## 4 Discussion  
For the first time, the hydrolates of _T. serpyllum_ and _C. limon_ were used to reduce the concentration of NoV during oyster deprivation. The results revealed the effectiveness of _C. limon_ hydrolate in reducing the concentration of NoV RNA, resulting in a 0.2 log  
Figure 4: Overall sensory scores given by the tasters to untreated oysters and oysters treated with _C. limon_ hydrolate (LH) and _T. serpyllum_ hydrolate (TH). reduction (corresponding to a mean reduction of 37.7%) compared to the negative sample, after 24 h of treatment. Interestingly, this reduction occurred only for NoV genogroup II while no effect in reducing the concentration of NoV RNA was observed for genogroup I. Therefore, the data obtained in this study demonstrate that the investigated hydrolates exhibit varying effects against the two genogroups of NoV. Previous studies have observed that different norovirus genotypes bind to different carbohydrate ligands present in oyster tissue. In particular, NoV genogroup I binds mainly to digestive tissues but not to other organs, while genogroup II binds to both digestive tissue and the gills, albeit to a lesser extent [40]. Depending on the ligand to which the two genogroups are bound, differences in the persistence of viral particles within the different organs may be observed. It has been hypothesized that the ligand recognized by GII can lead to a more rapid degradation or release, compared to the one recognized by GI, determining differences on the viral persistence within the body of the mollusks [40; 41; 42]. Based on this information, it could be hypothesized that the hydrolate of _C. limon_ may affect noroviruses linked to gill tissues, which are in closer contact with the hydrolates during filtration, while it may not have the same effect on noroviruses inside the digestive tissue, possibly due to interactions with the oyster's metabolism and digestive processes. In fact, genogroup I, which only binds to the digestive tissues, was not reduced by the treatment with the hydrosol. In this study, the mode of action of hydrosols against NoV was not investigated. Previous studies have revealed that the virucidal mechanism of plant compounds on non-enveloped viruses can vary, including 1. degradation of the viral capsid or nucleic acid; 2. interference with the absorption of the virus on the host cells by binding to the surface of the virus; and 3. interference with the attachment of the viral surface protein to the cellular receptors [43; 44; 45; 46]. Based on the chemical characterization performed, the _C. limon_ hydrolate used in this study contains limonene and beta-pinene as primary components. These compounds have demonstrated antiviral action in previous studies against both non-enveloped viruses such as norovirus [47] and enveloped viruses [34]. Also, the thyme hydrolate used in this study contains a high relative concentration of carvacrol (58.67%), a compound with known antiviral activity [35; 36; 37]. However, in this study the thyme hydrolate was not effective in reducing NoV concentration. In our previous in vitro study, where we evaluated the virucidal efficacy of _T. serpyllum_ and _C. limon_ hydrolates against MNV, a surrogate of NoV, we observed a reduction in viral infectivity of approximately 99% (2.9 log TCDI\({}_{50}\)/mL) for thyme and 92% (1.8 log TCDI\({}_{50}\)/mL) for lemon. Furthermore, thyme showed faster virucidal activity than _C. limon_. The infectivity of MNV immediately decreased by 2 log after treatment with 1% _T. serpyllum_ hydrolate, while the reduction in MNV after treatment with 1% _C. limon_ hydrolate was about 1 log immediately and an additional 1 log after 24 h treatment [33]. Despite using the same hydrolates at the same concentration, the results obtained in the in vivo application for the reduction in NoV in oysters were notably different. However, these differences are not surprising for several reasons.