## 2 Results and Discussion
### Comparison of Headspace Extraction Methods
#### 2.1.1 Static Headspace Solid Phase Micro Extraction with Car/PDMS  
Fiber (HS-SPME-Car/PDMS)  
The number of compounds identified (\(n=17\)) and the total FID peak area (TPA) associated with the volatile profile obtained by this method is relatively weak (Figure 1). Aldehydes, carboxylic acids and ketones are the major families of compounds extracted by this method and represent more than 85% of the TPA. Pentanal (linear retention index, LRI: 980), hexanal (LRI: 1088) and benzaldehyde (LRI: 1563) represent 38% of the total chromatographic peak area associated with the HS-SPME extract (Table 1). In human milk, most aldehydes are oxidation products of oleic, linoleic and linoleic acids [25]. The following free fatty acids (acetic (LRI: 1460), butanoic (LRI: 1637), hexanoic (LRI: 1862), octanoic (LRI: 2076) and decanoic (LRI: 2172) acids) are also identified in the extract, representing more than 30% of the TPA. Among them, octanoic and decanoic acids are the most abundant in the present milk sample, in line with previous results on human milk analyzed with DVB/Car/PDMS SPME fibers [21]. Carboxylic acids are released from triglycerides and phospholipids by the action of lipases [25]. Besides, 2-propanone (LRI: 793), 2-butanone (LRI: 904) and 2,3-butanedine (LRI: 975) were also identified in the extract. These compounds represent 18% of the TPA associated with this HS-SPME extract and are considered to be degradation products from unsaturated fatty acid oxidation in dairy products [48]. Compounds from other chemical classes are detected in the volatile profile obtained with this milk extraction procedure, but to a lesser extent. Limonene (LRI: 1210) which is regularly detected in SPME extracts of human milk [39; 40], and 1,8-cineole (LRI: 1220) were also detected (<5% of TPA). Terpenes in breast milk are presumed to derive from environmental exposure (diet, cosmetics, skin care products) [27]. Furfural (LRI: 1486) is also detected in this extract (5% of the TPA). Already detected in human milk using other methods than HS-SPME extraction [19; 20; 21; 28], this compound is usually strongly related to heating as a Maillard product [27; 49]. Furthermore, \(\gamma\)-butylrolactone (LRI: 1685) is also identified in this HS-SPME extract. Several lactones have already been detected in human milk after SPME extraction but not \(\gamma\)-butylrolactone [20; 21], which was only detected in dairy products [50]. The origin of lactones in human milk is not elucidated, but the literature on cow's milk suggests these compounds could derive from fat [48]. The only alcohol detected in the HS-SPME-Car/PDMS extract is 1-pentanol (LRI: 1250, <1% of the TPA). In human milk, most alcohols come from the degradation of unsaturated fatty acids [25]. Styrene (LRI: 1275), also detected in the extract, was previously reported in human body fluids as an environmental contaminant [12; 13; 28]. Additionally, despite the great care taken during analyses (pre-cleaning glass vial, using hermic screw-caps), some detected sytrenes might originate in the laboratory environment or milk expression materials. However, this compound is regularly reported in breast milk even after corrections accounting for possible contamination format different stages (milk sampling, storage, or analysis) [12].