## 2 Results and Discussion
### Comparison of Headspace Extraction Methods
#### 2.1.2 Dynamic Headspace with Tenax (D-HS-Tenax)  
The visualization of the D-HS-Tenax extract profile reveals a strong increase in the TPA, which is enhanced by a 7-fold ratio compared to the HS-SPME-Car/PDMS extract. Moreover, 32 compounds were additionally detected in this D-HS-Tenax extract. Thus, this method can strongly increase the qualitative and quantitative recovery of compounds from human milk, in line with previous literature comparing these methods in dairy products [51]. Furthermore, the distribution of chemical families is significantly modified relative to the precedent extract, particularly for terpen, alcohols, aldehydes and carboxylic acids. Indeed, terpen represent 3% of the TPA in the SPME extract but represent more than 20% in the present D-HS-Tenax extract. Six terpen [\(\beta\)-pinene (LRI: 1114), 3-carene (LRI: 1156), \(\beta\)-myrrene (LRI: 1163), \(\beta\)-phellandrene (LRI: 1174), \(\gamma\)-terpinene (LRI: 1259), and \(\alpha\)-terpinolene (LRI: 1295)] are additionally detected in the D-HS-Tenax extract. Moreover, limonene and 1,8-cineole, identified in both extracts, are 40 times higher in the D-HS-Tenax extract. The increase in recoveries of terpen, which are mainly apolar, may be explained by the larger amount of the hydrophobic sorbent (Tenax-200 mg) used inthe D-HS method than in the SPME fiber (PDMS \(<\) 0.5 \(\upmu\)g). Furthermore, the dynamic mode of extraction could also be involved in this difference. Alcohols represent less than 1% of the TPA of the SPME extract but represent more than 10% of the volatile profile obtained with the present D-HS extraction. Five alcohols are additionally detected in the D-HS extract: 2-methyl-1-propanol (LRI: 1077), 1-butanol (LRI: 1140), (_E_)-2-penten-3-ol (LRI: 1154), 3-methyl-1-butanol (LRI: 1205) and 2-ethyl-1-hexanol (LRI: 1488). Moreover, 1-pentanol, detected in D-HS and SPME extracts, is found at a significantly higher level in the D-HS-Tenax extract with a 23-fold ratio increase. Aldehydes remain the most represented chemical class in both extracts. Their proportion increases from 38% for SPME to 56% in the present D-HS extract. Ten additional aldehydes were identified compared to the previous extract: heptanal (LRI: 1190), (_E_)-2-hexenal (LRI: 1233), octanal (LRI: 1295), (_E_)-2-heptenal (LRI: 1346), nonanal (LRI: 1409), (_E_)-2-octancal (LRI: 1445), (_E_,_E_)-2-4-heptdiagnal (LRI: 1484), decanal (LRI: 1498), (_E_,_Z_)-2,4-heptdiagnal (LRI: 1521), (_E_)-2-nonenal (LRI: 1563). Moreover, most aldehydes detected in both extracts were found significantly higher in the D-HS-Tenax extracts with a 10 mean ratio. The better sensitivity of D-HS for terpen, alcohols and aldehydes than HS-SPME was previously also noted in cola beverages or dairy products [44; 52; 53]. In addition, esters [ethyl acetate (LRI: 878), methyl decanoate (LRI: 1601) and ethyl decanoate (LRI: 1644)] were only detected in the profile obtained with the D-HS-Tenax extraction. However, they represent less than 1% of the total volatile profile. These compounds originate from the esterification of fatty acids [54]. Pyrazine (LRI: 1226) is also identified in the profile of the D-HS-Tenax extract. Pyrazines had never been instrumentally detected in human milk. However, an olfactometric analysis found one methoxyprazine in human milk that can be more sensitive than instrumental detection for compounds presenting a low odor threshold. Pyrazines are found in numerous products, especially roasted food products such as coffee [8]. Therefore, detecting these compounds in a human milk sample could be linked to maternal ingestion [11]. Conversely, carboxylic acids, which represented more than 30% of the TPA of the SPME extract, drop to 1% of the volatile profile obtained with the present D-HS-Tenax extraction. Two carboxylic acids were not even detected in the D-HS-Tenax extract. Thus, the HS-SPME extract with a Car/PDMS fiber is more efficient for extracting free fatty acids than D-HS-Tenax.