Beyond the Dairy Aisle

Whether it’s with your cereal first thing in the morning, or in a glass with some chocolate syrup at night, milk is a staple part of most people’s diets. If it’s anything like mine, your family probably goes through at least a few gallons of milk every week, if not more. Milk comes in all different forms, too: without milk, you wouldn’t be able to put that whipped cream on your apple pie, or butter your toast during breakfast. Although it seems pretty simple, the physical status of milk is actually extremely complex, especially when it comes to the chemistry behind it.

The Chemistry Behind Milk

If you were to leave a glass of milk to sit for some time on your countertop, you would begin to see a thin layer of cream form on the surface of the milk. What exactly is this? Well, if you were to view this layer under a microscope, you would see shapes floating around in the milk, which is the fat. In chemistry, this is known as an emulsion; specifically, an emulsion of fat in water. An emulsion is a mixture of two or more liquids that are non-mixable. If you were to shake the glass of milk, the emulsion would be broken down and the milk would go back to normal. However, milk does come in more than one form, such as butter – the difference is that butter is an emulsion of water in fat. So when the milk is churned into butter, there is a phase change that is involved in the process.

The fats that are present in milk are there for a reason- they act as a solvent for all of the fat-soluble vitamins in milk that make it so healthy, such as Vitamins A, D, E, and K. In the milk fats, the fatty acid molecules are made up of a hydrocarbon chain along with a carboxyl group, or COOH group, usually, consisting of all single bonds, one double bond, and an even number of carbon atoms. Structurally, these chemical molecules look something like this:

milk.PNG

Other properties of milk, such as the melting point and the hardness of the fatty acid, is affected by various factors such as the length of the previously mentioned carbon chain as well as the degree of unsaturation (when a molecule is unsaturated, this means that it does not have the greatest possible amount of hydrogen atoms that it can have for the number of carbon atoms that it has. In other words, fats with a lot of these high-melting fatty acids will be hard; but fats with a high content of low-melting fatty acids can make the spreadable butter that you put on your toast every morning.

Making Your Milk Taste Its Best

Depending on what kind of environment your store your milk in, you may notice that the milk tastes different. Changes in storage can cause different types of chemical changes to occur in the milk, one of them being oxidation. Although most people tend to think that milk changes or goes bad when it is left outside of a refrigerator because of the higher temperatures, there are actually a lot of chemical processes occurring in milk when it is exposed to lower temperatures as well, such as the oxidation of the fats in the milk.

Although the oxidation of the fats in the milk can be counteracted by reducing agents that are present in the milk, such as lactic acid bacteria, there are still many chemical changes that may cause some unwanted things to occur in your milk. For example, chemical change that occurs due to the oxidation of the fats in the milk is the “flavor” of the milk – although plain milk does not actually have a flavor to it, lower storage temperatures usually cause milk to develop an unpleasant flavor. This is why companies that produce milk place great emphasis on precise refrigeration for their milk, because nobody wants their milk tasting funky!

Got Milk?

Among the many beverages that have come to prominence in society throughout history, milk, along with water, is probably among those that will continue to be a mainstay in the diets of people both young and old. The small cardboard milk carton you get at lunch, the glass full of milk that you dip your Oreo in, the milk mustache you get on your upper lip when you take a sip. All of these are iconic images that come to mind when one thinks about milk throughout history. After taking away this information regarding the chemistry behind milk, one could also realize that not only will milk remain a staying force forever, but so will its chemistry.

Beavers and Vanilla

Why flavorings smell and taste the way they do

By Mark Sabini, Justin Yu, and James Lee

Imagine a cave of darkness lined with white pearly stalactites and stalagmites. On the ground is an organic carpet of living red, and there is an uncomfortable dampness in the air. Liquid flows all over the ground, making navigation difficult. Now imagine moving to another location with two doorways, side by side, carrying breezes of air in and out. They both look the same, mirror images of each other. Peering inside, you see what seems to be a grass of some sort, except that it grows all around the surface of the doorway, not just on the ground. You step inside, into a tunnel of blackness, and then whoosh! A strong breeze sucks you in, into oblivion. Now reflect on where you have just been: a human mouth and a human nose. Working together, these organs make up 40% of the five senses, and give flavor to food and aroma to flowers. How exactly do these marvels of nature function?

Taste and Smell

Taste relies on the transformation of chemicals from food (tastants) into nerve signals. The tongue’s mucous membrane is lined with tiny bumps called taste papillae. These little sensors responsible for taste perception consist of taste buds with sensory cells. The sensory cells form a little “cup” (see picture), which contains taste hairs. The proteins on the surface of the taste bud bind the chemicals from the food to the sensory cells for tasting. Then, the sensory cells transform the chemical signals into electrical signals that travel along nerves to the brain. Contrary to popular beliefall parts of the tongue are equally sensitive to the five tastes, sweetness, sourness, umami, bitterness, and saltiness, except the back of the tongue. The cells there are more sensitive to bitterness, most likely as a natural defense against swallowing bitter plants containing poisons.

