Coffee science and gastronomy

Rancidity of coffee

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“Production of disagreeable aromas and flavours with the initiation of a chain reaction  via autoxidation of coffee’s fatty acids” can be defined as the rancidity of coffee.

The chain reaction starts when fatty acids get in contact with oxygen, hydroxide ion together as they imputed by energy of a photon. While brewing water provides the hydroxide ions, direct or diffuse light provide the energy of photons (E=hv)*. The unsaturated part of the fatty acid has the ability to discharge a proton (H+) once it has been act upon light. This proton together with hydroxide ion creates a water molecule while fatty acid generates a free acid radical (R-C-). Once this free radical gets in contact with oxygen in the air, it creates a fatty peroxyl (lipid peroxyl) radical (lipid peroxyl radical) (R-COO-). This free radical has the ability to get in action with another fatty acids’ C-H arm to break the bond by acting as an electrophilic addition in order to create another free acid radical (R-C-) which continues the propagation of the chain reaction.

 Chain reaction {1}

800px-Lipid_peroxidation.svg

This is the usual mechanism of autoxidation of fatty acids. Compounds like 2, 4-decadienal and 2, 4-nonadienal predominantly bring to live by autoxidation of fatty acids bring the rancidity to our coffee.

2, 4-decadienal- C10H16O (molecular mass-152 g/mol)

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2, 4-nonadienal -C9H14O (molecular mass-138 g/mol)  

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Preventing the rancidity is a difficult aspect within the coffee gastronomy but phenol or phenolic compounds normally used as an antioxidant agent within food gastronomy. Delocalized  pi electrons clouds which hovering above the benzene ring of six carbon atoms, limit the free radical activities.

However, as ascorbic acid or citric acid compounds act as natural antioxidant agents, if any coffee contains above compounds within, have the potential of preventing those chain reactions.

Coffee’s higher amount of fatty acids and longer contact time with oxygen, can cause coffee to deteriorate and produce rancid flavours, once brewed. Therefore usage of an optimum roasting method and a proper storage method can be direct influences of rancidity of coffee, apart from the chemical composition of it.

Thinking along these parameters has brought out practically difficult but theoretically objective aspect of preventing rancidity at coffee brewing.By brewing coffee in the dark (as no photons are coming in to interact with coffee to create free radicals), can oxidative rancidity be prevented happening within the coffee?


*(E=hv), E-Energy, h- Planck constant (6.62606957(29)×10−34  m2 kg / s), v= frequency of EM wave

REF-{1},-http://en.wikipedia.org/wiki/Lipid_peroxidation#mediaviewer/File:Lipid_peroxidation.svg

(Special thanks to http://pubchem.ncbi.nlm.nih.gov/ for pictures of the molecular structures)

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2 thoughts on “Rancidity of coffee

  1. Pingback: Coffee Lipids and Grinders | coffeeperception

  2. Pingback: Coffee Lipids and Grinders – CAPITAL COFFEE CONSULTANTS

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