## 4 Discussion  
Water determination in bread samples is a challenge. The real water content of such complex food matrices is difficult to evaluate. There are many factors influencing the results, starting from the selection of the method to the composition and sample preparation. The water content ranges in the common values [20; 26; 48; 49], but with differences between bread samples. However, the water content of bread was close to the upper limit of the common range of water content values determined with standard thermal methods or even higher, if the two-component volumetric KFT technique was applied [48; 49]. The explanation is that the KFT is sensitive to water, while other methods such as oven drying determines the mass loss. This includes all volatiles that evaporate at the selected temperature, especially water but also aroma compounds. On the other hand, drying at elevated temperature can induces changes in the sample, sometimes with generation of volatiles [27; 31; 32; 33; 34; 50]. KFT analysis allows selecting the polarity of the solvent according to sample type and a temperature program for a complete extraction and titration of water [3; 37; 38; 39]. Generally, water content of non-packed bread or fresh from the manufacturer is higher, most probably due the water absorption from the environment during storage, transportation and commercialization. [PERSON] et al. (2003) evaluated the moisture content by oven drying and water activity of bread samples during storage. The moisture  
Figure 4: PCA results for the KFT data of all bread core and shell samples: (**a**) \(PC_{2}\) versus \(PC_{1}\) scores plot; (**b**) \(PC_{3}\) versus \(PC_{1}\) scores plot; (**c**) \(PC_{2}\) versus \(PC_{1}\) loadings plot; and (**d**) eigenvalues of the correlation matrix. Meaning of color lines in (**a,b**): Green—raw bread core (code “\(C\)”); pink—pre-dried bread core (code “\(Cd\)”); blue—raw bread shell (code “\(S\)”); red—pre-dried bread shell (code “\(Sd\)”). Meaning of color lines in (**d**): Green numbers—relevant eigenvalues. content increased by a few percent (sometimes by 12%) after four days, while the water activity also increased [20]. The water content of the bread crumb during the baking process can increase up to 2.5%, followed by a slow decrease up to the final baking step [51]. The maximum moisture content of the core can reach 51%, depending on the composition and baking conditions [26]. The differences between KFT water content of core (crumb) and shell (crust) of breads are obvious, the crust having consistently lower values (about half in comparison with the corresponding cores, Table 1). On the other hand, pre-drying of core and shell samples reveals completely different comparative values. Pre-drying lowered the water content of core samples only by a third, while the shell samples by 75-95%. It is clear that most of the water in the core samples are strongly retained, in comparison with that from shell samples, where a significant water fraction is \"surface\" water. This behavior can be explained by the presence in the bread core of less degraded starch and gluten, as well as other proteins, which absorb higher quantity of water. The absorbed water molecules are strongly retained by such flour and bread components. On the other hand, the bread crust (shell) has higher fraction of consistently degraded components and the absorbed water is mainly \"surface\" water. These water molecules are easily evaporated [3; 52; 53; 54]. [PERSON] and co-workers (2018) performed baking tests and oven drying moisture determinations on various regions on the bread. The top crust had a moisture content at the final of the baking process of 3.7-9.5%, depending on the baking temperature. The upper, lower and core crumb regions had approximately constant moisture content during baking, with a slight increase at the end of the baking process (up to 42-43%). On the contrary, the moisture content of various crust regions consistently decreases during baking process [26; 51].