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Graduate Program in Nutrition and Nutrition Department, The Pennsylvania State University, University Park, PA 16802
2To whom correspondence should be addressed at National Science Research Group, National Cancer Institute, Division of Cancer Prevention, 6130 Executive Blvd., EPN 212, Rockville, MD 20892. E-mail: milnerj{at}mail.nih.gov.
ABSTRACT
Allyl sulfur compounds are the major active constituents found in crushed garlic. Research has revealed that garlic and its lipid- or water-soluble components have many pharmacologic properties; however, studies also demonstrate that heating has a negative influence on these beneficial effects. We recently conducted several studies to investigate the influence of microwave or oven heating on the anticarcinogenesis property of garlic. Our studies showed that as little as 60 s of microwave heating or 45 min of oven heating can block garlic’s ability to inhibit in vivo binding of mammary carcinogen [7,12-dimethylbenzene(a)anthracene (DMBA)] metabolites to rat mammary epithelial cell DNA. Allowing crushed garlic to "stand" for 10 min before microwave heating for 60 s prevented the total loss of anticarcinogenic activity. Our studies demonstrated that this blocking of the ability of garlic was consistent with inactivation of alliinase. These studies suggest that heating destroyed garlic’s active allyl sulfur compound formation, which may relate to its anticancer properties.
KEY WORDS: • garlic • heating • DNA adducts
Garlic (Allium Sativum L.) is cultivated worldwide and its
potential medical properties have been recognized for thousands of
years. Garlic has acquired a reputation in many cultures as a
formidable prophylactic and therapeutic medical agent. Many recent
studies have demonstrated garlic’s pharmacologic effects, such as
antibacterial, antifungal, hypolipidemic, hypoglycemic,
antiothrombotic, antioxidant and anticancer properties (Bordia et al. 1975
, Conner et al. 1984
, Imai et al. 1994
, Lawson et al. 1992
, Mathew and Augusti 1973
, Rees et al. 1993
).
The evidence of an anticarcinogenic role for garlic comes from both
epidemiologic and laboratory investigations. A decade ago, for example,
a study from China indicated an inverse relationship in mortality
between stomach cancer and garlic consumption (Wei et al. 1988
), providing the first evidence of garlic’s anticancer
potential. The results of this study were corroborated by a study
conducted in Italy (Buiatti et al. 1989
). Similarly, a
lower risk of colon cancer for American consumers of garlic was
reported in the Iowa Woman’s Health Study (Steinmetz et al. 1994
). Although the minimum daily intake required to reduce
cancer risk remains to be determined, garlic had been categorized as a
dietary anticarcinogen (Lau et al. 1990
).
Laboratory investigations have shown that both water- and
lipid-soluble sulfur compounds from garlic provide its
anticarcinogenic benefits (Hussain et al. 1990
,
Ip et al.1992
, Liu et al. 1992
,
Perchellet et al. 1990
, Rao et al. 1990
,
Reddy et al. 1993
, Schaffer et al. 1997
,
Sumiyoshi and Wargovich, 1990
). Animal research has
demonstrated further that the protection offered by garlic is not
limited to only a specific tissue or specific carcinogen, but can occur
in several tissues and as a result of treatment of different types of
carcinogens (Belman 1983
, Dion et al. 1997
, Hong et al. 1992
, Sadhana et al. 1988
, Schaffer et al. 1996
, Shenoy and Choughuley 1992
, Wargovich et al. 1988
).
Studies have also demonstrated that garlic powder and its associated
allyl sulfur compounds are effective at both the initiation and
promotion phases of the cancer process (Liu et al. 1992
). Although Phase I and Phase II enzymes in liver and other
target tissues affected by organosulfur compounds may be involved in
carcinogen metabolism (Devasagayam et al. 1982
,
Ip and Lisk 1997
, Schaffer et al. 1997
,
Sparnins et al. 1988
), additional studies were required
to explain the precise mechanism.
