NMR spectroscopy and its application in food industry.

1.  NUCLEAR MAGNETIC
RESONANCE SECTROSCOPY

2. iNTRODUCTION
 Powerful analytical technique used to characterize organic molecules
by identifying carbon-hydrogen frameworks within molecules.
 2 Types :
 The source of energy in NMR is radio waves which have long
wavelengths, and thus low energy and frequency.
 This waves can change the nuclear spins of some elements, including
1H and 13C.
 Frequency in the range of 300Mhz-500Mhz.
13C -NMR1H -NMR

4.  Energy state
Less in no.
Anti parallel to
applied field.
Beta
More in no.
Parallel to
applied field.
Alpha
(Diff < 0.1cal)

6.  The frequency needed for resonance and the applied magnetic field
strength are proportionally related:
 These spectrometers use very powerful magnets to create a small but
measurable energy difference between two possible spin states

7. An NMR machine consists of:
 (1) A powerful, supercooled magnet (stable, with
sensitive control, producing a precise magnetic
field).
 (2) A radio-frequency transmitter (emitting a very
precise frequency).
 (3) A detector to measure the absorption of
radiofrequency by the sample.
 (4) A recorder (to plot the output).

8. diagram:

10.  An NMR spectrum is a plot of the intensity of a peak against its chemical
shift, measured in parts per million (ppm).

11. 1H NMR—The Spectrum
 NMR absorptions generally appear as sharp peaks.
 Increasing chemical shift is plotted from left to right.
 Most protons absorb between 0-10 ppm.
 The terms “upfield” and “downfield” describe the relative
location of peaks. Upfield means to the right. Downfield
means to the left.
 NMR absorptions are measured relative to the position of a
reference peak at 0 ppm on the d scale due to
tetramethylsilane (TMS). TMS is a volatile inert compound
that gives a single peak upfield from typical NMR
absorptions

12. 1H NMR—Number of Signals
 The number of NMR signals equals the number of different
types of protons in a compound.
 Protons in different environments give different NMR
signals.
 Equivalent protons give the same NMR signal.

13. 1H NMR—Position of Signals
 Since the electron experiences a lower magnetic field strength, it
needs a lower frequency to achieve resonance. Lower frequency is to
the right in an NMR spectrum, toward a lower chemical shift, so
SHIELDING shifts the absorption upfield.

17. Calculating SHIFT VALUES:
(H ydrogen under consideration)C C H
H
H
H
H
Cl
 
Base Chem ical Shift = 0.87 ppm
no substituents = 0.00
one  -Cl (CH 3) = 0.63
TO TAL = 1.50 ppm
(H ydrogen under consideration)C C H
H
H
H
H
Cl

Base Chem ical Shift = 1.20 ppm
one  -Cl (CH 2) = 2.30
no substituents = 0.00
TO TAL = 3.50 ppm

19. energetic status of cells
to monitor the
fermentation of yoghurts
(using phosphorus 31 LR
NMR)
Analysis of sample quality
and in process control
cooking of various types of
rice (proton NMR)
examination of cell cultures
in the mashing of beer
(using proton NMR)
Applications

20. Carbohydrate NMR
Spectroscopy
 structure of monosaccharides and oligosaccharides.
 sugar conformations.
 500 MHz or greater.
 3 – 6 ppm. (13C NMR chemical shifts of carbohydrate ring
carbons are 60 – 110 ppm).