Technical Note

Pyrazine Compounds in Canned Sweet Corn Flavour

ABSTRACT

Dimethyl pyrazine and dimethylethyl pyrazine were identified in canned sweet corn as important aroma compounds formed during thermal processing.

INTRODUCTION

Canned sweet corn has a characteristic flavour that differs from other canned vegetables. Cooked sweet corn has a smooth, cooked and appetising odour that fresh corn does not have. Several reports have been published on the flavour of field corn, but there are few on sweet corn flavour. Hougen et al. (1971) proposed gas-liquid chromatographic (GLC) analysis of headspace vapour of corn in order to classify the chemotaxonomic characteristics of the seed. His group (McKeag & Hougen, 1977) isolated aroma essences from fresh corn by steam distillation and compared varietal differences by the use of GLC peaks. Dimethyl sulphide is the compound that has been studied the most in both fresh and processed sweet corn (Self et al., 1963; Bills & Keenan, 1968; Williams & Nelson, 1973; Flora & Wiley, 1974). Walradt et al. (1970) identified thirty-six volatile compounds from popcorn and proposed that pyrazines, furans, pyrrols, carbonyls and substituted phenols are important components of popcorn flavour. This paper reports characteristic aroma compounds isolated from canned sweet corn.

MATERIALS AND METHODS

Two varieties of sweet corn (Style-Pack and Jubilee), grown in upstate New York and processed both at commercial plants and at the pilot plant of the Department of

319 Fd. Chem. (3) (1978)---© Applied Science Publishers Ltd, England, 1978 Printed in Great Britain

Fig.

1.

DM

P

DM

EP

TE

MP

I 6D

6

B

TIM

EI

8.8

R

ATE

4

.8Q

T

EM

P2

2B

B

TIM

E2

3

B.B

IH

J

TE

MP

2

58

2

58

F

ID

TE

MP

3

~8

3

B8

O

VE

N M

AX

2

25

CH

T

SP

D

8.5

8

AT

TH

2~

" 1

2

FID

S

~N

L

+8

S

LP

5

EN

S

1.a

B

RR

EA

R

EJ

8

FLO

W

A

26

FLO

W

B

[]

10

20

30

40

50

RE

TEN

TIO

N T

IME

(M

IN)

A t

ypic

al g

as c

hrom

atog

ram

of

cann

ed s

wee

t cor

n vo

lati

les

on a

n S

P-10

00 c

olum

n us

ing

a fl

ame

ioni

sati

on d

etec

tor.

DM

P:

2,5

dim

ethy

l py

razi

ne,

DM

EP

: 3,

6-di

met

hyl-

2-et

hyl

pyra

zine

.

t~J

hJ

C)

.(

PYRAZINE COMPOUNDS IN CANNED SWEET CORN FLAVOUR 321

Food Science and Technology, NY State Agricultural Experiment Station, were used for this study. Whole contents of three cans (No. 303) of corn were homogenised in a blender with 500 ml H20. The slurry was placed in a 5 litre pot attached to the modified Likens and Nickerson distillation apparatus (Flath & Forrey, 1977). A solvent flask containing hexane was attached to the left-hand side of the apparatus. The mixture was boiled for between five and six hours at atmospheric pressure while nitrogen gas was passing through the corn slurry. This extraction procedure was repeated five times and finally 0.4 g of volatile concentrate having a pronounced canned corn aroma was obtained after removal of the hexane solvent. The concentrate was analysed directly by GLC (HP-5830A) using a 2 m x 0.2cm id stainless steel column packed with 80-100 mesh SP-1000 with N 2 gas as a carrier gas. The GLC conditions used are given in Fig. 1. In order to determine the odour characteristic of each chromatographic peak, a sniffing device (Acree et al., 1976) was used on a Packard gas chromatograph Model 800 equipped with the same column material. Identification of compounds was accomplished by using a Varian 1400 gas chromatograph interfaced to a Bendix 12 Time of Flight mass spectrometer.

