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The chemistry of flavours and aroma

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Sabine Lengger

on 1 February 2016

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Transcript of The chemistry of flavours and aroma

Aldehydes have a low odour threshold. Many characteristic tastes of food come from aldehydes. Cucumber flavour, for examples, comes from
(E,Z)-nona-2,6-dienal
and
(E)-non-2-enal
. Most alcohols and ketones, however have higher odour thresholds and are less important flavour components.
The organic chemistry of flavours and aroma
Food, beverages, perfumes all have a distinctive flavour and aroma.
Responsible for these aromas and flavours is a complex mixture of chemical compounds.
These compounds interact with sensory receptors in the mouth, tongue and nose ...
... which send signals to our brain, resulting in the perception of a certain odour, flavour or aroma.

Here is an image showing how olfactory receptors work: http://d2jkam0hji0nkb.cloudfront.net/content/embor/8/7/629/F1.large.jpg


If you click on the link below, you will find the introduction to flavour chemistry from "Food Flavours: Biology and Chemistry".

http://dx.doi.org/10.1039/9781847550866-00001



* Please read p. 1-7. It will give you a brief introduction to flavours.
Note down the different classes of flavours and think of examples for them.

Extra reading


About the difficulty in naming odours: http://cls.ruhosting.nl/wp-content/uploads/2015/10/Odor-naming-is-difficult_CroijmansMajid2015.pdf

About memories and smell: http://www.nytimes.com/2008/08/05/science/05angier.html?_r=0

Rinaldi, Andrea. 2007. ‘The Scent of Life. The Exquisite Complexity of the Sense of Smell in Animals and Humans’. EMBO Reports 8 (7): 629–33. doi:10.1038/sj.embor.7401029. http://bit.ly/1mUXY48

Gaillard, I., S. Rouquier, and D. Giorgi. 2004. ‘Olfactory Receptors’. Cellular and Molecular Life Sciences CMLS 61 (4): 456–69. doi:10.1007/s00018-003-3273-7. http://bit.ly/1PBdAow

Damodaran, Srinivasan, Kirk Parkin, and Owen R. Fennema, eds. 2008. Fennema’s Food Chemistry. 4th ed. Food Science and Technology 169. Boca Raton: CRC Press/Taylor & Francis. (on Google Books: http://bit.ly/1NWugVb )

Flavour compounds
Non-volatile flavour compounds
Volatile flavour compounds
Only a few volatile compounds are detected by the taste buds of the tongue or the inner lining of the mouth. Most receptors in the mouth elicit a response from non-volatile compounds, which must be carried physically via food or saliva to these receptors. Non-volatile compounds, by definition, cannot have an aroma, but they can be broken down to release volatile compounds, such as by the hydrolysis of terpene glycosides or the enzymatic cleavage of glucosinolates.
Examples
- amino acids and peptides
- organic acids
- salts
- sugars
- flavonoids and alkaloids

* Think of examples for these tastes and note them in your labbook.
Aldehydes
Acids
Volatile acids do not only taste sour, they can also interact with odour receptors and impart a flavour.
Propionic acid
, for example, is an important component of swiss cheese flavour.
Esters
Aliphatic esters are responsible for many characteristic fruit flavours.
Hexyl acetate
, is the major component of the aroma of Cox's Orange Pippin apples.
Phenols
Terpenoids
Lactones
Lactones are internal esters, they give flavour to many foods. One example is the peach, which gets its flavour from
δ-decalactone
and other lactones.
Furans
Oxygenated furans stem from carbohydrates in the Maillard reaction and often have a caramel-like taste. They occur in heated foods.
2,5-dimethyl-4-hydroxyfuran-3(2H)-one
, for example, occurs in beef broth, pineapples and strawberries.
Phenols are prominent in smoked products and spices.
Eugenol
from cloves is a phenol and contributes strongly to the flavour of mulled, spiced wine.
Terpenoids are extremely common, important and diverse natural products. They have one common structural unit, the isoprene unit (5 carbons), which can be combined 2, 3, 4, and more times. Monoterpenoids, consisting of 2 isoprene units, are common flavour compounds in many herbs. One example is
menthol
from the mint plant.

More information on monoterpenoids: http://dx.doi.org/10.1021/cr00081a004
* What are the structures of the compounds in bold?

* Please read p. 8 - 14 of the introduction to flavour chemistry and record the different chemical compound classes of volatile flavours and examples for them.
http://pubs.rsc.org/en/content/chapterpdf/1997/9781847550866-00001?isbn=978-0-85404-538-9&sercode=bk


More info on Menthol can be found here:
http://dx.doi.org/10.1016/j.phytochem.2013.08.005

More info on characteristic flavours can be found on
Flavornet
http://www.flavornet.org/flavornet.html




Please go through this presentation, read it carefully and
carry out the activities marked with a *
- they are compulsory and we will get back to them once we are in the lab.


Pre-lab for the CHM3015 Laboratory.
As you can imagine, flavour chemistry forms a large part of the food industry.

* Please now read the BBC article about the flavourings industry linked to below:

http://www.bbc.com/future/story/20140829-the-secrets-of-fake-flavours

What are the positive and negative aspects of natural and synthetic flavourings?

Use the book: "Food Flavours: Biology and Chemistry" (the introduction is freely available online). Record the answers to these questions and bring them to the lab!

* Read page 1-7 and record the different types of flavour.

* Write down examples for the non-volatiles flavour compound classes.

* Draw the structures of the volatile flavour compounds marked in bold.

* Read 8-14 of the book and note the different chemical compound classes of volatile flavours.

* Read the BBC article "The secrets of fake flavours" and note down positive and negative aspects of natural and synthetic flavourings.
What to do before the 1st lab session
Summary
See you in the lab!
Sulfides
Sulfides are characteristic for e.g. allium species such as onion, garlic and chives. Processed (but not fresh) tomatoes contain
dimethylsulfide
, as well as as other sulfur compounds.
The book for this pre-lab session
Fisher, C. and Scott, T. R.

Food flavours: Biology and Chemistry
’.
1997. RSC Paperbacks, Cambridge: Royal Society of Chemistry.

http://dx.doi.org/10.1039/9781847550866


This first chapter of this book, which this presentation will link to, is freely available online. But you can also find the book in the library.
Other resources
Other resources are referred to with links or citations in this presentation. You will also find them in the reading list (on the Moodle website).
Bring your notes!
(When this presentation has finished, you will be able to zoom around in it on your own if you want to find something specific.)
(from: Rinaldi, 2007)
In the laboratory exercise in Advanced Organic Chemistry you will be confronted with a real-world problem from the flavourings industry.

Please make sure you have completed all the activities marked with a
*
in this presentation for the pre-lab session.
Full transcript