# Application of Sorbent-Based Extraction Techniques in Food Analysis
## 3 SPE in Food Analysis--Main Fields of Applications
### Flavor Analysis  
Flavor is an extremely important sensory factor that largely influences the choice and acceptance of food by consumers [74]. The great challenge in this field of analytical chemistry is the fact that there are enormously large differences in concentrations (high to traces) of compounds responsible for the taste or aroma. The crucial step for qualitative and quantitative determinations of flavor compounds is sample extraction and preparation. Traditionally the sample preparation for the analysis of flavor compounds, depending on the nature of the product and odorants, involves distillation methods, simultaneous distillation/extraction, and vacuum distillation to avoid the formation of artefacts, but also sorbent-based methods. The SPE technique fulfils many requirements because the ambient temperature of extraction prevents artefact formation, is robust and is not time-consuming. SPE eliminates the creation of emulsions and reduces the consumption of organic solvents. Another advantage is the possibility of using a wide range of sorbents with different properties. SPE has been effectively applied in the separation of flavor compounds from different food matrices [75]. Flavor compounds of tea arise from primary precursors amino acids/carbohydrates, carotenoids, glycosylides, isoprenoids, lipids, and polyphenols during enzymatic oxidation and hydrolysis, non-enzymatic degradation and oxidation, and the Maillard reaction [76; 77]. The aroma of the tea is caused by the quality of the plant, the climate in which the tea is grown (location, growing conditions) and the production process. To analyze over 160 VOCs in tea infusions, it was necessary to use comprehensive sample preparation methods: SPE, solvent-assisted flavor evaporation (SAFE) and SPME. SPE a silica cartridge provided aroma enrichment and a clean-up step mainly for compounds of lower volatility (benzyl alcohol, hexanoic acid, phenylacetaldehyde) in contrast to SPME, which is more sensitive with highly volatile compounds (acetaldehyde, dimethyl sulfide) [76]. The flavor of the wine is influenced by many components ranging from raw material, selected yeast, fermentation process and storage and ageing of the wine [78; 79]. The key stage in the analysis of wine is extraction, aimed to remove impurities originating from the matrix, the isolation of specific VOCs or the concentration of analytes present in trace amounts. SPE with C18 and XAD-2 resin sorbents has been commonly used for the extraction of the glycosidically bound parent compound in grapes and wines. Excluding limitations of using the SPE method to isolate VOCs, SPE was found to be an appropriate technique to determine 12 higher alcohols, esters, and acids in wines, which are VOCs produced by yeast during fermentation [78]. During the analysis of wine samples, particular emphasis should be placed on the fractionation of extracts by the use of silica sorbents. Selective elution of VOCs by solvents differs in polarity, making it possible to analyze \(\beta\)-damascenone, esters, and sulfur compounds [78]. Determination of VOCs at trace levels (ng/L) in complex matrices such as red wine with satisfactory precision still provides a challenge for analytical chemistry. Currently, the optimal method described for the extraction of aroma compounds in wine samples is SPE with a C18 cartridge, which is considered a well-established sample pre-treatment technique. Moreover, the SPE method enables preconcentration and isolating the target analyte in free or bounded form and it is effective against interferences [80]. In a variety of honey samples to date, over 600 different VOCs have been determined, which illustrates how complex and difficult the matrix is. The efficiency of the entire analytical process depends on the selection of the extraction method, which is extremely important because the sample obtained has to be representative in comparison to the starting product.