Thermal Generation of Aromas - American Chemical Society

Chapter 18

Downloaded by NANYANG TECHNOLOGICAL UNIV on September 24, 2017 | http://pubs.acs.org Publication Date: October 3, 1989 | doi: 10.1021/bk-1989-0409.ch018

Kinetics of the Formation of Alkylpyrazines Effect of pH and Water Activity 1

2

M. M. Leahy and Gary A. Reineccius 1

Ocean Spray Cranberries, Inc., One Ocean Spray Drive, LakevilleMiddleboro, MA 02349 Department of Food Science, University of Minnesota, St. Paul, M N 55108

2

Pyrazines are heterocyclic, nitrogen-containing compounds important to the flavor of many foods. Part One of this study reported on the effects of type of amino acid and type of sugar on the kinetics and distribution pattern of pyrazines formed. This study investigates the effect of pH and water activity on the kinetics of alkylpyrazine formation. One-tenth molar lysine/glucose solutions buffered at pH 5.0, 7.0 and 9.0 were heat-processed. Rates of pyrazine formation, as well as number of types of alkylpyrazines detected, were found to increase with pH and temperature. For the water activity (a ) study, the effect of increasing product aw over a range of 0.32 to 0.85 on the rate of pyrazine formation was investigated. Nonfat dry milk (NFEM) was chosen as a model system for this study. Rates of formation were found to increase with a up to 0.75. In both cases, samples were analyzed using a headspace concentration capillary gas chromatographic technique with nitrogen-selective detection. w

w

T H E IMPORTANCE O F M A I L L A R D R E A C T I O N PRODUCTS TO T H E FLAVOR O F FOODS HAS RECEIVED CONSIDERABLE ATTENTION. ONE GROUP OF MAILLARD PRODUCTS, THE ALKYLPYRAZINES, A R E THOUGHT TO C O N T R I B U T E ROASTED, T O A S T E D A N D NUTTY F L A V O R NOTES TO A V A R I E T Y O F FOODS. SEVERAL REVIEWS HAVE DETAILED THE PRESENCE OF PYRAZINES I N A WIDE VARIETY OF FOODS ( 1 - 7 ) . C O N S I D E R A B L E WORK H A S P R E V I O U S L Y F O C U S E D O N M E C H A N I S M S OF FORMATION AND T H E E F F E C T S O F VARIOUS PARAMETERS ON P Y R A Z I N E FORMATION ( 8 - 1 7 ) . PART ONE OF T H I S STUDY REPORTED ON T H E E F F E C T S OF TYPE OF AMINO ACID AND TYPE OF SUGAR ON THE KINETICS AND D I S T R I B U T I O N P A T T E R N O F P Y R A Z I N E S FORMED ( 1 8 ) . T H E CURRENT STUDY I N V E S T I G A T E S T H E E F F E C T O F P H A N D WATER A C T I V I T Y O N T H E K I N E T I C S O F A L K Y L P Y R A Z I N E S FORMATION. P R I O R S T U D I E S R E L A T I N G TO P Y R A Z I N E FORMATION H A V E FOCUSED THE EFFECT OF DRASTIC EXTREMES I N P H . FOR EXAMPLE, KOEHLER AND

0097-6156/89/0409-0196$06.00/0 e 1989 American Chemical Society Parliment et al.; Thermal Generation of Aromas ACS Symposium Series; American Chemical Society: Washington, DC, 1989.

ON

18. LEAHY AND REINECCIUS ODELL

(19)

SODIUM

REACTED EQUAL

HYDROXIDE

L-ASPARAGINE RESULTED

Kinetics ofthe Formation ofAlkylpyrazines

IN

UPON

IN

A

EQUIVALENTS

REACTION

DIETHYLENE

ADDITION

GLYCOL.

OF

THE

METHYLPYRAZINE Y I E L D TENFOLD TO T H E S Y S T E M WITHOUT ADDED (14,

15)

ALSO

FOUND THAT

( 0 . 1 MOLE)

SYSTEM A

ACID,

OF

YIELD

WHILE

OF

0.1

SULFURIC ACID

MOLE OF

D-GLUCOSE

PRACTICALLY

ADDING

BASE

197

OR AND

ZERO

INCREASED

AND DIMETHYLPYRAZINE FIVEFOLD A C I D OR B A S E . SHIBAMOTO AND

A D D I T I O N OF NAOH INCREASES TOTAL

RELATIVE BERNHARD YIELD

UP


TO A P O I N T . ACIDITY/BASICITY E F F E C T S WERE A L S O S T U D I E D B Y K B E H L E R AND ODELL ( 1 9 ) . THEY REACTED GLUCOSE WITH ASPARAGINE, ASPARTIC A C I D AND A S P A R T I C A C I D WITH NAOH ADDED. Y I E L D S W I T H A S P A R T I C A C I D WERE LOWEST, W I T H A D D I T I O N O F OBTAINED WITH ASPARAGINE. OUR

CURRENT

CONTAINS

LITTLE

PREVIOUS

TWO

RANGE

HAS

PH

(5-9)

AMINO GROUPS A V A I L A B L E

I S A COMMON S U G A R I N WORK

OF

TO

THOSE

THE WAS

IT

A

UP

ONE

GLUCOSE BECAUSE I T

ON

ALMOST

WHICH

AND

FOCUSED

BRINGING YIELDS

C O U L D E X P E C T TO F I N D U N D E R NORMAL FOOD P R O C E S S I N G C O N D I T I O N S . REACTANTS L Y S I N E A N D G L U C O S E WERE CHOSEN FOR T H I S S T U D Y ; L Y S I N E CHOSEN BECAUSE

STUDY

BASE

FOCUSED

FOR

REACTION

FOODS.