Figure 1: Diagram of a typical taste bud
Figure 2: Video about taste

Smell works slightly differently from taste, but still employs the same basic principle: the transformation of chemical signals to electrical signals. At the top of every person’s nasal passage is a patch of neurons that is exposed to air. The neurons have small hairlike projections called cilia, to which volatile food chemicals (odorants) bind and cause transmission of electrical signals along the neurons to the olfactory bulbs on the underside of the frontal lobe. As a result of this mechanism, only volatile compounds will have smells. While they might seem unrelated, taste and smell work hand in hand. The data from the two senses is merged in the insula, a part of the brain, to put together what we know as flavor. This is why you cannot sense flavor when your nose is blocked – the smell component of flavor is missing.

Figure 3: Diagram of the Olfactory System. The patch of neurons located at the top of the nose feed into the olfactory bulb which sends signals directly to the brain.

The Chemistry of Flavorings

Esters are a class of organic compounds that have distinctive tastes and smells, and are used widely in the food industry.The ester octyl acetate, for example, is responsible for the characteristic citrus smell and taste of oranges. Esters can be prepared through Fischer-Speier esterification, in which a carboxylic acid and alcohol are reacted in the presence of an acid catalyst. The strong smell of esters is attributed to their volatility and the functional groups attached to the ester group. A list of commonly-used esters and their tastes and smells is shown below.

Figure 4: Fischer Esterification Figure 5: Chemical structures of some common esters

Other flavoring ingredients come from more natural sources, albeit quite strange ones. One example is castoreum, a brown, slimy secretion from the castor sacs located near a beaver’s anal glands. It has a vanilla taste after some processing, as it is originally mixed in with beaver urine and other impurities from the animal. Castoreum contains chemicals such as phenols and ketones, all contributory towards the smell and taste. According to MSU flavor chemist Susie Bautista, castoreum is not used much (since it is not kosher), but greatly enhances vanilla flavor. A similar chemical to castoreum is vanillin, a phenolic aldehyde. Vanillin is a component in both natural and artificial vanilla flavoring. Occurring in natural vanilla pods, vanillin can be extracted from the natural source. Otherwise, it can be synthesized from a chemical called guaiacol and glyoxylic acid. Chemical synthesis accounts for the vast majority of vanillin production in the world.

Figure 6: Left: Castor sacs from a beaver and castoreum. Right: Vanilla Pod
Figure 7:Vanillin and4-Ethylphenol1,2-dihydroxybenzene, and 3-hydroxyacetophenone: three components of castoreum; there are clear similarities between the chemical structures which accounts for their similarity in taste/odor

Figure 8: Chemical synthesis of vanillin from guaiacol

Another chemical that has gained much publicity is monosodium glutamate, MSG for short. MSG contains around 80% glutamic acid and contributes to the taste ‘umami,’ which is a taste found in cured meats, mushrooms, and cheeses. MSG is used as a flavor enhancer to greatly improve the flavor of many foods. It does so by providing glutamic acid to bind to the glutamate receptors on the tongue, allowing food to taste “meatier”, and therefore tastier. However, its wondrous properties do not come without negative effects. MSG can lead to eye damage, depression, and a whole host of other problems, as well as cause “Chinese Restaurant Syndrome,” which affects MSG over consumers with headache and asthma. This chemical is one example of why are chemical food flavorings require careful scrutiny. The benefits of taste may be outweighed by the health related downsides.

Figure 9: Structure of glutamic acid, a major component of MSG.

Conclusion

Smells and tastes are caused only by the chemical binding of compounds to receptors in the tongue and nose. In order to be smelled, a chemical must be volatile, or no odor components will enter the nose. Many chemicals play important roles in tastes and smell. For example, esters are a class of organic compounds with strong smells commonly found in fruits such as bananas and apples. Other flavor compounds include vanillin and castoreum, which are both used as vanilla flavorings. While both compounds emulate the same flavor, vanillin, a phenolic aldehyde, is found naturally in vanilla pods, while castoreum, a mixture of phenol and ketones, is produced in beaver castor glands. These compounds easily highlight the ability to “fool” the taste buds. Finally, monosodium glutamate, MSG, is a chemical responsible for the umami taste in foods. Its numerous adverse effects show the potential dangers of using flavorings and the need for in-depth analysis of the effects of flavor compounds on humans. The complexity of flavors highlights the need for humans to scrutinize the additives in their food. Who knows – the next vanilla iced coffee you drink might not actually have vanilla.

Beat the Heat: Investigating Garlic Powder

The ingredients list as seen on a typical bag of Flamin’ Hot Cheetos.

