1 Flavor Chemistry FST 820 Flavor Chemistry Winter quarter. 3 credits. Course Description Chemical properties, isolation, separation, identification, formation and interaction mechanisms, and application of flavor compounds. Instructor: Dr. David B. Min Telephone 292-7801(O), 436-9289 (H) e-Mail [email protected]
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Course Description Chemical properties, isolation, separation, identification,
formation and interaction mechanisms, and application of flavor compounds.
Instructor: Dr. David B. Min Telephone 292-7801(O), 436-9289 (H) e-Mail [email protected]
2
General Objective The objective of this course is to teach students the role of flavor chemistry in food quality. Chemical structures and formation of flavor compounds, organic, bio, and analytical chemistries involved in flavor research, the effects of processing, packaging and storage conditions on the flavor quality and stability of foods, and current research related to flavor are covered. Upon completion of this course, students should be able to:
1 Understand Chemical reactions involved in flavor compounds formation in
natural and processed food.
2 Comprehend the effects of food components, processing parameters and storage
conditions on flavor quality of foods.
3 Understand principles, techniques and applications of analytical instruments
involved in flavor analysis.
4 Optimize ingredient concentration, processing parameters, packing materials and
storage conditions for optimum quality and stability.
5 Develop simple research programs of flavor chemistry.
6 Specify the flavor qualities of raw ingredients.
Evaluation Midterm Examinations (2) 40% Final Examination 30% Home Work and Class Participation 30%
3
1. INTRODUCTION
I. Definition of Flavor II. Classification of Food Flavor III. Scope of Flavor Chemistry
1. Chemical compounds responsible for food flavor 2. Flavor of foods 3. Reconstitution of flavor compounds 4. Precursors of the flavor compounds 5. Mechanism for the formation of flavor compounds and precursors in
foods 6. Relationship between physical properties and its flavor
IV. Objectives of Flavor Chemistry
2. ISOLATION AND SEPARATION OF FLAVOR COMPOUNDS
I. Objective II. Prerequisites III. Apparatus for Isolation
IV. Extraction and Concentration V. Preliminary and Final Fractionation VI. Dynamic Headspace analyzer VII. Solid Phase Microextraction Analysis
3. FLAVOR IDENTIFICATION BY SPECTROMETRIC METHODS
I. Introduction of Spectrometric Analyses II. Ultra Violet Spectrometry III. Infrared Spectrometry IV. Nuclear Magnetic Resonance Spectrometry
4
V. Mass Spectrometry 1. Furans 2. Pyrroles 3. Thiophenes 4. Pyridines 5. Pyrazines
4. MANUFACTURE OF FOOD FLAVOR
I. Natural or Imitation Flavor II. Problems of Using Natural Flavor III. Disadvantages of Using Imitation Flavor IV. Advantages of Imitation Flavor V. Methods in Synthetic Flavor Reconstitution
5. CHEMISTRY OF FLAVOR PRECURSORS I. Flavor Compounds from Carbohydrates and Proteins
1. Isolation, separation and identification of cheese flavor 2. Biological pathways of fat in cheese flavor 3. Reaction products of methionine 4. Biochemical pathways of cheese flavor formation from protein 5. 2-Butanone and 2-Butanol formation from diacetyl and acetone 6. Biochemical pathways of cheese flavor formation from lactose
7. Lactone formation 8. Mechanisms of methyl ketone formation
7. MEAT FLAVOR CHEMISTRY
I. Effect of Psychrotropic Bacteria on the Volatile Compounds of Raw Beef
1. Introduction 2. Effects of light and dark storage on the volatile compounds of asceptic
raw ground beef 3. Effects of psychrotropic bacteria on the volatile compounds of aseptic
raw ground beef
6
II. Isolation, Separation, and Identification of Roast Beef Flavor III. Simulated Meat Flavor Formation
8. ORANGE FLAVOR STUDY BY PULSED ELECTRIC FIELD PROCESS
9. INTERACTION OF FLAVOR COMPOUNDS WITH
FOODS
I. Physical and Chemical Stability of Flavor II. Effects and Interactions of Lipids with Flavor Compounds III. Effects and Interactions of Carbohydrates with Flavor Compounds IV. Effects and Interactions of Proteins with Flavor Compounds
10. PACKAGING AND FLAVOR COMPOUNDS
INTERACTION
I. Effects of Packaging Materials on the Flavor Quality of Food II. Sorption of Orange Flavor Compounds by Packaging Materials
11. FAVOR COMPOUNDS AND SOLVENT INTERACTION
I. Commercial Cherry Flavor and Solvent Interaction II. Acetal Formation
7
Reference Acree, T. E., Teranishi, R. Flavor Science: Sensible Principles and Techniques. American Chemical Society, Washington, D.C., 1993. Ashurst P. R. Food Flavorings. AVI, New York, 1991. Bellanca, Furia. Fenaroli Handbook of Flavor Ingredients. The Chemical Rubber Company. 1972. Bills, D. D., Mussinan, C. J. Characterization and Measurement of Flavor Compounds. American Chemical Society, Washington, D.C., 1985. Charalambous, G. Flavors and Off-flavors '89. Elsevier Science Publishing Company INC, New York, 1989. Charalambous, G. Food Science and Human Nutrition. Elsevier Science Publishing Company INC, New York, 1992. Charalambous, G. Frontier of Flavor. Elsevier Science Publishing Company INC, New York, 1988. Charalambous, G. Off-flavors in Foods and Beverages. Elsevier Science Publishing Company INC, New York, 1992. Charalambous, G. Shelf Life Studies of Foods and Beverages. Elsevier Science Publishing Company INC, New York, 1993. Department of Army, Advisory Board of Quartermaster Research and Development. Chemistry of Natural Food Flavors. 1957. Gabelman, A. Bioprocess Production of Flavor, Fragrance, and Color Ingredients. John Wiley & Sons, New York, 1994. Ho, C. T., Hartman, T. G. Lipids in Food Flavors. American Chemical Society, Washington, D.C., 1994. Ho, C. T., Manley C. H. Flavor Measurement. Marcel Dekker, INC., New York, 1993.
8
Hornstein, Irwin. Flavor Chemistry, A Symposium. American Chemical Society, Washington, D.C. 1966. Ikan, R. The Maillard Reaction: Consequences for the Chemical and Life Sciences. John Wiley & Sons, New York, 1996. Labuza, T. P., Reineccius, G. A., Monnier, V., O'Brien, J., Baynes, J. Maillard Reactions in Chemistry, Food, and Health. The Royal Society of Chemistry, Cambridge, 1994. Min, D. B. Akoh C. C. Food Lipids. Marcel Dekker, Inc. New York, NY,1998. Min, D. B. McDonald R. E. Food Lipids and Health. IFT. Marcel Dekker, Inc. New York, NY,1996. Min, D. B., Smouse, T. H. Flavor Chemistry of Fats and Oils. The American Oil Chemists' Society, Champaign, Illinois, 1985. Min, D. B., Smouse, T. H. Flavor Chemistry of Lipid Foods. The American Oil Chemists' Society, Champaign, Illinois, 1989. Morton, I. D., Macleod A. J. Food Flavor: Part A. Introduction. Elsevier Science Publishing Company INC, New York, 1982. Morton, I. D., Macleod A. J. Food Flavor: Part C. The Flavor of Fruit. Elsevier Science Publishing Company INC, New York, 1990. Ohloff, G. and A. F. Thomas. Gustation and Olfaction. Academic Press. New York. 1971. Parliment, T. H., Morello, M. J., McGorrin, R. J. Thermally Generated Flavors: Maillard, Microwave, and Extrusion Processes. American Chemical Society, Washington, D.C., 1994. Piggott, J. R., Paterson, A. Understanding Natural Flavors. Blackie Academic & Professional, New York, 1994. Reineccius, G. Source Book of Flavors, 2nd Edition. Chapman & Hall, New York, 1992.
