Tag Archive for: flavor

Chocolate

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Photo credit: Eli Duke (eliduke/Flickr)

Photo credit: Eli Duke (eliduke/Flickr)

There are few things sweeter in life than chocolate, which is probably why it’s one of the most popular flavors in the world. We can thank the cacao trees (Theobroma cacao) for this gift, which are only grown within a region known as the Cocoa Belt, 10° to 20° north and south of the equator [1]. Chocolate is produced from the seeds of the pods that grow from the cacao trees; these seeds are better known as cocoa beans.

Chocolate is a complex flavor, containing over 200 different flavor compounds [3]. While the type and mixture of cocoa beans that go into a chocolate bar play a role in determining the final flavor, chocolate is the kind of food where its taste is influenced by how it’s made rather than what it’s made of [4]. The chocolate-making process varies among types of chocolate (milk, dark, bittersweet, etc.), but also depends on the style of the chocolate maker. So while the general principles and chemical processes at each step remain the same, chocolate-making is a delicious art form.

Straight off the trees, cocoa beans are bitter. When cacao pods are harvested, they are cracked open and left to sit for a couple of days, depending on the tree varietal. (5–6 days for forastero versus 1-3 days for criollo [2].) This allows the cocoa beans to undergo fermentation, a process that is carried out by naturally occurring yeast and bacteria. During fermentation, the microorganisms digest the pulp in the pods, which aids in converting the sugars in cocoa beans into acids. These acids decrease the overall bitterness of the beans. Notable flavor compounds, such as pyrazines, are also generated during fermentation, making the beans slightly more floral in aroma [2]. After fermentation, the beans are scraped from the pods to dry. Drying releases certain molecules from the beans that would otherwise make chocolate taste smoky and sour [2].

Roasted cocoa beans. Photo credit: AnubisAbyss/Flickr

Roasted cocoa beans. Photo credit: AnubisAbyss/Flickr

The dried cocoa beans now taste nutty, bitter, and acidic; to drive out volatile (easily evaporating) acidic molecules, the dried beans are further processed by roasting. The elevated temperatures of roasting (120–150°C) also facilitate Maillard reactions that yield flavor molecules that are distinct to chocolate [2]. These reactions are sensitive to both temperature and pH, so both the roasting temperature and bean acidity contribute to the final composition of flavor molecules that form during these Maillard reactions. Typically, milk and certain dark chocolates are made from beans that have been roasted at lower temperatures [2]. The shells of roasted beans are then removed, leaving behind pieces called cocoa nibs. Depending on the chocolate-maker, cocoa nibs may undergo alkalization, whereby they are treated with an alkaline solution in order to further decrease their acidity. Alkalization also causes flavonoids to polymerize (link together), which reduces the astringency of the nibs [2].

The final phase in chocolate manufacturing is a two-step process known as conching. At this stage, the nibs have a gritty texture; the first step in conching turns this into a paste through grinding and heating. Acidic compounds and water are evaporated in this process. More importantly, many flavor compounds formed during fermentation and roasting that are responsible for astringent and acidic notes become oxidized during conching, which mellows the flavor of the final product [2]. In the second step, cocoa butter and soy lecithin are added, decreasing the viscosity of the chocolate mixture to make it flow more easily.

Cocoa beans go through quite a long journey, from the cacao tree to the candy wrapper, where each step plays a role in producing the final combination of flavor molecules that makes chocolate such a beloved treat. This is just one of many reasons to savor your next taste of chocolate.

References Cited

  1. “Cacaoweb.” About the Cacao Tree and Cacao Varieties. <http://www.cacaoweb.net/cacao-tree.html>.
  2. Afoakwa EO, Paterson A, Fowler M, Ryan A. Flavor Formation and Character in Cocoa and Chocolate: A Critical Review. Critical Reviews in Food Science and Nutrition. October 2008; 48(9): 840-857, DOI: 10.1080/10408390701719272.
  3. Schieberle, P. and Pfnuer, P. Characterization of Key Odorants in Chocolate. Flavor Chemistry: 30 Years of Progress. 1999: 147–153, DOI: 10.1007/978-1-4615-4693-1_13.
  4. Ziegleder G, Biehl B. Analysis of Cocoa Flavour Components and Precursors. Analysis of Nonalcoholic Beverages: Modern Methods of Plant Analysis. 1988; 8: 321-393.