DIRECTLY

ON

THE

IINPACT

OF

WATER CONTENT ON T H E FORMATION O F P Y R A Z I N E S . KBEHLER AND ODELL (19) S P E C I F I C A L L Y C H O S E A S O L V E N T S Y S T E M O F LOWER WATER C O N T E N T F O R T H E I R STUDY; MAGA AND S I Z E R (20) INVESTIGATED THE EFFECTS OF INITIAL MOISTURE CONTENT AND TEMPERATURE OF EXTRUSION ON T H E FORMATION OF P Y R A Z I N E S I N POTATO F L A K E S . OUR STUDY A L S O I N V E S T I G A T E D T H E E F F E C T O F WATER A C T I V I T Y (A^) ON T H E K I N E T I C S OF T H E FORMATION OF P Y R A Z I N E S . WATER A C T I V I T Y IS D E F I N E D A S T H E R A T I O O F P A R T I A L P R E S S U R E O F WATER I N A FOOD TO T H E V A P O R P R E S S U R E O F P U R E WATER AT A G I V E N T E M P E R A T U R E . NONFAT DRY M I L K ( N F E M ) WAS C H O S E N A S A M O D E L S Y S T E M F O R T H I S S T U D Y S I N C E N F E M AND L A C T O S E / C A S E I N S Y S T E M S WHICH HAD UNDERGONE NONENZYMATIC BROWNING WERE FOUND TO CONTAIN PYRAZINES (21, 22). THE CURRENT STUDY I N V E S T I G A T E S T H E E F F E C T O F I N C R E A S I N G PRODUCT A ^ OVER T H E RANGE OF 0 . 3 2 TO 0 . 8 5 ON T H E RATE OF FORMATION OF P Y R A Z I N E S . EXPERIMENTAL

SECTION

FOR THE P H STUDY, T E N M L OF BUFFERED SOLUTIONS AT P H 5 . 0 , 7 . 0 AND 9.0 O F 0 . 1 M L - L Y S I N E ITONOHYDROCHLORIDE AND 0 . 1 M D-GLUCOSE (SIGMA CHEMICAL C O . , ST. L O U I S , MO) W E R E H E A T E D I N T E F L O N - C A P P E D 2 5 M M ( O . D . ) Χ 1 5 0 M M P Y R E X T E S T T U B E S I N A WATER B A T H AT 7 5 , 8 5 , A N D 9 5 ° C FOR U P TO 2 4 HR. CITRATE-PHOSPHATE BUFFERS (0.1M) WERE U S E D TO A C H I E V E A P H O F 5 . 0 A N D 7 . 0 A N D B O R A T E B U F F E R ( 0 . 1 M ) WAS U S E D F O R A PH OF 9 . 0 (23). S A M P L E S WERE T A K E N AT 7 TO 8 T I M E INTERVALS. E I G H T E E N TO 2 2 TOTAL S A M P L E S P E R TEMPERATURE AND P H WERE A N A L Y Z E D . A F T E R H E A T T R E A T M E N T E A C H S A M P L E WAS A D J U S T E D T O P H 9 . 0 W I T H 0 . 1 N NAOH. ONE ML OF A SOLUTION CONTAINING 2-METHOXYPYRAZINE IN D I S T I L L E D W A T E R ( 2 P P M ) WAS A D D E D A S A N I N T E R N A L S T A N D A R D . FINAL S A M P L E V O L U M E WAS 1 5 M L . P Y R A Z I N E S WERE T H E N I S O L A T E D , SEPARATED AND Q U A N T I F I E D U S I N G A N AUTOMATED H E A D S P A C E CONCENTRATION SAMPLER (HEWLETT PACKARD 7 6 7 5 A PURGE AND TRAP) COUPLED TO A HEWLETT PACKARD 5880A GAS DIROMATCGRAPH WITH N I T R O G E N — PHOSPHORUS DETECTION. S P E C I F I C S O F SAMPLE P R E P A R A T I O N AND CHROMATOGRAPHIC A N A L Y S I S HAVE BEEN DESCRIBED PREVIOUSLY ( 1 8 ) . Q U A N T I F I C A T I O N O F T H E P Y R A Z I N E S WAS ACCOMPLISHED USING 2-METHOXYPYRAZINE AS AN INTERNAL STANDARD. PYRAZINE PEAK IDENTIFICATION WAS INITIALLY ACCOMPLISHED BY

Parliment et al.; Thermal Generation of Aromas ACS Symposium Series; American Chemical Society: Washington, DC, 1989.

THERMAL GENERATION OF AROMAS

198

AXIIRANATOGRAPHY WITH STANDARDS, ( P Y R A Z I N E S P E C I A L T I E S , ATLANTA, T H E N F U R T H E R C O N F I R M E D B Y G A S CHRCANATOGRAPHY/MASS S P E C T R O M E T R Y . FOR MAPLE FOR

THE

WATER

ISLAND,

2

ACTIVITY

INC.

WEEKS

AT

STUDY,

(STILLWATER, ROOM

FRESH

MN).

TEMPERATURE

NFCM

FIVE

IN

WAS

30 G

OBTAINED

SAMPLES

EVACUATED

(MALLINCKRODT, MEASURED HYGROSKOP


ST

LOUIS,

MD)

TO

ACHIEVE

0 . 5 8 , 0 . 7 5 AND 0 . 8 5 , RESPECTIVELY

THE

HELD

DESICCATORS

WATER

(24).

FROM

WERE

SATURATED SALT SOLUTIONS. T H E S A L T S U S E D WERE M A G N E S I U M SODIUM BROMIDE, SODIUM CHLORIDE AND POTASSIUM 0.32,

GA)

AFTER

OVER

CHLORIDE, CHLORIDE

ACTIVITIES STORAGE,

OF

AW W A S

USING AN ELECTRIC HYGROMETER (THE KAYMONT-ROTRONICS D P , KAYMONT INSTRUMENT C O R P . , HUNTINGTON STATION, NY).

