# Application of Sorbent-Based Extraction Techniques in Food Analysis
## 4 SPME in Food Analysis--Main Fields of Applications
### Flavor Compounds
A few basic steps are involved in their identification--first, gathering information about the analyzed product origin, subsequently extraction and concentration of VOCs, GC-O and GC-MS to, respectively, select and identify compounds responsible for unpleasant odors and finally spiking the analyzed product with the identified compound to confirm the obtained results [117]. Sulfides are widely distributed in both animal and plant products and they are quite problematic for instrumental analysis [118]. Apart from low concentrations that occur in foodstuff, the main issue is their reactivity taking place during isolation as well as during injection on a chromatograph. It was observed that thiol oxidation was minimized during sampling. CAR/PDMS was found to be the most adequate fiber for their analysis; due to their high volatility, the best results were observed after extraction in low temperatures [119]. Many studies about key aroma compounds in selected food products involve SPME, but mostly as an addition to exhaustive extraction techniques like SAFE and SDE [120]. SPME usually is less efficient in the extraction of aroma compounds than exhaustive techniques. In contrast, SPME was found to be more sensitive to esters and highly volatile compounds than SAFE isolated from apple cider [121]. The authors claimed that both techniques should be used to provide a more complete aroma profile [121]. [PERSON] and [PERSON] [122] compared the suitability of the SAFE, SPME and SDE methods for the isolation of flavor compounds from extruded potato snacks. According to the authors, SPME itself is not enough for full characterization of potato snack aroma, mostly due to the absence of VOCs of higher weight. An exhaustive technique like SAFE was necessary for a full characterization of aroma-active compounds in the matrix. Sniffing the extract from SPME did not reveal more than a few important compounds; however, this technique was very precise, sensitive and suitable for the analysis of low-boiling compounds [122]. Moreover, SPME is also important for identifying compounds in the first few minutes, hidden under the solvent peak on the GC-MS chromatogram. The extraction of VOCs from watermelon juice allowed for the identification of 40 aroma-active compounds--among them, 30 were identified by SPME and 28 by SAFE. SPME was better for the extraction of aldehydes and alcohols, while SAFE showed better effects in sulfur extraction [123]. Nevertheless, in studies dealing with the determination of key aroma compounds in certain food products, SAFE remains the preferred technique. The application of a low temperature in combination with a high vacuum during the procedure led to obtaining a high-quality extract. The extract is enriched with VOCs of different polarities and a broad range of molecular masses. Moreover, a sample can be frozen and reused, which is especially important during working with fresh material, the chemical composition of which can change significantly during storage. In flavor research, aroma-food matrix interactions have aroused special attention. VOCs presented in the headspace are particularly interesting because they can travel to the nose receptors during chewing [124]. An exhaustive isolation technique would not enable the inclusion of the effect of food components (like protein, lipids or carbohydrates) on the partition coefficient of aroma substances, while headspace techniques (including SPME) are able to show how matrix impacts the release of aromas. To date, most available research treated SPME as a valuable tool for qualitative analysis, and a minority used it for quantitative purposes. Its sensitivity, selectivity and reproducibility make it an adequate tool for quantitative analysis. The utility of SPME in aroma studies is especially visible in the targeted analysis of odorants, rather than research focusing on the determination of key aroma compounds. SPME extract is a relatively poor representation of the real product aroma.