Science Activity

Food of the gods…

The cacao seed is also ~65% water. Cacao fruit is a pod filled with many cacao beans/seeds embedded in a sugary pulp. When the fruit is mature, the pulp and seeds are removed and fermented. During fermentation the sugary pulp is consumed by yeast and bacteria. The yeast convert sugar (C6H12O6) to ethanol (C2H6O), and the bacteria use oxygen to convert the ethanol (C2H6O) into acetic acid (C2H4O2, the acid in vinegar).

glucose ( C 6 H 12 O 6 ) C C C C C O H OH H H OH H OH CH 2 H HO OH yeast H 3 C CH 2 OH + 2 CO 2 2 O 2 H 3 C C OH O acetic acid ethanol O 2 2 bacteria destroys cell membranes of cacao beans	Over time, the acetic acid breaks down cell membranes of the cacao seed, and the defensive compounds mix with enzymes and air.
Figure 30.2. Fermentation of the cacao fruit pulp converts glucose sugars into acetic acid.

As we have seen with browning of fruits and vegetables (Activity 21_Plants and Color), when phenolics mix with enzymes and air, oxidation turns the astringent phenolics into brown colored compounds that are less astringent. When the membranes are weakened by acid, released enzymes also break down the proteins inside the seed/bean into amino acids. After the fermentation, the beans are dried in preparation for roasting.

Roasting uses dry heat to remove much (but not all) of the vinegary acetic acid by evaporation, and generate the browning Maillard reactions between the amino acids and sugars. Finally the heat develops flavor molecules from the Maillard reactions and the breakdown of some defensive compounds. This is similar to the process used to roast coffee beans. Chemists have detected over 600 different kinds of volatile molecules in chocolate – making it one of the most aromatic foods in the world.

The particles are so small that the resulting material - called chocolate liquor - is essentially the molecules (protein, fiber, starch, sugar phenolics, alkaloids) suspended in the fat. Chocolate liquor has a concentrated chocolate taste, but is still quite bitter, astringent and acidic. The chocolate liquor is further modified to make the chocolate we are used to eating. If most of the fat is extracted from the chocolate liquor, the resulting powdery solid is made into unsweetened cocoa powder – often used in baking. The isolated fat or cocoa butter can be added back to the chocolate liquor to increase the total amount of fat and change the consistency of the final chocolate.

Vanilla (bean, extract or artificial) and lecithin are also common additives to eating chocolate. Remember lecithin is a soy derived phospholipid emulsifier, and emulsifiers are amphiphilic molecules that help mix polar (hydrophilic) and non-polar (hydrophobic) molecules. Lecithin is especially useful in dark and milk chocolate where there is a large amount of added sugar. The lecithin helps the fat mix with the sugar . Typically lecithin is no more than 0.3-0.5% of the chocolate weight.

“Dutch” or alkalized cocoa powder is produced from cacao beans that have been treated with the alkaline substance, potassium carbonate. This raises the pH of the cacao beans to a neutral pH 7 or a slightly alkaline pH 8. The change in pH also has effects on the chemistry of the chocolate, the most notable of which is the reaction of flavor molecules with phenolics to produce flavorless dark colored compounds. Thus, alkalized cocoa powder is milder in flavor and has a darker color. Since natural cocoa powder is acidic and “Dutch” or alkalized cocoa powder is neutral or basic, using the right one for a recipe is important.

Questions:

1. A raw cacao bean has a purple colored interior. Which of the defensive compounds within the cacao bean could be responsible for the purplish color of its interior?

2. Why is chocolate liquor…

a. …essentially molecules suspended in fat?

b. …acidic?

3. What molecule(s) are primarily responsible for the bitter taste of dark chocolate (the darkest chocolate is synonymous with bittersweet)?

4. Why does unsweetened cocoa powder have less than half the total fat content of unsweetened baking chocolate?

5. White chocolate seems like an oxymoron….

a. Does white chocolate contain caffeine? Why or why not?

b. White chocolate has no chocolate flavor. What is the chemical explanation for this (i.e. what molecules are responsible for chocolate flavor and why doesn’t white chocolate have any?)

c. Some white “chocolate” is made with solid or hydrogenated vegetable fats instead of cocoa butter. Is this stuff rightly called white chocolate? Why or why not?