T R I P L I C A T E 5 G SAMPLES I N 7 5 MM ( O . D . ) Χ 1 5 0 MM PYREX CULTURE TUBES W I T H T E F L O N - S E A L E D C A P S WERE H E A T - P R O C E S S E D I N A 9 5 ° C WATER B A T H FOR FIVE

SAMPLING TIMES,

R A N G I N G FROM 0 . 5 TO

3 HR.

THEN COOLED TO

TEMPERATURE. P R I O R TO A N A L Y S I S , T H E SAMPLE C A K E I N T H E WAS B R O K E N U P I N T O A P O W D E R W I T H A G L A S S R O D O R S P A T U L A , AND ANALYZED TECHNIQUE. TRUE

USING

THE

AUTOMATED

QUANTIFICATION

OF

HEADSPACE

PYRAZINES

IN

ROOM

TEST TUBE VORTEXED,

CONCENTRATION

THE

POWDERED

GC

SAMPLES

P R E S E N T E D SOME D I F F I C U L T Y . DUE TO S E N S I T I V I T Y PROBLEMS I N S A M P L I N G R E C O N S T I T U T E D S A M P L E S , T H E D E C I S I O N WAS M A D E T O P U R G E T H E P O W D E R E D NFEM. A N INTERNAL STANDARD COULD NOT B E E A S I L Y ADDED TO A DRY SAMPLE, SO QUANTIFICATION WAS ACCOMPLISHED CALCULATING CONCENTRATIONS R E L A T I V E TO R E S P O N S E FACTORS DETERMINED FOR EXTERNAL STANDARD SOLUTIONS. STANDARDIZED CONCENTRATION UNITS WERE DETERMINED U S I N G T H E FOLLOWING R E L A T I O N S H I P S : RF

WHERE R E L A T I V E

= CONCENTRATION (UA/ML) INTEGRATED PEAK AREA

CONCENTRATION

STANDARDIZED

= SAMPLE AREA Χ

= RELATIVE

CONCENTRATION

(1)

RF

CONCENTRATION

I N I T I A L D R Y WT.

OF

100

X

SAMPLE

UNITS SINCE

5

STANDARDIZED THE

SAMPLE

G

(WET

WEIGHT)

CONCENTRATIONS WERE

SAMPLES RELATIVE

DETERMINED.

HAD TO

MOISTURE

BEEN

THE

TAKEN

INITIAL

ANALYSIS

U S I N G T H E G C METHOD O F R E I N E C C I U S AND A D D I S

AT DRY

WAS

EACH

AW,

WEIGHT

OF

ACCOMPLISHED

(25).

RESULTS AND DISCUSSION KINETIC

STUDIES.

DETERMINED WITH

USING

THE THE

KINETICS BASIC

OF

THE

EQUATION

FORMATION FOR

THE

OF

RATE

PYRAZINES OF

TIME: DA = DEWHERE

A

KA

CONCENTRATION TIME

(HR)

K

RATE

CONSTANT

η

REACTION

WERE

CHANGE O F

N

OF PYRAZINE (PPM)

ORDER


(2)

A

18.


LEAHY A N D REINECCIUS

INTEGRATING ZERO,

THIS

AND A ,

EQUATION

BETWEEN

T H E CONCENTRATION A

FOR A

ZERO

OF A

IS

ORDER R E A C T I O N .

CONSTANT

REACTANTS.


THIS

CASE,

CONCENTRATION

TIME 0

FIRST

THE OF

THIS

RATE

OF

H A V E B E E N FOUND TO

AT

IMPLIES

THAT T H E OF

RATE

THE

OF

FORMATION

CONCENTRATION

FORMATION

REMAINING.

OF

YIELDS THE RELATIONSHIP: '

I N A Q + ΜΘ·

FOLLOW E I T H E R

TIME

(3)

ORDER R E A C T I O N T H I S

REACTANTS

A

YIELDS

= AQ+

IN A = IN

THE

AT

WITH T I M E AND INDEPENDENT

FOR A

CONCENTRATION

AQ,

OF A

199

(4)

OF

A

IS

DEPENDENT

REACTIONS

IN

FOODS

PSEUDO ZERO OR F I R S T

ON

THE

GENERALLY

ORDER

KINETICS

(26).

ONE

IS

GENERALLY

USING

THE

PSEUDO

S A F E R WHEN D I S C U S S I N G R E A C T I O N

TERM

"PSEUDO",

REACTION

ORDERS

CORRELATION

Υύφ

DUE

IN

(R )

FOODS

FOR

2

A

FORMATION OF PRODUCT AND T I M E THE

(R )

FIT

OF

2

CURVE

OF THE

GREATER

RATHER

ANALYSIS ZERO

OF

POINTS

TESTED

OF PYRAZINES

AT

TIMES.

LINE,

THAN

THAN THE

A

THE

GENERALLY

FIT

FOR

WOULD

A

IN

FOODS

THE

IN

SYSTEM.

ASSIGNED BECAUSE

RELATIONSHIP

A

BETWEEN

ZERO ORDER R E A C T I O N .

A BE

PSEUDO

FIRST

OBTAINED.

TIMES VS.

COLLECTED

WAS

OF

CONSTANTS

TREATED

THE

REACTION,

LEAST

DUPLICATE

TRIPLICATE

GAVE

DETERMINATION

ORDER

GENERAL

COMPUTE RATE

PLOTTING

REACTION

COEFFICIENT

EACH REGRESSION.

SAMPLING POINT

OF

EXISTS.

WAS U S E D T O

EARLY DATA

ORDERS

COMPLEXITY

FORMED V E R S U S T I M E O F

0 . 9 5 .

