Mutagens Produced by Heating Foods - American Chemical Society

28 Mutagens Produced by Heating Foods M. NAGAO, S. SATO, and T. SUGIMURA

Downloaded by UNIV LAVAL on July 13, 2016 | http://pubs.acs.org Publication Date: April 29, 1983 | doi: 10.1021/bk-1983-0215.ch028

National Cancer Center Research Institute, Biochemistry Division, 1-1, Tsukiji 5-chome, Chuo-ku, Tokyo, 104 Japan

G r i l l i n g fish or meat on a naked gas flame or an electric hot plate produced mutagens. Mutagenic activity of such products to S. typhimurium TA98 in the presence of S9 mix increased with an increase of cooking time. 2-Amino-3-methylimidazo[4,5-f]quinoline (IQ) and 2-amino-3,4dimethylimidazo[4,5-f]quinoline (MeIQ) were identified as mutagens in sun-dried sardine g r i l l e d over a bare flame. From fried beef, 2-amino-3,8-dimethylimidazo[4,5-f] quinoxaline (MeIQx) was isolated as a mutagen. IQ and MeIQ induced diphtheria toxin-resistant mutation in Chinese hamster lung c e l l s . The presence of other mutagenic heterocyclic amines, which had been isolated from pyrolysates of amino acids and protein, was confirmed in cooked food. Some of them were proved to be carcinogenic. Roasting coffee beans resulted in the formation of genotoxic substance(s) towards E. coli, S. typhimurium, and Chinese hamster lung c e l l s . Methylglyoxal was identified as one of the major mutagens.

5

Humans have used f i r e f o r cooking since about 10 years ago. The presence of p o l y c y c l i c aromatic hydrocarbons i n b r o i l e d foods such as beefsteak and b r o i l e d f i s h has been reported (_1,2). The presence of genotoxic substances i n b r o i l e d foods other than t y p i c a l carcinogenic hydrocarbons was detected a f t e r the development of Ames Sa tmoneI la/mammalian-microsome t e s t (3). Charred p a r t s of b r o i l e d f i s h and meat showed mutagenicity towards Salmonella typhimuriiori TA98, a frameshift mutant of h i s t i d i n e auxotroph, i n the presence of S9 mix, a mixture of r a t l i v e r 1

0097-6156/83/0215-0521$06.00/0 © 1983 American Chemical Society

Waller and Feather; The Maillard Reaction in Foods and Nutrition ACS Symposium Series; American Chemical Society: Washington, DC, 1983.


522

M A I L L A R D REACTIONS

postmitochondrial supernatant f r a c t i o n and NADPH (4,5»). Products of p y r o l y s i s of proteins and amino acids also showed strong mutagenicity towards TA98 with S9 mix (6,7). Since mutagens i n pyrolyzed amino acids and b r o i l e d f i s h or meat have several common c h a r a c t e r i s t i c s ( s p e c i f i c induction of revertants of TA98, requirement of S9 to e x h i b i t mutagenicity, and b a s i c nature), we f i r s t t r i e d to i s o l a t e and determine the s t r u c t u r e s of mutagens from pyrolysates of amino acids which showed strong mutagenic a c t i v i t y ^ — t r y p t o p h a n , glutamic a c i d , l y s i n e , and o r n i t h i n e (8-11). Then the s t r u c t u r e s of mutagens i n b r o i l e d f i s h and meat were a l s o determined (12-15). A l l the mutagenic compounds i s o l a t e d from the various p y r o l y s i s products were h e t e r o c y c l i c amines with one exception. Carcinogenic a c t i v i t i e s of some of these mutagens were proved with long-term i n v i v o animal experiments. Heating carbohydrates also r e s u l t e d i n the formation of mutagens but the mutagenic p r o p e r t i e s were d i f f e r e n t from those produced by heating p r o t e i n foods, p r o t e i n s , or amino a c i d s . Mutagens from carbohydrates were d i r e c t - a c t i n g towards S. typhimurium TA100, a base-pair change mutant of h i s t i d i n e auxotroph. Mutagen(s) present i n coffee f e l l i n t h i s type (16,17). F r e s h l y brewed and i n s t a n t , r e g u l a r , and c a f f e i n e - f r e e coffees were a l l mutagenic. Mutagenic a c t i v i t y of coffee was produced by r o a s t i n g green coffee beans. Recently, a s s o c i a t i o n s between human pancreatic and ovarian cancer, and coffee intake were reported (18,19,20), although c o n t r a d i c t o r y reports are also a v a i l a b l e (21,22_) . Heating or cooking foods makes them e a s i l y d i g e s t i b l e , and increases t h e i r n u t r i t i o n a l value. However, heating foods can y i e l d various mutagens. I s o l a t i o n of mutagens from p y r o l y s i s products, and examination of t h e i r carcinogenic e f f e c t s on labor a t o r y animals, may be u s e f u l i n f i n d i n g a clue to human cancer prevention. Mutagenicity

