###### Abstract
Hence, milk from multiple mothers was often pooled before extraction, limiting the characterization of individual samples' chemodiversity and excluding the characterization of between-mother variations. Recently, headspace extraction techniques have been favored to analyze the volatile fraction of human milk, making solvents unnecessary and extraction temperatures and sampling volumes much lower. Among these methods, headspace solid phase microextraction (HS-SPME) exploited the high ad/boxption power of a fused silica fiber coated with a specific extraction sorbent material [34]. This method allows several combinations of sorbents onto fibers to extend the range of chemical classes extracted for several biological matrices [35]. The divinylbenzene/Carboxen/polydimethylsiloxane (DVB/Car/ PDMS) fiber allowed the extraction of various compounds from processed human milk [20; 21]. Still, the car/PDMS fiber recovered the largest profile of VOCs from dairy products [36; 37]. Moreover, this type of fiber allowed extracting a profile of odorants resembling the one of the original matrix [38], suggesting that it tends to trap a representative volatile profile. However, the small amount of coating material on SPME fibers relates to limited sensitivity [35]. Compounds can be pre-concentrated in a prior step of extraction to increase the extraction capacity of the HS-SPME. For example, solid phase extraction (SPE) was applied to pre-concentrate target compounds from human milk before using HS-SPME extraction [39]. However, due to polarity compatibility issues of the two consecutive extractive materials, a loss of some VOCs may have occurred, limiting the use of this method in a non-targeted approach. The stir-bar sorptive extraction (SBSE) and its headspace form, the headspace sorptive extraction (HSSE), were also used to resolve the lack of sensitivity of SPME. Being coated with a greater volume of the extraction phase, the stir-bar allows the recovery of more volatiles and decreases to 5 mL the volume of human milk required for analysis [26]. However, the dual-phase equivalence of Car/PDMS SPME fibers (i.e., polar and apolar) for the SBSE bar lacks availability, and the apolar PDMS phase remains the polymer currently used in SBSE methods, making it difficult to implement for recovering analytes that are both polar and highly volatile [40]. Dynamic headspace (D-HS) extraction is a valuable approach for the non-targeted exploration of analytes from various matrices because of the wide range of available sorbentsand the large amounts of extractive materials. The sample is purged with an inert gas to sweep out volatiles and trap them on a sorbent. Accordingly, the sample's headspace is constantly renewed, leading to the volatile enrichment of the trap and correlative depletion in the sample. Tenax was used for many applications because of its low selectivity and thermal stability [41]. It enabled the identification of several compounds in human milk [27; 28]. However, due to its molecular size screening and hydrophobicity, Tenax is limited for extracting highly volatile and polar molecules. Hence, tubes packed with a series of discrete beds of different sorbent materials with increasing strength, such as graphitized carbon black or carbon molecular sieves, were developed to increase the range of extracted compounds [41]. However, such multibed traps were suboptimal for extracting volatiles from cow's milk since much vapor is retained on these traps leading to water issues in the desorption system [42]. Besides, the combination of Tenax and Carbograph 5 TD, which is supposed to trap smaller compounds (C < 7), does not lead to the identification of additional compounds in human milk compared to the use of Tenax alone [43]. Another strategy was applied to obtain a more exhaustive volatile profile of human milk, using different methods with complementary extractive properties on several sample replicates.