9
Scanlan, R. A. Flavor Quality: Objective Measurement. American Chemical Society, Washington, D.C., 1977. Schultz, H. W., E. A. Day, and R. V. Sinnhuber. Lipids and Their Oxidation. AVI Publishing Company, Inc., Westport, Connecticut. 1962. Shahidi, F. Flavor of Meat and Meat Products. Blackie Academic & Professional, New York, 1994. Spanier, A. M., Okai, H., Tamura, M. Food Flavor and Safety: Molecular Analysis and Design. American Chemical Society, Washington, D.C., 1993. Supran, M. K. Lipids as a Source of Flavor. American Chemical Society, Washington, D.C., 1978. Teranishi, Roy, Phillip Issenberg, Irwin Hornstein, and Emily L. Wick. Flavor Research, Principles and Techniques. Marcel Dekker. 1971. Vernin, G. Chemistry of Heterocyclic Compounds in Flavors and Aromas. John Wiley & Sons, New York, 1982.
10
1. INTRODUCTION
I. Definition of Flavor 1. “Flavor is the sensation produced by a material taken in the mouth, perceived
principally by the senses of taste and smell, and also by the general pain, tactile, and temperature receptors in the mouth. Flavor also denotes the sum of the characteristics of the material which produces that sensation.”
2. “ Flavor is one of the three main sensory properties which are decisive in the
selection, acceptance, and ingestion of a food.” Stimulus Man Senses Response (sensory property)
III. Scope of Flavor Chemistry 1. Chemical compounds responsible for food flavor 1) Even distribution: Brandy 2) Star compound: A star compound can not be identical to the total true flavor but is
close and can not produce the true flavor without the star compound.
12
Almond: benzoaldehyde
C H O
Green pepper: 2-methoxy-3-isobutyl-pyrazine
N
N
OCH3
CH2CHCH3
CH3
Both pyrazin and thiazol are important flavor compound groups
N
S1
2
34
5
N
N
pyrazine thiazol
13
Vanilla: 4-hydroxy-3-methoxy-benzolaldehyde
CHO
OHOCH3
Cucumber: 2-trans-6-cis-nonadienal
CH 3 CH2 C CH H
CH2 CH2C C CHOH
H
Reversion flavor of soybean oil: 2-pentylfuran and 2-pentenylfuran
O (CH2)4 CH3
14
2. Flavor of foods 1) Desirable flavor orange juice potato chip roast beef 2) Undesirable flavor (off-flavor) oxidized stale rancid
warmed-over 3. Reconstitution of flavor compounds GC composition 4. Precursors of flavor compounds linoleate 2-pentylfuran 1) Non-enzymatic reaction Precursor of beef flavor can be isolated as a white fluffy powder. White fluffy powder Oil Water broil stew beef broth Amino acid + Sugar Maillard reaction
15
2) Enzymatic reaction Processed banana no fresh banana flavor enzyme extracted from banana peel Fresh banana flavor 5. Mechanisms for the formation of flavor compounds and precursors in foods 1) Volatile flavors developed in most food plants mainly at the ripening stage - the result of plant metabolism through enzymatic reaction. 2) Raw meat must be heated before it develops any organoleptically acceptable flavor. meat flavor (boiled beef)
S S
S CH3H3C4
3
1 2
5
3, 5-dimethyl-1,2,4-trithiolane
16
Model studies:
CH3CHO + H 2SSS
S
H2S + CH3CHO CH3 CH S CH CH3
SH SH
( S )
( O )
S S
S CH3H3C
HS C C COOHNH2
are precursorsCH3CHO, H2S Therefore,
B e e f f la v o r ( r e a c t io n f l a v o r )
Apply the knowledge we gained from the mechanism and precursor studies to processed food.
a. Enhance the desirable food flavor. b. Elimination of the undesirable food flavor. c. Application of heated model system to processed foods.
17
6. Relationship between physical properties of a compound and its flavor B.P.(0C) 760 mm-Hg Solubility in H2O
The series has an increase b.p. and decreased solubility in H2O The vapor compositions of flavor compounds are effected by the medium. head space analysis compound (conc. 200ppm) aq. System ( peak area ) corn oil system
IV. Objectives of Flavor Chemistry 1. To understand the chemical composition of natural flavors and the mechanism of
their formation. 2. To retard or prevent the development of the off-flavors in foods. reversion flavor in soybean oil hexenal, 2-pentyl furan ( they are resulted from polyunsaturated triglycerides,
i.e.: linolenate, linoleate ) 3. To restore the fresh flavor to a processed food 4. To improve the flavor of food by the addition of synthetic flavor. 5. To produce new foods with special flavor such as potato chip flavor. 6. To improve flavor by the acceleration of reactions which produce desirable flavor compound (onion flavor: pH 5~7). 7. To assist geneticist to breed food raw material with improved flavor compounds or flavor precursors. 8. To specify raw material and to control quality of food products. The price of tea can be correlated with GLC peak of linalool.
CH 3 C
CH3
CH CH2 CH2 C CH CH2
CH3
OH
Ceylon tea contains cis-hexenol, India tea doesn’t contain cis-hexenol
19
2. ISOLATION AND SEPARATION OF FLAVOR COMPOUNDS
I. Objectives Produce volatile flavor compounds of the true flavor of the original with minimum artifact. 1. Selection of “Good flavor sample” 2. Isolation of Volatile Flavor Compounds (VFC) 3. Extraction and Concentration 4. Fractionation 5. Preparation of pure compound 6. Identification 7. Synthesis 8. Reconstitution of the flavor II. Prerequisites 1. Selection of sample 2. No alternation of the original flavor 3. No artifacts due to : decomposition autooxidation
20
III. Apparatus for Isolation 1. Headspace analysis 1) Without enrichment
can
siliconerubberstopper
syringe
2) With Enrichment
Using inert gas
21
Apparatus for the isolation of trace volatile constituents from relatively large amount of food.
22
2. Continuous Solvent Extraction
Continuous Liquid-liquid extractor for use with solvents lighter-than-water
Beverage sample
23
3. Steam Distillation and Continuous Solvent Extraction
Improving Sensitivity of Solid PhaseMicroextraction
• Solid Phase Thickness
• Extraction Temperature and Time
• Sample Agitation and Concentration
• Direct sampling versus Headspace Sampling
• Selection of Proper Solid Phases• Saturation of Sample with Proper Salts
• Maximum Ratio of Sample to Headspace Volume
• Large Sampling Vial
46
Conclusion
• Reproducible
• Economic
• Simple
• Sensitive
The SPME-GC is a
for the analysis of volatile compounds inmost foods.
47
3. FLAVOR IDENTIFICATION BY SPECTROMETRIC
METHODS I. Introduction of Spectrometric Analyses II. Ultra Violet Spectrometry III. Infrared Spectrometry IV. Nuclear Magnetic Resonance Spectrometry V. Mass Spectrometry
48
I. Introduction of Spectrometric Analyses The study how the sample interacts with different wavelenghts in a given region of electromagnetic radiation is called spectroscopy or spectrochemical analysis. The collection of measurements signals (absorbance) as a function of electromagnetic radiation is called a spectrum.
Energy Absorption
The mechanism of absorption energy is different in the Ultraviolet, Infrared, and Nuclear magnetic resonance regions. However, the fundamental process is the absorption of certain amount of energy. The energy required for the transition from a state of lower energy to a state of higher energy is directly related to the frequency of electromagnetic radiation that causes the transition.
Spectral Distribution of Radiant Energy
X- ray U.V. Visible I.R. Microwave V' = Wave number (cm -1) λ = Wave length (nm) C = Velocity of Radiation (constant) 3× 1010 cm/sec V = Frequency of Radiation (cycles/sec) V' = = (The energy of photon) E = Vh (Planck's Constant 6.62× 10-27 erg - sec) E = Vh = h
C = V λ V =
200 400 800
C
V
λ
1
λ
C
λ
C
Wavelength (nm)
Wave number (cycles/cm)
The Electromagnetic Spectrum.
γ- ra
y χ-
ray
ul
travi
olet
visi
ble
viol
et
bl
ue
gr
een
yello
w
400 500
1020 1018 1016 1
Wavelength, λ,
49
in
frar
ed
m
icro
wav
e
radi
o
or
ange
014 1012 10 8 6 104 102
m
frequency, ν, (cycles/sec)10 10 10
ed
visible region
10-10 10-8 10-6 10-4 10-2 1 102 104 106
8
r
700 800
600 Wavelength, λ, n
50
II. Ultra Violet Spectrometry The absorption of ultraviolet radiation by molecules is dependent upon the electronic structure of the molecule. So the ultraviolet spectrum is called electronic spectrum.