Garlic is a rich source of water- and lipid-soluble organosulfur compounds, but the constituents responsible for the health benefits of garlic may vary in type and concentration, depending on different processing, preparation and soil conditions. This paper briefly reviews organosulfur compounds found in garlic and the influence of heating on garlic’s benefits, especially on its anticancer ability.
Organosulfur compounds in garlic and their roles.
The remarkable, high sulfur content of garlic distinguishes it from
many other vegetables. Evidence from laboratory research suggests that
a large group of allyl sulfur compounds may be responsible for the
biological and medical functions of garlic (Augusti 1974 and1975
, Murthy and Amonkar 1974
,
Sparnins et al. 1988
, Wargovich 1987
,
Wargovich et al. 1988
, Yamada and Azuma 1977
). The major representatives of these allyl sulfur
compounds and their liaisons are shown in Table 1
and Figure 1
.
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-Glutamylcysteines serve as important storage compounds in garlic
cloves and have been shown to play a significant role in the production
of additional alliin during the early developmental stages of the
garlic plant (Lancaster and Shaw 1989
). Although
alliin has been reported to have antioxidant properties
(Rabinkov et al. 1988
), other studies have found that
alliin is unable to inhibit in vitro cholesterol biosynthesis
(Gebhardt 1993
). Similarly, we found that alliin was
ineffective in retarding 7,12-dimethylbenzene(a)anthracene
(DMBA)3
adducts in cancer prevention.
Chopping or crushing garlic releases alliinase, which rapidly converts
alliin (S-alkyl-L-cysteine sulfoxide)
to allicin (dialkly thiosulfinate) (Lawson 1993
). Alliin
is the parent compound of allicin, and allicin is the parent compound
of diallyl disulfide (DADS). Allicin is the major thiosulfinate
compound found in crushed garlic, but it is quite unstable and quickly
converts into diallyl sulfide (DAS), DADS, diallyl trisulfide (DATS)
and polysulfide compounds (Block 1985
). Allicin is not
only responsible for the characteristic odor of fresh garlic
(Whitaker 1976
), but is also considered one of the most
important biologically active compounds found in crushed or homogenized
garlic (Koch and Lawson 1994
). A number of therapeutic
applications of garlic involve allicin and compounds derived from it
(Augusti 1974 and1975
, Murthy and Amonkar 1974
, Sparnins et al. 1988
, Wargovich 1987
, Wargovich et al. 1988
, Yamada and Azuma 1977
). Allicin and allicin potential have been used
commercially as indices to evaluate and compare the medical value of
commercially available prepared garlic. During the alcoholic
fermentation of garlic, such as in some deodorized commercial
preparations, S-allylcysteine (SAC) is converted from
-glutamyl-S-allylcysteine, a precursor of alliin.
Although experiments have shown SAC to be an active compound found in
garlic, its presence in whole garlic cloves is variable and has been
ignored by researchers.
Alliinase (EC 4.41.4), a glycoprotein, is responsible for the
conversion of alliin to allicin. Alliinase can be activated only when
garlic cloves are crushed or cut; like other enzymes, it is
thermolabile (Jansen et al. 1989
). When alliinase is
inactivated by heating, the cascade of thiosulfinate formation is
blocked from alliin, and allicin and its derivatives cannot be formed.
Our research has shown that as little as 60 s of microwave heating
can totally destroy alliinase enzyme activity, whereas microwave
heating for 30 s inhibited 90% of alliinase activity compared
with unheated garlic.
Heating and its negative effect on garlic’s performance.
Heating can have different effects on food component viability.
