Synthesis, Transformation And Stability Of Allicin

Firstly, ozone was used as oxidant to oxidate diallyl disulfide(DADS) to be allicin, and the effects of four key acting factors(i.e., temperature, time, and reactant concentration and ozone flow) on the productivity of allicin were investigated. Results showed that the productivity of allicin was increased when the reaction time was extended; however, when the reaction time exceeded four hours, the byproducts started generating; the productivity of allicin was first increased and then decreased with the increasment of the reaction temperature, the reactant concentration and the ozone flow. The optimum synthesis conditions of this reaction concluded from the respond surface methodology, were as followed: the reaction time was 4h, the reaction temperature was 8 ℃, the ozone flow was 0.25 L·min-1 and the reactant concentration was 0.20 mmol·m L-1. When the ozone was used to oxidize the garlic oil under these optimized synthesis conditions, the productivity of allicin was as high as 63.96%, and the content of the allicin in the garlic oil was substantially increased.In addition, the kinetic parameters for the decomposition of allicin in pentane or ethanol were determined. The activation energy was 56.0 k J·mol-1 in pentane and 72.0 k J·mol-1 in ethanol, and the pre-exponential was 9.2×105 in pentane and 1.5×106 in ethanol respectively. The intermolecular interaction energy between allicin and solvent was calculated by density functional theory(DFT) at the B3LYP/6-31+G(d+P) level. The intermolecular interaction energy between allicin and ethanol(31.18 k J·mol-1) was higher than that between allicin and pentane(1.12 k J·mol-1). NBO analysis showed that the anti-bonding orbital stabilization energy between the lone pairs of O(13) in allicin and H(20) of ethanol molecule was 45.45 k J·mol-1, indicating there was strong hydrogen bonding interaction between them, and the stabilty of allicin in ethanol was increased.Furthermore, the effects of allicin and extractant on alliinase activity and the influence of the extractant on the composition of garlic oil were investigated. The results showed that allicin inhibited alliinase activity, but did not lead to complete inactivation; organic solvents had different effects on alliinase activity, that chloroform and methylene chloride could cause alliinase completely inactivated, and n-hexane and n-pentane could not significantly affect the activity of alliinase. GC-MS and two-dimensional nuclear magnetic resonance spectroscopy were employed to characterize the components of garlic oil. When the allicin was extracted by non-polar solvent such as chloroform and hexane, the main components in garlic oil were 3-vinyl 1,2-disulfide cyclohex-4-ene(4X) and 3-vinyl 1,2-disulfide cyclohex-5-ene(5X); however, when the allicin was extracted by polar solvents like acetic acid, the main ingredients of garlic oil tended to be diallyl sulfide(DATS) and diallyl disulfide(DADS).Ultimately, five novel phenolic compounds were identified, namely, 8-(3-methyl-(E)-1-butenyl) diosmetin, 8-(3-methyl-(E)-1-butenyl) chrysin, 6-(3-methyl-(E)-1- butenyl) chrysin, and Alliumones A and B, and eleven known compounds 6-16 from the ethanol extract of garlic were isolated. The structures of these five novel phenolic compounds were established via extensive 1D-and 2D-nuclear magnetic resonance spectroscopy experiments. The effects of the phenolic compounds isolated from garlic on the enzymatical or nonenzymatical formation of sulfur-containing compounds produced during garlic processing were examined. Compound 12 significantly reduced the thermal decomposition of alliin, whereas compound 4 exhibited the highest percentage of alliinase inhibition activity(36.6%).