of B r o i l e d F i s h and Meat

B r o i l i n g or g r i l l i n g f i s h and meat produces mutagens. Dimethyl s u l f o x i d e or methanol extracts of smoke condensates and charred parts of various f i s h obtained by g r i l l i n g were mutagenic to S. typhimurium TA98 i n the presence of S9 mix 04,5). Charred parts of beefsteak and the hamburger were also mutagenic (4,23). The mutagenic a c t i v i t i e s of methanol extracts of sun-dried sardine and hamburger increased with cooking time, as shown i n Figure 1. A naked gas flame and an e l e c t r i c hot p l a t e were used f o r cooking the f i s h and the hamburger, r e s p e c t i v e l y . B r o i l i n g sun-dried sardine and hamburger f o r 5-7 min and 15-20 min, r e s p e c t i v e l y , y i e l d e d the best t a s t e . Methanol e x t r a c t s of sun-dried sardine were 10 times as mutagenic as those of hamburger (Figure 1). The d i f f e r e n c e may not be due to the d i f f e r e n c e i n the q u a l i t y of p r o t e i n but to the water content (24) and the cooking method. 3



.

NAGAO E T A L .

Mutagens Produced

by Heating Foods

523

Cooking time (min) Figure 1. Mutagenicities of sun-dried sardine broiled over naked gas flame (a) and hamburger cooked in electric hamburger cooker (b). Methanol extracts of cooked materials were tested for their mutagenicities with S. typhimurium ΤΛ98 with or without S9 mix.


524

MAILLARD RE ACTIONS


Mutagens Isolated from P y r o l y s a t e s of Amino Acids and P r o t e i n , and from Cooked Foods During an e a r l y stage of our studies of mutagens i n cooked foods, we found that mutagens which mainly induced f r a m e s h i f t mutation i n the presence of S9 mix were produced by p y r o l y z i n g p r o t e i n s or amino acids (Table I ) . P y r o l y s i s of tryptophan, glutamic a c i d , l y s i n e , and o r n i t h i n e produced mutagenic a c t i v i t y which was stronger than that found f o r other amino a c i d s . From a basic f r a c t i o n of tryptophan p y r o l y s a t e , mutagenic compounds were p u r i f i e d and two c r y s t a l l i n e substances were obtained. T h e i r s t r u c t u r e s were determined, by X-ray c r y s t a l l o g r a p h y , to be 3-amino-l,4-dimethyl-5#-pyrido[4,3-2>]indole (Trp-P-1) and 3amino-l-methyl-5#-pyrido[4,3-2?]indole (Trp-P-2) (8). These s t r u c t u r e s were confirmed by chemical synthesis (8). S i m i l a r l y , the f o l l o w i n g compounds were i s o l a t e d : 2-amino-6-methyldipyrido[ l , 2 - a : 3 2 ^ i ] i m i d a z o l e (Glu-P-1) and 2-aminodipyrido[1,2-a 3 , 2 - d ] i m i d a z o l e (Glu-P-2), both from glutamic a c i d p y r o l y s a t e ; 3,4-cyclopentenopyrido[3,2-a]carbazole (Lys-P-1), from l y s i n e p y r o l y s a t e (10); 4-amino-6-methyl-l#-2,5,10,10b-tetraazafluoranthene (Orn-P-1), from o r n i t h i n e pyrolysate (11); and 2-amino5-phenylpyridine (Phe-P-1), from phenylalanine p y r o l y s a t e (8) . A l l these are new compounds. f

f

f

f

:

f

Table I. Mutagenic a c t i v i t y of condensate of smoke formed by p y r o l y s i s of biomacromolecules and of amino acids

