Guest post by Earlene Mulyawan
Whether it is adding chili flakes to top off your pizza, Tabasco to your omelet, chili oil to your ramen, there’s no doubt adding these condiments can add flavor intensity to all our dishes. Interestingly, the burning sensation is actually not a taste, since the sensation does not arise from taste buds. Capsaicin stimulates nerves that respond only to mild increases in temperature, the ones that give the sensation of moderate warmth . Capsaicin sends two messages to the brain – intense stimulus and warmth. The burning sensation you feel when eating spicy food is due to the combination of these two messages.
What is the science behind all this magic? The answer to that is a supernatural compound capsaicin (or 8-methyl-N-vanillyl-6-nonenamide). Capsaicin is a common pungent molecule. It is found in capsicum fruits that are used in a variety of cuisines.
Pure capsaicin is colorless, odorless, and crystalline-to-waxy solid at room temperature. The Scoville Heat Scale for pure capsaicin is about 16,000,000 SHU (Scoville Heat Units). SHU is a measurement of pungency. Ghost pepper is approximately 1,000,000 SHU; cayenne is approximately 40,000 SHU. Capsaicin is a hydrophobic molecule, meaning that it preferentially partitions into fatty environments. When consumed, capsaicin binds with pain receptors in the mouth and throat, which are normally responsible for sensing heat . The taste buds on our tongue contain taste receptors. Taste buds sense tastants (taste molecules) and send the information from the tastants to the brain, where the molecule is processed as a certain taste. There are five main tastes: bitter, salty, sweet, sour and umami (savory) . “Spicy” or “hot” is not sensed by our taste buds; instead, they are sensed by pain receptors, which are also found in the tongue. These receptors send pain signals via our nerve fibers to the brain, where it is perceived as a sensation of pain and heat.
But how does capsaicin give us the sensation of “tongue on fire”? Capsaicin is the active component of chili peppers that produces a burning sensation in any tissue it comes in contact with. How does this signal get conveyed? There are three classes of nerve fiber in our central and peripheral nervous system – the ‘C’ type of nerve fiber are the ones that are stimulated by capsaicin – specifically the molecule binds to the vanilloid receptors (VR-1, TRPV1) on the nerve endings of the C-fibers. These receptors are ligand-gated ion channels that are closed in the absence of capsaicin. When they are stimulated by capsaicin, they open and allow an influx of sodium and calcium ions, which initiate an action potential across the fibers. This action potential is what allows us to feel the burn. Normally, physical heat stimulates these receptors. However, capsaicin can also interact with these receptors and activate proteins that cause the same signal to be transmitted to the brain into thinking that it is being burned.
How often we consume spicy food can affect the sensitivity of these receptors. If you consume them too frequently you can essentially “kill” your receptors. This is one of the factors that contribute to different people having a different spice tolerance level. The other factor is genetics. Our vanilloid receptors can be mutated such that they are less susceptible to capsaicin. Thus, it can be implied that we can inherit our tolerance for spices and also why different cultures and genetic populations can have different spice tolerances.
Although chili can add some flavor and magic to our dishes, it can also be unpleasant and painful for some people who are not used to it. When chili becomes too hot or too painful to handle, dairy products can come to your rescue. Understanding the physical properties of capsaicin can help to explain why milk can help rescue you from the fire on your tongue.
Capsaicin has a long hydrophobic tail, which allows it bind with high affinity to protein receptors on the tongue, which have hydrocarbon side chains of their own. This fatty tail of capsaicin also allows the molecule to diffuse through cell membranes, making the burn more pervasive and persistent. While water may offer a temporary relief, it is not entirely effective because capsaicin oil and water do not mix. In fact, water will actually spread the capsaicin oil instead of soothing the burn. By contrast, milk contains proteins and fat globules that the capsaicin can partition into. For example, casein is a milk protein that has a higher affinity to capsaicin and can compete with our lipoprotein receptors, surrounding capsaicin molecules and relieving the burn.
: Ann M. Bode and Zigang Dong. “The Two Faces of Capsaicin.” 15 April 2011.
: Ann M. Bode and Zigang Dong. “The Two Faces of Capsaicin.” 15 April 2011.
