## 3 Results
### Statistical Analysis by Mechanical Texture, Color RGB, Color Lab, Texture GLCM  
The dried sweet potato slices were subjected to instrumental analysis in order to determine the color and texture discriminants (i.e., shearing force, skin elasticity, and work of shearing) of obtained dried material. Graphs of texture discriminants (Figure 2) illustrate slight differences between classes resulting from each variable, i.e., shearing force, skin elasticity, and work of shearing. The \"maximum shearing force\" and \"skin elasticity\" variables proved to be the best at discriminating variables between samples. Analysis of variance showed that class 3 (80 \({}^{\circ}\)C) showed statistically significant differences from classes 1 and 2 falling into the second homogeneous group together with class 4. In the case of the color parameters expressed in the CIE L* a* b* system (Figure 3), a decreasing trend was observed for the L* parameter describing brightness and an increasing trend was observed for the b* parameter, which represents the yellowing of the tested samples with the increase in drying temperature. The a* parameter characterizing the green-red color axis is not characterized by an unambiguous decreasing or increasing trend. The analysis of variance of the L* variable showed the existence of four homogeneous groups, with the existence of four classes. The neighboring classes in this case overlap to form one homogeneous group for each pair of neighboring classes. The class affiliations for groups a, b, c, and d are as follows: 1d, 2b, 3 ba, and 4a. The decreasing trend indicates a darkening of sweet potatoes as the drying temperature increases. For the parameter a*, two homogeneous groups were observed: 1 ba, 2a, 3 ba, and 4b. This means that classes 2 and 4 are distinguishable at an accepted level of significance. There were no statistically significant differences between classes 1, 2, and 3 and classes 1, 3, and 4. For the parameter b*, the existence of three completely separable homogeneous groups was observed, which, relative to the classes, are as follows: 1a, 2b, 3b, and 4c. This means that the change in parameter b* with the increase in drying temperature by each 20 C resulted in a significant variation in the color of dried slices. Figure 2: Average values of shearing force, skin elasticity, and work of shearing for samples belonging to classes 1–4, which corresponded to drying temperatures of 60, 70, 80, and 90 C.  
The change in color caused by convective drying is explained by two phenomena: Maillard reactions and enzymatic browning. The Maillard reaction is a reaction occurring between amino groups of free amino acids, peptides, or proteins and reducing sugars [46; 47]. Products of this reaction are known as Amadori products--compounds with a brown color and a characteristic smell of roasted meat, but which are impossible to describe with a chemical formula due to their diversity caused by the variety of substrates in a given environment [48]. In food processing, decisive factors that positively influence the formation of Maillard reaction products are time, temperature, and water activity. This may indicate a potentially important role of non-enzymatic browning in color changes of convective-dried sweet potato slices. The second phenomenon affecting the color change of raw plant materials during processing is enzymatic browning. An increase in temperature has a positive effect on the intensity of the browning reaction until the enzyme proteins start to denature. The products affecting the color change are melanin compounds formed in damaged plant cells. One of the enzymes involved in the formation of melanin compounds is polyphenol oxidase. Its action negatively affects the content of phenolic compounds in raw plant materials, which are desirable due to their antioxidant activity [49].