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Chocolate Chemistry

September 8, 2011

I wrote about chocolate in a previous article (The Chemistry of Chocolate, January 08, 2007). Chocolate is appealing to chemists both as a delightful food and as an interesting object for study. There has been much research in the chemistry of chocolate, the most recent of which was reported at the 242nd National Meeting of the American Chemical Society, August 28 -Sept. 1,2011.[1-2]

chocolate

Chocolate

Per capita chocolate consumption in the US is about ten pounds per year, but northern Europeans consume about twice that amount.[3]

(Photograph by André Karwath, via Wikimedia Commons))


The primary ingredient of chocolate is cocoa, an apparently non-toxic natural product that has been consumed by humans for thousands of years. Cocoa may be non-toxic to humans, but its toxicity in some animals, including dogs, is well known. Less than one ounce of baker's cocoa can bring about symptoms such as epileptic seizures, heart attacks, internal bleeding, and death in a medium-sized dog.

As a counterexample, the small pet dog of prominent US chemist, W.E. Wallace, with whom I worked for several years, consumed about half a bag of milk chocolate kisses, including much of their aluminum wrapping, with no apparent effect. Perhaps the cocoa content was too small, or the aluminum neutralized the effects.

Cocoa contains about 550 chemical compounds identifiable by gas chromatography. Thirty-five of these have an odor. Many of these chemicals are not found in the cocoa bean, itself, but they're produced by the processes used in cocoa production, such as fermentation, roasting, grinding, dissolving, heating, pressing and drying.[4] A good chocolate aroma requires only 25 of the volatile compounds in cocoa.[1]

An article in the July, 2006, issue of the Journal of Agricultural and Food Chemistry reported on research in the principal odoriferous chemicals that define chocolate.[5] The authors validated their analysis by combining twenty four of the most potent aromatic ingredients to reproduce the scent of cocoa.

Some of the principal odorants were those for cabbage, sweat, honey, potato chips, caramel, malt, popcorn, and sulfur.[4-5] Other odorants resemble cooked meat, peaches, raw beef fat, earth and cucumber.[1] Can I offer you a cabbage-filled bon-bon?

Here's a short list of some of the chemicals in cocoa.[6-8]
•  Indole, also present in coffee, tobacco, olive oil, and wine.

•  Anandamide, present in small quantities, is an endogenous cannabinoid.

•  Caffeine, in modest quantities.

•  Theobromine, a mild stimulant. The combination of theobromine and caffeine may be responsible for the "chocolate buzz." Theobromine is the chemical that's toxic to some animals.

•  Magnesium. Magnesium deficiency exacerbates pre-menstrual symptoms, so chocolate would be a palliative.

•  Phenylethylamine, an amphetamine-like chemical. Its presence in very small quantities may explain how chocolate seems to sooth depression.

•  Tetrahydro-beta-carbolines. These neuroactive alkaloids are found also in beer, wine and liquor. Perhaps this explains the addictive power of chocolate.

•  Phenylethylalanine, a supposed aphrodisiac.

Chocolate has one quality other than chemical that adds to its appeal. That's mouthfeel, which is not just texture, but a combination of manifold properties. Mouthfeel was one of those scientific tidbits that I would utter at the dinner table that would bring my children to near hysterics. Why is it that they never laughed at my real jokes?

Peter H. Schieberle of the Technical University of Munich, an author of the study in the 2006 issue of the Journal of Agricultural and Food Chemistry, was also the author of the recent chocolate paper at the ACS-Denver meeting.[2] The ACS paper specifically examined the chemical reactions that are responsible for the malty and honey aromas of chocolate.

In his continuing work, Schieberle characterized and quantified the principal aroma and taste compounds of roasted and fermented cocoa. The malty and honey aromas of chocolate arise from the Strecker reaction, a chain of chemical reactions in which amino acids are formed from aldehydes. This reaction occurs during roasting and fermentation, but also during mastication in the human mouth.[2] Says Schieberle,
"When you put chocolate in your mouth, a chemical reaction happens... Some people just bite and swallow chocolate. If you do that, the reaction doesn't have time to happen, and you lose a lot of flavor."[1]

Science is good, but better chocolate is wonderful. Schieberle discovered a simple processing change that lowers the astringency of cocoa. He found that adding some sugar to cocoa before Dutch processing generates new, velvety tasting compounds from the formation of previously unknown taste components.[1]

References:

  1. Michael Bernstein and Michael Woods, "What's really in that luscious chocolate aroma?" American Chemical Society Press Release, August 29, 2011.
  2. Peter H. Schieberle, "Colorful chemistry of cocoa and chocolate: Flavor creation by processing and eating," Paper AGFD-27 of the 242nd ACS National Meeting (Denver, Colorado), August 29, 2011
  3. F.H. Seligson, D.A. Krummel and J.L. Apgar, "Patterns of chocolate consumption," American Journal of Clinical Nutrition, vol 60, no. 6 (December 1, 1994), pp. 1060S-1064S; PDF file available here.
  4. Megha Satyanarayana, "A Whiff of What?"
  5. Felix Frauendorfer and Peter Schieberle, "Identification of the Key Aroma Compounds in Cocoa Powder Based on Molecular Sensory Correlations,"J. Agric. Food Chem., vol. 54, no. 15 (July 26, 2006), pp. 5521-5529.
  6. Dhara Thakerar, "Chocolate's chemical charm."
  7. E.D. Tomaso, M. Beltramo, and D. Piomelli, "Brain cannabinoids in chocolate," Nature, vol. 382, no. 6593 (Aug. 22, 1996), pp. 677ff.
  8. Chocolate (http://www.chocolate.org).                                   

Permanent Link to this article

Linked Keywords: Chocolate; chemist; 242nd National Meeting of the American Chemical Society; André Karwath; Wikimedia Commons; cocoa; toxicity in some animals; dog; epileptic seizure; myocardial infarction; heart attack; counterexample; William E. Wallace; W.E. Wallace; Hershey's Kisses; milk chocolate kisses; aluminum; chemical compounds; gas chromatography; cocoa bean; fermentation; roasting; grinding; solvation; dissolving; expeller pressing; pressing; volatile compound; Journal of Agricultural and Food Chemistry; cabbage; sweat; honey; potato chips; caramel; malt; popcorn; sulfur; cooked meat; peaches; beef fat; earth; cucumber; bon-bon; indole; coffee; tobacco; olive oil; wine; anandamide; endogenous; cannabinoid; caffeine; theobromine; stimulant; magnesium; pre-menstrual symptoms; phenylethylamine; amphetamine; depression; tetrahydro-beta-carboline; alkaloid; beer; liquor; phenylethylalanine; aphrodisiac; mouthfeel; Technical University of Munich; Strecker reaction; amino acid; aldehyde; mastication; astringent; sugar; Dutch process chocolate.

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