Electronic Excitation
The absorption of light energy by organic compounds in the visible and ultraviolet region involves the promotion of electrons in σ, π, and n-orbitals from the ground state to higher energy states (This is also called Energy Transition). These higher energy states are molecular orbitals called antibonding.
Ener
gy
* Antibonding
σ
* * * * Antibonding
π*
n
σ →
σ
π→
π
n →
σ
n →
πNonbonding Bonding
π
Bonding
σ
51
Electronic Molecular Energy Levels The higher energy transitions (σ →σ*) occur a shorter wavelength and the low energy transitions (π→π*, n →π*) occur at longer wavelength.
Energy
σ* σ*
hv
h
σ
π2
hv
π3
π1
π*
nπ
hvv
σ
π3
π2
π1
Ground Electronic State
π→π*
n →π*
Exited Electronic State
52
53
Chromophore is a functional group which absorbs a characteristic ultraviolet or visible region. UV
Radiation energy in the infrared region is absorbed by the organic compound and converted into
energy of molecular vibration.
The energy absorption pattern thus obtained is commonly referred to as an infrared spectrum which
has the plot of intensity of radiation absorption versus wavelength of absorption.
Some Molecular Vibrations
C C
O
O HH
H
H
Stretch
Unsymmetrical bend
Symmetrical bend
55
Atom, Group, and Molecular Rotations
IR
3.4 µm Alkane 6.0 µm cis-Double Bond 10.3 µm trans-Double Bond 5.8 µm Carbonyl 3.7 µm Hydroxyl Stretching of Acid Group 2.9 µm Hydroxyl
C C
O
O HH
H
H
X
YZ
OH group rotation
H atom rotation COOH group rotation
CH3 group rotation Molecular rotation
Center of gravity of the molecule is at the origin
IV. Nuclear Magnetic Resonance Spectrometry
Spinning charge in proton generates magnetic dipole
Proton precessing in a magnetic field Ho
Om
Ho
Precessional orbit
Nuclear magnetic dipole µ
Spining proton
Oscillator
axis of nuclear rotation
Low energy precession Nuclear Spin
Nuclear magnetic dipole µ
Rotation component of
56
Precession -Energy Rscillator generates rotating component of
agnetic field H1
Ho
Coil Re
High energy precession
Precessional orbit Low energy spin state (-1/2)
ference axis
Precessional orbit High energy spin state
elationship
57
H1 (Magnetic component of radio frequency from oscillator coil): oscillator frequency H1 can be resolved into 2 components rotating in opposite directions.
(1) Rotating in the same direction in the precessional orbit of the molecular magnetic dipole
(2) Rotating in the opposite direction as the precessional orbit of the nuclear magnetic dipole ; disregard
Magnetic Properties of Nuclei Nuclei of certain atoms posses a mechanical spin or angular momentum. The total angular momentum
depends on the nuclear spin or spin number (spin quantum number) I.
The numerical value of the spin number ( I ) is related to the mass number and the atomic number.
Each proton and neutron has its own spin and I is a result of these spins.
Mass Number Atomic Number Spin Number
Odd Even or odd 1/2, 3/2, 5/2,---- Even Even 0 Even Odd 1, 2, 3, ---
The magnetic nucleus may assume any one of ( 2 I + 1) orientations with respect to the directions of
the applied magnetic field.
Therefore, a proton (1/2) will be able to assume only one of two possible orientations that correspond
to energy levels of + or -µ H in an applied magnetic field, where H is the strength of the external
magnetic field.
If proper v is introduced, the Wo will be resonance with the properly applied radio frequency (Hi) and
the proton will absorb the applied frequency and will be raised to the high spin (energy) state.
Even though the external magnetic field strength (Ho) applied to the molecule is the same, the actual
magnetic field strength exerted to the protons of the molecule are different if the protons are in the
different electronic chemical environment.
Fundamental NMR Equation of Radio Frequency and Magnetic Field Strength The energy difference between the two states is
V =
γ : (Magnetogyric Ratio) : CV : Electromagnetic frequencHo : An external magnetic fieWo = γHo γHo = 2πV Therefore Wo = 2πV γ = 2πµ / hI µ = Magnetic Moment (Magnh = Planck's Constant I = Spin Number
Relationship between Radio Frequen
Radio Frequency (Mega Hertz) 60 100 300 500
1.4 T 60 MHz
2.35 T 100 MHz
4. 20
2π
γHo
58
onstant and a fundamental nuclear constant. y in radio frequency ld
etic Dipole Moment)
cy and Magnetic Field Strength for Proton
Magnetic Field (Gauss) 14,100 23,500 70,500 117,500
7 T
0 MHz
∆E = hv
7.0 T 300 MHz
59
Schematic Diagram of an NMR Spectrometer
Chemical Shift The difference in the absorption frequency of a particular proton of the samp
absorption frequency (position) of a reference proton.
The protons at the electron rich environments (strong electonegaticve molecu
oxygen and halogens) will feel less external magnetic field strength because
strength generated by electrons surrounding the proton will counteract the ap
field strength (Ho), which can be said deshielded proton.
Therefor, the Wo of the protons in the electron rich chemical environments w
require less radio frequency to be resonance with the applied radio frequency
protons in the electron poor chemical environments.
δ ppm = (reference frequency - sample frequency) × 106
R-F ° ° transmitter
Sweep ° °generator
Magnet
Transmitter coil Receiver coil
Sweep coils
Sample
Operating instrument frequency
° ° R-F receiver
and
le from the
les such as
the magnetic field
plied magnetic
ill be less and
compared to the
° ° Recorder
The Reference Compounds : TetraMethylSilane (TMS)
General Regions of Chemical Shifts
56 10 7 8 9
Aldehydic
Aromatic and heteroaromatic
Olefin
α-Disu
Acetylenic
β-Substituted aliphatic
c
S i C
C
C
C H H
H
H H
H
H
H H
H H
H
α-Monosubstituted aliphatic
60
3 4 2
ic
bstitutid aliphatic
Aliphatic alicycli
0 δ 1
61
Rest of the protons on CH3 and CH2 absorb at 0.8 - 2
broad, big peak
Spin-Spin Coupling (
Spin-Spin Coupling is the indirect coupling of proto
It occurs because there is some tendency for a bondi
nearest protons. The spin of a bonding electron havi
Coupling is ordinarily not important beyond 3 bonds
bridged systems, or bond delocalizaion as in aromati
•
R C H C H C H 2 C H C H C H C
O
O C H
• • •
2 3
5.3 δ 2.7 δ
.0 δ very crowde
Spin-Spin Splitting)
n spins through the inter
ng electron to pair its sp
ng been thus influenced.
unless there is ring stra
c or unsaturated systems
3.6 δ
2.0 δ
d area, usually see a
vening bonding electrons.
ins with the spin of the
ins as in small rings or
62
Signal a is split into a doublet by coupling with one proton; signal b is split into a triplet by two
protons. Spacing in both sets is same (Jab).
Information from NMR Spectrum
The Number of signals
The Position of signals
The Intensity of signals
The Splitting of signals
a b
Jab
Jab
Jab
b
a C H 2 B r C H B r 2
63
NMR of Fatty Acid Methyl - Ester
CH3 CH2 CH CH (CH2 CH CH)2 CH2 (CH2)5 CH2 CO
OMe
Methly linolenate C 1 9 H 3 2 O 2
a e e c e e b
Chemical shift (ppm) a 0.97 e ca.5.38 b 1.33 c 2.80 d 3.67
d
64
V. Mass Spectrometry
Definition A mass spectrometer bombards a substance under investigation with an electron beam and
quantitatively records the result as a spectrum of positive ion fragments. This record is a Mass
Spectrum. A mass spectrum is a presentation of the masses of the positively charged fragments vs.
their relative concentration. Separation of the positive charge ion fragment is on the basis of mass.