Lycopene bioavailability, for example, has been shown to improve by
heating tomato in oil (Stahl and Sies 1992
). However,
Chen et al. (1985)
found that boiling garlic at 100°C
for 20 min completely suppressed its antibacterial activities. Research
also showed that increasing the temperature from 60 to 100°C produced
a significant decrease in the inhibitory effect of garlic bulbs against
the fungi tested (Yin and Cheng 1998
). Although garlic
has been suggested for many years by epidemiology and laboratory
experiments to have cardiovascular benefits, these health effects are
lost in heat-treated garlic. In a recent study (Bordia et al. 1996
), a dose-dependent inhibition of serum thromboxane
B2 (TXB2) concentration was
observed in rats treated with aqueous extracts of raw garlic. However,
boiled garlic extracts had little effect on TXB2
synthesis, even at a high concentration. Ali (1995)
also
found that boiled garlic had little effect on inhibition of
cyclooxygenase activity in rabbit tissue compared with raw garlic.
Similarly, heating garlic to 100°C for 20, 40 or 60 min can reduce
its antioxidant activity (Prasad et al. 1996
). A more
complete list of the effects of heating on garlic’s functioning can be
found in Table 2
.
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Heating blocks the anticancer ability of garlic.
Research has revealed that garlic powder and its water- or
lipid-soluble allyl sulfur compounds can protect against chemically
induced experimental animal tumors (Amagase and Milner 1993
, Amagase et al.1996
). In our recent studies
(Fig. 2
), supplements with raw garlic given by gastric gavage reduced
DMBA-induced DNA adduct formation by 64%. Microwave treatment of
garlic for 30 s did not influence the degree of protection;
however, garlic crushed or not crushed before microwave heating for
30 s resulted in a 62 and 61% reduction, respectively, in adduct
formation. Microwaving uncrushed garlic for 60 s completely
blocked the ability of garlic to suppress the adduct formation.
Crushing and immediately microwaving for 60 s similarly blocked
the protection offered by garlic. However, maintaining crushed garlic
at room temperature for 10 min before 60 s of microwave heating
partially restored the anticarcinogenic properties, although the
protection was 30% less than that for unmicrowaved garlic. Similarly,
oven-heated whole garlic (garlic without cutting the top) for 45
min thoroughly obstructed the anticarcinogenic benefit of garlic. If
intact garlic was cut at the top and allowed to "stand" for 10 min
before oven heating, it still maintained partial protection
compared with unheated garlic. Additional study showed that SAC and
DADS could decrease the formation of DNA adducts, whereas isomolar
alliin did not alter the occurrence of adduct formation (Fig. 3
).
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Summary
These studies reveal that garlic’s benefits are lost due to the
heating process. According to Ali (1995)
, the reason
that boiled garlic has little effect on cyclooxygenase activity may be
related to the fact that the active component of raw garlic is
destroyed upon heating. Our studies demonstrated that the loss of
protection against DMBA-induced adducts due to heating may be
related to a loss of alliinase activity. The present studies reveal
that after garlic is heated for 30 s in a microwave oven, only
10% of its original alliinase activity remained. It is possible
that this residual alliinase was sufficient to convert alliin to active
compounds and to continue garlic’s ability to alter the occurrence of
DNA adducts. However, 60 s of heating in a microwave not only
resulted in almost undetectable alliinase activity but also
eliminated garlic’s ability to suppress DMBA-induced DNA-adduct
formation. It remains to be determined whether there is a direct link
between depression of alliinase activity and the loss of the ability to
alter DMBA bioactivation. Furthermore, our studies give evidence that
10 min "standing" time after crushing garlic is necessary for
the biologically active generation of compounds to reduce the blunting
effects of heating.
Although garlic is known for its many pharmaceutical effects, these abilities can be depressed by preparation or processing methods. The negative influence of heating may be related to suppression of the activity of the enzyme alliinase. Additionally, our studies suggest that the generation of biologically active allyl sulfur compounds is dependent not only on total alliinase activity, but also the time for which it is allowed to function.