Guest post by Nessa Riazi
When thinking of an airy, sugary meringue, baked Alaska or pavlova may be the first words to come to mind, but smog? Not quite.
You may have heard of the term terroir which explores changes in flavors based on differences in geographical locale, but aeroir is a rather new phenomenon. How can one possibly explore the tastes of air– or rather air pollution? At the Center for Genomic Gastronomy, food scientist Nicola Twilley whipped up a simple solution for this fascinating question. Why not make smog-flavored meringues! Upon reading Harold McGee’s bible of food science– On Food and Cooking: The Science and Lore of the Kitchen– co-founder of the Center for Genomic Gastronomy, Zach Denfeld discovered that meringue foam is 90% air. Thus, emerged the ingenious idea of “harvesting” the air quality of various cities. In a quasi-sensory explosion for your taste buds, but more so a commentary on the politics behind urban pollution, Twilley and fellow scientists “harvested” air once the egg-white foam reached the ‘stiff peak’ stage.
The meringues were whipped up in various locations such as on rooftops, roadsides, and waterways.
In the process of recreating smog conditions, scientists injected calculated amounts of precursor chemicals into a Teflon smog chamber, where UV light was shone to catalyze the chemical reactions that form smog. As each city contains unique precursor emissions, varying in weather conditions from temperature and humidity to precipitation, each geographical region thus has a uniquely flavored meringue. For instance, in recreating the smog of an agricultural setting, students combined “ammonia and amines from feedlot manure lagoons and other organic waste…[mono-nitrogen oxides] NOx and incompletely combusted hydrocarbon emissions from cars, power plants, and industry…”  Harold McGee describes how these chambers were constructed to replicate air pollution around the globe, drawing chemicals emitted from tailpipes, smokestacks, and feedlots . Variations of smog can thus be created with the help of ultraviolet lights.
As scientists create meringues for various cities around the globe, we can better understand the how air quality and pollution can affect the flavor of foods we eat. The atmosphere in Atlanta is one of the worst air qualities, running alongside that of Los Angeles . Ten percent of emissions consist of terpenes–which are chemicals that stem from organic matter, whether that be pine trees or green matter that is decaying .
In addition to these fascinating studies, the Center for Genomic Gastronomy also publishes the journal, Food Phreaking, which explores up and coming experiments within food science and examines the places where food, culture, and technology intersect. As technology becomes progressively more intertwined with everyday life, our experiences with food can reach new and fascinating heights. Could tasting the cloudiness and mugginess of a smog meringue be the recipe for combatting air pollution?
 Smog Tasting: Four Years of Tasting Unexpected Ingredients. The Center for Genomic Gastronomy with Nicola Twilley. The Forager Magazine.http://www.theforagermagazine.com/4/7
 McGee, Harold. The Flavor of Smog. Lucky Peach Magazine. http://luckypeach.com/the-flavor-of-smog/
 Twilley, Nicola. Smog Meringues. Edible Geography: Thinking Through Food. http://www.ediblegeography.com/smog-meringues/ 30 May 2015.
“Suprême” refers to the classic culinary technique of removing the flesh of citrus from the pith, or the white spongy layer in between citrus segments composed mainly of pectin and cellulose. Removing the pith, which is characterized by a distinctly bitter flavor, enhances the perceived sweetness in citrus fruit . Though “suprême” may sound like a fancy-schmancy technique reserved for the finest of dining, citrus suprême can be found in common everyday foods such as mandarin orange slices on salads and garnishes in cocktails. Classic citrus suprême is made by cutting off the top and bottom of the fruit, removing the pith with a knife, and cutting each segment out from between the membrane. However, this produces a lot of waste, as it is not possible to completely clean the pith of the fruit. It is also not efficient for large-scale industrial processing. Solution: pectinase.
Pectinase is a general term for an enzyme that breaks down pectin, or the polysaccharide contained in plant tissue . I set out to test the efficacy of pectinase in my own kitchen. I used the pectinase Pectinex Ultra SP-L, a polygalacturonase that is derived from the fungus Aspergillus Aculeatus . Using a recipe from Chef Steps, I proceeded with the following protocol:
Recipe for Citrus Suprême :
250g Citrus (About ½ pound citrus, or about 2 tangerines)
250g Water (About 1 cup water)
2.5g Pectinex Ultra SP-L (About ½ teaspoon)
Place Peeled citrus, water, and Pectinex in a bowl.
