Tài liệu Techniques for Analyzing Food Aroma pptx

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Page aa
Techniques for Analyzing Food Aroma
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Food Science and Technolo
gy
A Series o
f
Mono
g
ra
p
hs, Textbooks, and Re
f
erence Books
EDITORIAL BOARD
Owen R. Fennema
University of Wisconsin – Madison
Marcus Karel
Rutgers University
Gary W. Sanderson
Universal Foods Corporation
Steven R. Tannenbaum
Massachusetts Institute of Technology
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Wageningen Agricultural University
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16. Sensory Evaluation of Food: Statistical Methods and Procedures,
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Ra
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Marsili
Additional Volumes in Pre
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Food Proteins and Their A
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Page i
Techniques for Analyzing Food Aroma
Edited By
Ra
y
Marsili
Dean Foods Company
R
ock
f
ord, Illinois

MARCEL DEKKER, INC.
NEW YORK • BASEL
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Page ii
Librar
y
of Con
g
ress Catalo
g
in
g
-in-Publication Data
Techniques for analyzing food aroma / edited by Ray Marsili.
p
. cm.— (Food science and technology ; 79)
Includes index.
ISBN 0-8247-9788-4 (hardcover : alk. paper)
1. Food—Sensory evaluation. I. Marsili, Ray.
II. Series: Food science and technology (Marcel Dekker, Inc.) ; 79.
TX546.T43 1997
664'.07—dc20 96–36593
CIP
The publisher offers discounts on this book when ordered in bulk quantities. For more
information, write to S

p
ecial Sales/Professional Marketin
g
at the address below.
This book is
p
rinted on aci
d
-free
p
a
p
er.
Co
py
ri
g
ht © 1997 b
y
MARCEL DEKKER, INC. All Ri
g
hts Reserved.
N
either this book nor any part may be reproduced or transmitted in any form or by any
means, electronic or mechanical, including photocopying, microfilming, and record-
ing, or by any information storage and retrieval system, without permission in writing
from the
p
ublisher.
Marcel Dekker, Inc.

270 Madison Avenue, New York, New York 10016
Current
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rintin
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(
last di
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)
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PRINTED IN THE UNITED STATES OF AMERICA
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Page iii

To Laura, Am
y
Nathan, and Jason
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Page iv
The search for Truth is in one way hard and in another way easy. For it is evident that no one can master it fully nor
miss it completely. But each adds a little to our knowledge of Nature, and from all the facts assembled there arises a
certain grandeur.
Aristotle
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Page v
Preface
Flavor is of major concern to food scientists because it is a significant factor influencing the public's
food-buying decisions and its perception of food quality. Analyzing the volatile and semivolatile
organic compounds that impact the flavor and aroma of foods can be a daunting task, and obtaining
useful information from such measurements can be even more challen
g
in
g
.
It is the intention of the authors to describe analytical techniques that can be applied to the detection
and quantitation of volatile aroma chemicals in foods and to explain how the sense of smell
(olfactory detection) can be incorporated with these techniques to resolve important, practical
p
roblems related to food aromas. Advantages, disadvantages, and biases of each technique are
discussed, as well as when and wh
y
s
p
ecific techni
q
ues should be selected or avoided.

The chapters contain dozens of examples of applications showing how real food aroma problems
have been resolved through the use of modern analytical instruments and olfactometry. Specifically,
the book discusses various sample preparation techniques for isolating and concentrating food
aroma compounds prior to gas chromatographic (GC) analysis; how GC column technology, column
manipulation techniques, and GC/MS detection can be used to maximize resolution, discrimination,
identification, and sensitivity for detecting important aroma-influencing components; and how
sensor
y
techni
q
ues, includin
g
the use of an olfactometr
y
detector, can be combined with
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Page vi
instrumental methods to create powerful systems for problem solving. Included in several chapters
are discussions that critically review CharmAnalysis and aroma extraction dilution analysis
(AEDA), two useful techniques for interpreting GC-olfactometry results. Valuable suggestions and
ancillar
y
techni
q
ues for su
pp
lementin
g
CharmAnal
y
sis and AEDA studies are
p
resented.
Also included is a chapter discussing the operation and application of the ”electronic nose,“ a new
chemical sensor array-based instrument that emulates the human nose. While some excellent flavor
work has been done with HPLC, supercritical fluid extraction (SFE), supercritical fluid
chromatography (SFC), and other analytical methods, GC techniques are emphasized in this work
since they are generally more applicable to the analysis of volatile organic polar compounds, which
are fre
q
uentl
y
the most im
p
ortant contributors to food aroma.
The dedication, persistence, and splendid cooperation of all contributing authors, as well as the