WERE U S E D FOR

EACH

ARE

USUALLY WITH A

LINE

DATA

THE

MATHEMATICAL

FORMATION O F P Y R A Z I N E S

CONCENTRATIONS BETTER

TO

A

SQUARES

(27).

TWO

SAMPLES

SAMPLES

WERE

AT

SEPARATELY

LATER IN

THE

REGRESSION ANALYSES. ACTIVATION

ENERGIES

FOR

THE

FORMATION

CALCULATED U S I N G THE ARRHENIUS RELATIONSHIP, CONSTANT,

K,

TO

(ABSOLUTE)

R

= GAS CONSTANT,

Τ

= TEMPERATURE I N ° K

REGRESSION

TEMPERATURE

ON

INCREASE

RATES

THE

DATA

FORMATION OF

ALTHOUGH

THE

CONCENTRATION, REACTANT/ AND

EXHIBIT LABUZA LOSS (30)

OF

IT

OF MAY

SIDE

WHICH I S

PSEUDO ET

AL.

MUST

APPARENT

MULTIPLICITY

REACTIONS. ORDER (28) ( 2 9 ) AS

EFFECTS FOUND I N

OF

PH

TABLE

INCREASE I N

AND

I.

AN

EITHER

OF BE

REACTANT A

DUE

FUNCTION TO

KINETICS AND WELL

H A S G E N E R A L L Y B E E N SHOWN T O

AS

THE

FORMATION

BY

MANY

OF

IN

HIGH

FORMATION

THE

RESEARCHERS,

WARMBIER

EXHIBIT

REACTANT

RELATIVELY

MAILLARD

H A S A L S O B E E N SHOWN

FORMATION FIRST

ET OF

TO

INCLUDING

AL.

AMADORI

ORDER

OF

CONCENTRATION.

OF STEPS I N PYRAZINE

PIGMENT

FOR

SUGGESTS THAT T H E RATE

ALSO A MULTI-STEP PROCESS,

ZERO

REACTANTS

THIS

INDEPENDENT BE

IS

OF DETERMINATION WERE Q U I T E H I G H

FORMATION NOT

PRODUCT R A T I O ,

COMPETING

REACTION,

RATE

IS

THE

PYRAZINES

OF T H E DATA.

PYRAZINES

CONSTANT

1 . 9 8 6 CAL/MOLE ° K

OCCURRED WITH A N

OR P H . C O E F F I C I E N T S OF

RATE

KCAL/MOLE

SUMMARIZING OF

FORMATION

A PSEUDO ZERO ORDER F I T FORMATION

RATE

(5)

E

E A = ACTIVATION ENERGY I N

TEMPERATURE

WERE

THE

= KOE- A/RT

WHERE KO = P R E - E X P O N E N T I A L

IN

PYRAZINES

TEMPERATURE: K

LINEAR

OF

WHICH RELATES

( 2 9 ) . CONFOUNDS

KINETICS.



200

Table I . Regressions f o r t h e formation o f p y r a z i n e s (0.1M l y s i n e - g l u c o s e systems) Compound

Tenperature

k

2

intercept

n*

r

3.596 0.490 0.214 1.346 0.159 0.0957 0.0938 0.0232 0.00356

0.0596 0.458 0.279 0.762 0.609 -0.0014 -0.0647 -0.0586 -0.0185

22 22 20 19 22 22 22 22 17

0.994 0.960 0.965 0.962 0.899 0.989 0.984 0.966 0.928

2.837 0.422 0.159 1.367 0.276 0.0945 0.00636 0.00279

-0.104 0.142 0.091 -0.070 0.204 0.028 -0.00212 -0.00430

22 22 20 19 22 22 22 22

0.995 0.967 0.941 0.981 0.967 0.981 0.890 0.912

0.186 0.0247 0.00668 0.0630 0.00949 0.00209

-0.0457 -0.00604 -0.00536 -0.0051 -0.00229 -0.00574

20 22 16 19 22 14

0.976 0.985 0.942 0.965 0.974 0.857

0.0229 0.00309 0.000677

-0.0057 -0.00017 -0.00086

16 18 12

0.948 0.978 0.958

(ppn/hr)


PYRAZINE pH 9.0

pH 7.0

pH 5.0

95°C 85°C 75°C 95°C 85°C 75°C 95°C 85°C 75°C

2-MEIHYLPYRAZINE pH 9.0

pH 7.0

pH 5.0

95°C 85°C 75°C 95°C 85°C 75°C 95°C 85°C

2,5-DIMETHYLPYRAZINE pH 9.0

pH 7.0

95°C 85°C 75°C 95°C 85°C 75°C

2,3-DIMEIHYLPYRAZINE pH 9.0

95°C 85°C 75°C

*n = number o f d a t a p o i n t s


18. LEAHY AND REINECCIUS ACTIVATION ENERGIES FROM T H E (SEE

TABLE

II).

FOR

SUGGESTING CONDITIONS


ACTIVATION

FORMATION

THE

QUANTITATIVELY,

METHYL

FOR ALKYLPYRAZ I N E

SLOPE OF ARRHENIUS PLOTS,

2-METHYLPYRAZINE THOSE

Kinetics of the Formation ofAlkylpyrazines

FEWER EXIST

WERE

ENERGIES

DIMETHYLPYRAZ INES

FOR

FOR

OF

35

WERE FRAGMENTS

DIMETHYL

CALCULATED

4 5 KCAL/MOLE

PYRAZINE

AND

KCAL/MOLE,

WHILE

SLIGHTLY

PRODUCTION

CARBONYL

FORMATION

FROM 3 3 TO

APPROXIMATELY

DIMETHYLPYRAZ I N E AVAILABLE

FORMATION WERE

RANGING

201

WAS OR

HIGHER.

ALSO LESS

LOWER, DESIRABLE

VERSUS UNSUBSTITUTED

OR

PYRAZINE. TABLE

II.