Refrigerate for about 2 days. Rinse segments in water.
Voila! Perfect citrus supreme.
To speed up the reaction you can heat up the solution to 104°F/40°C for 30 minutes . However, because heat treatment is usually associated with nutrient degradation, this will likely lead to the partial deterioration of some nutrients in the citrus fruit.
Pectinases degrade the pectin in citrus pith by cleaving the bonds between the pectic polysaccharides. All three major types of pectin contain D-galacturonic acid, which is the target for polygalacturonase, the enzyme present in Pectinex Ultra SP-L. By hydrolytically cleaving the alpha 1,4-glycosidic linkages within the D-galacturonase backbone, polygalacturonase breaks down the structure of pectin . The enzymatic breakdown of pectin, which is one of the main structural components of the pith, can explain why we are able to wash away the remains of the pith to easily make citrus suprême.
In addition to citrus suprême, pectinases have many other industrial applications, including in the juice and wine industry. The utilization of pectinases enhances how much juice can be extracted from the fruit pulp, which ultimately increases yields and profits; pectinases also make processing more efficient and clarifies the juice to create a product with fewer solids that also looks more appealing too . Taken together, pectinases contribute to the production of products that are more visually appealing from citrus supreme to juices and wines; they also help to reduce waste in food and beverage production to promote more sustainable processing in the food industry.
About the author: Ashton Yoon received her B.S. in Environmental Science at UCLA and is currently pursuing a graduate degree in food science. Her favorite pastime is experimenting in the kitchen with new recipes and cooking techniques.
Amidst the assortment of homemade pies and pillowy mashed potatoes, a moist, flavorful turkey is the hallmark of any traditional Thanksgiving. We’ve all been guilty of it though—feigning enjoyment while choking down tough, dry turkey that can’t be salvaged with even the most decadent of gravies. Brining offers a magic solution to your Thanksgiving turkey woes.
Brining is a simple technique that can promise your turkey a coveted, juicy tenderness. To brine a turkey, you immerse it in a solution of 3-6% salt by weight, for anywhere from a few hours to two days. After cooking, your meat will be noticeably juicier. This transformation isn’t just your turkey absorbing fluid like an enormous meat sponge, but is instead an intricate interplay of diffusion, osmosis, and protein biochemistry.
Meat proteins typically respond to heat by unraveling like balls of yarn. Once unraveled, they tangle with each other and coagulate, causing the meat proteins to pack together more densely. This process forces water out, and coupled with the heat-driven evaporation of water, explains why meat shrinks when cooked. But when submerged in brine, meat is at the mercy of the salt molecules. Salt molecules are small and mobile and can easily move through muscle proteins. As they diffuse through the turkey, they partially dissolve proteins and interact with the charges on them, preventing the proteins from packing as tightly together and altering the overall structure of the meat (1). The movement of salt also drives water into the meat proteins since water tends to move from a higher concentration (the brine) to a lower concentration (within the meat). The combination of less tightly packed proteins and the gradient driving water in ultimately boosts the water-holding capacity of your turkey.
As with any cooking method, brining has its pros and cons. While the meat it creates may be juicier, a common complaint is that it is unsurprisingly (and to some, unpalatably) salty. Brines typically start at around 3% salt by weight—comparable to ocean water at 3.5% salt by weight. The takeaway from all this: if you suffer from dry turkey mouth year after year, brining may be a viable option, but flavors in your turkey should otherwise be balanced and boosted.
About the author: Mai Nguyen is an aspiring food scientist who received her B.S. in biochemistry from the University of Virginia. She hopes to soon escape the bench in pursuit of a more creative and fulfilling career.
Read more by Mai Nguyen
Eat local. Avoid red meat. Beef is bad. The media is full of messages about food. Navigating the world of food choices can be challenging and overwhelming. Here is where some knowledge of food, and bit of science, can help. With science, we can identify the number of calories in a food item. We can also easily understand the amount of protein or fat to help us choose to eat – or avoid – particular foods.
