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UNDER THE MICROSCOPE

A New Series

Turning up the Heat on Acrylamide

WELCOME, READERS, to Under the Microscope, a new series of scientific articles dedicated to exploring coffee science. In the coming months, we’ll take a deeper look at coffee and probe into the chemistry behind this mystical bean. We’ll take a classroom approach to discussing coffee’s most interesting aspects, including flavor development during roasting, affects of altitude on quality, formation of Ochratoxin A, total dissolved solids (TDS) and brewing, adulteration in coffee, acrylamide formation and much, much more. We hope this new series will bring out the “inner geek” in all of us and provide a better understanding behind the science of this complex beverage. For now, sit tight, open your notebooks and sharpen your pencil as we get ready to take coffee “under the microscope.” Class is now in session, shhhhh…

     As a child, one of my favorite memories was waking up every Saturday morning to the smell of freshly baked sweet bread and coffee from my mom’s kitchen. Other times, it was the smell of hand-made tortillas and the savoring aroma of carne asada from a mid-Saturday afternoon BBQ. In looking back at these different sensorial memories, one would immediately assume that these products share nothing in common. But probing a bit further, one would discover that they indeed do share a common denominator, at least in terms of flavor development, during preparation. Enter Flavor Chemistry 101.
     During thermal processing, be it baking, frying or roasting, food products undergo a simple yet complex array of chemical reactions combining available amino acids with carbohydrates in a process called the Maillard reaction. Occurring at roughly 150° C (302° F), the Maillard reaction is what makes coffee as we know it today, as the intensely aromatic “nectar of the Gods”—without it, coffee would be a dull green bean with no more than a mere handful of earthy aromas. Indeed, the Maillard reaction is the most critical reaction for all thermally processed foods, and it’s responsible for creating hundreds of savory aromas in products such as toasted bread, steak, beer, coffee and many others. It’s been estimated that in coffee alone, more than 800 aromatic compounds are formed during this reaction, many of which remain unidentified today.
     But the Maillard reaction goes much further than just creating pleasant aromas, for the very color of coffee, its flavor, its complex aroma and many of the recently discovered therapeutic compounds are a direct result of this reaction. Furan, or the compound responsible for the “nutty/caramel” aroma in coffee, is also a potent antioxidant and potential anti-carcinogen. Melanoidins—the long-chained polymers responsible for creating coffee’s color—are also potent antioxidants, making up 25 percent of brewed coffee’s composition. Other studies suggest that coffee is a rich source of niacin (vitamin B3), potassium and soluble fiber and is ultimately believed to prevent many debilitating diseases.
     Alongside these myriad beneficial compounds comes the formation of a recently discovered questionable by-product. According to a Swedish study, coffee, along with several other thermally processed foods, contains relatively low levels of the by-product “acrylamide.” Acrylamide, which is commonly used in manufacturing a broad range of industrial products including plastic, contact lenses and paper pulp, is classified as a “probable” carcinogen by the International Agency for Research on Cancer (IARC). Although there have been numerous animal studies conducted, there is no direct link to date, correlating the consumption of acrylamide with formation of certain cancers in humans.
     Acrylamide’s accidental discovery in potato chips and french fries by Swedish scientists in 2002 shocked the food safety world and made it the center of headlines in recent years. Since then, the World Health Organization (WHO), the United Nations and the European Union have launched more than 200 research projects throughout the world in an effort to assess the risk and prevalence of acrylamide in other thermally processed foods.

Acrylamide Formation During Roasting

In much the same the way the Maillard reaction produces its beneficial compounds, the same reaction is also believed to be the pathway for acrylamide formation in coffee. The relatively low concentrations of the amino acid asparagine and free sugars in both arabica and robusta coffee provide just enough reagent to form acrylamide. Although published concentrations on acrylamide in food vary, its formation is generally dependent upon a number of factors, including frying/baking time, temperature, storage conditions, and exposure to UV light. As shown in Figure 1, ordinary food products such as baby food, cereals, potato chips, coffee and french fries all contain some residual level of acrylamide. Interestingly, one often overlooked factor—surface area—also plays a critical role in acrylamide formation during processing. It is no surprise then, that potato chips, with their relatively large surface area, contain 8–16 times the concentration of acrylamide than coffee. French fries come in at a distant second. And although acrylamide concentrations are quite significant, one must remember that potatoes, in general, contain a much greater concentration of asparagine than what would ever be found in green coffee.

