## 4 Discussion  
As presented above, ingesting the natural food additive containing PPs and PPO can successfully reduce the emission fluxes of cutaneous DADS and AMS. Emission fluxes of human skin gases vary greatly from person to person [25; 30; 31]. However, the three healthy male subjects exhibited common time-course profiles in the dermal emission fluxes of both organosulfur compounds, with little individual variations observed, which is mainly ascribable to the consumption of large amounts of garlic. The mechanisms associated with the generation of garlic body odour and the removal of organosulfur compounds by natural food additives are shown in Figure 6 based on  
Figure 4: (**a**) Influence of the ingestion of the natural food additive and (**b**) 0.5 g of each ingredient on the total emission of DADS from the skin surface after garlic consumption, as calculated using Equation (2). Significant differences: * \(p\) < 0.05, ** \(p\) < 0.01, two-tailed paired \(t\)-test against control. Figure 5: (**a**) Influence of the ingestion of the natural food additive and (**b**) 0.5 g of each ingredient on the total emission of AMS from the skin surface after garlic consumption, as calculated using Equation (2). Significant differences: * \(p\) < 0.05, ** \(p\) < 0.01, two-tailed paired \(t\)-test against control. the results presented above. Alliin is converted into allicin when garlic is consumed orally, and allicin is a precursor of a variety sulphur-containing organic compounds in the body, including allyl mercaptan and DADS, which are subsequently metabolised to other compounds, including AMS. Volatile sulphur compounds, typically DADS and AMS, are transferred to the skin surface via the blood and released, causing garlic body odour. The shift in the peak observed in the AMS time course (Figure 3b) is most likely related to AMS formed from DSDS and allyl mercaptan and is consequently somewhat latent in the skin layer after leaving the bloodstream [17]. The PPs in the natural food additive is readily oxidised to the corresponding \(o\)-quinones by oxygen and water, and this process is promoted by PPO [21; 22; 30]. According to [PERSON] and [PERSON] [32], (\(-\))-epigallocatechin gallate (EGCg) exhibits odorising activity against methyl mercaptan (CH\({}_{3}\)SH) because the methylthio group (CH\({}_{3}\)S-) adds to the \(o\)-quinone; however, it exhibits no activity against dimethyl disulfide (CH\({}_{3}\)S-SCH\({}_{3}\)), which suggests that the \(o\)-quinone generated from the natural food additive eliminates allyl mercaptan rather than DADS. The results shown in Figure 4b support the notion that no significant change is observed by ingesting green coffee-bean extract alone. However, the slight decrease in the dermal emission was observed when 0.5 g of the burdock powder was consumed; this probably reflects the fact that a DADS reducing agent is present in the burdock powder, with a formation of allyl mercaptan from DADS. Consequently, dermal emissions of DADS were significantly reduced by the natural food additive because both ingredients are mixed. Meanwhile, only cutaneous AMS emissions were significantly lowered by the ingestion of green coffee-bean extract (Figure 5b). This is because AMS is produced through the rapid methylation of allyl mercaptan by S-adenosylmethionine and gut microflora [16; 17]. The resulting conjugates are either odourless or have different smells. Based on the series of reactions examined in this study, we propose that ally mercaptan acts as a key garlic-body-odour-reducing substance through the ingestion of natural food additives rich in PPs and PPO. Figure 6: Metabolic pathways for the synthesis of DADS and AMS from alliin and the elimination of organosulfur compounds by ingested natural food additives containing PPs and PPO. The black arrows show the metabolic pathway of alliin via allicin, while the orange arrows show the reaction routes induced by the ingestion of the natural food additive.