Need more vitamin C? Food labels can also help us identify vitamin contents. Want to know whether a product is clean label? Food labels have your answer! However, a lasting challenge we have as consumers is being able to identify and assess the environmental impact of foods that we eat. In comes the CO2 equivalent as a solution. CO2 equivalent, or CO2e, is a common unit of measurement that allows us to standardize greenhouse gas emissions. For example, is it worse for the environment to eat 118 apples or a quarter pounder burger?
To standardize measurements of greenhouse gas emissions, grams CO2 equivalent (or CO2e) is a common unit of measurement. CO2e is calculated by multiplying the global warming potential (GWP) of the greenhouse gas (GHG) emissions produced by each food component by the amount of GHG produced. For example, beef production generates carbon dioxide, methane, and nitrous oxide. Since each of these three greenhouse gases has a different potency for environmental effects, they each of have their own pre-calculated global warming potential, or GWP. Thus, the relative effects of each GHG can be determined by multiplying this GWP factor by the amount of each GHG produced (ex. GWP(methane) x GHG(methane) = grams CO2e for methane). Then the CO2e for each GHG can be added together to yield the total grams CO2e for a particular food component . By converting units to CO2e, we can easily compare the approximate carbon footprint of different foods.
To illustrate the carbon footprint of a beef versus vegetarian food, see this infographic (Fig. 1) that we created together with Professor Jenny Jay and the UCLA Healthy Campus Initiative. It is remarkable to see how one beef burrito produces 896 grams of CO2 equivalent, which is just over ten times the amount of CO2 equivalent of a veggie burrito at 88 grams CO2e . In fact, a quarter pounder burger has the same CO2 equivalent as 118 apples .
Livestock contributes a remarkable 14.5% to global GHG emissions , in addition to water pollution, destruction of land, and and species extinction. Beef production is particularly demanding, requiring on average 28 times more land, 11 times more water, and producing 5 times the GHGs than the average of any other type of protein such as pork or chicken . What we take away from this information is ultimately our own personal choice. However, knowledge of how the foods we eat impact our environment can ultimately empower us to make informed decisions – allowing us to make a responsible and educated choice whether to dig into that burger or break out the veggie patty!
The Impact of What We Eat: From Science & Technology to Eating Local
March 8, 2016
As part of our 2016 public lecture series, we explored the environmental and social impacts of food with a focus on science and technology. A major theme of this panel was how we can initiate change through consciously making food choices. For this discussion our panelists included Chef Daniel Patterson, Dr. Paul B. Thompson, and Dr. Kent Kirshenbaum. Chef Daniel Patterson shared how his restaurant LocoL strives to enhance and empower local communities. Dr. Paul B Thompson of Michigan State University discussed the ethical and philosophical implication of agricultural practices and food infrastructure on food producers. Dr. Kent Kirshenbaum of NYU Chemistry explored the latest scientific advances in food technology.
Check out the highlights or watch the full lecture below
Chef Daniel Patterson on how Locol acts as both a business and a charity
Chef Patterson discusses how his restaurant is “a profitable business that’s also compassionate” by bringing healthy and delicious food to an underserved community, while also encouraging economic development in the area.
Dr. Paul Thompson on balancing local and regional food production
Dr. Thompson explains that foods like fruits and vegetables can produced locally, while basic grains are best produced regionally in places best suited for their growth.
Dr. Kent Kirshenbaum on scientific advances in food that reduce our environmental impact
Dr. Kirshenbaum talks about plant-based meat substitutes as well as isolating components from environmentally sensitive ingredients to create more sustainable foods.
Dr. Paul Thompson talks about how farming practices are important for food safety
Dr. Thompson discusses the natural dangers of foods and shares how potato farmers use careful breeding to reduce the naturally occurring toxicity of the potato plant.
Dr. Kent Kirshenbaum explains how traditional cooking practices don’t ensure healthy food
Dr. Kirshenbaum explains how all food technology needs to be evaluated for safety and how even traditional practices like cooking over an open flame can cause a risk to health.
Chef Daniel Patterson explores deliciousness and the need for collaboration
Chef Patterson talks about how subjective taste and deliciousness can be and the importance collaboration between scientists and chefs for new food technology. Here, Chef Patterson recalls his experiences with new plant-based meats.