Snacking is a quintessential pastime in American culture. At many times, we have seen ourselves mindlessly reaching for the nearest box of Cheez-Its simply because, well, we need something to reduce our cravings before our next main meal. And the snack companies are aware of our almost subconscious cravings such that the potato chip company, Lay’s has its slogan as “Betcha can’t eat just one,” essentially taunting the hunger-stricken American public in the process. Personally, a favorite snack of mine is a nice bag of Flamin’ Hot Cheetos. This modern delicacy is extremely addicting, and as its name implies, is intensely spicy, so much that your nose might drip a bit as you inhale the strong spices in the bag. Curious to why this snack caused this reaction in me, I decided to ask the heads at Frito-Lay themselves about their product. What ingredients in the Cheetos make this notorious spicy flavor? I wrote to them:

I was eating Flamin’ Hot Cheetos the other day, and I took a look at the ingredients list because I was curious at what spices made the Cheetos so hot. I specifically noted the onion powder, garlic powder, and natural flavor. Is the spiciness of your product because of these three ingredients or are there others on the list to enhance the spicy flavor? Also, I was wondering what is ”natural flavor” and what is it made up of? Thanks so much, hope to hear from you soon! 

Frito-Lay replied with the following:

Thank you for writing to us. 

The “heat” in Cheetos Crunchy Flamin’ Hot is a secret–and that’s why it’s included under “natural flavors.” Using terms like “spices” and “natural flavors” on ingredient statements, is the way food companies protect their proprietary recipes. 

You’re right about the other seasonings like garlic and onion (two ingredients that must always be listed when used). They are included in the seasoning to enhance the flavor.

We consider you a valued consumer and hope you will continue to enjoy snacks from Frito-Lay. 

Best regards,

Linda

Frito-Lay Consumer Relations

It was understandable for Linda to not disclose what exactly is “natural flavor,” but nevertheless, I could deduce that the garlic and onion powder contribute to the Cheetos’ distinct flavor. And with this information, let’s look into the contents of specifically, garlic powder.

The Chemistry of Garlic Powder

Biologically active (or “bioactive”) components are the biomolecules that are responsible for influencing the various metabolic processes in foods. It is because of these bioactive food components that foods display their health benefits. For example, bioactive compounds such as dietary fiber found in many fruits and vegetables such as apples, broccoli, and carrots allow for capturing of harmful toxins in the digestive tract. Once completing its function in the digestive tract, this all-important bioactive food component consequently prevents constipation in the body and possibly even lowering one’s risk of heart disease or diabetes. Garlic powder is an interesting ingredient in that it does not actually contain the major biologically active component of garlic, allicin. In fact, fresh garlic in general does not directly contain allicin either! This apparent commodity can all be explained once the intricate chemistry of garlic is investigated.

A visual representation of the chemical reaction that forms allicin from alliin.

Within a sample of fresh garlic is a chemical known as alliin, which is its natural constituent. In addition, the enzyme, alliinase, is also found in fresh garlic. Like most enzymes, alliinase acts as a catalyst in a chemical reaction. Because the alliinase molecule acts as the catalyst, it would consequently lower the activation energy of the reaction to speed up the process. In this case, it would speed up the creation of allicin.

However, alliinase acts in perhaps the most important chemical reaction regarding fresh garlic. As we all know, garlic is noted for its strong smell and flavor, but most notably, its ability to generate tears when cut. Chemicals that give garlic these distinct qualities are supplied via this reaction between alliin and alliinase. Alliinase is released and subsequently reacts with alliin to make the aforementioned component allicin. Of course, the evident ambiguity of all these terms makes the reaction somewhat difficult to comprehend, but from a wider perspective, it really is nothing we haven’t seen before. As a matter of fact, this conversion to allicin actually occurs when you cut or crush garlic with a knife! This explains the tear effect, as it is when garlic is cut that its bioactive component, allicin finally appears.

 The act of chopping or crushing garlic releases the allicin in the cloves of garlic.

Once the allicin is produced, it will take a short time for the odor from the garlic to go away. As it turns out, allicin has quite a short half-life (2.5 days at 23°C,  to be exact!). It can be assumed that the reaction is first order with respect to allicin, since the half-life is constant at certain temperatures and not dependent on the initial amount of allicin produced. This is convenient for the production of allicin, as it helps to maintain the preservation of alliinase and alliin so more future allicin can be produced. This allicin production occurs very quickly and within a small surface area of the clove (where the garlic is being cut), meanwhile the alliinase and alliin remain sustained in other parts of the clove. In other words, even though allicin generates a large amount of odor albeit briefly, as long as the alliinase and alliin persist in their respective section of the clove, then allicin can continue being made repeatedly.

Moving Forward with Allicin

In this video, a man gives a humorous account of how he tried to make allicin by directly consuming cloves of garlic.

Now knowing that allicin is produced when garlic is chopped or crushed, it would probably not be a very good idea to chew garlic directly, especially multiple cloves. Obviously, for the man in the video who tried to receive the effects of allicin directly in the body, it did not turn out too well as he received nausea as a result. There could be a possibility that this is why even though garlic powder does not contain allicin, it still achieves intense flavor and odor when consumed. Ingesting allicin in large amounts would cause potential uncomfortability in the body but not when derived into its chemicals such as alliinase and alliin as is with garlic powder in Flamin’ Hot Cheetos  and other garlic supplements in other food products. Garlic powder achieves similar effects to garlic but none that would be seriously detrimental to the body. With this, Flamin’ Hot Cheetos can acknowledge garlic powder’s contents for its intense heat, advantageously applying bioactive components of garlic for its effect. It is something to keep in mind for the next time you mindlessly munch on this interesting snack.

