VOLATILE COMPOUNDS GENERATED FROM THERMAL-DEGRADATION OF ALLIIN AND DEOXYALLIIN IN AN AQUEOUS-SOLUTION

Aqueous solutions of alliin, one of the major flavor precursors of garlic, and deoxyalliin, one of the thermal degradation products of gamma-glutamyl-S-allylcysteine, which also is one of the major flavor precursors of garlic, were dissolved in water and heated in a closed system at 180 degrees C under different pH conditions. The volatile flavor compounds generated were isolated by Likens-Nickerson simultaneous distillation/solvent extraction and quantified and identified by GC and GC-MS. The major volatile compounds generated from the degradation of alliin at pH 3, 7, and 9 were allyl alcohol and acetaldehyde. At pH 5, the major volatile compounds generated from the degradation of alliin were acetaldehyde, 2-acetylthiazole, sulfur dioxide, ethyl acetate, and 1-propene. The major volatile compounds generated from the degradation of deoxyalliin at pH 5, 7, and 9 were diallyl sulfide, 2-methyl-1,4-dithiepane, (allylthio)acetic acid, diallyl disulfide, 2-ethyl-1,3-dithiane, 4,6-dimethyl-1,2,5-trithiepane,3,6-dimethyl-1,4-dithiane, and allyl mercaptan. At pH 3, the major volatile compounds generated from the degradation of deoxyalliin were (allylthio)acetaldehyde, 3-(allylthio)propanal, 3,6-dimethyl-1,2,5-trithiepane, and (allylthio)acetic acid.