A C T I V A T I O N E N E R G I E S FOR

OF PYRAZINES

( 0 . 1 M LYSINE-GLUCOSE (E

PYRAZINE

A

FORMATION SYSTEMS)

I N KCAL/MOLE) 35.8

PH

9.0

PH

7.0

33.4

PH

5.0

41.8

2-MEIHYLPYRAZINE PH PH

36.7

9.0 7.0

34.0

2,5-DIMETHYIPÏRAZINE PH

9.0

PH

7.0

41.9 43.7

2,3-DIMETHYLPYRAZ INE PH

9.0

44.8

IT I S I N T E R E S T I N G TO NOTE THAT FOR P Y R A Z I N E , THE ACTIVATION ENERGY IS LOWEST AT PH 7.0 AT 33 KCAL/MOLE. THE RATE OF AMINOCARBONYL REACTIONS HAS P R E V I O U S L Y B E E N SHOWN T O E X H I B I T PH DEPENDENCE, WITH T H E MAXIMUM OCCURRING AT SOME I N T E R M E D I A T E P H . S I N C E R A T E CONSTANTS WERE D E T E R M I N E D AT ONLY 3 T E M P E R A T U R E S , ONLY 3 DATA P O I N T S WERE U S E D TO D E T E R M I N E A C T I V A T I O N E N E R G I E S . DATA AT OTHER TEMPERATURES I S N E C E S S A R Y TO MAKE A N Y FURTHER COMPARISONS AMONG A C T I V A T I O N E N E R G I E S . A C T I V A T I O N E N E R G I E S HAVE B E E N REPORTED FOR OTHER A S P E C T S O F T H E MAILLARD REACTION. T H E A C T I V A T I O N ENERGY FOR BROWNING A S MEASURED FOR PIGMENT PRODUCTION RANGES FROM 15.5 KCAL/MOLE FOR A G L Y C I N E - G L U C O S E S Y S T E M ( 3 1 ) TO 3 3 KCAL/MOLE FOR A S O L I D I N T E R M E D I A T E M O I S T U R E MODEL FOOD S Y S T E M ( 2 9 ) . THE CURRENT RESEARCH INDICATES THAT T H E ACTIVATION ENERGIES FOR P Y R A Z I N E FORMATION ARE HIGHER, SUGGESTING A DIFFERENT RATE-CONTROLLING STEP. P H STUDIES - THE EFFECT OF SEEN I N TABLES I AND I I .

P H ON T H E FORMATION OF P Y R A Z I N E S MAY R A T E CONSTANTS FOR T H E FORMATION


BE OF

202


PYRAZINES

INCREASED

PYRAZINES

FORMED.

THE PYRAZINES CONSTANTS GOOD

WITH

RELATIONSHIP

PH,

ALONG WITH

BETWEEN

PH

AND

THE THE

RATE

I S GRAPHICALLY DEPICTED I N FIGURE FOR P Y R A Z I N E AND 2 - M E T H Y L P Y R A Z I N E

FIT

OF

THE

RESPECTIVELY.

LINE,

WITH

R

NUMBER OF

FORMATION

OF

0.974

AND

QUANTIFICATION

AN I N C R E A S E I N T H E RATE OF SUGAR MUTAROTATION W I L L UNDER

III

THESE

LISTS THE

CONDITIONS,

TOTAL A S WELL

CONCENTRATIONS AS

THE

THE

GREATER THAN FORMATION OF

PYRAZINES WITH INCREASING PH FOR TWO REASONS. AT N U C L E O P H I L I C ATTACK OF T H E AMINO A C I D ON A CARBONYL I S TABLE

OF

0.999

OF

D I M E T H Y L P Y R A Z I N E S COULD ONLY B E ACCOMPLISHED AT P H ' S 5.0 ONE MIGHT ANTICIPATE AN INCREASE I N THE RATE OF


SUBSTITUTED

1. REGRESSING THE RATE FORMATION ON P H G A V E A

VALUES

2

UNFORTUNATELY,

OF

HIGH PH A FAVORED AND

OCCUR ( 3 2 ) .

OF PYRAZINES

PERCENTAGE

OF

PRODUCED

EACH

PYRAZINE

O F T H E TOTAL AMOUNT. E F F E C T O F P H O N Y I E L D WAS G R E A T , W I T H A T O T A L O F 1 3 , 0 0 0 P P B P Y R A Z I N E S PRODUCED AT P H 9 . 0 AND ONLY 2 4 P P B AT PH 5.0. THE DIFFERENCES I N PYRAZINE DISTRIBUTIONS N O T A P P E A R T O B E G R E A T A S SHOWN I N T A B L E III. TABLE

III.

EFFECT

OF PYRAZINES

-

AT

OF P H ON D I S T R I B U T I O N

0 . 1 M LYSINE-GLUCOSE,

PH

5.0

VARIOUS

PH'S

DO

PATTERN

2 HR,

PH 7.0

95 C

PH 9.0

% PYRAZINE 2-METHYLPYRAZINE

63.2 36.8

2,5-DIMETHYLPYRAZINE 2,3-DIMETHYLPYRAZ INE

TOTAL

(PPM)

