent with the desired beer’s flavor profile3. Instead, when using ultrapure water, the brewers had the freedom to build in whichever flavors they desired. The hops, grains, yeast, and additional spices controlled the beer’s flavor profile rather than the water.

Currently in the U.S., recycled water typically cannot be used directly as drinking water, regardless of how much it is cleaned. Generally, recycled water is only used to water landscape, cool power plants, or flush the toilet. But with growing concerns over shrinking water sources, these views are changing. In 2010, a study by the California State Water Board examined the potential contaminants in recycled water, current water treatment technology, and human health studies of exposure to these contaminants. The conclusion was that recycled water could be safe for human consumption4. These results have been confirmed by other research as well5.

Projects like this may cause you to re-evaluate your bias about the source of your water (and beer). Regardless of the origin of your water, advances in water treatment technologies may enable us to produce safe drinking water from wastewater. But the question still remains: would you feel comfortable raising a glass of beer made from recycled waste water to your lips or would you pour it down the drain?

Learn More

  1. Water and Wasterwaster: Treatment/Volume Reduction ManualBrewers Association.
  2. Is Sewage Beer The Next Big Thing?Huffington Post.
  3. To Grow A Craft Beer Business, The Secret’s In The WaterNPR: The Salt.
  4. Final Report: Monitoring Strategies for Chemicals of Emerging Concern (CECs) in Recycled WaterState Water Resources Control Board.
  5. Rodriguez, C., Buynder, P.V., Lugg, R., Blair, P., Devine, B., Cook, A., Weinstein, P. Indirect Potable Reuse: A Sustainable Water Supply Alternative. International Journal of Environmental Research and Public Health. March 2009; 6(3): 1174-1209.

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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Flavor without the Calories: Scientists Create a Digital Taste Simulator

Think of any task and chances are someone is developing a new mobile electronic device for it. Technologies exist that pay for your coffee, track your UV light exposure, and even drive your car, but can one also simulate flavor? With that question in mind, scientists led by Nimesha Ranasinghe at the National University of Singapore are developing a device that can scintillate your tongue with sour, bitter, salty, and sweet tastes without the use of any chemicals or actual food.

The “Tongue Mounted Digital Taste Interface” uses a two-probe system to send electrical and thermal signals to the tongue to produce taste. By altering the magnitude of the electric currentA (20 – 200 mA), frequency of electric pulsesB (50-1000 Hz), and temperature (20 – 35 °C [68 – 95°F] ), the interface changes the flavor profile and intensity the wearer experiences. For example, increasing the magnitude of the electrical current strengthens sour, bitter, and salty sensations1.

Tongue_interface

Figure 1: Schematic of the Tongue Interface1

device_tongue

Figure 2: Interface applied to tongue1

To understand how this system works, you have to first understand the anatomy of a taste bud (Figure 3).

Taste_bud

Figure 3: Diagram of a Taste Bud2.

When food enters the mouth, it is broken by chewing and mixed with saliva, which dissolves small food molecules like salts and sugars. These small molecules enter the taste pore and react with taste receptor cells. These taste receptor cells activate attached nerves, which transfer electrical signals to the brain that transmit the sensation of taste. In other words, a molecular signal is converted into an electrical one. Direct stimulation of taste receptors with electricity bypasses the need for initiating the signal using molecules and directly triggers signals to the attached nerves cells, which produce taste. This is supported by research that shows electric stimulation of the tongue alone has produced sour, bitter, and salty sensations2.

In addition to an electrode, a temperature probe was also included, as changing temperatures can trigger taste sensations. For example, a previous study found that warming the front of the tongue evoked a sweet sensation, while cooling caused a salty/sour taste3. These scientists suggested this property of taste might be part of the hard wiring of the taste bud because the reverse had been shown to occur. Temperature specific nerve cells in the mouth were shown to respond to bitter and sour substances. Therefore, if temperature receptors can respond to taste, then taste receptors may also react to temperature.

While this technology is still in its infancy, it has the potential to enhance the overall gastronomic experience. Movies, video games, and TV shows could have flavor simulators that immerse your sense of taste into their world. Alternatively, chefs might be able to share the flavors of their dish remotely with patrons in the comfort of their own homes. Whatever its ultimate use, Nimesha Ranasinghe and his team’s work challenges our expectations of how flavor can be experienced and encourages others to push the boundaries of how new technologies interact with food.