See the Entire Lecture Here
How obsessed with spicy are you? Ecologist Joshua Tewksbury from the University of Washington is willing to travel thousands of miles to Amboró National Park in central Bolivia just to answer one burning question: Why are chilies spicy? For those who prefer a different kind of spicy, a study in the Journal of Medicinal Chemistry can shed light on why turmeric is a better spice than a home remedy.
With the abundance of food in America, few people give a second thought to eating summer produce in the middle of winter. The majority of salad greens and tomatoes sold in winter are imported to colder states from warmer climates. With the help of greenhouses, however, it is entirely possible to have locally grown lettuce in the midst of a snowy December! Paul Lightfoot, founder and CEO of the company Brightfarms, explains the pros and cons of greenhouse farms. The availability of wheat, however, may not be as celebrated by some people. Mark Kelley investigates the movement that’s changing the way we eat.
Guest post by Nessa Riazi
Bustling with delighted customers unwrapping banana leaves to discover hidden curries and stewed meats, Indonesian restaurant Simpang Asia is a gastronomic awakening; its market next door is another. My sister recently introduced me to this restaurant nestled in Palms that is now my favorite Indonesian restaurant in LA. The best part is that as you wait for your table, you are able to explore and happily distract yourself in the aisles of the eclectic supermarket next door. During my quest to find a new ingredient to experiment with in my daily cooking endeavors, I came across dried basil seeds, or mangluck in Thai.
Binomially they are called Ocimum basilicum, coming from the sweet basil plant.
Not having reached the same level of mainstream popularity in the culinary world as chia seeds, or Salvia hispanica L., could basil seeds potentially be the next chia seed? Their unique genus may suggest that more differences exist; however, based solely on physical observations and their reactivity to water, basil and chia seeds seem closely related. How do these seeds compare?
Dry Basil seeds (left) and chia seeds (right) | Photocred: thenaturalhealthmarket
One of the most defining features of chia and basil seeds is that when in contact with water, both swell up into gelatinous pearls. The layer of mucilage formed is not only safe to consume, but it is associated with soothing abilities for one’s digestive tract, sealing the mucous membranes and acting as a barrier to irritation of nerve endings . Mucilage is a polar glycoprotein that is texturally characterized by a dense stickiness, and it can be found in a number of plants such as aloe vera, psyllium husks, and okra. It has been known since ancient times to have medicinal benefits .
Basil seeds after immersion in water | photocred: Hubpages and Chia seeds after immersion in water | photocred: chiaseedinwater
Basil seeds predominated throughout India and other parts of Southeast Asia as well as Iran and Africa . Closely resembling black sesame seeds in appearance, they are extracted from the popular basil plant. Basil seeds go by several other names such as sabja or tukmaria in Hindi and falooda in Arabic. When soaked in liquid, their pericarp or outer epidermis expands into a gelatinous bubble of a beautiful purple-greyish color. Unlike chia seeds, they are not to be eaten raw. Basil seeds have been used for both medicinal and culinary purposes. For example, it is said that traditional Persian herbalists administered soaked basil seeds to help with coughs, asthma, or colds due to their antispasmodic effects . Basil seeds have also been used for digestive issues such as constipation, as well as for alleviating stress levels and depression . In addition to their benefits for the digestive system, basil seeds have a high iron content, supplying 40 percent of one’s RDA per 100 grams (3.17 mg per 100 mg). Being a key ingredient to rose-water infused beverages such as Persian faloodeh or Thai nam manglak, basil seeds can create a nice refreshing drink when combatting hot weather . Talk about food and functionality!
Chia seeds—one of the more popular items in the current food market and a so-called “superfood”—look almost like miniature dinosaur eggs. In attempting to bite down on these tiny seeds, it seems as though the mouthfeel of chia is characterized by a crisper pop, while basil seeds are squeakier and take on a more tapioca-like texture due to the enlarged, thicker pericarp.This latter seed similarly puffs up when immersed in water–due to the hydrophilic nature of its soluble-fiber seed coat– though it has a longer expansion time. Chia’s soluble fiber is a large contributor to its hydrophilic quality because as these soluble fibers dissolve in water, they absorb water to create the characteristic gelatinous pericarp . Interestingly, chia seeds can absorb anywhere up to 12 times their weight! Due to their high absorption of liquid, they help keep the body hydrated . The gel that forms around the seed coat acts as a barrier between the digestive enzymes and carbohydrates, which in turn slows down the rate at which the carbohydrates are turned into sugar. As a result, blood sugar levels can be regulated, helping to lessen the risk for diabetes.
