viernes, 29 de julio de 2016

DECODE science: Chemistry of Chocolate SUMMERS

About Vincent Summers

Vincent Summers holds a Bachelor of Science in Chemistry, and worked for the National Radio Astronomy Observatory for 23 years. Vincent was involved in NASA's extended Voyager2 program while there.
Vincent has taken as many graduate-level organic and quantum chemistry courses as were available under the University of Virginia's Citizen Scholar Program.

The Manufacture and Chemistry of Chocolate

Cacao Pods
Cacao pods contain the makings of chocolate, but the contents must first go through a fermentation and drying process. Image by Medicaster.
Some years ago, someone made the claim that genuine chocolate isn’t ‘good for you’ – saying that artificial chocolate made from carob beans is superior.
Thank goodness, science now concedes that chocolate is not all that bad; most of us can eat and enjoy at least some chocolate.
And now that we know it’s OK to eat chocolate – and it may even be good for us – did you ever wonder: How do we make cocoa from cacao, and what is the chemistry behind this treat?

Chocolate Chemistry: The Cacao Bean

The fruit pod of the Theobroma cacao tree has a tough rind encasing pulp as well as some 20 to 50 beans. The beans are typically white to violet in color before they are exposed to air and sun.
The part of the pod we want is the bean without its papery skin; to get to the cacao bean, manufacturers remove the rind and heap up the pulp and seeds to them to ferment.
Naturally-occurring fungi (Geotrichum & Candida) enables the fermentation of the pulp sugars (notably glucose, fructose and sucrose) into acetic acid, which improves the beans by killing the embryo within the seed plus imparting flavor and reducing bitterness.
The fermentation process also liquefies the pulp. The 6 carbon glucose and fructose sugars are fermented via the pathway
C₆H₁₂O₆ → C₂H₅OH → CH₃COOH
Very similarly, the 12 carbon sucrose sugar is fermented via the pathway
C₁₂H₂₂O₁₁ → C₂H₅OH → CH₃COOH
That may look a little simpler if you look at it like this:
Sugar –> Ethyl alcohol –> Acetic acid
For simplicity, we don’t list the byproduct CO₂ (carbon dioxide), as it is not of particular importance to the end result achieved by the fermentation. The manufacturer then removes the beans, dries them (in the sun or in ovens) and ship them off to factories for further processing or packaging.

Cacao Beans: Roasting and Skin Removal

Manufacturers roast the Cacao (Cocoa) beans, and remove the thin shell mechanically by a process called ‘winnowing’. Skin removal is a simple process, as can be seen in the video below, which demonstrates removal by hand.

In addition to taking off the skins, mechanical winnowing breaks the beans into small pieces called ‘nibs.’ Interestingly, during the fermentation process, the fungus killed the embryo of the seed by converting sugars within the pulp into acetic acid.
Chocolate makers remove this most volatile acid by roasting the beans. The process of removing volatile acids -those acids that largely boil away during the roasting process – affects flavor in chocolate, just as roasting changes the flavor of coffee.
Since there are some 400 to 500 chemicals making up the flavor of chocolate, it is difficult to provide a profile of flavor. However, there among the varieties of flavor-producers are alcohols, aldehydes, esters, ethers, furans, ketones, pyrazines and thiazoles.

Processing Cacao Nibs

Chocolate-makers first grind the cacao nibs into a paste called chocolate liquor. They can then separate this material into two components — cocoa powder and cocoa butter.
Cocoa powder (not the same as the cocoa powder sold in grocery stores) contains the alkaloid theobromine — which possesses stimulative properties, but which is milder than caffeine. Cocoa powder also contains polyphenols. But what is an alkaloid?
An alkaloid is any of a group of nitrogenous organic compounds found in plants that have pronounced physiological actions on humans. Famous examples include: morphine, atropine and strychnine.
Theobromine Alkaloid Image by Jynto
Cocoa contains theobromine, an alkaloid that is a stimulant, but less powerful than coffee. Image by Jynto.
The word polyphenol indicates the joining of many phenol rings (C₆H₅OH) connected to each other. Polyphenols are prevalent in tea, red wine, coffee and olives, and are antioxidants, esteemed for health benefits.
However, those benefits may be partly offset if an abundance of other ingredients is present, for example dairy (creamer) and excessive sugar.
Cocoa butter is an edible fat or triglyceride of palmitic, stearic and oleic long-chain fatty acids.
Palmitic and stearic acids are saturated, whereas oleic acid is monounsaturated. Cocoa butter is very stable, with a low melting point.

Chemistry of Chocolate

We may process cocoa powder in a number of ways, including by alkali-treatment (dutch chocolate), and may use it separately, or combined with refined cocoa butter and other substances, to form a variety of chocolate products for baking, candies and syrups. However we process the cacao bean, if we want the result to be chocolate, there’s going to be chemistry involved.
© Copyright 2014 Vincent Summers, All rights Reserved. Written For: Decoded Science

Original note, HERE.

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