Even Katy Perry can’t deny the delicious taste of Flamin’ Hot Cheetos!

LE CHOCOLAT

Chocolate. As addicting as it may be, ever wonder how chocolate comes to taste as amazing as it does? The rich and creamy taste of good sweetness in your mouth every time you take a bite out of your favorite chocolate bar just seems too irresistible. Or maybe you’re one of those people who prefer the aerated chocolate bars, infused with gas and is even creamier than regular chocolate. No matter your preference, the beautiful and unique taste of chocolate is due to the rigorous and complex processes it undergoes. Consistency is perfection and is tied directly to thermodynamics and the chemical compounds that are integral in the production of chocolate. From cacao bean to the bar you wish you were holding in your bar right now, let it be put that the perfect chocolate is not as easy to make as it may seem.


Figure 1. Theobroma cacoa, the cacao tree.

First, the cacao pods from the cacao tree Theobroma cacoa are harvested and the beans and pulp are extracted from the pod. They are left to ferment for a few days and then laid out in the sun to dry. Roasting the beans is one of the most important steps in making chocolate. It kills the lingering mold and bacteria (because that wouldn’t be too yummy to ingest now would it?) The roasting of the beans is also what changes the flavor and removes some of the bitterness. Now to the chemistry. The cacao bean  is comprised of 55% fat, 12% protein, 11% fiber and 6% starch. Roasting the beans removes fatty acids that are unwanted such as ethanoic acid. The roasting generates a chemical reaction called non-enzymatic browning, more specifically, the Maillard reaction. The Maillard reaction occurs when the carbonyl group of sugars reacts with the amino acid group and produces N-substituted glycosylamine and water. It then undergoes the Amadori rearrangement to form ketosamines that react further with brown nitrogenous polymers. The reactions of the Amadori rearrangement inclue mainly fission, dehydration, and degradation At this point, the beans have off-flavors and off aromas. But have no fear, these bitter and rancid-smelling beans do become the sweet chocolate we all enjoy and love through a few more processes. The beans are ground into cocoa liquor and then pressed to separate the liquor from solids. The solid is also known as cocoa butter and this key ingredient continues onto conching and tempering to become chocolate.

Conching  removes volatile compounds such as methanol and acetic acid, as well as adjust moisture content and viscosity. This is a mixing process that aerates the mixture for 24-60 hours at 110°F, to stimulate interactions between ingredients and molecules. As this occurs, flavor and aroma develop as acidity and the bitterness of the cocoa are lost and moisture content is reduced.

Tempering is but a complex cooling process, to make the cocoa butter seeds uniform in size and shape and to stack these molecules tightly together in a nice crystalline structure. Imagine a bunch of LEGOs, all different shapes and sizes. If piled together, it is not very efficient and unstable. But, if packed tightly and orderly, the structure is stable. The process of tempering is simply stacking cocoa butter seeds to be as stable as possible.

The main component of tempering is temperature. As the chocolate cools, the cocoa butter forms stable and unstable seed crystals. These crystals are proportional to the six different crystalline forms of cocoa butter. This means that the atoms are the same but they may be arranged differently. Relating back to LEGOs, there are many different types of arrangements but it will always be the same types of LEGOs you use to create something. The ability of having multiple arrangements or shapes is called polymorphism. It is found that the tastiest, most stable, and ideal form is Form V, or beta crystals. The melting point for the Form V polymorph is about 33.8°C, about 92.8°F. This temperature is about the temperature of a person’s mouth, unless they submerged their tongue in something cold for a long period of time. Because this polymorph’s melting point is nearly identical to our mouths’ internal temperature, chocolate basically spontaneously melts, which is chocolate is so irresistible. The lower the melting point of the polymorphs, the thicker and stickier it feels in the mouth. Polymorph VI, unfortunately, is produced after 4 months a room temperature, has a higher boiling point and is much more stable. Fats melt quickly because the carbon atoms within the fat form long chains of atoms. Intermolecular forces affect these chains, so the more fat chocolate has, the faster it melts due to the intermolecular forces caused by the carbon chains.


Figure 2. Different cocoa butter polymorphs and corresponding melting points.

Figure 3. Form V Polymorph

To keep only stable beta seed crystals, the chocolate is warmed again to a temperature between the melting point of beta crystals and the temperature at which beta crystals form. The mixture is then cooled at around 13-15°C, or 55-59°F, to promote preferential growth of the stable crystals. If the temperature were too high, the cocoa solids and other dry ingredients from the cocoa butter would separate, thus resulting in a dry paste. Likewise, if the chocolate’s moisture level increased even the slightest, the dry particles in the mixture would be saturated and detach from each other, maintaining a liquid form. Though this does not result in a chocolate bar, it is a useful technique to add water to chocolate when making chocolate sauces or syrups.