FOOTNOTES
1 Presented at the conference "Recent Advances on the Nutritional Benefits Accompanying the Use of Garlic as a Supplement" held November 15–17, 1998 in Newport Beach, CA. The conference was supported by educational grants from Pennsylvania State University, Wakunaga of America, Ltd. and the National Cancer Institute. The proceedings of this conference are published as a supplement to The Journal of Nutrition. Guest editors: John Milner, The Pennsylvania State University, University Park, PA and Richard Rivlin, Weill Medical College of Cornell University and Memorial Sloan-Kettering Cancer Center, New York, NY. 
3 Abbreviations: DADS, diallyl disulfide; DAS, diallyl sulfide; DATS, diallyl trisulfide; DMBA, 7,12-dimethylbenz(a)anthracene; SAC, S-allylcysteine; TXB2, thromboxane B2.
REFERENCES
1. Ali M. Mechanism by which garlic inhibits cyclooxygenase activity. Effect of raw versus boiled garlic extract on the synthesis of prostanoids. Prostaglandins Leukot. Essent. Fatty Acids 1995;53:397-400[Medline]
2. Ali M., Angelo-Khattar M., Farid A., Hassan R. A., Thulesius O. Aqueous extracts of garlic (Allium sativum) inhibit prostaglandin synthesis I the ovine ureter. Prostaglandins Leukot. Essent. Fatty Acids 1993;49:855-859[Medline]
3.
Amagase H., Milner J. A. Impact of various sources of garlic and their constituents on 7,12-dimethylbenz(a)anthracene binding to mammary cell DNA. Carcinogenesis 1993;14:1627-1631
4. Amagase H., Schaffer E. M., Milner J. A. Dietary components modify garlic’s ability to suppress 7,12-dimethylbenz(a)anthracene induced mammary DNA adducts. J. Nutr. 1996;126:817-824
5. Augusti K. T. Lipid lowering effects of allicin (diallyl disulfide-oxide) on long term feeding to normal rats. Experientia 1974;30:468-470[Medline]
6. Augusti K. T. Studies on the effect of allicin (diallyl disulfide-oxide) on alloxan diabetes. Experientia 1975;31:1263-1265
7.
Belman S. Onion and garlic oils inhibit tumor promotion. Carcinogenesis 1983;4:1063-1065
8. Block E. The chemistry of garlic and onions. Sci. Am. 1985;252:114-119[Medline]
9. Bordia A., Bansal H. C., Arora S. K., Singh S. V. Effect of essential oils of garlic and onion on alimentary hyperlipidemia. Atherosclerosis 1975;21:15-19[Medline]
10. Bordia T., Mohammed N., Thomson M., Ali M. An evaluation of garlic and onion as antithrombotic agents. Prostaglandins Leukot. Essent. Fatty Acids 1996;54:183-186[Medline]
11. Buiatti E., Palli D., Decarli A., Amadori D., Avellini C., Bianchi S., Biserni R., Cipriani F., Cocco P., Giacosa A., Marubini E., Puntoni R., Vindigni C., Fraumeni J., Blot W. A case-control study of gastric cancer and diet in Italy. Int. J. Cancer 1989;44:611-616[Medline]
12. Cellini L., Di Campli E., Masulli M., Di Bartolomeo S., Allocati N. Inhibition of Helicobacter pylori by garlic extract (Allium sativum) FEMS Immunol. Med. Microbiol. 1996;13:273-277
13. Chen H. C., Chang M. D., Chang T. J. Antibacterial properties of some spices plants before and after heat treatment. Chung-Hua Min Kuo Wei Sheng Wu Chi Mien I Hsuech Tsa Chih 1985;18:190-195
14. Conner D. E., Beuchat L. R., Worthington R. E., Hitchcock H. L. Effects of essential oils and oleoresins of plants on ethanol production, respiration and sporulation of yeast. Int. J. Food Microbiol. 1984;1:63-74
15. Devasagayam T. P. A., Pushpendran C. K., Eapen J. Diallyl disulphide induced changes in microsomal enzyme of suckling rats. Indian J. Exp. Biol. 1982;20:430-432[Medline]
16. Dion M. E., Agler M., Milner J. A. S-Allyl cysteine inhibits nitrosomorpholine formation and bioactivation. Nutr. Cancer 1997;28:1-6[Medline]
17. Gebhardt R. Multiple inhibitory effects of garlic extracts on cholesterol biosynthesis in hepatocytes. Lipids 1993;28:613-619[Medline]
18.