(Mass/Charge)
Essential Features of Mass Spectrometer (1) Sample Inlet System
65
a) GC inlet system - The samples separated by gas chromatography are introduced into the ion
source of mass spectrometer.
b) Heated expansion reservoir - Pure liquid and gas samples are conveniently injected by syringe
into the all glass heated expansion reservoir and leaked into the ion source of mass
spectrometer through a vernier value
- Temp. 250°C at 10-2 Torr.
c) Direct Introduction Probe (DIP) - Solids and viscous liquids are introduced directly into the
ion source of the mass spectrometer by the direct introduction probe. The sample is placed in a
glass capillary and gently heated to produce the required vapor pressure without thermal
decomposition.
(2) Ion Source (Ionization Chamber)
The stream of vaporized sample molecules from sample injection (Inlet) system entering the ion
source interact with the beam of electrons to form positive ions. The electron beam is emitted from
a hot filament.
(3) Accelerating Chambers
The positive ions are pushed out of the source by relatively small "repeller" potential, and then
accelerated by a large potential difference (1 to 10KV - a strong electrostatic field) between the
first and second accelerating slits. Small potentials can be applied to the repeller and ion focus slit
to produce a defined beam of positive ion.
(4) Analyzer (Ion Separation)
The collimated ion beam for the ion source can be separated according to the respective masses of
the ions by a variety of techniques such as magnetic deflection in a magnetic field by varying
either the magnetic field applied to the analyzer tube or the accelerating voltage between the first
and second ion slits. The mass which passes through the exit slit is dependent upon the radius (4
66
cm) of the ion path in the magnetic field, the magnetic field strength (B, gauss) and the ion
accelerating potential (V, volt) is defined by the fundamental equation:
m/e = 4.82 x 10-5 B2 r2 /v
Changing the magnetic field changes the amount of ion deflection, bringing a different m/e into
focus on the collector slit, continuously changing the magnetic field while recording the ion
signals on a strip chart and then producing a mass spectrum.
(5) Ion Collector The positive ions striking the collector produce a flow of ions proportional to the ion abundance.
The ions are amplified by an ion multiplier.
(6) Recorder The amplified ion currents (signals) are measured on a photographic paper.
67
Fatty Acids Molecular ion peak of a straight chain monocarboxylic acid is weak but usually discernible. The most characteristic peak (sometimes the base peak) is at m/e 60 due to McLafferty rearrangement .
Methyl - Ester of Fatty Acids The mass spectrum of a methyl - ester is very similar to that of corresponding carboxylic acid. The methyl ester is more volatile than the free fatty acids and therefore the easier to examine. m/e 74; Corresponding to the m/e 60 peak of fatty acid is usually base peak or predominant
O
C O H C H 2
C H 2
C H R
H
H 2 C C H R
McLafferty Rearrangement
C H O C H 2
O H
H O C
O
H
C H 2
•
•
+ + •
• • •
H O C
O
H
C H 2
• • • • +
•
• + • •
• • + • • • +
• • •
+
O
C C H 3 O C H 2
C H 2
C R 2
H R 2 C C H 2
O
H
C C H 3 O
C H 2
O
H
C C H 3 O C H 2
O
H
C C H 3 O
C H 2 •
•
•
68
+
+ •
m/e 108
m/e 79 [C6H7]+
C H 2 O H O H
H H
•
-H
69
+
-H2
m/e 107
m/e 77[C6H5]+
H
H
H
+
-CO
H
H
70
m/e 91
+ • + + •
H
H
C H 3
+ • + •
H C H 2
H H
H
H C H 2
C H R H
C H 2 C H R
H
H
H H
H H
C H 2
CH3
CH3
- CH3 •
71
72
73
74
75
1. Furans Furan is an example of a 6-electron heteroaromatic system. Its stability is evidenced by an intense molecular ion in the mass spectrum accounting for 25% of the total ion current. Theoretical considerations indicate that the most energetically favored bond-cleavage in the furan molecular ion is that of a carbon-oxygen bond, and it results in the ring-opened molecular ion 1a, which may then undergo electronic rearrangement to 1b. Homolytic cleavage of the C 4 - C 5 bond in 1b results in elimination is the base peak in the mass spectrum and is best formulated as the cyclopropenyl ion (1c), a stable 2 -electron aromatic system. Heterolytic cleavage of the C4-C5 bond in 1b would result in elimination of the cyclopropenyl radical and formation of the formyl ion 1d.
O
42
40
39
29
68 (M+)
76
O1
2
34
5( )O+
O
C3H3-HC O+
m/z 29
HH
m/z 40 m/z 39 (base peak )
-CHO
-H)( +
M+ m/z 68 (1a)(1b)
(1d)
(1c)
+
- CO
HH
+
+
)(+
In 2-methylfuran cleavage of the O-C2 or the O-C5 bond may occur, resulting in two different ring-opened molecular ions (2a and 2b, respectively). These fragments by the progresses described for furan, giving the intense cyclopropenyl and methylcyclopropenyl ions as well as a weaker acetyl ion.
O CH3
( )+
O CH3O CH3
-CH3
(2a)
CHO
H3C C O+
m/z 43m/z 39(20% Σ) (4.4% Σ)
(2b)(15.9% Σ)
(2)
m/z 53(21.6% Σ)
(base peak)
+)(
- C3H3- C2H3O
+)(
77
With larger 2-substituents ring fragmentation with resultant formation of cyclopropenyl or acyl ions is unimportant, and B-fission becomes the dominant fragmentation process.
O CH2 CH2 CH3
β γ
O
m/z 81
(43.1 % Σ)
C2H5-
β
m/z 110 (11.9% Σ)
+ +
Cleavage to the furan ring with loss of the alkyl group is insignificant as it leads to an unfavored vinyl or diradical ion.
O R O O or
+
+
α
78
If the 2-site-chain is n-propyl or longer, a McLafferty rearrangement can occur. Thus with 2-n-butyl- and 2-n-pentylfuran the loss of propene and butene, respectively, results in m/z 82 as the most intense ion in both spectra.
With 2-n-propenylfuran loss of H is favored relative to ring-opening since it gives the fully conjugated oxonium ion. Loss of CO occurs as the second step, forming the intense benzonium ion which further loses a molecule of hydrogen to give the phenyl ion.
O CH CH CH2 H+ O CH CH CH2+
H H
+ C6H5 +H2-
m/z 77(8.1 % Σ)
m/z 79(15.1% Σ)
CO-
m/z 107 (3.5% Σ)
H-
M+m/z 108
(16.7% Σ)
- CH2= CHR
79
In the mass spectrum of 2-(1-pentenyl)furan, a character-impact compound of reversion flavor of soybean oil, the base ion observed at m/z 107 may be produced by the loss of CO from the parent ion with recyclization to form the cyclopentadiene radical ion which further loses a hydrogen atom forming the stable cyclopentadienyl ion (m/z 107). Alternatively, loss of CHO from the parent ion also leads to the cyclopentadienyl ion. The metastable ion observed at m/z 84.2 confirms that the m/z 107 ion is the daughter ion of m/z 136. The fragmentation mechanism for the observation of metastable peaks at 65 and 58.3 confirms the following transitions:
136+ 94+ + CH3 CH CH2
and 107+ 79+ + CH2 CH2
cis-2-(1-pentenyl)furan
m/z
39 50 77
81
94
107
135
80
H H
H CH2CH2CH3HH
m/z 108
H H
HCH2CH2CH3H
- H
+
m/z 107
OCH CHCH2CH2CH3
m/z 136
-CO
-CHOH2C CHCH3-
OCH CH2
m/z 94
136 94+ CH3CH=CH2+
81
O+
m/z 81
OCHCH=CHCH2CH3
+
-CH CCH2CH3
OCH=CHCH2CH2CH3
-Hm/z 136
-CO
CH2CH3H
+
m/z 79 m/z 77
C6H5+
107 79+ +CH2=CH2
+
HH
- H2
- CH2=CH2
m/z 107
- CH=CHCH2CH3
82
The mass spectra of 2-furanaldehydes are characterized by an abundant parent ion and an abundant M-1 ion, the resonance-stabilized furoyl cation. This further fragments by loss of two molecules of carbon monoxide, forming a cyclopropenyl ion.