6. In the Joy of Cooking, the authors recommend the following substitutions for natural or Dutch processed (alkalized) cocoa powder – if you find yourself without the necessary cocoa powder for the recipe:

· Substitution for 3 tablespoons (18 grams) Dutch-processed cocoa:   3 tablespoons (18 grams) natural cocoa powder plus pinch (⅛ teaspoon) baking soda

· Substitution for 3 tablespoons (18 grams) natural cocoa:   3 tablespoons (18 grams) Dutch-processed cocoa plus ⅛ teaspoon cream of tartar or ⅛ teaspoon lemon juice or vinegar

What is the chemical reasoning behind these recommended substitutions?

What makes chocolate so special?

Model 2. One of the reasons chocolate is special is the temperature at which it melts. Chocolate melts between 94-97°F thanks to the sharp melting point of cocoa butter (the fat that comprises over half of the chocolate weight), which is right at human body temperature (~98°F). Chocolate literally “melts in your mouth”. Although cocoa butter is a plant fat, is it comprised of over half saturated fats. These saturated fats make cocoa butter a solid at room temperature (hence the “butter” reference), and the relatively small number of fatty acid types makes the cocoa butter solid melt over a relatively narrow temperature range (remember, the melting temperature of a solid is influenced by the purity/homogeneity of the solid – Activity 11).

Diets high in saturated fats may raise the risk for heart disease, which sounds like bad news for eating chocolate! However….despite cocoa butter’s higher than typical concentrations of saturated fats, the saturated fat in largest concentration – stearic acid – is immediately converted by the enzymes in the body to oleic acid, a cis monounsaturated fat. So, chocolate’s effective saturated fat content is lower thanks to the stearic to oleic acid conversion, and scientists do not believe that chocolate consumption poses cardiovascular risks.

C O O C H 2 C C CH 2 C H 2 H 2 C C H 2 H 2 C C H 2 H H C H 2 H 2 C C H 2 H 2 C C H 2 H 2 C C H 2 H 2 C C H 2 H 2 C C H 2 H 2 C C H 2 H 2 C C H 2 H 2 C CH 3 H 2 C C O O C H 2 H 2 C C H 2 H 2 C CH 2 H 2 C H 3 C Stearic Acid - an 18 carbon, saturated fatty acid (found in high concentrations in cocoa butter) part of tricglyceride part of tricglyceride enzymes in the human body Oleic Acid - an 18 carbon, cis monounsaturated fatty acid

Figure 30.4. The conversion of stearic acid (a saturated fatty acid) to oleic acid (a cis monounsaturated fatty acid) by enzymes in the human body.

Many people believe chocolate can alter their mood, and chocolate does contain molecules that have effects on the brain. These molecules are part of the cacao seed’s chemical defenses against predators and are present in the bean when it is harvested, fermented and roasted.

Table 30.4. Psychoactive molecules found naturally in the cacao bean and therefore in chocolate
Molecule	Structure	Physical Effects
Caffeine	N C N C C C N C H N O O H 3 C C H 3 C H 3	Stimulant of the central nervous system
1oz of unsweetened chocolate contains 30 milligrams of caffeine (~⅓ that found in a cup of coffee)
Theobromine	H N C N C C C N C H N O O C H 3 C H 3	Stimulant of the central nervous system (although weaker than caffeine) and toxic to dogs .
1oz of unsweetened chocolate contains ~300 milligrams of theobromine
Anandamide	H 2 C C C C C C H 2 C H 2 C C C C C H 2 H 2 C C H 2 C O N H H 2 C C H 2 O H H 2 C C H 2 H 2 C C H 2 C H 3 H H H H H H H H	A molecule found in chocolate and also produced naturally by the human brain that blocks pain and depression
If anandamide looks a little like a cis polyunsaturated fatty acid to you…you would be right – that’s what anandamide is made from.
Phenylethylamine (PEA)	H C H C C H C H C H C H 2 C C H 2 N H 2	A molecule found in chocolate and also produced naturally by the human brain which stimulates the parts of the brain that keep you alert and mimics the brain chemistry of a person in love.
Scientists believe that other molecules in chocolate inhibit the breakdown of PEA in the brain, allowing its effects to last longer.