Learn more about Digital Taste Interface

http://www.nimesha.info/digitaltaste.html#dti

 

References Cited

  1. Ranasinghe, N. et al. 2012. Tongue mounted interface for digitally actuating the sense of taste. 2012 16th Annual International Symposium on Wearable Computers (ISWC): 80-87
  2. Chandrashekar, J. et al. 2006. The receptors and cells for mammalian taste. Nature 444 (7117): 288-294
  3. Plattig, K. and Innitzer, J. 1976. Taste qualities elicited by electric stimulation of single human tongue papillae. Pflugers Archive European Journal of Physiology 361(2):115–120
  4. Cruz, A. and Green, B. 2000. Thermal stimulation of taste. Nature 403 (6772): 889-892.

Footnotes

  • A altering the magnitude of the electric current: The electric current, a measure of the flow of electric charges across a surface, is measured in amperes. A portable hearing aid is powered by about 0.7 microamperes, which is 3.5 times higher than the upper range of the taste electrode.
  • B frequency the electric pulses: The frequency of electric pulses is measured in hertz, which is defined as cycles per second. It is standard for the electricity (AC current) that you receive from an outlet in the US to operate at 60 Hz.

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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Sky-High Spuds

In the not-so-distant future, surfing the web at 35,000 feet will be just as reliable as going online at your favorite coffee shop. Who do we thank for this aeronautical innovation? Teams of engineers have been leading the charge to bring us quality in-flight internet, but there’s another WiFi hero you probably didn’t expect… potatoes!

Photo credit: Boeing

Photo credit: Boeing

Providing strong and consistent WiFi throughout a crowded airplane cabin presents an interesting challenge. Because the human body can interfere with WiFi signals, a cabin full of passengers can wreak havoc on an otherwise stable internet connection. But running rigorous WiFi tests on a full, airborne flight is impractical. And holding passengers hostage for days in a grounded airplane cabin is just unthinkable.

Enter the potato. Potatoes and humans have comparable dielectric properties, meaning that they similarly interact (and interfere) with WiFi signals. Engineers at Boeing used this to their advantage, creating a new way to test the quality of airline WiFi sans humans. The aptly named “project SPUDS” (Synthetic Personnel Using Dielectric Substitution) used 20,000 pounds of potatoes to quickly optimize the effectiveness and safety of WiFi signals aboard decommissioned airplanes.

When this breakthrough hit newsstands back in 2012, Boeing made it clear that potatoes weren’t in their original plan. In reality, SPUDS serendipitously took off when the research team stumbled across a paper from the Journal of Food Science describing the dielectric properties of 15 fruits and vegetables.

It turns out that food scientists have been studying the dielectric properties of fruits and vegetables for quite some time, as these properties determine how foods behave in a microwave oven. Dielectric properties describe how materials interact with electromagnetic waves, including those emitted by microwave ovens. In particular, dielectric properties determine how much energy a food can absorb in a microwave oven and how far into the food the microwaves will penetrate. Such information is especially useful to industrial food processors who often use microwaves to cook, pasteurize, dry, or preserve various food products.

WiFi signals are typically transmitted at a frequency (2.40 GHz) that is remarkably close to the frequency produced by microwave ovens (2.45 GHz). Thanks to the work of food science researchers, Boeing engineers could confidently choose the potato as their ideal human stand-in.

Thinking about this story, it’s hard not to marvel at the interconnectedness of science. Those food scientists probably never imagined that their work would eventually help improve internet access. And those Boeing engineers must have been pretty surprised to find themselves perusing the latest in food science research. It can be difficult to predict where our ongoing pursuit of knowledge will lead us, but one thing is clear—when it comes to expanding our view of science and making new connections, the sky’s the limit.


Liz Roth-JohnsonAbout the author: Liz Roth-Johnson is a Ph.D. candidate in Molecular Biology at UCLA. If she’s not in the lab, you can usually find her experimenting in the kitchen.