O CHO( )
+
O C O+ O+
CO
O +
+
M+, m/z 96 (21.8% Σ)
H_
CO_m/z 95 (21.2% Σ)
m/z 67(1.6% Σ)
CO_
m/z 39
(27.6% Σ) An intense furoyl ion is also observed in the spectra of 2-furyl alkyl ketones. If the side chain is n-butyryl or longer, the McLafferty rearrangement involving the carbonyl group becomes an important process. Thus, it gives the base peak of the spectrum of 2-n-valerylfuran, competing favorably with formation of the furoyl ion.
O C O+
O C
HCHCH2
CH2
CH3O+
αO C
CH2
OH
+
C3H6_- C4 H9
•
83
2. Pyrroles N- and C- alkylated pyrroles show marked differences in fragmentation. The mass spectrum of 1-methylpyrrole is shown below.
NCH3 81 (M +. )
80
39 53
42 55
78
m/z It is noted that the chief feature of the spectrum is the strong M-1 ion which may be the ring-expanded species.
CH3 N CH+
N
CH3
N +
CH2
NH
+
m/e 80
(strong peak)
C4H5+
m/e 53
HCN_
M+
m/e 81
m/e 39
C2H4N_
m/e 42
C3H3_ - H
+
CH3 N CH•
84
The fragmentations of certain long-chain N-alkylpyrroles have been studied in some detail by means of labeling and high-resolution techniques. The best peak (m/z 81) of the mass spectrum of N-butylpyrrole was initially thought to result from transfer of the terminal methyl group to nitrogen.
N
H 2 C C H 2
C H 2
C H 3 N
C H 3
N
H 2 C C H 2
C H 2
H N
H 2 C H
+
+ C H 2
or
C 3 H 6 _
•
•
•
85
In the mass spectra of C-alkylpyrroles, the β-cleavage is the predominant fragmentation.
N CH2 HH
N CH2
H
+NH
+ NH
CH2 CH3+
M+
m/e 95m/e 80
base peak
H_
M+m/e 81 m/e 80
- CH3
The spectra of 2-formyl and 2-acetylpyrroles show the expected fragmentation with the intense acylium cation being presumably well-stabilized by resonance.
N CO
R N C O N COH H
+ + +
H
M+ m/e 94
- R
86
3. Thiophenes The mass spectra of 2- and 3- alkylthiophenes have been studied, and in all cases the base peak is the ion C5H5S+, m/z 97, resulting from fission of the bond in the alkyl group between the carbon atoms in position and B relative to the ring.
S
R C H 2
S C H 2
S S
C H 2
+
+ β α
R _
or
Thiopyrilium ion
m/e 97
m/e 97
87
The close resemblance to the fragmentation of toluene is immediately apparent, and the thiopyrilium ion has been suggested for the species m/z 97. For disubstituted thiophenes, the stability of the neutral fragment controls the major mode of fragmentation.
S CC
C+
S CH2 CH2 CH3H3C + SH3C+
H_C2H5
_
m/e 139 (10%)M+
m/e 140m/e 111 (100%)
S+
S S+
m/e 125 (100%)
C2H5_CH3
_
m/e 139 (10%)
88
4. Pyridines In pyridine and methyl derivatives molecular ions are the base peaks as expected for aromatic rings. Mass spectra of the methylpyridine isomers show three important primary processes arising from the molecular ions.
(i) M+ m/z 92
(ii) M+m/z 78
(iii) M+ m/z 66
H_
CH3_
HCN_
•
•
• The cleavage processes of pyridines substituted with higher alkyl groups can be classified in three categories. (1) β-Cleavage in ethyl derivatives is easier in the 3 position than in other positions. This is attributed to the relatively high electron density at this position. Thus the resulting fragment is the base peak in 3-ethylpyridine.
N
C H 2 C H 3
N
C H 2
N
+
+
C H 3 _
( ) +
+
HCN _
m/z 92
m/z 65
•
•
89
These fragments undergo further elimination of hydrogen cyanide leading to the peak at m/z 65. (2) γ-cleavage is especially favored in 2-alkylpyridines. The relative intensity of the
resulting fragment ion depends on the nature of the radical lost.
N C H 2 C H 2 R
( ) +
N C H 2 C H 2
+
R _
N +
• •
•
•
(3) The McLafferty rearrangement takes place when the adjacent position to the
heteroatom bears a side-chain with at least three carbon atoms.
N CH2 CH2 CH2 CH2 CH3+N CH2
H
+
m/z 93 (100%)
base peak
- C4H8
90
5. Pyrazines The mass spectrum of parent pyrazine is dominated by the loss of HCN molecules. The fragmentation of 2-methylpyrazine involves losses of HCN and CH3CN from the molecular ion. a b
CH
NCH
N
N CH3
+ +
CH3CN_ HCN_
a b HCN
CH3
+
H3C C CH( )+H2C C CH+
H_
m/z 39
HC CH( ) +
m/z 26
HCN_
m/z 67m/z 53
HCN_
HC CH+ + HH
)( +
HH
+
m/z 40
91
Pyrazines which possess an n-propyl or longer side chain (containing -hydrogen) undergo McLafferty rearrangement. In general, this gives the base peak for most pyrazines containing long side chain. The fragmentation of 2-n-pentyl-5,6-dimethylpyrazine is shown below.
N
N
N
N
HN
N
CH2H
CH2HC
H2 C CH3
-
m/z 122 (100%)m+
178
- C3H7
N
N
+ +N
N
+N
N
- C2H5- CH3
m/z 135 (50%) m/z 149 (36%) m/z 163 (10%)
92
4. MANUFACTURE OF FOOD FLAVOR I. Natural or Imitation Flavor 1) Price 2) Availability of raw material 3) Permissibility under current legislation (toxicity test) 4) Type of end product in which the flavoring is to be used II. Problems of Using Natural Flavors 1) Many natural flavor have low intensity, it should be used at a high dosage which results in an unsatisfactory texture and poor stability. 2) Concentration of natural flavors is usually accompanied by significant changes in the flavor profile. 3) Natural flavors exhibit variations in strength and quality. 4) The supply of natural materials is becoming uncertain. 5) Most natural flavors are unstable and undergo changes during postharvest handling, processing or storage. 6) Many natural products contain enzyme systems which may result in the formation of off-notes. 7) The toxicity of many natural products has yet to be established. III. Disadvantages of Using Imitation Flavors 1) Original natural flavor more subtle imitation flavor maybe described as “chemical” 2) Difficulties in “labeling” 3) Many natural flavors have a built in reservoir of flavor precursors which can result in the generation of additional flavor imitation flavors are not. 4) Imitation flavor generally require the use of either a solvent or a carrier 5) Restriction by legislation 6) Problems with texture in the end product
93
IV. Advantage of Imitation Flavor 1) Cheaper than natural flavor 2) Stable 3) Can be design to withstand severe processing condition 4) Can be produced in a variety of forms ( e.g., alcohol-based, oil-based, or encapsulated powders ) 5) Generally readily available 6) Consistency of quality
94
V. Methods in Synthetic Flavor Reconstitution 1) Scientific Approach
Isolation of flavor concentrate
Separation of components
Identification Quantitative GC analysis
Synthesis
Scientifically reconstituted formulation (correct until GC identical )
Organoleptically adjusted formulation
Process and product development
1) Application 2) Physical formulation 3) Synthetic process development
Manufacture and end use in consumer product
95