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

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Photo credit: Wikimedia Commons

Photo credit: Wikimedia Commons

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

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

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

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

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

References Cited

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

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

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Photo credit: Chris Battaglia (photog63/Flickr)

Hazelnut

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Photo credit: Chris Battaglia (photog63/Flickr)

Hazelnuts may not be as popular as other nuts in the U.S., but they have quite the culinary versatility, enjoyed in pralines, Nutella, and even as themselves. These nuts grow on hazel trees, of the genus Corylus. Depending on the plant species and nut shape, hazelnut also refers to the filbert nut or cobnut. Filbert nuts have an elongated shape that tapers into a “beak”, and are found on the Filbert (C. maxima), Colchican Filbert (C. colchica), and Turkish Hazel (C. colurna). Cobnuts are generally rounder, and grow on the American Hazelnut (C. americana) and the more commercially recognized Common Hazel (C. avellana) [1].

Whether in the form of a nut, essence, or oil, hazelnuts owe their sweet, buttery flavor profile to the molecule filbertone. Interestingly, filbertone can be used to test for the authenticity of olive oil. Olive oils are sometimes cheapened by mixing in hazelnut oil [2]. As filbertone is one of the components of hazelnut oil, testing for its presence can determine whether or not a sample of olive oil is impure [3]. Although hazelnut oil is less expensive compared to olive oil, it has a strong, robust flavor that makes it a great substitute in salad dressings and baked goods.

Filbertone_Hazelnut-02

Like many nuts, hazelnuts are a good source of protein and monounsaturated fats. Further, they contain a significant amount of thiamine, various B vitamins, and especially vitamin E [4]. Need another reason to try out hazelnuts this month? The warm, rich, velvety taste of roasted hazelnuts in decadent truffles or comforting lattes has a way of slowing down time. Try it for yourself.


References Cited

  1. Flora of North America: Corylus. <http://www.efloras.org/florataxon.aspx?flora_id=1&taxon_id=108088>
  2. Arlorio M.; Coisson JD; Bordiga M.; Garino C.; et al. “Olive Oil Adulterated with Hazelnut Oils: Simulation to Identify Possible Risks to Allergic Consumers.” Food Addit Contam Part A Chem Anal Control Expo Risk Assess. 2010 Jan; 27(1):11-8. doi: 10.1080/02652030903225799.
  3. Flores, G.; Ruiz del Castillo, M.L.; Blanch, G.P.; Herraiz, M. “Detection of the Adulteration of Olive Oils by Solid Phase Microextraction and Multidimensional Gas Chromatography”. Food Chemistry, 2006 Jul; 97(2): 336–342.
  4. Nutritional Value of Hazelnuts. < http://www.aboutnuts.com/en/encyclopedia/hazelnuts>

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

Read more by Alice Phung

Peppermint

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Peppermints_LisaBunchofpants

Photo credit: Lisa Bunchofpants (bunchofpants/Flickr)

Seasonal winter treats somehow seem incomplete unless they are imbued with a frosty, peppermint flavor. This is easily accomplished by enhancing the recipe with peppermint oil or peppermint extract, cultivated from the leaves of the peppermint plant. This plant’s scientific name is Mentha x piperita, the “x” indicating that it is a hybrid mint, formed by crossing watermint (Mentha aquatica) and spearmint (Mentha spicata). As a hybrid plant, peppermint is sterile, unable to produce seeds. Instead, it reproduces via rhizomes, bulbous plant masses found underground that are very similar to ginger and turmeric roots. Like many rhizomes, peppermint rhizomes can be planted almost anywhere, growing quickly once sprouted. For this reason, the peppermint plant is listed as invasive in Australia, the Galapagos Islands, New Zealand, and the Great Lakes region of the U.S. [1].

