# Analysis of Volatiles in Food Products
## 2 Isolation and Concentration as a First Step to the Analysis of Volatile Components
### SPME as a Method of Extraction  
According to the description, the SPME technique is based on the divide of equilibrium of the analytes between the extracted matrix and extraction phase (in this case, fiber) [62]. The SPME fiber can be exposed directly to the media by direct immersion (DI) or in its head-space (HS) [42]. At the GC injection port, the analytes are thermally desorbed and then transferred to the chromatographic column using a carrier gas for their separation [63]. The universal schema of the SPME technique is shown in Figure 2. Concerning polarity of chemicals, different sorts of coatings might be implemented for extraction, such as polyacrylate coating (PA), carboxen (CAR), polydimethylsiloxane (PDMS), polydimethylsiloxane-divinylbenzene (PDMS/DVB), divinylbenzene-carboxen-polydimethylsiloxane (DVB/CAR/PDMS), or with another type of sorbents. The success of the SPME method might be connected with its timesaving feature and possible options for automatization, as well as non-solvents usage [58]. The positive aspect of the SPME usage is that it can cover multiple steps of analysis such as sampling, separation of compounds of interest from the other matrix compounds, transfer of analytes from outside to the laboratory, and transport of analytes to the instrument. Despite these advantages offered by SPME, [PERSON] et al. [64] enumerated few limitations of SPME use in analysis of food, e.g., (1) a narrow amount of commercially available coatings, (2) the relatively low temperature to operating due to coatings' poor thermal stability, (3) de-stability and probable swelling of the coating by organic solvents; and (4) the quiet short period of the coating physical usage. Figure 2: The scheme of the SPME technique. The SPME was introduced into numerous applications in cannabis, environmental, forensic, and food analysis. As said by [PERSON] et al. [65], the main five classes of food products that the SPME was implemented for aroma analysis are: beverages, dairy, fruits/vegetables, honey, meat, seafood, and wine [66; 67; 68; 69; 70]. Usage of SPME in the determination of volatile chemicals extracted from various food samples is presented in Table 2. Furthermore, the main problems that were solved by using SPME are: studies of volatiles in different varieties of food products, profiling individual molecules reliable for food aroma, categorization of foodstuffs, also proof their authenticity, analysis of particular compounds responsible for food quality, to screen the technological process influences on aroma properties, screening chemical and biochemical processes related to transformations of aroma molecules, and to linked SPME with gas chromatography-olfactometry (GC-O) to describe the characteristic aroma of volatiles extracted by the coating of the fiber. Over thirty years on the market, the SPME technology is still developing. [PERSON] et al. [71] presented the SPME arrow as a new concept of SPME device that can limit the low inter-device reproducibility, as well as a little volume of mobile phases. [PERSON] et al. [72] suggested also miniaturization of the SPME device to make it portable and to allow sampling also not in a laboratory environment. Moreover, [PERSON] et al. [73] demonstrated that volatile compounds analysis with SPME is a favorable tool to determine also the quality of functional food and designing the product for consumer's needs. [PERSON] et al. [9] found out SPME as an appropriate method to separate volatile components from the oil matrix and afterward to determine compounds responsible for oil quality during storage. Furthermore, SPME coupled with GC/MS, and with other techniques of analysis, e.g., ATR-FTIR could be a promising possibility to prove the authenticity of food products [23]. [PERSON] et al. [74] admitted that in comparison to other extraction methods SPME is useful to determine more aroma-active regions of analyzed products whereas [PERSON] et al. [75] showed a high, 90% recovery of volatiles and semi-volatile using SPME technique. [PERSON] et al.