0.0239

58.7 39.6

55.8 41.5

1.7

2.4 0.3

6.19

13.1

S I N C E T H E E F F E C T O F P H O N T H E F O R M A T I O N O F P Y R A Z I N E S WAS T H E F O C U S O F T H I S S T U D Y , E F F O R T S WERE MADE TO S T A N D A R D I Z E ALL OTHER VARIABLES. B U F F E R E D S O L U T I O N S WERE U S E D TO R E S I S T L A R G E C H A N G E S I N P H D U R I N G THERMAL P R O C E S S I N G . CITRATE-PHOSPHATE B U F F E R S WERE U S E D T O A C H I E V E A P H O F 5 . 0 A N D 7 . 0 , W H I L E A B O R A T E B U F F E R WAS C H O S E N T O ACHIEVE A PH OF 9.0. PREVIOUS WORK HAS DEMONSTRATED BUFFERS ACCELERATE THE NON-ENZYMATIC REACTION. S P A R K ( 3 3 ) DEMONSTRATED THAT B R O W N I N G O F G L Y C I N E - G L U C O S E WAS A C C E L E R A T E D I N T H E P R E S E N C E O F A BUFFER (PHTHALATE, PH 6.2). BURTON AND MCWEENEY (35) FOUND PHOSPHATE A C C E L E R A T E D I N I T I A L BROWNING REGARDLESS O F A N Y B U F F E R I N G E F F E C T A N D P R O P O S E D THAT P H O S P H A T E S A C T E D TO D E C R E A S E T H E INITIAL S T A B I L I T Y OF THE ALDOSE SUGAR. ALTHOUGH BOTH PHOSPHATE AND BORATE B U F F E R S WERE U S E D I N T H E CURRENT S T U D Y , I T WAS T H E C A S E T H A T A C H A N G E I N B U F F E R T Y P E D I D NOT A F F E C T P Y R A Z I N E FORMATION. WATER A C T I V I T Y IN

THE

STUDY.

HEAT-PROCESSED,

P Y R A Z I N E AND 2-METHYLPYRAZINE HUMIDIFIED

NFEM

SAMPLES

BY

WERE

IDENTIFIED

RETENTION


TIMES

18.

LEAHY AND REINECCIUS

Kinetics of the Formation ofAlkylpyrazines

203


A N D CXX±IRCAIATOGRAPHY W I T H S T A N D A R D S ( P Y R A Z I N E S P E C I A L T I E S , ATLANTA, GA) U S I N G NITROGEN-PHOSPHORUS DETECTION. PYRAZINE AND 2-METHYLPYRAZINE HAVE PREVIOUSLY B E E N I D E N T I F I E D I N A LACTOSE-CASEIN SYSTEM H E L D A T 75% R E L A T I V E H U M I D I T Y (21) A N D T H E L A T T E R I N A 2 - Y E A R - O L D N F E M SAMPLE (22). I N I T I A L WATER A C T I V I T I E S O F T H E H U M I D I F I E D N F E M S A M P L E S WERE D E T E R M I N E D T O B E 0 . 3 1 9 , 0 . 5 8 3 , 0.747 A N D 0 . 8 4 1 . R A T E CONSTANTS WERE D E T E R M I N E D F O R A PSEUDO ZERO ORDER R E A C T I O N F O R T H E FORMATION O F P Y R A Z I N E A N D 2 - M E T H Y L P Y R A Z I N E W I T H T I M E A T E A C H O F T H E S E AWS ( T A B L E I V ) . F I G U R E S 2 AND 3 D E P I C T T H E RELATIONSHIP O F CONCENTRATIONS O F P Y R A Z I N E AND 2-METHYLPYRAZINE A S A FUNCTION O F T I M E AT EACH A . R E A C T I O N R A T E S I N C R E A S E D W I T H AW O V E R T H E R A N G E O F 0.32 T O 0 . 7 5 A N D A M A X I M U M O C C U R R E D A T A T AW O F 0 . 7 5 . L A B U Z A E T A L . (28) A T T R I B U T E D T H E R E A C T I O N R A T E D E C R E A S E A T H I G H E R AWS T O A D I L U T I O N O F R E A C T A N T S WHILE RELATING T H E DECREASED REACTION RATE AT LOW AWS T O A N INCREASING DIFFUSION RESISTANCE WHICH LOWERS THE MOBILITY OF REACTANTS. T H I S AW M A X I M U M A T A N I N T E R M E D I A T E M O I S T U R E C O N T E N T A L S O E X P L A I N S T H E R E S U L T S O F M A G A A N D S I Z E R (20) WHO F O U N D Y I E L D S O F P Y R A Z I N E S WERE G R E A T E S T I N T H E E X T R U S I O N O F POTATO F L A K E S I N T H E P O T A T O S L U R R I E S C O N T A I N I N G T H E L O W E S T A M O U N T S O F A D D E D W A T E R (25% V E R S U S 48%). I N THAT STUDY, T H E AW A T W H I C H M A X I M U M R A T E OF P Y R A Z I N E FORMATION RESULTED CORRESPONDED TO A N INTERMEDIATE V E R S U S H I G H I N I T I A L MOISTURE CONTENT. W

TABLE IV. R E G R E S S I O N S FOR T H E FORMATION O F P Y R A Z I N E S I N N F E M A S A F U N C T I O N O F T I M E ( P P M / H R ) A T 9 5 ° C A T AWS 0 . 3 2 , 0 . 5 8 , 0 . 7 5 A N D 0.84 PYRAZINE AW 0.32 AW 0 . 5 8 AW 0 . 7 5