Revertants/mg smoke condensate TA100 TA98 S 9 mix +S9 mix +S9 mix -S9 mix

Substrate pyrolyzed Lysozyme Histone DNA RNA Starch Vegetable o i l

8,311 5,012 278 83 0 0

0 0 0 0 0 0

2,319 1,311 170 0 70 85

0 0 0 0 338 0

Tryptophan Glutamic a c i d Lysine Ornithine Cysteine Valine

22,420 13,800 5,250 8,290 324 0.9

0 0 0 0 0 0

2,500 3,400 608 560 965 0

0 0 0 0 0 0

3

Adapted from Nagao, et a l * ( 6 ) and Kosuge, et a l . ( 6 0 ) a. Tar obtained by dry d i s t i l l a t i o n was subjected to t e s t .


28.

NAGAO E T A L .

Mutagens

Produced

by Heating

Foods

525

Yoshida et a l (25) i s o l a t e d 2-amino-9#-pyrido[2,3-2?]indole (AaC) and 2-amino-3-raethyl-9#-pyrido[2,3-2?]indole (MeAaC) from p y r o l y s a t e of soybean g l o b u l i n . From g r i l l e d sun-dried sardines, two mutagenic f r a c t i o n s were obtained with high performance l i q u i d chromatography using yBondapak C i e . Their s t r u c t u r e s were determined, by 270 MHz H-NMR and low- and h i g h - r e s o l u t i o n mass spectra, to be 2-amino3-methylimidazo[4,5-/]quinoline (IQ) and 2-amino-3,4-dimethylimidazo[4,5-/]quinoline (MelQ) (12,13,14). The s t r u c t u r e s of these new compounds were confirmed by chemical s y n t h e s i s . From f r i e d beef, another new compound, 2-amino-3,8-dimethylimidazo[4,5-/]quinoxaline (MelQx), was i s o l a t e d , and i t s s t r u c t u r e was confirmed by chemical synthesis (15). The s t r u c t u r e s of a l l the compounds i s o l a t e d from pyrolysates of amino acids and a p r o t e i n , and from cooked f i s h and meat, are shown i n Table I I . Q u a n t i t a t i v e analyses of these newly found mutagenic compounds i n cooked foods are important f o r estimating the hazards for humans. Although methods of a n a l y s i s have not been standardized yet, p a r t i a l p u r i f i c a t i o n of methanol e x t r a c t s of cooked foods with acid-base p a r t i t i o n , s i l i c a - g e l or Sephadex LH-20 column chromatography and high performance l i q u i d chromatography are recommended. For the i d e n t i f i c a t i o n of compounds, gas chromatography /mass spectrometry (GC/MS) with m u l t i p l e ion d e t e c t i o n (MID) and high performance l i q u i d chromatography monitored with fluororaetry are u s e f u l . One gram of b r o i l e d sun-dried sardine was found to contain 13.3 ng and 13.1 ng of Trp-P-1 and Trp-P-2, r e s p e c t i v e l y (26). Trp-P-1 was also detected i n beef g r i l l e d over a naked flame (27). A deuterium d i l u t i o n technique using a [ H ] C H d e r i v a t i v e as the standard compound made analyses more p r e c i s e . The amounts of IQ i n sun-dried sardine and f r i e d beef were 158 ng/g and 0.59 ng/g, r e s p e c t i v e l y (28). Q u a n t i t a t i v e analyses of mutagens i n cooked foods are summarized i n Table I I I .