Peppermint oils and extracts get their characteristic Christmas-in-your-mouth flavor from their two main constituents, menthol and menthone. Of the two, menthol may be the more recognizable: When ingested, applied topically, or inhaled, menthol triggers cold-response sensory receptors, which cause that familiar cooling sensation [2]. You may have experienced this from chewing minty gums, using toothpaste, or applying Bengay to sore muscles.

PeppermintFlavors

Menthone is structurally related to menthol, but it affects a different sense in peppermint-flavored treats. This molecule gives rise to the icy, minty scent reminiscent of evergreen winters. Its distinctive fragrant property makes it popular in perfumes, cosmetics, and scented oils.

If you indulge in something peppermint this month, take some time to appreciate the menthol and menthone that makes this essence a holiday classic. Feel the sharp chill in your mouth while you bask in the warmth of a heated room. Take in the scent of cool mint while the winter wind outside whirls away. ‘Tis the season.

References Cited

  1. Pacific Island Ecosystems at Risk: Mentha x piperita <http://www.hear.org/pier/species/mentha_x_piperita.htm>.
  2. Knowlton, Wendy M., et al. “A Sensory-Labeled Line For Cold: TRPM8-Expressing Sensory Neurons Define The Cellular Basis For Cold, Cold Pain, And Cooling-Mediated Analgesia.” Journal Of Neuroscience 33.7 (2013): 2837-2848. Academic Search Complete. Web. 23 Nov. 2013.

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

Read more by Alice Phung

Why Do We Bother to Eat Bitter?

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Photo credit: Melissa McClellan/Flickr

Mustard Greens (photo credit: Melissa McClellan/Flickr)

Through exploration of the ancestral context of taste, scientists can better understand how modern humans use the sense of taste to make decisions and survive. Evolution has shaped our sense of taste to guide us to seek the food we need to survive, while steering clear of foods harmful to us. It is understandable that early humans who avoided spoiled meat and poisonous berries were able to pass down their genes, giving modern humans the ability to avoid them too. But what explains the countless humans who voluntarily consume, and even enjoy, some bitter foods? Why do we eat bitter greens? Brussels sprouts? Hoppy beers? Why do we tolerate some bitter flavors and not others?

Tastes can be positively or negatively palatable depending upon their context among other food flavors. Sour fruit flavors like grapefruit or cranberry can be refreshing and delicious to eat, but sour milk clearly signals that the food has expired. These matches between tastes and flavors are called flavor congruencies.

Most taste-odor flavor pairings are learned associatively through eating. Flavors associated with calories and nutrients become more pleasurable with time, whereas poisoning and illness teach us to associate foods with an unpleasant taste or disgust. For omnivores like us, learning the consequences of eating different foods is an indispensable survival tool. Because our range of food option is so vast, it is essential to sample many foods and connect their post-ingestive consequences with their perceived tastes. Bitter-tasting substances are innately disliked by infants and children presumably because most bitter compounds are toxic. Most children are drawn to all things sickeningly sweet, but as adults enjoy eating eat bitter Brussels sprouts. We learn to enjoy the taste of mildly bitter foods, especially when paired with positive metabolic and pharmacological outcomes. The more your body benefits from an ingested food, the more palatable it becomes [1].

Our bodies require phytonutrients such as flavonoids that cannot be physically separated from their vegetable carriers. Humans learn to tolerate low levels of bitterness in foods as they co-occur with nutrients in plants through a post-digestive reward/punishment system. For example, rhubarb contains 0.5% oxalic acid by weight, a substance that in large doses can cause joint pain and fatal kidney stones. The first time a child eats rhubarb, the initial taste response tells the brain that the food is bitter, toxic, and should be avoided. However, as the body begins to benefit from the essential nutrients in rhubarb without suffering any damage, the rhubarb becomes more and more palatable. Experiments show that rats can very quickly learn associations between tastes and metabolic and physiological consequences, perhaps in a matter of days. These associations occur after only a single trial and are strong enough to resist fading away even after multiple presentations of the food with no physiological consequences [2].