Hong J. Y., Wang Z. Y., Smith T. J., Zhou S., Shi S., Pan J., Yang C. S. Inhibitory effects of diallyl sulfide on the metabolism and tumorigenicity of tobacco-specific carcinogen 4-methylnitrosamino-1–3-pyridyl 1-butanone (NNK) in A/J mouse lung. Carcinogenesis 1992;13:901-904
19. Hussain S. P., Jannu L. N., Rao A. R. Chemopreventive action of garlic on methylcholanthrene-induced carcinogenesis in the uterine cervix of mice. Cancer Lett 1990;49:175-180[Medline]
20. Imai J., Ide N., Nagae S., Moriguchi T., Matsuura H., Itakura Y. Antioxidant and radical scavenging effects of aged garlic extract and its constituents. Planta Med 1994;60:417-420[Medline]
21. Ip C., Lisk D. J. Modulation of phase I and phase II xenobiotic-metabolizing enzyme by selenium-enriched garlic in rats. Nutr. Cancer 1997;28:184-188[Medline]
22. Ip C., Lisk D. J., Stoewsand G. S. Mammary cancer prevention by regular garlic and selenium-enriched garlic. Nutr. Cancer 1992;17:279-286[Medline]
23. Jansen H., Muller B., Knobloch K. Characterization of an alliin lyase preparation from garlic (Allium sativum). Planta Med 1989;55:434-439[Medline]
24. Koch H. P., Lawson L. D. Gaelic, the science and therapeutic application of Allium Sativum L, and related species 1994 Williams & Wiklins Baltimore, MD.
25. Lancaster J. E., Shaw M. L. Gamma-glutamyl peptides in the biosynthesis of S-alk(en)yl-L-cysteine sulphoxides (flavour precursors) in allium. Phytochemistry 1989;28:455-460
26. Lau B.H.S., Tadi P. P., Tosk J. M. Allium sativum (garlic) and cancer prevention. Nutr. Res. 1990;10:937-948
27. Lawson L. D. Bioactive organosulfur compounds of garlic and garlic products: role in reducing blood lipids. Chem. Abst. 1993;119:216-660
28. Lawson L. D., Ranson D. K., Hughes B. G. Inhibition of whole blood platelet aggregation by compounds in garlic clove extracts and commercial garlic products. Thromb. Res. 1992;65:141-156[Medline]
29.
Liu J. Z., Lin R. I., Milner J. A. Inhibition of 7,12-dimethylbenz(a)anthracene-induced mammary tumors and DNA adducts by garlic powder. Carcinogenesis 1992;13:1847-1851
30. Mathew P. T., Augusti K. T. Isolation of hypo- and hyperglycaemic agents from Allium cepa Linn. Indian J. Exp. Biol. 1973;11:573-575[Medline]
31. Murthy N.B.K., Amonkar S. V. Effect of a natural insecticide from garlic (Allium sativum) and its synthetic form (allyl disulfide) on plant pathogenic fungi. Indian J. Exp . Biol. 1974;12:208-209
32. Perchellet J. P., Perchellet E. M., Belman S. Inhibition of DMBA-induced mouse skin tumorigenesis by garlic oil and inhibition of two tumor-promotion stages by garlic and onion oils. Nutr. Cancer 1990;14:183-193[Medline]
33. Prasad K., Laxdal V. A., Yu M., Raney B. L. Evaluation of hydroxyl radical-scavenging property of garlic. Mol. Cell. Biochem. 1996;154:55-63[Medline]
34. Rabinkov A., Miron T., Konstantinovski L., Wilchek M., Mirelman D., Weiner L. The mode of action of allicin: trapping of radicals and interaction with thiol containing proteins. Biochim. Biophys. Acta 1988;1379:233-244
35. Rao A. R, Sadhana A. S., Goel H. C. Inhibition of skin tumors in DMBA-induced complete carcinogenesis system in mice by garlic (Allium sativum). Indian J. Exp. Biol. 1990;28:405-408[Medline]
36.