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The Benefits of Well-Rested Produce

Cabbage - credit postbear

Beauty rest isn’t just for people—cabbages also benefit from a good night’s sleep. (photobear/Flickr)

In 400 BCE, the Greek admiral Androsthenes wrote* of a tree that

“opens together with the rising sun . . . and closes for the night. And the country-dwellers say that it goes to sleep.”

Over the next 2000 years, researchers discovered that the daily cycles first observed by Androsthenes fall into 24-hour periods similar to our own cycles of waking and sleeping [1]. In plants, these circadian rhythms help control everything from the time a plant flowers to its ability to adapt to cold weather [2]. Plants can even use their internal clocks to do arithmetic calculations to budget their energy supplies through the night [3].

But what happens when part of a plant is harvested for food? In a recent study, researchers at Rice University and UC Davis showed that cabbages can exhibit circadian rhythms as long as a week after harvest.

As with any plant, cabbages experience circadian rhythms while growing out in the field; however, cabbages stuck in the constant dark of a delivery truck or light of a 24-hour grocery store will inevitably lose their sense of time. Like travelers adjusting to a new time zone, cabbages deprived of cyclic light conditions suffer a severe bout of veggie jet lag. And just as travelers overcome jet lag by readjusting their sleep cycles, cabbages can “re-entrain” their circadian rhythms by being exposed to cyclic light conditions. This also works with spinach, zucchini, sweet potato, carrots, and blueberries, suggesting that post-harvest circadian rhythms are a general characteristic of many, if not all, fruits and vegetables.

The ability to re-entrain circadian rhythms in produce presents an intriguing new way to improve the palatability and even nutrition of our fruits and vegetables. In the wild, circadian rhythms can help plants defend themselves against hungry herbivores. The researchers showed that cabbages with re-entrained circadian rhythms use a similar mechanism to avoid becoming an afternoon snack for plant-eating larvae—with less damage from hungry larvae, re-entrained cabbages appear fresher and tastier than cabbages kept under constant light or dark conditions.

Circadian rhythms help protect produce from herbivores. Samples from cabbages kept in (A) cyclic “in phase” light, (B) constant light, or (C) constant dark conditions were fed to larvae. Cabbages kept in constant light or constant dark sustained the most damage.

Cabbages fight off larvae and other pests thanks to molecules called glucosinolates. Any cabbage can produce these molecules, but re-entrained cabbages produce glucosinolates in sync with their circadian rhythms. Because larvae also experience circadian rhythms, re-entrained cabbages get an extra boost of molecular larvae-fighting power just when they need it the most.

While glucosinolates are bad news for larvae, they have valuable anti-cancer properties when consumed by humans. In fact, the very molecules that plants create to defend themselves against their environment are often beneficial for our own health. Future research will show whether such phytonutrients in other types of produce can also be reconditioned to accumulate in predictable 24-hour cycles. Taking advantage of circadian rhythms in fresh produce could then give us more control over the way phytonutrients accumulate over time, helping us maximize the nutritional benefits of our fruits and vegetables. Improving the nutrition of our food could be as simple as giving our produce a good night’s sleep.

 

*The original Greek passage comes from Botanische forschungen des Alexanderzuges [4] with a very special thank you to Tovah Keynton for the English translation. The drawings (also from Botanische) depict the tree leaves transitioning into and then assuming their “sleeping position.”
TamarindTreeRhythms

References Cited

  1. McClung CR (2006) Plant Circadian Rhythms. PLANT CELL ONLINE 18: 792–803. doi:10.1105/tpc.106.040980.
  2. Kinmonth-Schultz HA, Golembeski GS, Imaizumi T (2013) Circadian clock-regulated physiological outputs: Dynamic responses in nature. Semin Cell Dev Biol 24: 407–413. doi:10.1016/j.semcdb.2013.02.006.
  3. Scialdone A, Mugford ST, Feike D, Skeffington A, Borrill P, et al. (2013) Arabidopsis plants perform arithmetic division to prevent starvation at night. eLife 2: e00669–e00669. doi:10.7554/eLife.00669.
  4. Bretzl H (1903) Botanische forschungen des Alexanderzuges. B. G. Teubner.