quality of information they have presented, are to be commended. Also, I would like to
acknowledge my indebtedness to my associates, Gregory J. Kilmer, Nadine Miller, and Ronald E.
Simmons, and to my supervisor, Dr. Scott Rambo, for their advice, encouragement, and continual
support. Special thanks go to my wife, Deborah, for reviewing the chapters and for her patience and
words of encoura
g
ement.
RAY MARSILI
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Page vii
Contents
Preface v
Contributors ix
Thomas H. Parliment
1. Solvent Extraction and Distillation Techni

q
ues 1
Thomas P. Wampler
2. Analysis of Food Volatiles Using Headspace-Gas Chromatographic
Techni
q
ues
27
Casey C. Grimm, Steven W. Lloyd, James A. Miller, and Arthur M.
Spanier
3. The Anal
y
sis of Food Volatiles Usin
g
Direct Thermal Desor
p
tion 59
Alan D. Harmon
4. Soli
d
-Phase Microextraction for the Anal
y
sis of Flavors 81
Donald W. Wright
5. Application of Multidimensional Gas Chromatography Techniques to
Aroma Anal
y
sis
113
Alexander Bernreuther, Ulrich Epperlein, and Bernhard Koppenhoefer

6. Enantiomers: Wh
y
The
y
Are Im
p
ortant and How to Resolve Them 143
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Page viii
Charles K. Huston
7. Ion Tra
p
Mass S
p
ectrometr

y
for Food Aroma Anal
y
sis 209
Ray Marsili
8. Off-Flavors and Malodors in Foods: Mechanisms of Formation and
Anal
y
tical Techni
q
ues
237
Behroze S. Mistry, Terry Reineccius, and Linda K. Olson
9. Gas Chromatography-Olfactometry for the Determination of Key
Odorants in Foods
265
Imre Blank
10. Gas Chromato
g
ra
p
h
y
-Olfactometr
y
in Food Aroma Anal
y
sis 293
Diana Hodgins
11. The Electronic Nose: Sensor Array-Based Instruments that Emulate the

Human Nose
331
Index 373
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Page ix
Contributors
Alexander Bernreuther
Joint Research Center, Environment Institute, Is
p
ra, Ital
y
Imre Blan
k
Research Centre, Nestec Ltd., Lausanne, Switzerlan
d
Ulrich E

pp
erlein
Universit
y
of Tü
b
in
g
en, Tü
b
in
g
en, German
y
Casey C. Grimm
Southern Regional Research Center, Agricultural Research Service, United States
De
p
artment of A
g
riculture, New Orleans, Louisiana
Alan D. Harmon
Research and Technical Development, McCormick & Co., Inc., Hunt Valley,
Mar
y
lan
d
Diana Hod
g
ins

