## 3 Results and Discussion
### Characterisation of Urinary Volatile Metabolites
Nevertheless, many metabolites belonging to these chemical families originate from endogenous metabolic processes in our organism, namely \(p\)-cymenene, \(p\)-cymene, \(2\)-bromophenol, phenol, and \(p\)-cresol [47]. Terpenes come from  
Figure 2: Example of typical GC-qMS urinary volatilomic profile of prostate cancer and control samples. Most important peaks: (1) Dimethyl disulfide; (2) 4-Heptanone; (3) o-Cymene; (4) p-Cymenene; (5) Dihydromycenol; (6) 2-Ethyl-1-hexanol; (7) Menthol; (8) D-Carvone; (9) \(\beta\)-Damascenone; (10) Phenol; (11) 4-Methylphenol; (12) \(\beta\)-Ionone; (13) 2-Bromophenol. (A) 3-Octanol, internal standard. the prevalent acid pathway [35; 43] and can also result from the consumption of foods and beverages [47]. 3,5-Dimethylbenzaldehyde, 2-methoxy-5-methylthiophene (MMT), 1,1,6-trimethyl-1,2-dihydronphthalene (TDN), and 2-ethyl-1-hexanol were the most abundant metabolites in the PCa group. TDN is typically found in liquorice tasting, alcoholic beverages and fruits [44; 47]. 2-Ethyl-1-hexanol is a fatty alcohol in lipid molecules; it can be found in foods such as different kinds of tea, cereals and cereal products, fats and oils, and alcoholic beverages [44; 47]. Furthermore, 2-ethyl-1-hexanol has been detected in five types of cancer, namely lung, laryngeal, thyroid, colorectal, and breast [8]. \(o\)-Cymene has been proposed as a putative biomarker of citrus ingestion since this compound is frequently found in citrus fruits [44; 47]. According to the literature, ketones are one of the most abundant chemical families in the volatile profile of urine [43; 48]. They are products of different metabolic pathways, namely carbohydrate metabolism and lipid oxidation processes [49; 50]. A few studies have proposed that a considerable fraction of ketones in urine arises from the action of gut bacteria, but ketones can also come from exogenous sources, such as food (beverages, foods, and flavouring ingredients) or environmental pollution [8]. 2-Pentanone, the simplest ketone identified, has been found in different foods, including fruits, cereals, milk, herbs and spice, fats, and oils. Moreover, 2-pentanone has been linked to diseases such as ulcerative colitis, non-alcoholic fatty liver disease, [PERSON]'s disease, and also to the inborn metabolic disorder of celiac disease [47]. 4-Heptanone is one of the most common VOMs in urine; its origin is still unknown, but it may be associated with the \(\beta\)-oxidation of 2-ethylhexanoic acid [8]. In addition to dietary sources, 3-hexanone has been associated with several diseases, including non-alcoholic fatty liver disease, autism, and inborn metabolic disorder celiac disease [8]. Similar to ketones, sulfur compounds have been described to possess a high expression in the human urinary volatilomic profile [35; 51]. Most of these metabolites are produced during the transamination pathway by the incomplete metabolism of methionine and cysteine [35; 52; 53; 54]. During transamination, methionine and cysteine are transformed into methanethiol [55]. Then, methanethiol is easily oxidized to dimethyl disulfide and  
Figure 3: Chemical family distribution of the peak total area in the PCa (\(n=26\)) and control (CTRL, \(n=30\)) groups. Ket: Ketones; Ald: Aldehydes; Est: Esters; Alc: Alcohols; CA: Carboxylic Acid; SC: Sulfur Compounds; BD: Benzene Derivatives; ND: Naphthalene Derivatives; PC: Phenolic Compounds; FC: Furanic Compounds; Hc: Hydrocarbons; HHc: Heterocyclic Hydrocarbons; Ter: Ter: terpen; Nor: Norisopenroids; Ses: Sesquiterpenenes. dimethyl trisulfide [53]. It has been described that Gram-negative bacteria may also produce considerable amounts of methanethiol and dimethyl disulfide [56]. Furthermore, these compounds can also result from dietary sources since dimethyl disulfide and dimethyl trisulfide are present in many foods and beverages. MMT is one of the most abundant sulfur compounds among the PCa group.