X

2

3

Genotoxic A c t i v i t y of Pyrolyzed Products Trp-P-1, Trp-P-2, Glu-P-1, IQ, MelQ and MelQx were very strongly mutagenic to S. typhimurium TA98 (a frameshift mutant of h i s t i d i n e auxotroph which has plasmids pKMlOl) i n the presence of S9 mix. MelQ and MelQx were also s t r o n g l y mutagenic to S. typhimurium TA100 (a base-pair change mutant of h i s t i d i n e auxotroph which has plasmids pKMlOl) with S9 mix, but Trp-P-1, Trp-P2, and Glu-P-1 were not as strongly mutagenic to TA100. S p e c i f i c mutagenic a c t i v i t i e s of the compounds i s o l a t e d from p y r o l y s i s products i n c l u d i n g those of t y p i c a l carcinogens, are shown i n Table IV. I t i s i n t e r e s t i n g that S. typhimurium TA1535, which has the same genetic p r o p e r t i e s as TA100 except that i t lacks plasraid, did not respond to any of these p y r o l y s i s products. These p y r o l y s i s products were mutagenic towards Escherichia coli WP2 uvrA (trp , a base-pair change mutant), and t h e i r mutagenicities were enhanced by introducing plasmids pKMlOl t o E. coli WP2 uvrA (29).


526

MAILLARD

REACTIONS

Table I I . Mutagens i s o l a t e d from pyrolysates


Chemical name

Abbreviation

Source of isolation

Structure

3-Amino-1,4-dimethyl5#-pyrido[4,3-2?]indole

Trp-P-1

3-Amino-l-methyl-5#pyridof 4,3-2?] i n d o l e

Trp-P-2

2-Amino-6-methyldipyrido[ 1,2-a: 3\2'-d] imidazole

Glu-P-1

2-Aminodipyridο[1,2-a: 3 \ 2'-d] imidazole

Glu-P-2

Glutamic a c i d p y r o l y s a t e (9)

3,4-Cyclopentenopyrido[3,2-a]carbazole

Lys-P-1

Lysine p y r o l y s a t e (10)

4-Amino-6-methyl-l#2,5,10,10b-tetraazafluoranthene

Orn-P-1

2-Amino-5-phenylpyridine

Phe-P-1

2-Amino-9#-pyrid o[2,3-2?] i n d o l e

Aac

2-Amino-3-methyl9^-pyrido [2,3-2?] i n d o l e

MeAaC

2-Amino-3-methylimidazo[4,5- / ] q u i n o l i n e

IQ

2-Amino-3,4-dimethylimidazo[4,5-/]quinoline

MelQ

2-Amino-3,8-dimethylimidazo[4,5-/]quinoxaline

MelQx

γ

Tryptophan NH p y r o l y s a t e (8) 2

N

— f | ^ A ^ N H N

L

Tryptophan p y r o l y s a t e (8)

2

JL c C ^

Glutamic a c i d p y r o l y s a t e (9)

NH

Ornithine 2 p y r o l y s a t e (11)

^|T~f^ ]] ^N^

Phenylalanine p y r o l y s a t e (8)

N H 2

N^N H

^ / ^

Ν

^ Χ

Ν

^NH

^ Ν Η

Soybean g l o b u l i n p y r o l y s a t e (25)

2

Soybean g l o b u l i n p y r o l y s a t e (25)

2

H

I

Y

,N-CH

3

B r o i l e d sardine (12,13)

N-CH

B r o i l e d sardine

3

(12,13)

H C^ 3

N

N-CH

3

F r i e d beef (15)


28.

NAGAO E T AL.


Table III.

Food material Sun-dried sardine

Mutagens

Produced

by Heating

Example of q u a n t i t a t i v e analyses f o r i n cooked foods

Method of cooking Naked flame

Methods of identification and q u a n t i f i c a t i o n GC/MS with MID

527

Foods

mutagens

Mutagens i n cooked m a t e r i a l (ng/g) Trp-P-1 Trp-P-2

13.3 13.1

(26)

Sun-dried sardine

Naked flame

GC/MS with MID by a d d i t i o n of CD 3-substituted MelQ

IQ MelQ

158 72

Beef

E l e c t r i c hot plate

GC/MS with MID

IQ MelQx

0.59 2.4

Beef

Naked flame

I d e n t i f i e d by fluorescence and MF, quant i f i e d by GC/MS

Trp-P-1

53

(27)

Chicken

Naked flame

Fluorescence

AaC MeAaC

180 15

(61_)

Sun-dried cuttlefish

Naked flame

I d e n t i f i e d by UV, q u a n t i f i e d by MF

Glu-P-2

280

a . ng/g of raw beef b. ng/g of sun-dried m a t e r i a l


(28)