Wheatham
p
stead, Hertfordshire, En
g
lan
d
Charles K. Huston
Varian Chromato
g
ra
p
h
y
S
y
stems, Walnut Creek, California
Berhard Koppenhoefer
Institut für Organische Chemie der Universität, University of Tübingen,
Tü
b
in
g
en, German
y
Steven W. Lloyd
Southern Regional Research Center, Agricultural Research Service, United States
De
p
artment of A
g

riculture, New Orleans, Louisiana
Ra
y
Marsili
Dean Foods Com
p
an
y
, Rockford, Illinois
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Page x
James A. Miller
Southern Regional Research Center, Agricultural Research Service, United States
De
p
artment of A

g
riculture, New Orleans, Louisiana
Behroze S. Mistr
y
As
p
en Research Cor
p
oration, St. Paul, Minnesota
Linda K. Olson
As
p
en Research Cor
p
oration, St. Paul, Minnesota
Thomas H. Parliment
Kraft Foods, White Plains, New Yor
k
Terr
y
Reineccius
As
p
en Research Cor
p
oration, St. Paul, Minnesota
Arthur M. Spanier
Southern Regional Research Center, Agricultural Research Service, United
States De
p

artment of A
g
riculture, New Orleans, Louisiana
Thomas P. Wam
p
ler
CDS Anal
y
tical, Inc., Oxford, Penns
y
lvania
Donald W. Wri
g
ht
Microanal
y
tics Instrumentation Cor
p
oration, Round Rock, Texas
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Page 1
1
Solvent Extraction and Distillation Techni
q
ues.
Thomas H. Parliment
Kraft Foods, White Plains, New Yor
k
I. Introduction
The purpose of this chapter is to review techniques that have been published in the technical
literature and developed in our laboratory for the isolation and concentration of samples prior to
analysis by gas chromatography. It is our goal to emphasize those techniques that are easy to
employ, require minimal equipment, and produce reproducible, meaningful results. In a number of
cases, exam
p
les of the results will be
p
resented.
As has been described
p
reviousl
y

(
1
)

, sam
p
le
p
re
p
aration is com
p
licated b
y
a number of factors:
1. Concentration Level: Aromatics levels are generally low, typically in the ppm, ppb, or ppt range.
Thus it is not only necessary to isolate the components, but also to concentrate them by several
orders of ma
g
nitude.
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Page 2
Table 1
Classes of Aroma Compounds in Coffee
Chemical class Number of
compounds
Hydrocarbons 74
Alcohols 20
Aldehydes 30
Ketones 73
Acids 25
Esters 31
Lactones 3
Phenols (and ethers) 48
Furans 127
Thiophenes 26
Pyrroles 71
Oxazoles 35
Thiazoles 27
Pyridines 19
Pyrazines 86
Amines and miscellaneous
nitrogen compounds
32
Sulfur compounds 47
Miscellaneous 17
Total
791
Source: Ref. 2
2. Matrix: The volatiles are frequently intracellular and must be liberated by disruption. The sample
frequently contains nonvolatile components such as lipids, proteins, or carbohydrates, which

complicates the isolation process. These components may create problems of foaming and
emulsification during isolation procedures and will create artifacts if injected into a hot gas
chromato
g
ra
p
h
y
in
j
ector
p
ort.
3. Complexities of Aromas: The aromatic composition of foods are frequently very complex. For
example, coffee currently has almost 800 identified components, as shown in Table 1. Complicating
the picture is the fact that the classes of compounds present cover the range of polarities,
solubilities, and
p
Hs.
4. Variation of Volatility: The components possess boiling points ranging from well below room
tem
p
erature to those that are solids, such as vanillin
(
m
p
81°C
)
.
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5. Instability: Many components in an aroma are unstable and may be oxidized by air or degraded
by
heat or extremes of
p
H.
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Page 3
Regardless of which sample preparation technique is employed, it is critically important to assess
the organoleptic quality of the isolate. No single technique will prove optimal for every sample, and
evaluations should be made to ensure that decomposition and loss of desired components do not
occur. A very significant paper published by Jennings et al. (3) compared various sample
p
reparation techniques, including porous polymer trapping and distillation-extraction. Their
conclusion was that no isolation technique produced results that duplicated the original neat sample,
b
ut that distillation-extraction most nearl
y
a
g
reed
(
Fi
g
. 1
)
.
This is particularly important since current flavor research seems to be less directed to identification
for the sake of adding to the numbers of the compounds in the knowledge base, and more to
alternative reasons. At the present time it appears one purpose is characterization of components of
organoleptic importance. Three techniques for gas chromatographic individual component
assessment are in vogue: aroma extraction dilution analysis (AEDA), calculation of odor units, and
Charm Analysis (see Chapter 9). Another purpose of flavor research is to analyze products and to

