## 1 Introduction
There are many advantages for water determination by KFT: cover all water content ranges (ppm to 100%, by selecting coulometric, single- or bi-component volumetric techniques), determination of both free and \"strongly retained\" water, a wide range of solvent polarity and temperature of analysis, which allows protecting less stable/degradable samples, rapid and simple technique and equipment, increased sensitivity and accuracy and possibility of coupling with other equipment such as oven or distillation apparatus [38, 39, 40]. On the other hand, some compounds can interfere with the KFT reagents (such as aldehydes and ketones, which react with the alcohol used as solvent, or compounds that react with iodine--reducing agents) [27,31,33]. The KFT working parameters can be selected according to the composition and characteristics of the food sample. If the food product has a high content of oil and/or fat and lower content of water, the coulometric KFT technique can be used. On the other hand, these types of food products having higher content of water, such as in the case of butter, require volumetric KFT working with more hydrophobic solvent mixtures (e.g., methanol-decanol). The electrode coating for lecithin-based samples can be prevented by adding chloroform and formamide. Soybean, rapeseed, sunflower, sesame and pumpkin seed oils have been analyzed by coulometric KFT. The water content was in the range of 0.098-0.689% by automated coulometric KFT and 0.079-0.684% for manual KFT [38]. On the contrary, butter oil had 0.061-0.108% and 0.079-0.099% water by volumetric KFT working in methanol/chloroform and methanol/hexanol solvent mixtures, respectively [41]. Cereals, cereal-based products, sugars and dairy food ingredients and products have been widely studied from the KFT water content point of view. They generally have higher water content. On the other hand, the highly hydrophilic components (carbohydrates such as starch, mono- and disaccharides such as sucrose and lactose and proteins such as gluten) strongly interact with water molecules. Such components are less soluble in the KFT working medium and the extraction of water from the sample particles are enhanced by increasing the temperature analysis, using the homogenization or milling, and increasing the solvent polarity by adding polar solvents (e.g., formamide). Water content of wheat and rye flour mixtures have been determined using volumetric KFT at elevated temperature [3; 12], while for sorghum the KFT water content at 65 \({}^{\circ}\)C slowly decreased from 12.9% to 12.25% by increasing the grinding time from 10 to 90 s [39]. Other studies used starch, chick-pea flour, dry alimentary small paste or toasted ground barley for the determination of water content by volumetric KFT. For a better accuracy, the determination temperature was increased to 50 \({}^{\circ}\)C, where the water content was up to 0.7% higher than for the analysis temperature of 25 \({}^{\circ}\)C [42]. Invert sugar and fructose syrups have been compared for their water content and the corresponding mass loss at elevated temperature. They have a water content of 26.67% and 29.46% for invert sugar and fructose syrups, respectively. On the other hand, the mass loss was in the range of 26.4-26.7% for inverted sugar syrup dried at 105 \({}^{\circ}\)C, while for fructose syrup the mass loss had no significant variation by halogen drying at 100-115 \({}^{\circ}\)C (mass loss of 29.06-29.46%) [32]. Similar observations were accounted for maltose (5.1-5.64% KFT water content or halogen drying mass loss), glucose monohydrate (8.34% by KFT and 7.72% mass loss), sucrose (0.024% by KFT and 0.055-0.062% mass loss) or isomalt- and sorbitol-based candies [30]. All determinations required elevated temperature (50 \({}^{\circ}\)C), formamide addition and internal homogenization. Sucrose I and II and fructose had the KFT water content of 0.0552-0.0556%, 0.0464-0.0469% and 0.0800-0.0803%, respectively, while for glucose monohydrate the determined water content was consistently higher (8.84%).