Y

AW 0 . 8 4

Y

Y Y

= 0.324X + 0.00856 = 0.681X - 0.110 = 1.371X - 0.102 = 1.318X + 0.0307

N* N N N

= = = =

17 17 17 18

R2

17 17 17 18

R2 R2 R2 R2

R2 R R2 2

0.895

= =

0.930

=

0.940

0.971

2-METHYLPYRAZINE AW AW AW AW

0.32 0.58 0.75 0.84

Y Y Y Y

= = = =

0.271X 0.626X 0.886X 0.718X

- 0.0199 - 0.135 - 0.133 - 0.0838

*N = NUMBER O F DATA

N N N N

= = = =

= = =

0.922 0.899 0.975 0.955

POINTS

A F U R T H E R R E L A T I O N S H I P B E T W E E N R E A C T I O N R A T E A N D AW H A S B E E N PROPOSED B Y LABUZA. A L I N E A R R E L A T I O N S H I P BETWEEN T H E LOGARITHMS O F R E A C T I O N R A T E C O N S T A N T S A N D AW W A S F O U N D T O E X I S T F O R M A N Y F O O D S W I T H I N A R A N G E O F AW 0 . 3 T O 0 . 8 . FIGURE 4 DEPICTS THIS RELATIONSHIP FOR T H E RATE O F FORMATION O F P Y R A Z I N E A N D 2 - M E T H Y L P Y R A Z I N E A S A FUNCTION O F A . TABLE V L I S T S T H E REGRESSIONS DETERMINED FOR T H E THREE RATE CONSTANTS WHICH F E L L W I T H I N T H I S RANGE. CORRELATION C O E F F I C I E N T S ( R ) F O R T H E S E R E G R E S S I O N S WERE Q U I T E H I G H , A T 0.99 F O R BOTH P Y R A Z I N E AND 2-METHYLPYRAZINE. W

2


204



0

0.4

0.8

1.2

1.6

2

2.4

2.8

Time (hr) F I G U R E 2.

EFFECT 95°C I N

O F WATER A C T I V I T Y O N T H E

FORMATION O F P Y R A Z I N E

NFEM.


AT

18. LEAHY AND REINECCIUS


3.0 - r 2.8 -


2.6 -

0.0

0.4

0.8

1.2

1.6

2.0

2.4

2.8

7îm« (hr) FIGURE 3 .

E F F E C T O F WATER A C T I V I T Y O N T H E FORMATION O F 2-METHYLPYRAZINE AT 9 5 ° C I N NFEM.

0.4

Water Activity (Aw) F I G U R E 4.

NATURAL

LOGARITHM O F RATE CONSTANT

FOR T H E FORMATION O F

P Y R A Z I N E AND 2-METHYLPYRAZINE WITH T I M E V S .

WATER

ACTIVITY.


205

206

THERMAL GENERATION OF AROMAS TABLE V . R E G R E S S I O N S O F I N R E A C T I O N R A T E S (ppm/hr) F O R T H E F O R M A T I O N O F P Y R A Z I N E A N D 2 - M E T H Y L P Y R A Z I N E A T 95°C I N N F E M A S A F U N C T I O N O F WATER A C T I V I T Y

PYRAZINE

IN

Y = 3.318x - 2.222

Η = 3

R 2 = 0.986

Η = 3

R2 =

2-MEIHYLPYRAZINE


IN

Y = 2.806X - 2.174

0.990

M T H O U G H A MAXIMUM RATE O F FORMATION O F P Y R A Z I N E S OCCURRED A T A P P R O X I M A T E L Y AW 0.75 I N T H E N F E M S A M P L E S I N T H I S S T U D Y , O N E C A N N O T A S S U M E T H A T T H I S WOULD B E T H E C A S E I N A L L T Y P E S O F F O O D S O R R E A C T I O N SYSTEMS. ADDITION O F GLYCEROL AND HYDROPHILIC POLYMERS TO S U G A R / A M I N O A C I D S Y S T E M S H A S B E E N D E M O N S T R A T E D T O S H I F T T H E AW A T W H I C H V I S I B L E B R O W N I N G W I L L O C C U R (29, 34). I T I S MORE L I K E L Y THAT T H E RATE O F P Y R A Z I N E FORMATION I N C R E A S E S U P T O A MAXIMUM A T A N I N T E R M E D I A T E AW R A N G E A N D T H E N D E C R E A S E S A G A I N , B U T N O T N E C E S S A R I L Y A T AW 0.75. SUMMARY T H E E F F E C T S O F P H A N D WATER ACTIVITY ON T H E KINETICS OF THE FORMATION O F P Y R A Z I N E S WERE I N V E S T I G A T E D . FOR T H E P H STUDY, RATES OF FORMATION O F P Y R A Z I N E S WERE INVESTIGATED I N LYSINE-GLUCOSE SYSTEMS. R A T E S O F FORMATION O F P Y R A Z I N E S , A S WELL A S T H E NUMBER O F T Y P E S O F A L K Y L P Y R A Z I N E S D E T E C T E D , WERE FOUND T O I N C R E A S E W I T H P H A N D T E M P E R A T U R E O V E R T H E R A N G E O F P H 5.0 T O 9 . 0 . COEFFICIENTS OF D E T E R M I N A T I O N W E R E Q U I T E H I G H , U S U A L L Y G R E A T E R T H A N 0.90, F O R A PSEUDO ZERO ORDER F I T O F T H E DATA. ACTIVATION ENERGIES, DETERMINED U S I N G A R R H E N I U S P L O T S , W E R E A P P R O X I M A T E L Y 35 K C A L / M O L E F O R P Y R A Z I N E AND 2-METHYLPYRAZINE, EXCEPT I N T H E C A S E O F P Y R A Z I N E FORMATION A T P H 5.0. QUANTITATIVELY, D I M E T H Y L P Y R A Z I N E P R O D U C T I O N WAS A L S O LOWER, S U G G E S T I N G FEWER A V A I L A B L E CARBONYL FRAGMENTS A N D M E C H A N I S T I C A L L Y L E S S D E S I R A B L E CONDITIONS E X I S T FOR FORMATION O F DIMETHYL V E R S U S UNSUBSTITUTED OR METHYL P Y R A Z I N E . A LINEAR RELATIONSHIP O F HIGH CORRELATION WAS FOUND T O E X I S T BETWEEN P H A N D T H E RATE O F FORMATION O F P Y R A Z I N E S , WITH R V A L U E S O F 0.974 A N D 0.999 F O R PYRAZINE AND 2-METHYLPYRAZINE, RESPECTIVELY. EFFECT OF P HON YIELD WAS I N V E S T I G A T E D U N D E R S T A N D A R D C O N D I T I O N S (2 H R H E A T T R E A T M E N T A T 95°C). P H W AS F O U N D T O H A V E A G R E A T E F F E C T O N Y I E L D , W I T H A T O T A L O F 13,000 P P B P Y R A Z I N E S P R O D U C E D A T P H 9.0 A N D O N L Y 24 P P B A T P H 5.0. T H E D I F F E R E N C E S I N P Y R A Z I N E PRODUCT D I S T R I B U T I O N S WERE N O T GREAT. 2