(28)

(62)

528

MAILLARD

Table IV. Mutagenic a c t i v i t i e s of mutagens i s o l a t e d p y r o l y s i s products and t y p i c a l carcinogens

REACTIONS

from


Mutagenic a c t i v i t y (revertants/yg) TA98 TA100 P y r o l y s i s product MelQ IQ MelQx Trp-P-2 Orn-P-l Glu-P-1 Trp-P-1 Glu-p-2 AaC MeAaC Lys-P-1 Phe-P-1

a

661,000 433,000 145,000 104,200 56,800 49,000 39,000 1,900 300 200 86 41

30,000 7,000 14,000 1,800 3,200 1,700 1,200 20 120 99 23

T y p i c a l carcinogen AF-2 AFBi 4NQ0 B[aJP DEN DMN

6,500 6,000 970 320 0.02 0.00

42,000 28,000 9,900 660 0.15 0.23

Mutagenicity was tested with optimal amount of S9. a. S9 at the rate of 150 y l / p l a t e was used. AF-2, 2 - ( 2 - f u r y l ) - 3 - ( 5 - n i t r o - 2 - f u r y l ) a c r y l a m i d e ; AFBi, a f l a t o x i n B i ; 4NQ0, 4 - n i t r o q u i n o l i n e 1-oxide; Β [aJP, benzota]pyrene; DEN, d i e t h y l n i t r o s a m i n e ; DMN, dimethylnitrosamine.


28.

NAGAO E T A L .

Mutagens

Produced

by Heating

529

Foods

P y r o l y s i s products were also found to induce prophage λ i n l y s o genic E. coli K12, s t r a i n GY5027 (30), by Inductest I I I , which was developed by Moreau et a l . (31) (Figure 2 ) . The genotoxic e f f e c t s of p y r o l y s i s products on cultured mammalian c e l l s were a l s o i n v e s t i g a t e d . Trp-P-1, Trp-P-2, IQ and MelQ were found to induce d i p h t h e r i a t o x i n - r e s i s t a n t mutants of Chinese hamster lung c e l l s i n the presence of S9 mix. The mutation frequencies were 33, 160, 40 and 38 per 10 s u r v i v o r s per yg of Trp-P-1, Trp-P-2, IQ and MelQ, r e s p e c t i v e l y (32). These mutagenic a c t i v i t i e s were comparable to those of benzo[ci]pyrene and methyl methanesulfonate. Trp-P-1, Trp-P-2, Glu-P-1, and AaC induced s i s t e r chromatid exchanges i n human lymphoid c e l l s , NL-3 (33). Trp-P-1, Trp-P-2, Glu-P-1, Glu-P-2, AaC, and MeAaC induced chromosome aberrations i n Chinese hamster f i b r o b l a s t s (34). Carcinogenic a c t i v i t i e s of p y r o l y s i s products were studied i n v i t r o and i n v i v o . Trp-P-1, Trp-P-2 (35_), and Glu-P-1 (36) induced malignantly transformed f o c i i n the embryonic c e l l s of cryopreserved Syrian golden hamsters. The i n vivo carcinogenic a c t i v i t i e s of Trp-P-1, Trp-P-2, Glu-P-1, Glu-P-2, AaC, and MeAaC were detected i n CDFi mice by feeding. Mice which were fed a d i e t containing 0.02% Trp-P-1 or Trp-P-2 f o r an e n t i r e l i f e span developed s p e c i f i c a l l y hepato c e l l u l a r carcinomas; females were more s u s c e p t i b l e than males (37) (Table V ) . Female r a t s but not males fed a d i e t containing 0.01% Trp-P-2 developed hemangioendothelial sarcoma and neoplas t i c nodules of the l i v e r (38).


6

Table V.