RESULTS AND DISCUSSION

Figure 1 shows a typical chromatogram of volatiles from canned sweet corn. The characteristic odour of canned sweet corn (for both varieties) was located in the peaks having retention times of 18.4 and 23.0 min. Most other peaks possessed an undesirable odour usually described as 'harsh', 'green' or 'oxidised oil'. Therefore, no attempt was made to identify these compounds. The first peak was identified as 2,5-dimethyl pyrazine (DMP) whose mass spectrum (molecular ion 108, other important ions at 42, 39, 40, 81, 109 and 91) and G LC retention time were consistent with that of an authentic sample. The second peak was identified as 3,6-dimethyl-2- ethyl pyrazine (DMEP) with a mass spectrum (molecular ion 136, other major ions at 135, 42, 39, 108, 56 and 91) and GLC retention time which coincided with that of the authentic compound. These and other pyrazine compounds have been found in many other processed food products (Maga & Sizer, 1973), including potatoes (Deck & Chang, 1965; Buttery et al., 1971) and roasted peanuts (Mason et al., 1966). Koehler et al. (1969) have shown that the amino acid-glucose reaction in model systems produces a large amount of DM P and D M EP. It is generally conceded that pyrazine compounds are generated during the thermal processing of foods. The essence extracted from fresh sweet corn in this study did not show any detectable amounts of DMP and DMEP. Since sweet corn contains an appreciable amount of free amino acids and sugars, it is concluded that the two important pyrazine compounds identified in canned sweet corn were produced by the reaction of these substances during the course of canning.

322 c . v . LEE

REFERENCES

ACREE, T. E., BUTTS, R. M., NELSON, R. R. & LEE, C. Y. (1976). Sniffer to determine the odor ofgas chromatographic effluents, Anal. Chem., 48, 1821.

BILLS, D. C. & KEENAN, T. W. (1968). Dimethyl sulfide and its precursor in sweet corn, J. Agric. Food Chem., 16, 643-5.

BUTTERY, R. G., SEIFERT, R. M., GUADAGNI, D. G. & LING, L. C. (1971). Characterization of volatile pyrazine and pyridine compounds of potato chips, J. Agr&. Food Chem., 19, 969-71.

DECK, R. Z. & CHANG, S. S. (1965). Identification of 2,5-dimethyl-pyrazine in the volatile flavor compounds of potato chips, Chem. & lndust. (London), 1343--44.

DRAVNIEgS, A., REILICH, H. G., WHITFIELD, J. & WATSON, C. A. (1973). Classification of corn odor by statistical analysis of gas chromatographic patterns of headspace volatiles, J. Food Sci., 38, 34--9.

FLATH, R. A. & FORREY, R. R. (1977). Volatile components of papaya (Carica papaya L. solo variety), J. Agric. Food Chem., 25, 103-9.

FLORA, L. F. & WILEY, R. C. (1974). Influence of cultivar, process, maturity, and planting data on the dimethyl sulfide and hydrogen sulfide levels in sweet corn, J. Agric. Food Chem., 22, 816-19.

HOUGEN, F. W., QUILLIAM, M. A. & CURRAN, W. A. (1971). Headspace vapors from cereal grains, J. Agric. Food Chem., 19, 181-3.

KOEHLER, P. E., MASON, M. E. & NEWELL, J. A. (1969). Formation of pyrazine compounds in sugar- amino model systems, J. Agric. Food Chem., 17, 393-6.

MA.GA, J. A. & SIZER, C. E. (1973). Pyrazines in foods. A review, J. Agric. Food Chem., 21, 22-30. MASON, M. E., JOHNSON, B. & HAMMING, M. 0966). Flavor components of roasted peanuts. Some low

molecular weight pyrazines and a pyrrole, J. Agric. Food Chem., 14, 454-60. M CKEAG, R. C. & HOUGEN, F. W. (1977). Varietal differences in aroma essence from maize kernels (Zea

mays L.), J. Agric. Food Chem., 25, 417-18. SELF, R., CASEY, J. C. & SWAIN, T. (1963). The low-boiling volatiles of cooked foods, Chem. & lndust.

(London), 863-4. WALRADT, J. P., LINDSAY, R. C. & LIaBEY, L. M. (1970). Popcorn flavor: Identification of volatile

compounds, J. Agric. Food Chem., 18, 926-8. WILLIAMS, M. P. d~ NELSON, P. E. 0973). Effect of hybrids and processing on the dimethyl sulfide

potential of sweet corn, J. Food Sci., 38, 1136-8.

C. Y. LEE,

Department o f Food Science and Technology, New York State Agricul tural Exper imen t Stat ion,

Cornell University, Geneva, N Y 14456, USA