Chia seeds are an even better source of calcium—containing 3 to 6 times the amount found in milk. Per 100 gram, chia seeds contain, 631 mg of calcium, 7.72 g of Iron, 860 g of phosphorous and 23.665 g of polyunsaturated fatty acids . While both seeds are good sources of iron, chia seeds contain approximately 4.55 mg more of iron. Shown by the table above, chia seeds are higher in protein by 4.16% and fat by 8.99%. Possessing tryptophan—the infamous “turkey” amino acid– which is converted into serotonin, melatonin, and dimethyltryptamine, chia seeds are also supposed to induce good sleep. The absorptive characteristic of the chia seed is induced by tiny micro-fibers standing on the surface of its shell, which draw in the liquid . In its dried form, chia seeds are similar in size to basil seeds, but when wet, the gelatinous shell formed does not nearly reach the girth of that surrounding basil seeds. The texture provided by chia seeds have won them much favoritism amongst food experimenters as individuals incorporate them in homemade jams to add a desired level of viscosity and thickness.
Interested in learning more about the innovative ways to use chia in your everyday culinary affairs? Read Science and Food article “Chia Seed Apple Pie” to see how chia seeds can be used to create the perfect viscous pie filling. If you’re feeling daring, try making it with basil seeds!
 Chia “Superfacts” Infographic: The Hydrophilic Super Seed. (2014). Health Warrior. http://www.healthwarrior.com/chiahydrophilic/. Accessed 5 September 2016.
 Dr. Nancy. (2011). Five Amazing Benefits of Basil (Sabja) Seeds. TrueNHealth. http://truthnhealth.com/2011/10/5-amazing-benefits-of-basil-seeds/. Accessed 20 August 2016.
 Falkowitz, Max. “Spice Hunting: Chewy Drinks with Basil Seeds.” Serious Eats. http://www.seriouseats.com/2011/04/spice-hunting-basil-seed-beverage-falooda-faluda-nam-manglak-drinks.html. Accessed 5 September 2016.
 Kintzios, Spiridon and Olga Makri. (2008). Ocimum sp. (Basil): Botany, Cultivation, Pharmaceutical Properties, and Biotechnology. Journal of Herbs Spices & Medicinal Plants. 13(3):123-150. http://www.researchgate.net/publication/239314732_Ocimum_sp_Basil_Botany_Cultivation_Pharmaceutical_Properties_and_Biotechnology. Accessed 5 September 2016.
 Segura Campos, M. R. (2014). Chemical and Functional Properties of Chia Seeds (Salvia hispanica L.) Gum. http://www.hindawi.com/journals/ijfs/2014/241053/. Accessed 20 September 2016.
 My Seeds Chia Hydration: Amazing Soluble Fiber. MySeeds Chia. http://www.mychiaseeds.com/articlehydration.htm. Accessed 19 September 2016.
 Gums and Mucilages. Herbs2000. http://www.herbs2000.com/h_menu/gums_mucilages.htm. Accessed 20 September 2016.
 S. Jolly, Rajan. (2016). Benefits of Chia Seeds and How They Differ from Basil Seeds. CalorieBee. http://caloriebee.com/nutrition/Some-Amazing-Benefits-Of-Chia-Seeds. Accessed 24 September 2016.
 S. Jolly, Rajan. (2015). Sweet Basil, Sabja or Tukmaria Seeds And Their Health Benefits. HubPages. http://hubpages.com/health/Sweet-Basil-Herb-Sabja-Or-Tukmaria-Seeds-And-Their-Health-Benefits. Accessed 24 September 2016.
Have you ever wondered what exactly made Hot Cheetos flamin’ and hot? The folks over at Wired can fill you in. Apparently, without these ingredients, the Cheetos would look like whitish worms. Our squeamishness over bugs may put some of us off Cheetos for awhile, but that mindset could also be preventing us from harvesting the sustainable protein that insects offer to a rapidly growing world population.
