CHEM215 Lecture Notes - Lecture 13: Alkaloid, Sympathetic Nervous System, Coffee Production
Lecture 13 – Food Processing 2
Coffee processing:
Methods of processing coffee can have large affects on taste and aromas (ie quality).
1. Picking the fruit (cherries): usually picked by hand, so is labour intensive.
2. Hulling: process of disengaging the seed from the husk. Occurs either wet (cherry
is soaked in water then pulped and dried) or dry (husk is dried first then pulped)
3. Sorting/grading and storaged: this involves removing the broken/damaged
beans and sizing.
4. Roasting: Carried out at the final destination; gives rise to the aroma, flavour and
characteristics of coffee. Roasting involves a complex chemistry —> many
chemical reactions take place. The aroma profile contains over 600 chemical
species (gas chromatography is an analytical technique that can be used to
characterise aroma profiles)
Roasting techniques:
• Drying at a high temperature: 200-300˚C for 16-25mins.
• Commercial roasters process 5 tonnes/hour
• Coffee can be light roasted or dark roasted.
Changes during roasting:
• Chemical changes: aroma formation.
-Pyrolysis reactions of sugars, amino acids, organism acids and phenolic
compounds occurs
-Maillard Reaction
• Physical changes:
-expansion of the bean volume (by 100%)
-loss of CO/H2O/CO2 and other volatiles
-loses 15-23% of weight.
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Lecture 13 – Food Processing 2
Caffeine:
• caffeine is the most important member of a class known as the purine alkaloids.
Alkaloids are secondary metabolites found in plants —> contain a basic nitrogen
atom, usually as part of a heterocyclic ring system.
• Caffeine occurs in over 60 plants —> coffee, tea, cacao, and kola nuts
• Caffeine is biosynthesised by plants as insecticides —> it is very bitter.
• Caffeine is a planar molecule.
Caffeine structure:
Purine alkaloid: it is a five-membered ring joined to a six-membered ring, that contains a
basic nitrogen atom as part of a heterocyclic ring. It is a secondary metabolite —> an
organic compound that is not directly involved in the normal growth, development or
reproduction of an organism.
Pharmacological effects of caffeine:
• Only has an absorption half-time of 8mins.
• Elimination lifetime = T1/2 = 3-4 hrs.
• Acts as a stimulant for the sympathetic nervous system —> increases blood
pressure and heat rate. Affects glucose absorption and adrenaline/noradrenaline
release.
• Improves alertness if over 200mg consumed.
• Acts as a diuretic
• Has cardiovascular effects
• Is toxic in large amounts ( >1g quantities have been fatal).
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Document Summary
Methods of processing coffee can have large affects on taste and aromas (ie quality): picking the fruit (cherries): usually picked by hand, so is labour intensive, hulling: process of disengaging the seed from the husk. Roasting involves a complex chemistry > many chemical reactions take place. The aroma profile contains over 600 chemical species (gas chromatography is an analytical technique that can be used to characterise aroma profiles) Roasting techniques: drying at a high temperature: 200-300 c for 16-25mins, commercial roasters process 5 tonnes/hour, coffee can be light roasted or dark roasted. Changes during roasting: chemical changes: aroma formation. Pyrolysis reactions of sugars, amino acids, organism acids and phenolic compounds occurs. Caffeine: caffeine is the most important member of a class known as the purine alkaloids. Purine alkaloid: it is a five-membered ring joined to a six-membered ring, that contains a basic nitrogen atom as part of a heterocyclic ring.