 Figure 4. Comparing the compactness and stability cocoa butter polymorphs.

Speaking of different forms of chocolate, believe it or not shape and type actually do contribute to taste. These are components that affect how the chocolate breaks up in the mouth, thus it is opinionated on whether you prefer a normal chocolate bar to an aerated one, for example. The cocoa crystals in chocolate are about 0.01 to 0.1mm in diameter. This microscale structure however varies slightly with the way the chocolate is molded. Normal chocolate bars are molded after tempering while aerated chocolates receive a blast of a certain propellant. These propellants can vary from nitrogen to argon to regular CO2 or even nitrous oxide, also known as laughing gas. This gas is infused into the chocolate and turns the chocolate into a foam with the use of a siphon. After siphoning, the chocolate is cooled in a low pressure environment, like a vacuum, to let the gas bubbles expand. Depending on the propellant used, the sizes of the bubbles also alter the taste of the chocolate.  A study funded by Nestlé proved that chocolate foamed with nitogen and nitrous oxide had more intense tastes due to the larger bubbles these gases produced.

Figure 5. A chef using a siphon to aerate chocolate into a foam.

“Aerated chocolate is more gentle and creamy. Its density is so low that it takes seconds for the chocolate to meld down in the mouth. That is why its taste is so exquisite and great,” says Stephen Becket, a former researcher for Nestlé. This is because aerated chocolate is lower in density and has a lower melting point, being only more sensational in the mouth and stimulating what is called mouthfeel. No wonder truffles seem to just melt into your soul whenever you pop one into your mouth. It’s always been about chemistry.

We can all admit that chocolate is an amazing sweet itself, whether it’s satisfying a crave or bestowing this great treasure upon a significant other on Valentine’s Day. What’s even more amazing is how chemical and mechanical processes are able to turn a bitter cacao bean into the beautiful joy that eating chocolate may bring us all. With these processes, the most important thing to keep in mind is consistency. Our senses are able to discriminate taste based on the texture of chocolate and its feel, and that’s pretty cool. Just think the next time you taste your favorite chocolate, think not only of how it became that perfect shape and texture but how because of the way it feels on your tongue, your taste buds cannot seem to thank you enough.

Molecular Gastronomy The Science Behind the Cooking of Food

When cooking an egg, you often notice that the egg white (albumen) changes from a clear, runny liquid, to a firm, opaque, solid. Why does this happen? Similarly, why does yellow, unbaked bread dough, turn brown when put in the oven? These questions are answered in a branch of food science called molecular gastronomy. While this two-word phrase may seem intimidating, it simply refers to the study of the physical and chemical changes that happen to ingredients during cooking. The term was created by Hervé This and Nicholas Kurti in 1988 as the title of a series of workshops aimed at exploring the science behind the cooking of ingredients. The pivotal moment in molecular gastronomy came in 1969, when Kurti held a presentation called “The Physicist in the Kitchen” for the Royal Society of London, in which he performed food-based science experiments, including making meringue in a vacuum chamber (previously unheard of since meringue involves beating air into egg whites) and using pineapple juice to digest protein. In this blog post, we will explore three major applications of molecular gastronomy: spherification using alginate, transglutaminase meat glue, and sous-vide cooking. As will be seen, understanding the chemistry behind food allows for exotic and unique culinary creations to be realized.

Spherification with Alginate

One of the great wonders of molecular gastronomy is the process of reverse spherification, which allows one to create balls of liquid encapsulated in long-lasting, gelatinous shells, similar to caviar. How exactly does spherification work? The secret lies in the chemicals involved.

The first of two main components is alginate, which can be extracted from brown seaweed. Alginate is an anionic polysaccharide, and is often obtained as a sodium salt. It is important to know that alginate is not the only compound capable of performing the same role, as chemist and food enthusiast Martin Lerschasserts – a whole list can be found here. The large carbohydrate chains of alginate allow it to act as a thickening agent, but the real magic happens when the second of the main components is present – calcium ions. In contrast to alginate, it is preferred that the calcium ions already be present in the liquid being spherified. In the case that calcium is not already present, calcium lactate or calcium lactate gluconate can be added. What exactly happens between the alginate and the calcium ions that allows for the formation of liquid-filled spheres? The calcium ions fit between the strands of alginate, allowing them to interlock, creating a net of tangled polymers and form ing a gel. After knowing the chemistry behind spherification, the process is quite simple – the flavored liquid, containing calcium ions, is simply “dropped” using an eyedropper into a solution of sodium alginate.

 Left: Alginate, Right: Calcium lactate gluconate

However, before spherification can be guaranteed to happen, there is one parameter left to tweak – density of the flavored liquid. This physical property is extremely important due to surface tension, the net effect of the intermolecular forces between liquid particles at the surface. An underly dense liquid will not be able to penetrate the surface of the sodium alginate solution, while an overly dense one will not bead up into a sphere.

Spherification has had many creative applications to molecular gastronomy over the years. A popular experiment is to encapsulate tiny drops of fruit juice, creating “fruit caviar.” However, using larger drops allows one to also simulate many foods, like green olives and cheese.