Numbers of CDF mice with hegatic tumors induced by Trp-P-1 and Trp-P2 X

Hepatocellular carcinoma

T o t a l jiepatic tumor (%)

Sex

No. e f f e c t i v e animals

Trp-P-1 (0.02%)

Male Female

24 26

4 14

5 (21) 16 (62)

Trp-P-2 (0.02%)

Male Female

25 24

3 22 (2°)

4 (16) 22 (92)

Control

Male Female

25 24

Treatment

0 0

1 ( 4) 0 ( 0)

a. Adapted from Matsukura et a l (37) (Copyright 1981 by the American A s s o c i a t i o n f o r the Advancement of Science) b. T o t a l hepatic tumor contains h e p a t o c e l l u l a r carcinomas, h e p a t o c e l l u l a r adenoma, and hemangioma. c. Two mice had metastasis to the lung.



530

MAILLARD

REACTIONS

^g/plate Figure 2. Phage-inducing activities of mutagens isolated from pyrolysates (E. coli GY5027 was used). Key (S9 at 10 pL/plate): A , MelQ; A, IQ; ·, Trp-P-1; O , Trp-P-2; and M, Glu-P-1. Key (S9 at 30 pL/plate): • , Glu-P-2. Key (S9 at 50 μΣ/plate): • , MeAaC; 0, AaC; and X, Lys-P-1.


28.

NAGAO E T A L .

Mutagens

Produced

by Heating

531

Foods

Mice fed a d i e t containing 0.05% of Glu-P-1 or Glu-P-2, or 0.08% of MeAaC, mainly developed hepatic tumors and hemangiosarcomas i n the brown f a t t i s s u e of the i n t e r s c a p u l a (39). The incidence of hepatic tumors produced by these three compounds was higher i n females than i n males, but the incidence of hemangiosarcoma i n males and females was s i m i l a r . AaC a l s o induced hepatic tumors and hemagiosarcomas by feeding.


Mutagens i n Coffee F r e s h l y brewed and i n s t a n t , r e g u l a r , and c a f f e i n e - f r e e coffees were mutagenic to S. typhimurium TA100 without S9 mix (16,17). The a d d i t i o n of S9 mix abolished or reduced mutagen icity. E. coli WP2 mtfVl/pKMlOl also responded to these types of c o f f e e , but those s t r a i n s which had no plasmids, such as S. typhimurium

TA1535 and E.

coli

WP2

uvrA,

d i d not.

All

coffees

a l s o induced prophage λ i n E. coli K12, s t r a i n GY5027 (Table V I ) . One cup of coffee contained mutagens which induced 4-10 x 1 0 revertants of S. typhimurium TA100 by the Ames method (3) with some m o d i f i c a t i o n s (40). One cup of coffee i s equivalent to 800 y g of W-methyl-# -nitro-W-nitrosoguanidine i n prophage λ-inducing a c t i v i t y . These genotoxic a c t i v i t i e s were shown t o be produced by r o a s t i n g coffee beans; coffee prepared from green c o f f e e beans d i d not show any mutagenic a c t i v i t y or prophage λ-inducing a c t i v i t y (41). Recently, some of the mutagenic compounds i n coffee have been i d e n t i f i e d . They are dicarbonyl compounds, methylglyoxal, d i a c e t y l and g l y o x a l (42). One gram of i n s t a n t c o f f e e contains 150 yg of methylglyoxal and 100 yg of d i a c e t y l and g l y o x a l . S p e c i f i c mutagenic a c t i v i t y of methylglyoxal was highest among these, and one mg of methylglyoxal induced 1 10 revertants of TA100. Mutagenic a c t i v i t i e s of d i a c e t y l and g l y o x a l are much 4

f

x

Table VI.

Amount (mg/plate) Instant

Genotoxicity

5

of coffee i n b a c t e r i a

Mutagenicity ( r e v e r t a n t s / p l a t e ) S. typhvmurium E. coli WP-2 TA100 TA1535 ww?i4/pKM101 uvrA

Phage-inducing activity (plaques/plate)

coffee 0 2 5 10 20 50

89 225 361 621

59 40 51 60

58 97 106 127

17 23 18 19

22

46 146 576


532

MAILLARD

Table V I I .