It happens to all of us but don’t worry it’s completely natural. When food smells waft into our nostrils a host of physiological reactions occurs. We almost immediately begin to salivate (if not drool) and our stomach roars beckoning you to get a taste. These reactions are innate physiological properties of your digestive system that prepares your body for the food that it thinks you’re about to consume.
The digestive system is composed of three primary organs: the small intestine, stomach, and large intestine (or colon). These digestive compartments work cooperatively with other secondary organs, including the pancreas, liver, and gallbladder, to break down larger macromolecules into nutrients that our body can use for energy. But where does it all begin? The mouth.
The salivary glands in our mouth secrete saliva to initiate enzymatic digestion of our meal. Saliva also make our food more pliable so it can be broken down by chewing. An important component of your saliva is a-amylase, which breaks down large polymeric sugar molecules (starch) into shorter oligosaccharides and polysaccharides. Once our food is swallowed it passes through the esophagus down into the acidic environment of the stomach. The low pH of our stomach helps to neutralize any pathogenic, disease-causing opportunistic microbes. The muscles in the stomach contract, which helps to mix the food before delivery into the small intestine.
When our food enters the small intestine it travels through three major compartments: the duodenum, jejunum, and the ileum. Within these compartments, food macromolecules are subject to further enzymatic digestion by lipases (enzymes that break down lipids/fat), amylases (further breaks down sugars/carbohydrates), and trypsin (breaks down proteins). The cells that line the inside of the small intestine, or lumen, are known as epithelial cells that have a distinct morphology relative to the epithelial cells of the large intestine. The luminal epithelial cells of the small intestine have structures known as villi that play an important role in nutrient absorption of small molecules such as monosaccharides, amino acids, fatty acids, and glycerol.
The final route of our food through the digestive system is the large intestine. Most of the important nutrients from our food have already been absorbed once it enters the colon. However, there is still a portion of food that we eat that remains resistant to digestion by our own body’s enzymes. At this point, this non-digested food mass will be bombarded by our intestinal microbiota. The large intestine is a reservoir for the trillions of bacterial microbes that reside within us and are collectively known as the gut microbiome. The microbiota within the colon possess an arsenal of unique digestive enzymes that can break down our food even further. From the products of these reactions, the bacteria use nutrients that are optimal for their growth while releasing other metabolites that we can use for energy. Generally, our relationship with our microbial counterparts is symbiotic or mutually beneficial.
In 2011, researchers characterized the gut microbiome found in humans into three distinct clusters also known as enterotypes. These enterotypes classify taxonomically the myriad of bacterial microbes that live inside our gut. For example, type 1 is defined by high levels of bacteria known as Bacteroides, while type 2 has low levels of Bacteroides and higher levels of Prevotella, and type 3 has elevated levels of Ruminococcus . Generally, our body mass index, age, and gender cannot give us information about our enterotype, however we can use information about our gut microbiome to predict these attributes . One of the major factors that can contribute to our own enterotype is our long-term diet. Therefore, the foods we eat play a significant impact on the composition of bacteria that can colonize our guts and can influence our health or disease.
For example, the gut microbiota has been implicated in the onset of metabolic diseases such as obesity and type II diabetes . Specifically, a decrease in the prevalence of Bacteroides and an increase in bacteria known as Firmicutes and Actinobacteria is linked to obesity [3,4]. There is intense clinical interest in understanding the gut microbiota and learning how to adopt dietary interventions that might correct the imbalance of pathogenic versus commensal bacteria. In fact, in obese subjects it was shown that a reduced caloric diet was beneficial in reconstituting the loss of Bacteroidetes while decreasing Firmicutes resulting in loss of body weight .
Knowledge of the human microbiome is highly relevant to today’s eating consumption habits as our diet can influence the ecology of our gut microbiota. These dietary-mediated shifts in our intestinal microbiome in turn can have either beneficial or adverse effects on our health. By taking a closer look at our microbial residents we might better understand the pathogenesis of certain inflammatory and metabolic diseases while simultaneously engineering more precise treatments in the future.