This document discusses stereochemistry in food, specifically enantiomers. It begins by defining chiral carbon atoms and how they give rise to two distinct spatial arrangements called enantiomers. While enantiomers are mirror images with identical physical and chemical properties, they differ in how they rotate polarized light. The document then covers three naming conventions - D,L notation used for sugars and amino acids; R,S system (CIP system); and differences in properties between enantiomeric forms like differing tastes, smells, and toxicity. Enantiomers found in nature are often pure forms produced through stereospecific biosynthesis, while synthetic equivalents are often racemic mixtures for easier production.

1. FOOD CHEMISTRY
STEREOCHEMISTRY IN FOOD
By:
AZHAR
AIZAT

2. INTRODUCTION
• Chiral carbon atoms - carbon atom that is
bonded to four different groups
– which bring about two distinct spatial
arrangement of molecule, called
enantiomers.
Similarity
• Enantiomers are mirror image of each other,
have identical physical and chemical
properties

3. Differences
 One of them will rotate the plane of polarization of
plane polarized light in a clockwise direction
 This enantiomer is said to be dextrorotatory (+ or d)
and has a positive specific rotation value.
 Another enantiomer will rotate the plane of
polarization of the plane polarized light in an
anticlockwise direction.
 It is said to be laevorotatory (- or l) where it has
negative specific rotation value.

4. F9.1: Explain the three different
conventions used for naming the different
enantiometric forms
1) D, L notation
• An older convention used for sugar and amino
acids.
• The absolute configuration of other sugars about
each chiral centre is then named by analogy:
o If the C=O pointed away, the –OH group on the right then
it is a D-isomer.
o And if the C=O pointed towards you , the –OH group on
the left then it is a L-isomer

5. • The D,L system is also applied to amino acids.
• Using the “CORN” rule, the “COOH”, “R-side
chain group”, “NH2” are around the Carbon atom.
• CORN rule:
o Molecule is viewed with the C-H bond pointed away from
the observer (same as in the R,S system)
o Made up of COOH, R and NH2 arrange around the carbon
atom.
 If it is arranged clockwise – D-form
 If anticlockwise – L-form

6. • Almost all naturally occurring amino acids are the
L-form and are usually tasteless.
• Synthetic D-amino acids taste sweet and most
naturally occurring sugars are D-form.
• Enantiomers that does do not occur naturally cannot
be metabolized by our body.
• SUGARS  contain an aldehyde or ketone, and all
carbons which do not have it is attached to an
alcohol.
• Amino acids  contain carboxylic acid (COOH),
Hydrocarbon chain (R) and amino group (NH2)

7. 1) R,S system (CIP system) Cahn, Ingold & Prelog
• Used for other groups of compounds.
• Involve 3 steps:
i. Atom bonded to the chiral carbon are ranked in order of
increasing atomic number – most common would be 
(H<C<N<O<F<Cl<Br)
ii. When 2 @ more atoms have the same atomic no. (eg: -CH3
& -COOH) , the 2nd atoms are used to rank the substituents
(so –COOH >CH3, since atomic no of 3xH < O) . And if the
2nd atom is also the same, then move on the next atom and
so on. (remember that double bond count as double -
COOH = 3O, since one of O have double bonds.
iii. View the double molecule with the lowest ranking is
pointing away from you, other three substituent must either
decrease in order in a clockwise direction (R-enantiomer)
@ in an anti clockwise direction (S-enantiomer)

8. F9.2: DISTINGUISH BETWEEN THE
PROPERTIES OF ENANTIOMERIC FORMS
OF STEREOISOMERS FOUND IN FOOD

9. • Enantiomers may be similar but different enantiomeric
forms of molecule have different taste smells and
toxicity.
• This is because biological systems are much more
sensitive to the shape of molecule
• E.g.:
 Carvone:
 R-form= Laevorotatory= has smell and flavour of spearmint.
 S-form= Dextrarotatory= has the smell and flavour of
caraway seeds.
 Limonene:
 +(d) = Smells of oranges
 -(l)= Smells of lemons

10. • Sometimes, a natural flavour is a pure enantiomer,
because it is biosynthesis tends to stereo specific.
• Synthetic equivalence is often a racemix mixture 
mixture of equal amounts of the enantiomers .
(easier to synthesis)
• E.g.:  alphaionone in raspberries.
• As for toxicity it can varies tremendously
between the different enantiomer, as become
tragically apparent in the Thalidomide disaster.

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