T H E E F F E C T O F WATER A C T I V I T Y O N T H E R A T E O F F O R M A T I O N O F P Y R A Z I N E S W A S I N V E S T I G A T E D I N N F E M S Y S T E M S O V E R T H E AW R A N G E O F 0.32 T O 0.84. R A T E S O F FORMATION WERE FOUND T O I N C R E A S E W I T H AW, U P T O AW 0.75. A LINEAR RELATIONSHIP WAS FOUND T O E X I S T FORT H E L O G A R I T H M S O F T H E R A T E O F FORMATION O F T H E S E P Y R A Z I N E S V E R S U S AW-


18. LEAHY AND REINECCIUS Kinetics of the Formation ofAlkylpyrazines 207 Literature Cited 1. 2.


3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 15. 16. 17. 18.

19. 20. 21. 22. 23. 24. 25. 26.

Maga, J.A. and Sizer, C.E. In Fenaroli's Handbook of Flavor Ingredients; Furia, T.E., Bellanca, Ν., Eds.; CRC Press: Cleveland, 1975; Vol. 1, p. 47. Maga, J.A. In Food Flavours. Part A. Introduction; Morton, I.D., MacLeod, A. J., Eds.; Elsevier Publishing Co.: Amsterdam. 1982; p. 283. Maga, J.A. CRC Crit. Rev. Food Sci. Nutr. 1982, 16, 1. Ohloff, G. and Flament, I. In Fortsch. Chem. Org. Naturst.; Herz, W., Grisebach, H., Kirby, G.W., Eds; , Springer Verlag: Vienna, 1979, p.47. Barlin, G.B. The Chemistry of Heterocyclic Compounds; John Wiley & Sons; New York, 1982, Vol. 41. Vernin, G. and Vernin, G. In The Chemistry of Heterocyclic Flavouring and Aroma Compounds; Vernin, G., Ed. Ellis Horwood, Ltd., Chichester, England, 1982; p. 120. Shibamoto, T. In Instrumental Analysis of Foods; Charalambous, G., Inglett, G. Eds., Academic Press, New York; 1983; Vol. 1, p. 229. Dawes, I.W., Edwards, R.A., Chem. Ind., 1966, 2203. Newell, J.A., Mason, M.E. and Matlock, R.S., J. Agric. Food Chem. 1967, 15, 767. Wang, P.S., Odell, G.V., J. Acrric. Food Chem. 1973, 21, 868. van Praag, Μ., Stein, Η., Tibbetts, Μ., J. Agric. Food Chem. 1968, 16, 1005. Kbehler, P.E., Mason, M.E. and Newell, J.A., J. Agric. Food Chem. 1969, 17, 393. Rizzi, G.P. J. Agric. Food Chem. 1972, 20, 1081. 14. Shibamoto, T. and Bernhard, R.A. J. Agric. Food Chem. 1977, 25, 609. Shibamoto, T. and Bernhard, R.A. Agric. Biol.Chem. 1977, 41, 143. Wong, J. and Bernhard, R. J. Agric. Food Chem. 1988, 36, 123. Rizzi, G. J. Agric. Food Chem. 1988, 36, 349. Leahy, M.M. and Reineccius, G.A. In Flavor Chemistry; Teranishi, R., Buttery, R. and Shahidi, F., Advances in Chemistry Series NO. 388, American Chemical Society, Washington, DC, 1989, p. 76. Kbehler, P.E., Odell, G.V. J. Agric. Food Chem. 1970, 18, 895. Maga, J.A. and Sizer, C.E. Lebensm. Wiss. Technol. 1979, 12, 15. Ferretti, Α., Flanagan, V.P. and Ruth, J.M. J. Agric. Food Chem. 1970, 18, 13. Ferretti, A. and Flanagan, V.P. J. Agric. Food Chem. 1972, 20, 695. Colowick, S.P., Kaplan, N.O., Eds. In Methods of Enzymology. Vol. I. Acad. Press. N.Y. 1955. Rockland, L.B. Anal. Chem. 1960, 32, 375. Reineccius, G.A. and Addis, P.B. J. Food Sci. 1973, 38, 355. Labuza, T.P. 1981. In Applications of Computers in Food Research and Food Industry; Saguy, I., Ed., Marcel Dekker: New York. 1981.


208 27. 28. 29.


30. 31. 32. 33. 34. 35.


Steele, R.G., Torrie, J.H. 1980. Principles and Procedures of Statistics; McGraw-Hill: New York. 1980. Labuza, T.P., Tannebaum, S.R. and Karel, M. Food Technol. 1970 24, 35. Warmbier, H.C., Schnickels, R.A. and Labuza, T.P. J. Food Sci. 1976, 41, 981. Lee, C.M., Sherr, Β., Koh, Y-N. J. Agric. Food Chem. 1984, 32, 379. Stamp, J.A. and Labuza, T.P. J. Food Sci. 1983, 48, 543. Spark, A.A. J. Sci. Food Agric. 1969, 20, 308. Speck, J.C., Jr. Advan. Carbohyd. Chem. 1958, 13, 363. Eichner, K. and Karel, M. J. Agric. Food Chem. 1972, 20, 218. Burton, H.S. and McWeeney, D.J. Nature 1963, 197, 266.

Received May 31, 1989


Thermal Generation of Aromas - American Chemical Society

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