 Fortunately, acrylamide formation in coffee occurs during the early stages of roasting, and, due to its unstableness at high temperature, degrades progressively during the latter stages of roasting. As seen in Figure 2, during roasting acrylamide formation peaks at about 125° C (257° F) then begins to degrade, up to 95 percent, with darker roasting styles. But although darker roasts may mitigate acrylamide formation, it does so at a significant price. For darker roasts styles tend to disrupt much of the delicate organoletic, therapeutic and nutritive effects contained within the bean itself. And in coffee, with roasting and the Maillard reaction playing such a critical role, it’s nearly impossible to implement mitigation strategies without any effect on coffee quality. Thus roasters electing to use darker roast style place themselves in a delicate “risk-benefit” situation between choosing a roast profile that has the desired flavor characteristics (acidity, aroma, etc.) and one without them.
     These days, with the widespread use of temperature/time profilers on most commercial roasters, roasters now have greater control over acrylamide formation during roasts. One option available is the use of longer/lower temperature roast profiles, which allow for enough flavor compounds to develop within the bean, without the risk of excess acrylamide. Another method recently patented by Proctor and Gamble involves the use of an enzyme, asparaginase, to reduce asparagine levels in green beans prior to roasting. Nestlé and Frito Lay are believed to be working on a similar method to reduce acrylamide in several products, both before and after processing. Another method recently developed involves a combination of steam roasting with high temperature/short time profiles to minimize acrylamide formation. Interestingly, according to the Swedish Institute for Food and Biotechnology, its the duration of roast that is the greatest factor in acrylamide formation and not temperature as we would expect.
     Though the options and use of technology are endless, for now researchers are continuing their quest to reduce acrylamide in food with minimal affects on flavor.

Acrylamide During Storage

With the sheer complexity that roasting plays in flavor development, it would seem almost futile to attempt any control over acrylamide formation. Fortunately, when we cannot implement roasting strategies to mitigate acrylamide formation, we can turn to the next best thing under our control: packaging. Since acrylamide is not very stable, both before and after roasting, its condition during storage plays an important role in determining residual acrylamide content in coffee.
     According to one German study, coffee stored under non-vacuum conditions showed a 30 to 65 percent reduction in acrylamide during three to six months of storage. Higher levels of reduction were seen as the ambient storage temperature and exposure to light increased. Interestingly the reduction of acrylamide during storage was only seen for both whole bean and roasted and ground coffee, but remained effectively stable for soluble and coffee substitute type coffees. No degradation was seen for frozen coffee at -40o C.
     While many would not advocate consuming six-month old coffee, it does create a strong impetus for those consumers to switch from drinking soluble to specialty grade coffee. As it turns out, drinking stale old coffee may not be so bad after all (see Table 1.)
     Interestingly, nowhere is the impact of the Swedish study felt more in the world than in California. Acrylamide is classified as a carcinogen under the Safe Drinking Water and Toxic Enforcement Act, otherwise known as Prop 65. The law requires every food product containing additives “known to the state of California to cause cancer” to be properly labeled. Thus far two groups have already sued fast food manufacturers for failing to comply. Though there continues to be much debate on acrylamide, the FDA’s official statement on it says that “…research on acrylamide…is neither a warning to consumers nor a finding of risk with any particular food” and does not pose a significant health risk.
     Ironically, it is these same chemical reactions (responsible for creating coffee’s complex flavor and numerous therapeutic compounds) that create products such as acrylamide. For now, it looks like Starbucks and others who have traditionally used darker roasts may have accidentally been on to something early on. Now, it’s up to us to choose the best path. Class dismissed.

JOSEPH A. RIVERA is the director of science and technology at the Specialty Coffee Association of America (SCAA) and founder of the coffee science website, www.coffeechemistry.com.
He can be reached at jrivera@coffeechemistry.com.