p
erform flavor stabilit
y
studies.
At the present time, the two most common procedures reported in the literature for the isolation of
the aromatics are headspace methods and extraction. The former will be covered in the next chapter.
The purpose of this chapter is to review techniques for isolating and concentrating aromatics, which
include various distillation and extraction
p
rocedures.
A number of references exist on the topic of flavor isolation, and these provide a different
p
erspective on the topic (4–8). To quote Schreier (9): “It must be emphasized that sample
p
re
p
aration is the most critical ste
p
in the entire anal
y
tical
p
rocess of the investi
g
ation of volatiles.”
II. Direct In
j
ection of the Sam
p
le

A
. Essential Oils
Direct injection is by far the most convenient technique and works particularly well for essential
oils. The sample may have to be diluted with a solvent to obtain response within the limits of the
detector.
B
. A
q
ueous Sam
p
les
When concentrated aqueous samples are available, direct injection techniques can be employed. In
industry, aqueous materials are frequently available from industrial operations. Examples of this
would be condensates from coffee
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Page 4

Figure 1
Relative integrator response for various sample preparation
techniques. (From Ref. 3.)
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Page 5
grinders, vapors from chocolate conching operations, and aqueous materials from citrus juice
concentrators.
The aqueous phase may be injected if the sample is sufficiently concentrated. A number of problems
may be encountered under these circumstances. When water is converted to steam, the volume
increases dramatically; 1
μ
l of water becomes more than 1000
μ
l of steam. This is larger than the
injector volume of many current gas chromatographs, and the steam may degrade the performance
of the system. Polar gas chromatography liquid phases such as Carbowax and PEG will degrade in

the
p
resence of steam unless the
y
are bonded to the column.
If the aqueous sample contains dissolved solutes such as carbohydrates or proteins, additional
p
roblems will arise when the sample is injected. The nonvolatiles may decompose, leaving a
nonvolatile residue in the injector and at the head of the column. Many researchers use a guard
column of deactivated fused silica tubing between the injector and the analytical column. The guard
column can be replaced periodically when it becomes contaminated. The tubing contains no liquid
p
hase, thus it does not affect separation or retention time. The guard column can be connected to the
anal
y
tical column with various t
yp
es of
p
ress-ti
g
ht connectors
(
10
)
.
If the aqueous phase is too dilute, concentration techniques as described in the next section may be
em
p
lo

y
ed.
III. Direct Solvent Extraction of A
q
ueous Sam
p
les.
Aqueous samples are available from a number of sources. Industrial plant operations may yield such
p
roducts. Carbonated beverages, fruit juices, and caffeinated beverages can often be extracted
directly. Fruits and vegetables can be homogenized with water, treated with a pectinase enzyme to
destro
y
the
p
ectins, and filtered throu
g
h a bed of diatomaceous earth to remove
p
articulates.
A
. Extraction
When relatively large amounts of aqueous samples are available, then separatory funnels or
commercial liquid-liquid extractors may be employed. A large number of solvents have been
summarized b
y
Weurman
(
4
)

and reviewed b
y
Teranishi et al.
(
5
)
.
The solvents most commonly used today are diethyl ether, diethyl ether/pentane mixtures,
h
y
drocarbons, Freons, and meth
y
lene chloride. The
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latter two have the advantage of being nonflammable. Solvent selection is an important factor to