Various examples of spherification to create exotic foods

Provided here is a video demonstrating the spherification of foods

Transglutaminase Meat Glue

One of the topics in the field of molecular gastronomy that has generated heated discussion is a material colloquially called, “Meat Glue”. Chemically, meat glues are referred to as transglutaminase. Transglutaminase is an enzyme naturally found in blood which catalyzes the formation of a covalent bond between a free amine group and an acyl group which are found on the ends of proteins. These enzymes aid in the formation of strong protein bonds which do not degrade easily. These enzymes are frequently used to connect different pieces of protein-rich food stuff, mostly meats, together.

Schematic of bonding involved in use of transglutaminase

No US law requires chefs to disclose whether they use meat glues. However, many customers look down upon the practice, worried whether the meat they eat is actually one piece or a mixture of scrap meats. Another concern of critics is that by “gluing” pieces of meat together, the pathogen-covered surfaces of the meat, which are usually seared to kill these pathogens, are left unfettered and pose a health hazard to the consumer. In 2001, the USDA stated that any meat products produced through the use of meat glue must have it clearly marked on the label.

However, chefs defend the use of meat glue, stating that meat glues help reduce waste and allow them to create creative culinary masterpieces, making it possible to design foods with patterns and combine different types of foods together to create never before seen

Transglutaminase, aka meat glue, is sold under its brand name Activa. It is sold as a powder which can directly be applied to the surfaces of the foodstuffs that are being combined. After adding a little water, placing the conglomerate in a vacuum bag, and letting it set in a freezer overnight, the transglutaminase will form bonds. It is sold by the Ajinomoto company, the same company which produces other products such as the commonly utilized neurotoxin food additives, aspartame and MSG (monosodium glutamate). The U.S. Food and Drug Administration lists transglutaminase as “generally recognized as safe.” However, many people are hesitant of eating meat glue because they fear transglutaminase may also possess toxic properties. Transglutaminase is produced by cultivating bacteria using vegetable and plant extracts in the blood plasmas of pigs or cows. However, manufacturers are not required to share the exact method of synthesis, adding to the uncertainty and fear consumers hold regarding this product.

 Left: Meat-glued chicken and beef. Center: Meat-glued salmon and tuna. Right: Meat-glued lamb and scallops.

 

Production process of food using transglutaminase meat glue

Sous-vide Cooking

The last molecular gastronomy technique that will be discussed is sous-vide cooking. So what exactly is sous-vide cooking? This is a technique where food is vacuum packed in a plastic pouch and cooked a closely controlled temperature in a water bath. This allows for a great deal of control and the ability to cook food with extreme consistency. Many recipes can make use of this technique. So why spend the money on such expensive equipment in the first place?

Firstly, sous-vide involves vacuum packing the food product. This allows the carefully controlled temperature, usually around 122 to 149 degrees Fahrenheit to evenly cook the food in polyethylene bags.Polyethylene is a common plastic polymer that is generally regarded as safe for use with food.

Polyethylene

Another benefit of using the bag is that it allows, for example, meat to retain its juices while cooking. Volatile flavors are also saved. Sous-vide also prevents the development of odd flavors from oxidation. Since it is vacuum packed, the amount of oxygen in contact with the food greatly decreases, as does the chance of oxidizing the cooking oil when the oil nears its boiling point. Meat begins to turn to a red color and then to a grayer color when in contact with oxygen as myoglobin is oxidized to oxymyoglobin and then metmyoglobin. Bacteria may also begin to grow. These effects are greatly reduced by vacuum pack-cooking the food, since aerobic bacteria will not proliferate. This can also help reduce the need for adding nitrites, an anti-oxidizing agent

Left: Fresh meat which has not been oxidized. Right: Meat that has turned grayer after coming into contact with oxygen.

Conclusion

By implementing molecular gastronomy in cooking, exciting new kinds of food can be created. Shapes, textures, and even flavors can be generated using a variety of techniques such as spherification, sous-vide cooking, and meat-glue. Although some may stick to more traditional methods, the new wave of approaches to cooking give a contemporary spin on food. Many restaurants and chefs around the country have adopted molecular gastronomy such as Grant Achatz and Wylie Dufresne. Molecular gastronomy truly gives a glimpse into the kitchen of the future.

Say Cheese!

From being an integral component of fancy garden parties to an ingredient in your sandwich, cheese is an extraordinary delicacy. The processes that cheese-makers undergo, starting with milking either some sort of animal, are strenuous and time-consuming. The milk must be pre-cured into something called curds, which is then aged for weeks to years, depending on the type of cheese, before it ends up in your homes. There are also many different types of cheeses, all of which depend on the internal molecular structure of the milk from which it is produced from as well as manufacturing processes that affect its chemical makeup. Nonetheless, form and flavor are one of the two most important things to consider in making cheese, and we are going to tell you just how to make the perfect batch.