In humans, a large sugar molecule called maltooligosaccharide (MOS) presents a sweeter case of taste association. Human saliva transforms starch into MOS. Although MOS is tasteless, it activates brain reward centers in a manner similar to sugar, while non-nutritive sweeteners do not. Thus, a tasteless molecule that has positive metabolic outcomes can activate brain reward areas more effectively than a sweet-tasting substance that has little nutritional value [3].

The next time you eat mustard greens, stop to appreciate the complex process that allows you to taste and enjoy your leafy meal. Consider how your perception of taste has evolved, which has protected your ancestors from poisoning themselves. Reflect upon the incredible and complex mechanisms humans have developed to keep you well nourished. And if you still haven’t warmed up to greens, consider introducing them gradually into your diet.  By exploiting the body’s associative adaptation to taste, you could learn to love them.

References Cited

  1. Breslin, P. 2013, An Evolutionary Perspective on Food and Human Taste Current Biology, Vol. 23 Issue 9
  2. Sclafani, A., Azzara AV., Lucas, F. 1997, Flavor preferences conditioned by intragastric polycose in rats: more concentrated polycose is not always more reinforcing, Physiology & Behavior
  3. Chambers ES, Bridge MW, Jones DA., 2009, Carbohydrate sensing in the human mouth: effects on exercise performance and brain activity, The Journal of Physiology

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

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The Flavor Network

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Physicist Albert-László Barabási likes making connections. By studying networks, Barabási and his Northeastern University research group improve our understanding of everything from the internet to human disease.

Now Barabási and colleagues are using networks to learn more about the way we eat. In a paper published in Scientific Reports, Barabási’s research team posed the question:

“Are there any quantifiable and reproducible principles behind our choice of certain ingredient combinations and avoidance of others?”

In particular, the researchers call the food pairing hypothesis into question. First imagined in 1992 by chefs Heston Blumenthal and François Benzi, the food pairing hypothesis states that ingredients will work well together in a dish if they share similar flavors. Following this logic, chefs have come up with crazy new food combinations like Blumenthal’s infamous concoction of white chocolate and caviar.

Thanks to the efforts of food scientists around the world, we now have extensive information available about the many chemical compounds responsible for giving different foods their distinctive smells and tastes. Armed with this information, Barabási’s team created the flavor network, a giant web of ingredients linked by their shared flavor compounds.

The backbone of the flavor network. Each node represents a different ingredient, where the size of the node represents the ingredient’s prevalence in a variety of recipes. The thickness of a line between two nodes reflects the relative number of flavor compounds shared by the two ingredients.

Just as the food pairing hypothesis would predict, the researchers found that North American and Western European cuisines indeed favor ingredient combinations with many shared flavor compounds. The researchers also found, however, that East Asian and Southern European cuisines tend to avoid pairing ingredients with shared flavor compounds. Soy sauce, scallions, and sesame oil, for example, share hardly any flavor compounds but are commonly combined in East Asian cuisine.

These unexpected findings fundamentally question our previous notion of flavor pairing. Although the food pairing hypothesis still holds for some cuisines, it appears there are many more desirable flavor combinations available than previously imagined. As researchers continue to examine a wider variety of ingredients and cuisines, we will be able to build even larger, more robust flavor networks to gain insight into the fundamental principles behind our ingredient pairing preferences.

Such flavor networks will also benefit the next generation of “creative” computers. By combining our current knowledge of flavor networks with computer learning, scientists at IBM are now creating adaptive computer systems that will “learn” to create desirable and innovative food combinations. One day, these computers could help create better school lunches or design menus that meet strict dietary restrictions without sacrificing great flavor.

Of course, there’s more to cooking than lists of flavor compounds and networks of ingredients. Factors like color and texture can have play equally important roles in the palatability of a dish. It therefore seems unlikely that a computer will ever be able to replace the creativity and aesthetic prowess of human chefs. But then again, did anyone expect a computer to win Jeopardy?

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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