Chapter 10
Thermal Decomposition of Alliin, the Major Flavor Component of Garlic, in an Aqueous Solution 1
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Downloaded by UNIV OF ARIZONA on December 17, 2012 | http://pubs.acs.org Publication Date: December 20, 1993 | doi: 10.1021/bk-1994-0546.ch010
Tung-Hsi Yu , Chi-Kuen Shu , and Chi-Tang Ho
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Department of Food Science, Cook College, Rutgers, The State University of New Jersey, New Brunswick, NJ 08903 Bowman Gray Technical Center, R.J. Reynolds Tobacco Company, Winston-Salem, NC 27102 2
Aqueous solutions of alliin, the major flavor precursor of garlic, were heated in a closed system at 180°C under different pH conditions. The volatile flavor compounds generated were isolated by Likens-Nickerson simultaneous steam distillation/solvent extraction and quantified and identified by G C and GC-MS. A total of 49 volatile compounds were identified in this study. Except allyl alcohol and acetaldehyde, the majority of compounds identified were sulfur-containing compounds. A mechanism for the initial transformation of alliin to allyl alcohol and cysteine and further decomposition of cysteine was proposed which could explain the formation of many sulfur-containing compounds such as methyl sulfides, thiazoles, trithiolanes and dithiazines in this study.
Intact garlic cloves contain alliin (S-allylcysteine 5-oxide), a colorless and odorless compound. It is also well-known that the enzyme allinase, which is activated when the cellular tissue of garlic is disrupted, converts alliin to allicin (7). Boiling the garlic bulb or homogenizing the garlic bulb with alcohol containing limited quantities of water deactivates the enzyme; alliin is not converted to allicin and no pungent odor can be detected from the garlic samples (1,2). Allicin is very unstable and can be converted to allyl sulfides and dithiins, which contribute to the flavor of garlic products (1,3-6). pH and/or thermal effects on the volatile decomposition compounds of allicin, garlic homogenate, garlic oil and diallyl disulfide have been studied (5,7-77), but the thermal effects on the volatiles formed from the decomposition of alliin have not been studied. Several papers discuss the content of alliin in garlic products. Stoll and Seebeck (72) reported that intact garlic contains 0.24% (w/w) alliin. Iberl et al. (13) found that the alliin content in fresh garlic bulbs from different origins was approximately 0.9%. Ziegler and Sticher (14) reported that the alliin content in various garlic samples, including fresh garlic, dried extracts and garlic preparations ranges from