Reddy B. S, Rao C. V., Rivenson A., Kelloff G. Chemoprevention of colon carcinogenesis by organosulfur compounds. Cancer Res 1993;53:3493-3498
37. Rees L. P., Minney S. F., Plummer N. T., Slater J. H., Skyrme D. A. A quantitative assessment of the antimicrobial activity of garlic (Allium sativum). World J. Microbiol. Biotechnol. 1993;9:303-307
38. Sadhana A. S., Rao A. R., Kucheria K., Bijani V. Inhibitory action of garlic oil on the inhibition of benzo[a]pyrene-induced skin carcinogenesis in mice. Cancer Lett 1988;40:193-197[Medline]
39. Schaffer E. M., Liu J. Z, Green J., Dangler C. A., Milner J. A. Garlic and associated allylsulfur components inhibit N-methyl-N-nitrosourea induced rat mammary carcinogenesis. Cancer Lett 1996;102:199-204[Medline]
40. Schaffer E. M., Liu J. Z., Milner J. A. Garlic powder and allyl sulfur compounds enhance the ability of dietary selenite to inhibit 7,12-dimethylbenz(a)anthracene-induced mammary DNA adducts. Nutr. Cancer 1997;27:162-168[Medline]
41. Shenoy N. R., Choughuley A.S.U. Inhibitory effect of diet related sulphydryl compounds on the formation of carcinogenic nitrosamines. Cancer Lett 1992;65:227-232[Medline]
42.
Sparnins V. L., Barany G., Wattenberg L. W. Effects of organosulfur compounds from garlic and onions on benzo[a]pyrene-induced neoplasia and glutathione S-transferase activity in the mouse. Carcinogenesis 1988;9:131-134
43. Stahl W., Sies H. Uptake of lycopene and its geometrical isomers is greater from heat-processed than from unprocessed tomato juice in humans. J. Nutr. 1992;122:2161-2166
44.
Steinmetz K. A, Kushi L. H, Bostick R. M, Folsom A. R., Potter J. D. Vegetables, fruit, and colon cancer in the Iowa woman’s health study. Am. J. Epidemiol. 1994;139:1-15
45.
Sumiyoshi H., Wargovich M. J. Chemoprevention of 1,2-dimethylhydrazine-induced colon cancer in mice by naturally occurring organosulfur compounds. Cancer Res 1990;50:5084-5087
46.
Wargovich M. J. Diallyl sulfide, a flavor component of garlic (Allium sativum), inhibits dimethylhydrazine-induced colon cancer. Carcinogenesis 1987;8:487-489
47.
Wargovich M. J., Woods C., Eng V. W., Stephens L. C., Gray K. Chemoprevention of N-nitrosomethylbenzylamine-induced esophageal cancer in rats by the naturally occurring thioether, diallyl sulfide. Cancer Res 1988;48:6872-6875
48.
Wei C. Y., Blot W. J., Chang Y.S., Ershow A. G., Yang Z. T., An Q., Henderson B., Xu G. W., Fraumeni J., Wang T. G. Diet and high risk of stomach cancer in Shandong, China. Cancer Res 1988;48:3518-3523
49. Whitaker J. R. Development of flavor, odor and pungency in onion and garlic. Adv. Food Res. 1976;22:73-133
50.
Yamada Y., Azuma K. Evaluation of the in vitro antifungal activity of allicin. Antimicrob. Agents Chemother. 1977;11:743-749
51. Yin M. C., Cheng W. S. Inhibition of Aspergillus niger and Aspergillus flavus by some herbs and spices. J. Food Prot. 1998;61:123-125[Medline]
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