E f f e c t s of s u l f i t e on the mutagenicity and phage-inducing a c t i v i t y of c o f f e e

Revertants/10 Coffee (mg/plate)

None

8

survivors Sodium , sulfite


0

3

Coffee (mg/plate)

Plaques/plate Sodium , sulfite None

Instant "caffeine- free"

Instant "regular" 2.5 5.0 7.5 10.0

REACTIONS

43 120 238 365

0 0 0 0

2 10 20

8 93 305

23 37 52

a. S. typhimurium TA100 was used. The number of spontaneous revertants (163) was subtracted. b. 300 yg of s u l f i t e were added. c. E. coli GY5027 was used. The number of spontaneous plaques (62) was subtracted.

l e s s , being 360 and 9,000 r e v e r t a n t s per mg, r e s p e c t i v e l y . This i s i n accordance with a paper by other i n v e s t i g a t o r s (43). A simple c a l c u l a t i o n suggested that these d i c a r b o n y l compounds can account f o r about h a l f of the mutagenicity of c o f f e e . Both regular and c a f f e i n e - f r e e instant c o f f e e s , without S9 mix, also induced d i p h t h e r i a t o x i n - r e s i s t a n t mutants of Chinese hamster lung c e l l s (44). I t i s urgent that c a r c i n o g e n i c i t y of methylglyoxal be tested with animals. Mutagenic a c t i v i t y and phage-inducing a c t i v i t y of c o f f e e were suppressed by s u l f i t e or b i s u l f i t e (45). Both a c t i v i t i e s can be suppressed by adding about 300 ppm of s u l f i t e or b i s u l f i t e to c o f f e e served at home (Table V I I ) . S u l f i t e and b i s u l f i t e have already gained wide acceptance as food p r e s e r v a t i v e s and a n t i oxidants. However, a s c o r b i c a c i d , which i s also a reducing agent, enhanced the mutagenicity of i n s t a n t c o f f e e s e v e r a l f o l d . Epidemiological studies showed p o s i t i v e a s s o c i a t i o n of coffee d r i n k i n g and cancers of pancreas and ovary (18,19,20), although reports d e s c r i b i n g negative a s s o c i a t i o n are also a v a i l able (21^22). In an experimental animal study, no carcinogenic a c t i v i t y of c o f f e e was reported (46,47). However, t h i s data should be reconsidered i n terms of the genotoxic a c t i v i t i e s of coffee revealed i n b a c t e r i a and c u l t u r e d mammalian c e l l s . Discussion The Salmonella mutagenicity test i s a very powerful method for d e t e c t i n g genotoxic substances i n crude m a t e r i a l s , i n c l u d i n g



28.

NAGAO E T A L .

Mutagens

Produced

by Heating

Foods

533

cooked foods. We have already i d e n t i f i e d 10 new compounds from pyrolysates of amino acids and cooked foods. Among those, a l l 6 compounds which we tested were proved to be c a r c i n o g e n i c . However, there was no q u a n t i t a t i v e c o r r e l a t i o n between the c a r c i nogenic potency of these compounds and the mutagenic a c t i v i t y to Salmonella. Information on the carcinogenic potency of IQ, MelQ, and MelQx, which were i s o l a t e d from cooked foods, i s e s p e c i a l l y important f o r estimating the hazards that cooked foods hold f o r humans, and animal experiments with these three compounds are now under way i n our laboratory. Most mutagens are carcinogenic i n long-term animal t e s t s (48,49,50), but we observed exceptional cases i n which mutagens were not carcinogenic. For instance, quercetin, which i s widely d i s t r i b u t e d i n vegetables, i s moderately mutagenic towards b a c t e r i a (51-54) and cultured mammalian c e l l s (55,56). Never t h e l e s s , i n t e n s i v e studies i n Japan f a i l e d to demonstrate c a r c i nogenicity (57,58,59). There have been many epidemiological studies on coffee intake and human cancer. Since we have i n d e n t i f i e d one of major genotoxic substance i n c o f f e e , thorough experimental studies are urgently required to evaluate the hazards of c o f f e e . Acknowledgements This work was supported i n part by Grants-in-Aid f o r Cancer Research from the M i n i s t r y of Education, Science, and Culture, and the M i n i s t r y of Health and Welfare of Japan, and by a grant from the Nissan Science Foundation. Literature Cited 1. 2. 3. 4. 5.

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Mutagens Produced by Heating Foods - American Chemical Society

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