Cheese starts off as a milk conglomeration, or heterogeneous mixture, of lipids and proteins. The milk is prepared for curdling through a number of different ways, all including the addition of a culture ofLactococci, Lactobacilli, or Streptococci bacteria. Yuck! Do not fear because the types of bacteria used for cheese-making are strictly either isolated from either the dairy environment or plant material. They are the good kind of bacteria needed in the body to function, also known as probiotic strains. The bacteria cultures are fermented to convert lactose in the milk to lactic acid.

 
Figure 1. (from left to right) Lactococci, Lactobacilli, or Streptococci bacteria.

Once the milk is pre-cured, it is inoculated with the lactic acid bacteria and rennet. Rennet is a complex of enzymes, one of which being rennin. This specific enzyme converts uncoagulated protein in milk called caseinogen into coagulated and insoluble protein, called casein, with a two-stage process. Firstly, rennin splits a bond in the amino acid chain of kappa-casein, a mammalian milk protein. A glycopeptide is removed from the soluble casein, producing para-casein. This process causes an imbalance in intermolecular forces in the milk, causing hydrophilic macropeptides to be released into the whey. The second step requires colloidal calcium phosphate to bridge with a casein micellar structure to create a curd substance. Colloidal Calcium phosphate, also known as CCP, bridges hundreds of submicelles that form the casein micelles. The bonds are either covalent or electrostatic. The micelles that contain a lot of kappa-casein take a position on the surface whereas those with less stay in the interior. This new layer prohibits further accumulation of micelles.

 
Figure 2. Micellar structure consists or a hydrophobic tail and a hydrophilic head suspended in an aqueous solution.

The role the lactic acid plays in the cheese-making process is to denature milk proteins to coagulate. Milk contains about 80% casein and 20% whey protein, in which the casein has a negative charge. The H+ concentration turns the negatively charged casein micelles into neutral. At a pH of 4.7, the milk reaches a point where all charges are neutral, known as the isoelectric point. Since the micelle formation calls for hydrophilic ends to converge and the hydrophilic ends to be on the outer edges of the molecule, large molecules of casein proteins are suspended in the milk water. This creates a precipitate called acid casein, as seen in cottage and cream cheese.

Most cheeses use rennet to curdle. It sets the cheese into a stronger, rubbery gel, compared to the delicate curds made by acidic coagulation. Rennet also allows curdling to occur at lower acidity which will be a huge benefit when flavor-making bacteria is introduced. The rennin coagulum will have a fluffier texture than the acid precipitate. Rennet is used in the manufacturing of most cheese currently.

 
Figure 3. Curds are solid particles and whey is a liquid that is extracted from the milk-cheese process.

To watch a video on how cheese is made from milk, please click here.

Now to actual manufacturing and processing. The unique form and flavor of a cheese is dependent on choice of milk, the bacteria strains, salt, brining, and most importantly, aging. Firstly, the animal from which the milk is extracted from, for example goat, sheep, or cow, affects the flavor of the cheese due to their difference in structure and composition. There are different protein structures, fatty acids, and butterfat contents in the milk that differentiate the cheeses from one another. For example, cow’s milk is enriched with cream for soft cheeses, increasing their fat content. The fat content allows for different reactions during the cheese-making process, in which there is a greater amount of moisture in the cheese that gives it its softer texture. This is because the enzymes cannot break the fats into its smaller counterparts, which slows coagulation. The manufacturers from the Cabot Creamery in Vermont share that the “longer the cheese ages, the longer the enzymes have to break the fats and proteins down into their basic building blocks (fatty acids from the milk fat; amino acids and peptides in the proteins).” The structure of the milk cheeses contributes to aging times as well. Goat’s milk cheeses mostly cannot be aged as long as cow’s and sheep’s milk cheeses, for it will be dry and crumbly compared to the usual soft texture of cheese.

The different types of bacteria, as well as how they are treated during the cheese-making process affects the flavor of the cheese. Bacteria strains can be blended for a desired flavor. This is due to the bacteria’s acid tolerance, spore forming ability, and fermentative metabolism. If a bacteria strain cannot handle the H+ concentration needed to neutralize the negatively-charged casein micelles, its isoelectric point will be more basic, thus resulting in a softer cheese. Spore forming ability is also called a bacteria’s CO2-forming ability. Curd acidification is accompanied by the production of CO2, which results in the “holes” in cheese. This affects the texture and form of the cheese and the taste, for aerated cheese melts easier in the mouth and satisfies the taste buds more than firmer cheese would.

Figure 4. Swiss cheese has  a high spore-forming ability.

Brining is a process that preserves the cheese. Also known as salting, after whey is extracted from the curds, the reason for brining is to slow down or stop the bacteria from converting lactose to lactic acid, as well as contributing to taste. Most of the lactose is also extracted due to brining, increasing the cheese’s shelf life. The cheese curds are formed into their desired shapes before brining. They are then cooled to the temperature of the brine, to prevent the increase of rate of salt absorption. The brine has a pH of about 5.2 and through the process of osmosis, the cheese will stabilize its pH and absorb some of the salt from the brine solution. Cheeses will form their own brine due to surface moisture, creating a protective covering around the cheese.