Liz Roth-JohnsonAbout the author: Liz Roth-Johnson is a Ph.D. candidate in Molecular Biology at UCLA. If she’s not in the lab, you can usually find her experimenting in the kitchen.

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Human Cheese

Cheese1

Have you ever been offered a fancy cheese that smelled more like a used gym sock than something edible? Odor artist Sissel Tolaas and researcher Christina Agapakis took this idea and ran with it, with their project Synthetic Aesthetics. The duo used bacteria isolated from human hands, feet, noses, and armpits to generate cheese!

Many cheeses, like beer, wine, and yogurt, are the product of fermentation. Fermentation occurs when microorganisms such as yeast and bacteria convert carbohydrates such as sugar into alcohols, gasses, and acids to generate energy in the absence of oxygen. One common cheese-making type of bacterium, Lactobacillus, breaks down lactose, the primary milk sugar, to lactic acid. This results in lowering the pH of the milk, which as pointed out in a previous post, causes coagulation and solidification into cheese. The work of microorganisms in cheese also results in the creation of many other byproducts that give cheeses their unique smell, texture, and flavor profiles. For example, the bacterium, Propionibacterium freudenreichii, generates carbon dioxide gas in the process of making swiss cheese and causes its characteristic holes [1]. Penicillium roqueforti, which is related to the fungus that helps produce the antibiotic, penicillin, gives blue cheese it’s distinct aroma and look [1].

Microorganisms that use fermentation are found everywhere. Tolaas and Agapakis realized that the human body shared many characteristics with the environments for creating cheese. On a hot day or before a hot date, your armpits may be just as warm and moist as an industrial cheese incubator. Furthermore, cheese-making bacteria like Lactobacillus are common inhabitants in the mammalian gut [1]. With this information, they isolated bacteria from hands, feet, noses, and armpits and added them to whole milk to serve as starter cultures.

Figure 1. (A) Swabs from various human body parts incubating in raw milk. (B) Cheeses after solidifying. While no cheeses were consumed, they were evaluated with an odor survey and by DNA sequencing to identify the bacteria cultures present in each cheese.
Figure 2. Samples prepped for the smell survey. Participants of the survey were asked to smell the samples and provide a description of the odors they detected.

Here are the results:

Source Bacteria Isolated Odors
Hand-1 Providencia vermicola
Morganella morganii
Proteus mirabilis
yeast, ocean salt, sour old cheese, feet
Foot-1 Providencia vermicola
Morganella morganii
Proteus mirabilis
sweat, big toe nail, cat feet, sweet, milky, orange juice in the fridge too long, fungus, buttery cheese, soapy, light perfume
Armpit-1 Providencia vermicola
Morganella morganii
Proteus mirabilis
Feta cheese, Turkish shop, nutty, fruity, fishy
Nose-2 Providencia vermicola
Morganella morganii
Proteus mirabilis
cheesy feet, cow, cheese factory, old subway station, toilet cleaner
Armpit-2 Enterococcus faecalis
Hafnia alvei
neutral, perfumed, industrial, synthetic, fermentation, car pollution, burning, sharp, chemical
Armpit-3 Micobacterium lactium
Enterococcus faecalis
Bacillus pumilus
Bacillus clausii
neutral, sour, floral, smooth, yogurt
Foot-5 Providencia vermicola
Proteus mirabilis
yeast, jam, feet, putrid, sour, rotten
Armpit-4 Enterococcus faecalis yogurt, sour, fresh cream, butter, whey

The cheeses displayed a diverse range of bacterial species and odors. Interestingly while some cheeses smelled like “old subway station” or “cat feet,” others exuded the familiar & appetizing flavors of “yogurt,” “feta cheese,” and “light perfume.” Furthermore, some of the bacteria isolated were common to various cheeses. For example, Enterococcus faecalis is a lactic acid bacterium found in raw milk and cheeses, like farmhouse cheddar varieties [2]. Proteus mirabilis is related to Proteus vulgaris, which is responsible for giving surface-ripened cheeses like Limburger and Munster a strong aroma [3].