But can chocolate actually be good for your heath? As a seed, the cacao bean contains alkaloids (caffeine, theobromine), anthocyanins, phenolics and polyphenols (made from phenolics) for chemical defense. Molecules like phenolics and polyphenols are great antioxidants – they protect against oxidative damage from the oxygen we breathe by reacting harmlessly with reactive oxygen species (also known as free radical oxygen). Furthermore, scientists have shown that cocoa polyphenols act as antioxidants in the human body! The polyphenols also had additional beneficial effects on cardiovascular (i.e. heart) health. All good reasons to eat chocolate!

C H C C C C H C C H 2 C H C H O C C H C C H C H C O H O H H O O H O H C H C C C C H C C H 2 C C H O C C H C C C H C O H O H H O O H O H O H H C H C C H C H C H C O H H C C C H C C H C O H O H H O H C C C H C H C H C H O O H e p i c a t e c h i n e p i g a l l o c a t e c h i n p h e n o l p h e n o l i c c o m p o u n d s P o l y p h e n o l s a r e m a d e f r o m p h e n o l i c c o m p o u n d s Figure 30.5. Phenolic compounds and polyphenols found in cocoa.

7. Why is chocolate (a high fat food derived from a plant) a solid at room temperature when most plant derived fats are liquid oils?

8. Based on the structures of caffeine and theobromine, why does it make sense that both are stimulants of the central nervous system?

9. What type of “eating chocolate” (i.e. sweet dark chocolate, milk chocolate or white chocolate) is going to have the highest concentration of caffeine and theobromine and other psychoactive molecules? (i.e. what type of chocolate should you eat right before that tough final exam!)

10. Scientists at the University of Scranton have “discovered that in hamsters, cocoa powder at a dose equivalent to two dark chocolate bars per day significantly inhibited atherosclerosis, a type of heart disease in which fat clogs up arteries, and raised the levels of good cholesterol.”

a. Chocolate has high levels of saturated fat. Why does this not contribute to cardiovascular (i.e. heart) problems?

b. What molecules in chocolate are responsible for the beneficial cardiovascular effects?

Putting it all Together:

11. Chocolate is a high fat food – and since fats go rancid, most high fat foods have a limited shelf life. However, chocolate has a remarkably long shelf life for a food that is comprised of mostly cocoa butter (fat). As we saw in Activity 11, rancid fats arise from two sources – oxygen in the air causes oxidation of the double bonds and water causes hydrolytic rancidity. Since chocolate has little moisture, the most problematic type of rancidity would be from oxygen in the air.

a. What is it about the chemical composition of chocolate prevents oxidation of the fats?

b. What type of typical “eating” chocolate would be most capable of preventing this oxidation? What is the chemical explanation for why?

c. Chocolate’s ability to combat oxidation of its fats is also beneficial for human health. Explain why.

12. Your friend tried to make the following recipe for “Fudgy Brownies” from yummly.com - but they didn’t turn out quite as expected. The brownies were very dense and tasted less chocolatey than your friend wanted. Here is her ingredient list. Upon looking at the ingredients, you ask your friend – “what kind of cocoa powder did you use?” Your friend responds, “I forgot to buy cocoa powder at the store – so I used this Dutch cocoa powder that I found here in the pantry”

Can you diagnose the problem? Why is the type of cocoa powder so important to this particular recipe? What did NOT happen as a result of the wrong cocoa powder being used?

� See Activity 17_Browning for a lesson on Maillard reactions.

� Milk solids are dried milk protein and sugar

� Lecithin was discussed in Activity 12_Emulsions and emulsifiers

� Activities 10 and 11 talk about the solid vs. liquid nature of fats, as well as fat melting temperature.

� Food Fats and Oils, 9th edition. 2006. The Institute of Shortening and Edible Oils. � HYPERLINK "http://www.iseo.org/httpdocs/Publications/FoodFatsOils2006.pdf" �http://www.iseo.org/httpdocs/Publications/FoodFatsOils2006.pdf� Not every fatty acid is listed, so the numbers won’t add up perfectly to 100%

� These fatty acids are part of triglycerides within the fat/oil.

� Dogs can suffer serious poisoning from chocolate candies, which is perhaps evidence of the cacao bean’s powerful chemical defenses against would-be predators.