 

Figure 5. The higher pH level, the higher the viscosity of the milk-cheese mixture, resulting in a firmer cheese.

Lastly, and frankly the most popular process in the cheese industry, is aging. During aging, microbes and enzymes transform the texture of the cheese as well as intensify flavor. This is due to the breakdown of casein proteins and milk fat, resulting in a complex mix of amino acids, amines, and fatty acids. Aging is possible in cheese because of the bacteria that is present, all of which are alive. The bacteria have stopped undergoing lactic fermentation, but continue to break down the proteins and fat molecules in the milk cheeses due to the enzymes in the bacteria. The longer cheese is left to age, the firmer and more intense cheese. The cheese would be firmer since the moisture from the cheese would evaporate and the molecules would have time to coagulate.

This video shows a time lapse of cheddar cheese aging from 1-9 months. As you can see, the cheese darkens as it ages, and the cheese-makers rotate and flip the cheese every once in a while to make sure that it ages evenly. You can also see that the longer the cheese ages, the more pores begin to appear on the surface as well as the firmer the cheese gets.

Now you know that there are many processes that happen to turn milk into edible, tasty cheese. First, the milk has to be pre-cured, so that the enzyme rennin and lactic acid contribute to the breaking down of protein and fat bonds. The milk cheese then has to coagulate into what’s called curds, being formed and shaped to prepare for aging. Before aging, the cheese must be brined and the temperature of the cheese mixture must be at the perfect temperature to maintain its moisture content, as to prevent over-salting. Lastly, the cheese is aged to intensify flavors and allow for more breaking down of molecules to make the cheese firmer. So, the next time you decide to delight yourself with the wonder that is cheese, think of all the chemical processes that it had to undergo (and of course the live bacteria that you are eating), and how that tasty snack had to pay such an incredible price to become such a treat.

The Chemistry of Caramel

Close your eyes and imagine the sweet taste of caramel. Whether it be caramel sauce, chewy caramel, or toffee, the idea of that sweet candy can make anyone’s mouth water. But did you know how much chemistry goes into making caramel? Read on to find out!

Yummy caramel!

Caramelization consists of chemical reactions that can be very complicated, and some of these reactions are not yet entirely understood. It produces hundreds of chemicals! In this blog post, we will try to create a comprehensive view of the information we know about caramelization so far.

When we make caramel, whether as a candy or for a filling or topping on other food, we use sugar, butter, and water. Sugar is the main component we want to focus on. A small amount of water is added to sugar, sucrose, with addition of heat, and the sucrose breaks down into two simpler sugars, glucose and fructose.

Sugar

C12H22O11 (sucrose) + H2O (water) + heat —> C6H12O6 (glucose) + C6H12O6 (fructose)

This reaction, simplified into a chemical reaction above, is called sucrose inversion. The next step in caramelization starts off with the glucose and fructose, which are in solution (in water). These two molecules go through dehydration as the molecules are bonded together while giving off water. The hydroxyl group of one molecule and the hydrogen of the other combine together and leave as water, leaving these two molecules connected. This dehydration, also known as condensation, takes place with many of the glucose and fructose molecules. However, the products are not always the same, as the reaction can happen with any hydroxyl group within each molecule and any hydrogen ion within each molecule. The possibilities are endless. Additionally, the products vary even more because they begin rearranging themselves, creating many different isomers.

The above caramelization procedure was the procedure of making caramel from sucrose. The caramelization of other sugars, including fructose, galactose, glucose, and maltose, differ in the amount of heat necessary for the reaction to occur. Caramel’s taste can be attributed to the different compounds produced within the caramelization reactions, along with sweet sugars. For example, diacetyl is formed in the beginning of caramelization, and gives caramel a buttery, butterscotch-like flavor. Different compounds such as esters can give off rum flavors, while furans taste like nuts.

Many different types of sugars

The Maillard reaction is considered very similar to caramelization, but caramelization happens at a higher temperature, and is a reaction of sugar with itself. However, the Maillard reaction occurs with sugar and protein. Though both procedures include the dehydration synthesis, the Maillard reaction incorporates an amino acid from a protein and happens at a lower temperature. Many people may consider the Maillard reaction and caramelization to be the same thing, but they are slightly different from each other, so make sure not to get them confused!

Maillard reaction

Although the exact date of the discovery of caramel is not known, many believe that the Arabs were the first to consume sweet caramelized sugar, around 1000 AD. The caramel they knew, however, was the hard and crunchy kind that we know today as toffee. Around the 1850s, people began adding milk and fat to their recipes to create chewy caramel. However, caramel (including toffee and soft caramel) wasn’t nearly as popular at that time as it is today. This all changed when the Hershey company began adding caramel into its candies, creating the “Lancaster Caramel Company” – people began to love caramel much more. Because of Hershey, caramel is now a well known candy that comes in all shapes and sizes. Who knew a discovery over a thousand years ago would lead to a tasty treat that involves lots of chemistry to make it!

 A video showing how three different types of caramel is made!