While these bacterial cultures may not serve as the basis of a new type of artisan cheese, Agapakis notes:

“These cheeses are scientific as well as artistic objects, challenging us to rethink our relationship with our bacteria and with our biotechnology. . . . The cross-over between bacteria found on cheese and on human skin offers a tantalizing hint at how our bacterial symbiotes have come to be part of our culinary cultures.”

In the face of diminishing resources, we are reminded that untapped reservoirs, which may be literally under our noses, might contain hidden treasures that could change the way we generate and produce food.


Online Resources

  1. More about this project
  2. More about Christina Agapakis
  3. More about Sissel Tolaas
  4. More about bacteria found on the human body
  5. More about the basics of cheese making


References cited

  1. Agapakis, C. 2011. Human Cultures and Microbial Ecosystems. http://agapakis.com/cheese.pdf
  2. Gelsomino. R. et al. 2002. Sources of Enterococci in Farmhouse Raw-Milk Cheese. Applied and Environmental Microbiology 68(7): 3560-3565.
  3. Deetae. P. et al. 2009. Effects of Proteus vulgaris growth on the establishment of a cheese microbial community and on the production of volatile aroma compounds in a model cheese. Journal of Applied Microbiology 107(4):1404-1413.

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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Understanding Umami

Imagine taking a bite of your favorite food. Is it sweet? Salty? Does it have a sour bite or a hint of bitterness? Maybe even a touch of savory umami?

Every time we eat, our taste buds sample these five basic taste qualities. Taste receptors decorating the surface of each taste bud interact with specific molecules; the corresponding flavor sensation then gets sent to your brain. Umami receptors, for example, sense the molecule glutamate. When free glutamate in our food—either naturally occurring or from added MSG—interacts with an umami receptor, we taste a delicious savory flavor.

Although glutamate is the primary source of umami flavor, certain molecules called nucleotides can enhance the umami sensation. Because nucleotides make up the genetic material (DNA and RNA) of all living things, nucleotides are ubiquitous in many of the foods we eat. Nucleotides themselves cannot activate umami taste receptors, but they can intensify the umami sensation caused by glutamate. Intrigued by this phenomenon, scientists Ole Mouritsen and Himanshu Khandelia recently published a paper exploring how one nucleotide, guanosine-5ʹ-monophosphate (GMP), might work together with glutamate to activate umami taste receptors.

Only one of the three known umami taste receptors can interact with both glutamate and GMP. This so-called “T1R1/T1R3” receptor switches between two states: an “off” state when no glutamate is present and an “on” state when glutamate is attached to the receptor. To understand how GMP might affect these two states, Mouritsen and Khandelia ran a series of computer simulations testing the receptor’s behavior in the presence or absence of GMP. As expected, glutamate caused the receptor to exist in the “on” state more than the “off” state. When GMP was added to the simulation, both GMP and glutamate interacted with the receptor to further stabilize the “on” state.

Model of the T1R1/T1R3 umami taste receptor. The taste receptor (in blue) is “off” when no glutamate is present. Glutamate interacts with the receptor, stabilizing the “on” state and signaling an umami taste sensation. Glutamate and GMP together bind the receptor and further stabilize the “on” state, presumably leading to a longer, more intense umami sensation.

Besides providing a compelling molecular model for umami taste sensation, this and future work on taste receptors may help us become more savvy seasoners in the kitchen. Because umami taste receptors are similar to the taste receptors for sweet and bitter, understanding how molecules like GMP enhance umami sensations can help us develop enhancers for other taste sensations. Just as GMP makes glutamate taste more intensely umami, a sweet enhancer could make sugar taste sweeter with no added calories. Identifying more taste enhancing molecules like GMP could bring a whole new dimension to the way we cook in the future. Forget about salt and pepper—the flavor enhancers are coming.


ProfileImageSmallAbout the author: Liz Roth-Johnson is a Ph.D. candidate in Molecular Biology at UCLA. If she’s not in the lab, you can usually find her experimenting in the kitchen.

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Reinventing the Egg

Even if you’re not watching your cholesterol, there are plenty of reasons to avoid eating eggs. Ethical issues aside, industrial eggs provide only about 20% of the energy it takes to produce them. And while some egg substitutes do exist, they often pale in comparison to the real thing. Josh Tetrick, the CEO of Hampton Creek Foods, thinks we can do better. Read more