Limitations a. Some compounds decompose or do not come out of GC b. Wide variety of flavor threshold (Some compounds can not be identified. 2) Organoleptic Approach
Example Smell-taste analysis of food or flavor concentrate Blue cheese Resolution into subjective arbitrary Buttery, fatty, moldy quality components 1 buttery, 5 fatty, 3 moldy Assigning of rough intensity value to each quality component Diacetyl, methyl nonyl Association of quality components ketone, methyl amyl ketone with known flavor Formulation of reconstituted flavor 0.3% diacetyl 5% methyl nonyl ketone 1% methyl amyl ketone Same steps as in scientific reconstitution Limitations a. labeling b. toxicity c. no precursor d. an artistic craft rather than science
96
5. CHEMISTRY OF FLAVOR PRECURSORS I. Flavor derived from carbohydrate and proteins (Browning Reaction, Maillard Reaction)
Reducing Sugars and α-amino acids
N-glycosylamine or N-fructosylamine
1-Amino-1-deoxy-2-ketose (Amadori intermediate) or 2-Amino-2-deoxy-1-aldose (Heynes intermediate)
II. Thermal Degradation of Vitamin B1 1. Basic condition
2. Acidic condition
N
SH O
N
N
H 2N
H +
+N
N
C H O
H O S
NH +
HO
O
S H
C H3CC H(C H 2)2 + HCOOH +
H 2N
H 2NN
N
no odor
H 2N
coffee
H2O H2O+ +
H
H
Cl-+N
SHON
NH2N
N
SHO+
N
NH2N
no odor
has found some use in the flavor industry( identified in coffee aroma with meaty note )
- OH-
+ H2O CH3
116
3. Thiazole compounds
S
NHO
-H2O
S
N
Formed in cocoa
methyl-vinyl-thiazole
reduction
S
N
( cocoa, beef )
methyl, ethyl-thiazole 4. Furan compounds
H3C C CH CH 2 CH 2 OHO
S H
-SH
+ H+
H3C C CH2 CH2 CH2 OHO
O OH3C( coffee, tea )
cyclization
-H2O
Reduction
-H2
OOH
CH3
117
Cyclization Cyclization
118
III. Lipid Oxidation
1. Chemistry of triplet oxygen
Molecular Atomic Atomic
2Px 2Py 2Pz
*
2S
1S
Molecular Orbital o
σ
2Pz 2Py 2Px
*
*
f
σ
Triple
π
π
π*
π*
2S
σ
1S
σ
σ
σ
E
t Oxygen
119
2. General Mechanisms of Autoxidation
14 13 12 11 10 9
12 11
•
•
12 11
12 11
HYDROPEROXIDE DECOMPOSION
•
12 11
TERMINATION
•
C H 2 C H C H C H 2 C H C H C H 2 R ( C H 2 ) 3 C H 3
INITIATION (METAL)
( C H 2 ) 4 C H 3 C H CC H
( C H 2 ) 4 C H 3 C H C HC H
O
O PROPAGATION
C H C H C H( C H 2 ) 4 C H 3 O
O
H
( C H 2 ) 4 C H 3 C H C HC H
O
C H 3 ( C H 2 ) 3 C H 2
C H 3 ( C H 2 ) 3 C H
O C
H
•
- H 10 9
H C H C H C H 2 R
+ O2
10 9
•
C H C H C H 2 R
+ H
10
C H C H C H 2 R
- OH•
10 9
•
C H C H C H 2 R
C H C H C H C H C H 2 R
+ H
+
(PENTANE) 3
120
Mechanisms of Oxidation 1. Initiation 2. Propagation 3. Termination
• • +
• • +
• + + •
• • +
+ + • •
R O R R O R • •
•
+
• • +
R O R O O R O O R O 2 + + • 2 2 2
R H R H
R O 2 R O O
R O O R 1 H R O O H R1
R R R R
R O O R O O R O O R
R O O R R O O R
O 2
121
Oxidation of Mono-Olefines Oleic acid - 4 Hydroperoxides
12 11 10 9 8 7 12 11 10 9 8 7
11 10 9 8 7 9
8
11 10
C C C C C C
O
O
H
11 10 9 8 7
C C C C C C
O
O
H
C C C C C
O
O
H
C
C C C C
O
O
H
C C
Double bond shifts to
Hydroperoxides from Linolenate
9 C C C C C C
O
O
H
C C
16 15 14 13 12 11 10 9
16 15 14 13 12 11 10 9
12 C C C C C C C C O
O
H
16 15 14 13 12 11 10 9
13 C C C C C C C C
O
O
H
16 15 14 13 12 11 10 9
122
16 C C C C C C
O
O
H
C C
123
Peroxide Decomposition
General
Effects of Metal on Peroxide Decomposition
O H +
•
•
• +
or
R C
O
H R 1 + • • +
R ' O H R O H • +
+
R '
R ' H +
+ •
R C R 1
H
O
O
H
R C R 1
H
O
R C R 1
O
R ' H
R C R 1
H
O H
R 1 C H 1
O
R
R '
•
C u + R O O H R O O H - C u + +
C u + H + R O O R O O H C u + +
R O O H R O R O O H + O H -
H 2 O
+ + +
+ + +
+ + + 2
•
•
• •
124
C C C C
O
H C C C
H
H H H H
H
H H
R
C C C C
H H H H
R
H H
H H
O
C C C
O
O
H
C C C
O
H
H H H H
R C C C C
O
H
H
H
H H
R C C
C H 2 C H 2 C H C H R
O C
H
C H 3
O C
H
C H 2 C O
H
A B
125
Ethyl vinyl ketone isolated and identified in raw soybean
H 3 C C H 2 C C HO
C H 2 ( raw beany, grasoy )
H 3 C C H 2 C H C H C H 2 C H C H C C O O H O O H
H 3 C C H 2 C H C H C H 2
C H 2 C H H 3 C C H 2 C H
O 2 , RH
C H 2 C H C H 2 C H H 3 C O O H
C H 2 C H C H 2 C H 3 C O
126
Lactones in butter flavor Important lactones in butter are δ−decalactone δ−dodecalactone δ−tetradecalactone 5-20 ppm The lactones have coconut-like flavor which is desirable in molten butter, undesirable in fresh butter and dry whole milk.
fresh butter content of lactones is low heated butter lactone increases
thiosulfinate ( responsible for fresh flavor of onion and garlic )
CH CH S S CH CHO
H3C CH3 fresh onion odor
CH2 S S CH2
OCH CH2CHH2C fresh pleasant
garlic-like odor
144
S C H 2 C H C H 2 S C H 2 C H H 2 C typical garlic-like odor
H 2 C
H C N H
C H
C H 2 S O
C O O H H 3 C
cycloalliin ( no favor contribution )
isolated and identified
H C C H C H 2 S C H 2 C H N H 2 O H
O
C O O H
+H 2 O
C H S C H C H N H 2 C O O H
O C H H 3 C
R S S
O
R
R S S
O
R
O
R S O
O
(Thiosulfinate)
(Thiosulfonate)
Aged Flavor
Fresh Flavor
Bitter Flavor (Off Flavor)
- H 2 O
145
5. Biogenesis of Flavor Compounds in Tomato Important volatile flavor compounds in tomato 3-cis-hexenol “ green note “ isovalervaldehyde hexanol contribute “ green “ or grassy odor hexanal 2-trans-hexenal 2-cis-hexenal “ 2-isobutylthiazole “--- strong green leaf odor 3-methyl-1-butanol 1) amino acid precursors
[ADH] - alcohol: NAD + oxidoreductase alcohol dehydrogenase add to use l-[14C] leucine crude extract of fresh tomato --- get 14C label 3-methyl-1-butanol add to boiled extract of tomato --- no reaction indicates the enzymatic nature of this reaction
6. Asparagusic Acid in Asparagus asparagusic acid: 1,2-dithiolane-4-carboxylic acid
SS
COOH
asparagusic acid , its methyl and ethyl esters and several other sulfur compounds were synthesized in the intact plant cells of asparagus. This is an exceptional case of formation of sulfur-containing flavor components. Sulfur compounds in vegetables are normally formed by enzymic or chemical cleavage of nonvolatile precursors such as S-alkylcysteine sulfoxides and glucosinolates during the crushing of the plant material.
COOH
NH2
COOH
OCOOH
valine 2-methyl propanoic acid
COOH
S
COOH
CH3
SH
COOH
SH
COOH
S
COOH
C
CH3
O
S
COOH
C
CH3
O
SHSH
COOH
SH
SS
COOH
149
7. Mushroom Volatiles Edible mushroom like Agaricus Bisporus produce 1-octen-3-ol, 3-octanol, 2-octen-1-ol and 1-octen-3one as volatile constituents.1-octen-3-ol possesses a mushroom-like aroma and is known as “mushroom alcohol”. Tressel et al. investigated the enzymic conversion of linoleic and liolenic acids into C8 and C10 components by mushrooms. They proposed the presence of ahydroperoxide cleavage enzyme for the cleavage of 13- and 9-hydroperoxide into C8 and C10 components. Following figure shows the scheme proposed by Tressl for the formation of mushroom volatiles.