consider, and the current status has been summarized by Leahy and Reineccius (11). In general, the
following suggestions can be made. Nonpolar solvents such as Freons and hydrocarbons should be
used when the sample contains alcohol. Diethyl ether and methylene chloride are good general
p
urpose solvents. Ether can form explosive peroxides, and for that reason contains inhibitors (e.g.,
BHT), which will show up in gas chromatography/mass spectroscopy (GC/MS) analysis. We find
that methylene chloride is a satisfactory general purpose solvent, particularly for flavor compounds
with an enolone structure (e.g., Maltol and Furaneol). It is somewhat toxic and is an animal
carcinogen. To aid in extraction, sodium chloride may be added to the aqueous phase to salt out the
or
g
anics when low-densit
y
solvents are em
p
lo
y
ed.
If the sample contains any particulates, it should be filtered. A convenient way to filter samples is
through a syringe filter (e.g., Gelman Sciences, Ann Arbor, Mich.) of the type recommended for
HPLC sample preparation. These filters have a pore size of 0.45
μ
m and are solvent resistant.
Microt
yp
es with low solvent hol
d
-u
p
are available.

Figure 2 shows the total ion chromatogram of a coffee extract. In this case a decaffeinated roast and
ground coffee was brewed in a commercial system. The brew was filtered through a Gelman 0.45
μ
m GHP Acrodisc to remove particulates, and the aqueous phase was extracted with methylene
chloride. A highly complex chromatogram is evident. The large peak eluting at 25 minutes is
caffeine.
Continuous extractors have been described in the literature for solvents more dense and less dense
than water (e.g., Ref. 4) and are available commercially (e.g., ACE Glass, Vineland, NJ; Supelco,
Inc, Bellefonte, Pa) for $200–600 (Fig. 3). These are a pleasure to use (providing there is no solvent
loss and that emulsions don't occur) since they will operate relatively unattended. They are normally
o
p
erated for 2–4 hours, but ma
y
be o
p
erated overni
g
ht.
Liquid carbon dioxide was recommended as an extracton solvent as early as 1970 (12). It has the
advantages of being nontoxic and inexpensive. Liquid carbon dioxide is reported to have solvent
p
roperties similar to diethyl ether (12) and to be particularly selective for esters, aldehydes, ketones,
and alcohols. If water is
p
resent, it will be removed also.
A commercial liquid carbon dioxide Soxhlet extractor is commercially available (J&W Scientific,
Folsom, CA). The vessel holds a sample of 2.5 g. This apparatus seems to have achieved only
limited use, perhaps because of its cost ($1500 plus accessories) and limited sample size. Moyler
(

13
)
dis-
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Figure 2
Total ion chromatogram (TIC) of brewed R&G coffee extracted
with methylene chloride
cussed a commercial liquid carbon dioxide system and reported such extracts to be more
concentrated than the steam distillates or solvent extracts. More important, he reported that the
character was “finer.”
Supercritical carbon dioxide has been employed recently as an extraction solvent. When using
supercritical carbon dioxide, it is necessary to balance temperature, pressure, and flow rate, which
requires complex instrumentation. Several instrument vendors produce supercritical fluid extractors
in the
p

rice ran
g
e of $25,000-90,000. A
g
ain, sam
p
le ca
p
acit
y
is relativel
y
limited.
B
. Emulsions
Emulsions can be a problem, particularly if nonvolatile solutes are present. To prevent emulsions,
the followin
g
methods can be em
p
lo
y
ed:
Use
g
entle shakin
g
Filter the sam
p
le if

p
articulates are
p
resent
Kee
p
the s
y
stem cool
Be
p
atient
Ad
j
ust the
p
H of the a
q
ueous
p
hase
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Figure 3
Liquid/liquid extractor
concentrator apparatus. (Courtesy
Supelco, Inc, Bellefonte, PA.)
The latter technique is particularly effective if organic acid, basic, or amphoteric compounds are
p
resent. If emulsions occur, centrifu
g
ation ma
y
be em
p
lo
y
ed
(
but onl
y
for nonflammable solvents
)
.
C. Concentration
The final step is concentration of the solvent. We usually dry the solvent over sodium sulfate or

ma
g
nesium sulfate and then carefull
y
concentrate it on a
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