## 3 Discussion
### Sulfur-Derived Compounds  
Compounds containing sulfur can have a major impact on the overall flavor perception of fruits and vegetables. However, many of them are recognized as off-flavors of many foods due to their characteristic unpleasant odors, associated with a very low sensory detection threshold [35]. Off-notes typically increase in quantity as a consequence of heat treatment, such as sterilization techniques, used to ensure safety and extend the shelf-life of perishable foods [31; 35]. The concept of off-flavor can be considered partly subjective, depending on various factors, such as the type of analyzed matrix, the quantity of analytes considered, and the impact that their characteristic aroma has on the entire aromatic component of the food. In addition, considering that only odor-active compounds contribute significantly to the unpleasant taste notes, in this case, it was only possible to compare this family of analytes with the literature data, without speculating on how pronounced their impact on the entire flavor profile of the investigated samples was.  
In particular, we identified some sulfur compounds in the M_AI_V_t0 sample: dimethyl sulfide (DMS), dimethyl disulfide, dimethyl sulfoxide (DMSO), 3-methylthio-propanal, ethyl-methylthioacetate, 2,3-dihydro-thiophene and benzothiazole. Most of them have previously been identified in thermally treated melon juices [26; 30; 31; 35]. It has also been reported that some of these compounds, particularly dimethyl sulfide and dimethyl disulfide, originate from the degradation of sulfur amino acids, such as methionine, cysteine, and their derivatives, when involved in some reactions induced by heat (i.e., Maillard reactions).  
However, there is a big difference between our samples and those shown in the aforementioned papers. In our case, the fiber did not undergo any heat treatment, but was vacuum-freeze-dried, in order to preserve the original features of the pulp as much as possible. It was interesting to find that DMS, DMSO and, to a lesser extent, dimethyl sulfone are widely distributed in nature in various fruits; vegetables, including cucumber; forage; and also in some beverages [34]. In particular, DMS is responsible for the aroma of many foods and is supposed to play an important role in the natural transfer of sulfur of biological origin. Moreover, it has been shown in the literature that its photolysis in the presence of air generates DMSO [34]. However, it cannot be overlooked that DMSO is also widely used as an organic solvent to produce pesticides, and therefore, its presence could be partly due to some form of external contamination. In addition, we also detected 2,3-dihydroiophene--which is known to contribute to the aroma of white truffle [52]--and benzothiazole. These sulfur compounds have been found in various foods such as persimmons, potatoes, and tea [52], but may also partially result from Maillard reactions [31]. Furthermore, ethyl methylthio-acetate has also been previously found in various fruits, including melon [28; 52]. Finally, we report that none of the sulfur compounds were detected in the H\({}_{2}\)O\({}_{2}\)-bleached fibrous samples.