150
151
8. Flavor formation by Neurospora
Production of Fruity Aroma by Various Strains of Neurospora Neurospora Species Aroma Neurospora sitophila ATTC46892 Fruity Neurospora No 1 Fruity Neurospora No. 2 Fruity Neurospora No. 3 Fruity Neurospora No 4 Fruity Neurospora No 5 Fruity Neurospora No 6 Fruity Neurospora No 7 Fruity Neurospora tetrasperma NRRA2164 No aroma Neurospora crassa NRRA 2223 No aroma Neurospora sitophila NRRA 2884 No aroma Neurospora intermedia NRRA 5506 No aroma Neurospora sitophila ATTC46892, Neurospora No.1,2,3,4,5,6, and 7 were isolated from beiju. Tweenty strains of Neurospora sp.isolated from the state of Sao Paulo did not produce fruity aroma
152
153
Volatile Compounds (ppm) produced by Neurospora sp. Isolated from beiju
Ethyl Acetate
Ethanol 3-Methyl-1-butanol
Ethyl hexanoate
1-Octen- 3-ol
Neurospora sitophila
4.8 128 318 59 40
Neurospora Sp. 1
9.0 111 ND ND ND
Neurospora Sp. 5
0.9 111 117 10 50
Neurospora Sp. 6
2.8 99 208 20 ND
ND: Not detected
154
6. DAIRY PRODUCTS FLAVOR
1. Milk Flavor 1. Oxidized flavor Cardboard: due to some lactones Metallic: vinyl methyl ketone Oily: oct-1-ene-3-one Tallowy: 2t, 6t-nonadienal Preventive method
a. Avoid cupric iron and ferric ion b. Elimination of oxygen pack under vacuum or nitrogen c. Avoid light
Better quality milk, less bacteria, more susceptible to oxidized flavor. The bacteria can either using up the available oxygen or generate antioxidant compounds. 2. Rancid flavor Hydrolysis of triglycerides by lipase. The lipase are present in the aqueous phase of the milk at the time of secretion. Any process which alter the membrane, such as homogenization, agitation, and warming and cooling will accelerate the rancidity. 3. Heated flavor 1) General Pasteurization induces heated flavor.
Now people are used to Pasteurization and consider it as the flavor of normal milk. Cooked flavor is the off-flavor induced by temp. above 75 oC beyond the
pasteurization. Too much heat will develop caramelized flavor.
155
2) Origin a. Cooked flavor: protein H2S b. caramelized flavor
CH2 CHO from phenylalanine
H 3 C C H C O O H
N H 2
C H 2 C H O
( Strecker degradation )
pyruvic acid H 3 C C C O O H
O
C H 2 C H C O O H
N H 2
+
156
4. Microbiological flavor 1) Ggeneral Molds, yeast, bacteria can all grow in milk and effect flavor. 2) Origin a. Psychrophilic bacteria : Bitter, fruity, stale, putrid flavor b. Moldy flavor
Sunlight will induce oxidized flavor and sunlight flavor and hay-like flavor. Oxidized flavor Sunlight flavor: burnt cabbage
Burnt and cabbage flavor: Riboflavin is a catalyst for production of the sunlight flavor. 1) milk protein and riboflavin sunlight sunlight flavor 2) riboflavin increase in milk will increase the sunlight flavor 3) riboflavin removal prevent the sunlight flavor
Fig.2 Mass Spectrum of peak D (top) of Fig.1 and standard dimethyl disulfide (bottom)
Fig. 1. Effect of time of exposure to fluorescent light on headspace volatile compounds and dimethyl disulfide of skim milk. Peak A,B,C,D and E are 2-butanene, ehtanol, diacethyl, dimethyl disulfide, and n-butanol, respectively
159
160
Postulated mechanism of dimethyl disulfide formation by singlet oxygen oxidation of methionine
Effect of ascorbic acid concentration on dimethyl disulfide (Peak D) content in skim milk during light exposure for 1 hour.
161
II. Cheese Flavor 1. Isolation, separation, and identification of cheese flavor
Dynamic headspace analyzer, gas chromatographer, and mass spectrometer arrangement
162
Reproducibility of gas chromatograms of headspace volatile compounds of Brewster Cheddar cheese after one week of storage
163
164
165
Changes of total headspace volatile compounds of Cheddar cheese at 11°C, and Swiss cheeses at 21 °C during ripening
4. Biochemical pathways of cheese flavor formation from protein Products = Caseins (+trace of whey) Amines Peptides a-keto acids Acids Alcohols Phenols Amino Acids H2S NH3
169
5. Formation of 2-butanone and 2-butanol from diacetyl CH3COCOCH3 CH3CHOHCOCH3 Diacetyl Acetoin CH3COCH2CH3 CH3COH=COHCH3 2-Butanone 2,3-Butyleneglycol CH3CHOHCH2CH3 2-Butanol 6. Biochemical pathways of cheese flavor formation from lactose Lactose Lactic Acid Diacetyl Pyruvic Acid Ethanol Acetaldehyde Acetic Acid CO2
[H2]
[H2]
170
7. Lactone formation
H2C O C R
O
HC O C R1
H2C O C (CH2)3
O
O
CH
OH
(CH2)4 CH3
DG
HO C
O
(CH2)3 CH
OH
(CH2)4 CH3
-H2O
C (CH2)3 CH (CH2)4 CH3
O
O
+ H2O
171
8. Mechanism of Methylketone Formation
H2C O C R
O
HC O C R1
H2C O C (CH2)3
O
O
CH
OH
(CH2)4 CH3
DG
HO C
O
(CH2)3 CH
OH
(CH2)4 CH3
-CO2
+ H2O
C (CH2)n
O
H3C CH3
172
7. MEAT FLAVOR CHEMISTRY I. Effects of Psychrotropic Bacteria on the Volatile Compounds of Raw Beef
1. Introduction 1) Meat palatability a. Volatile flavor compounds b. Appearance c. Juiciness d. Tenderness 2) Factors affecting flavor or raw beef a. Breed, Sex, Diet, Age b. Fat, Microorganisms Sample preparation for isolation and separation of volatile compounds Ground beef: 5 g ground beef was transferred into 30 ml serum bottle and sealed air tightly. Analysis of volatile compounds a. Dynamic headspace sampler (DHS) b. Capillary-Gas chromatography (GC)
173
2. Effects of light and dark storage on the volatile compounds of asceptic raw ground beef
1) Storage condition a. Aseptic ground beef stored under light at 5oC b. Aseptic ground beef stored under dark at 5oC 2) Evaluations a. Dynamic headspace sample/gas chromatography b. TBA c. Panel Evaluation for off-odor 3. Effects of psychrotropic bacteria on the volatile compounds of aseptic raw
ground beef 1) Samples a. Aseptic ground beef b. Aseptic ground beef + Pseudomonas putrifaciens c. Aseptic ground beef + Acinetobacter spp. 2) Evaluations a. Dynamic headspace sample/gas chromatography/mass selective b. TBA value c. Total bacteria count d. Panel evaluation for off-odor
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3) Identification of volatile compounds of aseptic raw beef by DHS/GC/MSD Condition of Mass Selective Detector Column DB-5, 30m symbol 180 \f "Symbol" \s 12×} 0.25mm,
1.0symbol 109 \f "Symbol" \s 12µm film thickness Carrier gas Helium gas (99.999%) at 1 ml/min Ion source temp. 170oC Ionization voltage 70eV Mass scan range 25-250 a.m.u. Scan rate 1.0 scan/sec
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Diagram of Dynamic Headspace Sampler/Gas Chromatograph
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Chromatogram of 0 day storage
Chromatogram of 8 day under the dark storage
Chromatogram of 8 day under the light storage
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Total ion chromatogram of volatile compounds of (a) aseptic ground beef, (b) aseptic ground beef with Pseudomonas putrifaciens or (c) Acinetobacter spp.
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II. Isolation, Separation, and Identification of Roast Beef Flavor
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III. Simulated Meat Flavor Compounds Formation
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8. ORANGE FLAVOR STUDY BY PULSED ELECTRIC FIELD
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9. INTERACTIONS OF FLAVOR COMPOUND WITH FOODS I. Physical and Chemical Stability of Flavor Compounds 1. Mechanisms of flavor perception 1) Flavor compounds interact with olfactory and lingual receptors 2) Volatile compounds are generally responsible for odor perception and nonvolatile
compounds for taste. 2. Concentration of flavor compounds in the receptors 1) The rates of flavor compounds release from foods. 2) The concentration and disposition of flavor compounds in the food. 3) The components of the food. 4) The particle size of food components. 5) The extend of mixing. 6) The temperature of foods. 3. Factors affecting partition and release of flavor compounds in the mouth 1) Hydration 2) Dispersion 3) Reduction of Particle Size 4) Homogenization 5) Emulsification 4. Rate of volatilization 1) The partition coefficient of flavor compounds. 2) Molecular interaction between flavor compounds and food components. 3) The viscosity of food material.
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5. Physical and chemical states of flavor compounds in foods Flavor compounds may be dissolved, adsorbed, absorbed, or entrapped in food components depending upon functional groups, molecular size, shape and volatility, and chemical properties of the components in the food. 6. Importance of binding behavior of flavor compounds Knowledge of the binding behavior of flavor compounds to food components is: 1) Important in the flavor perception and the determination of relative retention of
flavor compounds during processing, storage and mastication. 2) Critical in a. the determination of appropriate flavor blend added to food b. the choice of methods for dispersing flavor compounds c. the selection of appropriate flavor compounds carriers d. the determination of improved conditions for efficient drying of flavored foods e. the minimization of flavor compounds loss. 3) Important in the determination of how to maximize flavor impact and minimize
cost. 7. Effects of selective binding on flavor perception The selective binding of one flavor compound of a blend to food components or packaging material can markedly alter the overall flavor impact. Binding limits its volatilization and diffusion and hence impairs its immediate perception as a components of an overall flavor when food is taken into the mouth. 8. Factors affecting partition coefficients 1) Temperature 2) The presence of soluble solutes and nonsoluble materials 3) Diffusion rates in the aqueous phase 4) Physical retention of flavor compound Air-Water Partition Coefficients for Homologous Series of Ketones and Aldehydes at 25oC
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Compounds Coefficients Compounds Coefficients Acetone 1.6x10-3 Acetaldehyde 2.7x10-3 Butan-2-one 1.9x10-3 Propanol 3.0x10-3 Pentan-2-one 2.6x10-3 Butanal 4.7x10-3 Heptan-2-one 5.9x10-3 Pentanal 6.0x10-3 Octan-2-one 7.7x10-3 Hexanal 8.7x10-3 Nonan-2-one 15x10-3 Heptanal 11x10-3 Undecan-2-one 26x10-3 Octanal 21x10-3 Nonanal 30x10-3 Types of Possible Interactions between Flavor Compounds and Food Components. Component Possible Interaction Lipids;
II. Effects and Interactions of Lipids with Flavor Compounds 1) Increase flavor compounds adsorption and retention 2) Decrease the partition coefficients 3) Increase the flavor threshold concentration Effects of Physical Phase on Perception of Flavor Compounds Compounds Threshold Concentration (ppm) Water Oil Octanoic acid 5.8 350 γ-decalactone 0.05 3.0 Pentanal 0.07 0.3 Hexanal 0.03 0.05 2,4-Decadienal 0.5x10-3 0.3
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III. Effects and Interactions of Carbohydrates with Flavor Compounds 1. Soluble sugars increase the vapor pressures of volatile compounds. 2. Polysaccharides stabilize flavor compounds in foods during processing due to
entrapment, adsorption, reduced mass transport effects due to increased viscosity. 3. Cellulose adsorbs flavor compounds in intramolecular region. 4. Amylose forms inclusion complexes with aliphatic flavor compounds which fit
inside the amylose helix. 5. The association constants with starch were 383, 930 and 2277 for limonene,
methanol and decanal, respectively.
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Adsorption and Desorption of Volatile Compounds to Polysaccharides (mol/kg) Polysaccharide Ethyl Acetate Ethanol Butylamine A B A B A B Cellulose 0.1 trace 2.2 0.2 11 0.3 Pectin 0.2 0.1 2.1 trace 46 4.0 Starch 0.2 0.1 4.5 1.0 27 2.2 A maximum adsorption; B vacuum desorption (Maier, 1975)
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IV. Effects and Interactions of Proteins with Flavor Compounds 1. The binding capacity of protein depends upon the surface topography, porosity,
and bulk density. 2. Proteins bind aldehydes and ketones to differing extents, indicating differences in
intrinsic binding affinities, structural features of the protein, differences in available surface area.
3. The Mechanisms of Flavor Compounds Interaction with Protein 1) Scatchard equation v/[L] = nK-vK v is the number of moles of flavor compounds bound per mole of protein. L is the molar concentration of flavor compounds. n is the total number of binding sites. K is the intrinsic binding constant. Plot of v/L vs. v gives a slope of -K and intercept on nK.
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2) Klotz equation 1/v = 1/n+1/nK[L] A plot of 1/v vs. 1/[L] Intercept = 1/n Slope = 1/nK 3) Determinations of Thermodynamic Parameters G = -RT ln K H = -R(dln/d(1/T)) S = -R(Ho-Go)/T Binding and Thermodynamic Data for the Interactions of Carbonyl Compounds with Soy Protein, b-Lactoglobulin and Bovine Serum Albumin Compounds Protein n Keq/M -G(Cal/M) 2-Heptanone Soy Protein 4 110 2.78 2-Octanone Soy Protein 4 310 3.39 2-Nonanone Soy Protein 4 930 4.04 2-Heptanone β-Lactoglobulin 1 152 2.98 2-Octanone β-Lactoglobulin 1 481 3.66 2-Nonanone β-Lactoglobulin 1 2439 4.62 2-Heptanone Serum Albumin 6 600 --- 2-Nonanone Serum Albumin 6 1800 4.90
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Binding and Thermodynamic Data for the Interactions of Carbonyl Compounds with soybean Protein, b-lactoglobulin an d Bovine Serum Albumin Ligand Protein n Keq/M -G(Kcal/M) Soy Protein 2-Heptanone Native 4 110 2.781 2-Octanone Native 4 310 3.395 2-Nonanone Succinylated 2 850 3.992 2-Nonanone Native (25C) 4 930 4.045 2-Nonanone Native (5C) 2 2000 4.221 2-Nonanone Heated (90C) 4 1240 4.215 β-lactoglobulin
2-Heptanone Native 6 500 --- 2-Nonanone Native 6 1800 4.900 Effects of Temperature and Modification on the Binding and Thermodynamic Data for Interactions of Carbonyl Compounds with Soy Protein Compounds Temperature n Keq/M -G(Cal/M) 2-Heptanone 5C 4 2000 4.22 2-Octanone 25C 4 930 4.06 2-Nonanone 90C 4 1240 4.21 2-Nonanone Succinylated-25C 2 850 3.99
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Urea Concentration (M)
Fluo
resc
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(nm
) (
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Effects of urea induced conformational change s reflected in fluorescence on the binding affinity of 2-nonanone for b-lactoglobulin
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Adsorption and Desorption of 2-Pentanone onto Whey Protein
Adsorption Desorption P/Pv Rel. Mass Gain P/Pv Rel. Mass Gain
Summary 1. Several mechanisms are involved in interaction of flavor compounds with food
components. 2. In lipid system, solubilization and rates of partitioning control the interactions
and partition coefficients, thus determine-s the rates of release. 3. In polysaccharide system, polysaccharides interact with flavor compounds by
nonspecific adsorption and formation of inclusion compounds. 4. In protein system, protein involves adsorption, specific binding, entrapment,
covalent binding and these mechanisms may account for the retention of flavor compounds.
5. Moisture affects diffusion and partition coefficients and macromolecular structures in the case of protein and polysaccharides and thereby affect the rate of release of flavor compound.
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10. PACKAGING AND FLAVOR COMPOUNDS
INTERACTION
I. Effects of Packaging Materials on the Flavor Quality of Food II. Sorption of Orange Flavor Compounds by Packaging Materials
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11. FLAVOR COMPOUNDS AND SOLVENT INTERACTION
I. Commercial Cherry Flavor and Solvent Interaction II. Acetal Formation