## 3 Results and Discussion
### Impact of Drying Method and Grinding Degree on Color Characteristics
\begin{table}
\begin{tabular}{c c c c c c} \hline
**Sample** & **L*** & **a*** & **b*** & **C*** & **h\({}^{\mathrm{o}}\)** & **BI** \\ \hline \multicolumn{6}{c}{Impact of drying technique} \\ \hline TPW-LIO & 56.0 \(\pm\) 0.1 \({}^{\mathrm{b,c}}\) & 28.2 \(\pm\) 0.0 \({}^{\mathrm{c}}\) & 52.1 \(\pm\) 0.1 \({}^{\mathrm{d}}\) & 59.2 \(\pm\) 0.1 \({}^{\mathrm{b}}\) & 61.6 \(\pm\) 0.0 \({}^{\mathrm{d}}\) & 0.76 \(\pm\) 0.0 \({}^{\mathrm{a}}\) \\ TPW-VAC & 48.6 \(\pm\) 0.0 \({}^{\mathrm{a}}\) & 31.2 \(\pm\) 0.0 \({}^{\mathrm{d}}\) & 50.6 \(\pm\) 0.1 \({}^{\mathrm{c}}\) & 59.4 \(\pm\) 0.1 \({}^{\mathrm{b}}\) & 58.3 \(\pm\) 0.1 \({}^{\mathrm{a}}\) & 0.74 \(\pm\) 0.01 \({}^{\mathrm{a}}\) \\ TPW-50 & 57.8 \(\pm\) 1.8 \({}^{\mathrm{c}}\) & 25.4 \(\pm\) 0.1 \({}^{\mathrm{a}}\) & 45.4 \(\pm\) 0.1 \({}^{\mathrm{b}}\) & 52.0 \(  
The samples dried under vacuum conditions showed the most intense red coloration. The values increased with the increased degree of milling, but only up to a certain point (18 s of milling). The b* values (yellow/blue axis) ranged from 32.5 \(\pm\) 0.1 (TPW-70-M0) to 52.1 \(\pm\) 0.1 (TPW-LIO), indicating dominant yellow hues in all samples. The most vivid yellow was observed in the samples exposed to mild drying conditions (vacuum drying and lyophilization) and an increased degree of milling. Chroma (C*), representing overall color saturation, was highest in samples exposed to mild drying conditions (vacuum drying and lyophilization), while the lowest chroma was measured in the non-grinded sample exposed to drying at 70 \({}^{\circ}\)C, indicating that vacuum drying/lyophilization and finer grinding can improve color brilliance. The hue angle (h\({}^{\circ}\)) ranged from 56.0\({}^{\circ}\)\(\pm\) 0.1 (TPW-70-M0) to 64.4\({}^{\circ}\)\(\pm\) 0.0 (TPW-70-M40), showing the variation in predominant hue from orange tones to more orange-yellow tones. Browning index was low, indicating the absence of the formation of Maillard reaction products under the tested drying conditions. Significantly lower BI of intact (ungrounded) sample might be because grinding increases the surface area exposed to heat and oxygen, enhancing the rate of Maillard reactions and pigment degradation [94]. The observed variation in the colorimetric parameters shows the considerable influence of the drying conditions and the grinding intensity on the final appearance of the tomato processing waste powder. Samples processed at higher temperatures (70 \({}^{\circ}\)C) and coarser particle size (M40) tended to have higher L* values, possibly due to surface lightening or degradation of pigments during prolonged exposure to heat [95]. In contrast, powders obtained by vacuum drying and fine grinding (M18) showed stronger red (a*) and yellow (b*) tones, indicating better preservation of carotenoids, especially lycopene [96]. This is consistent with our data showing significantly lower lycopene content in samples dried at 70 \({}^{\circ}\)C compared to other drying techniques (Table 7). The a* values indicating red coloration were the highest in samples dried under mild conditions and were positively associated with preservation of carotenoid content (Table 4) as indicated by mild positive correlation between a* and \(\beta\)-carotene and (to a lesser degree) lycopene (Figure S1). The higher chroma (C*) observed in finely ground samples can be attributed to the larger surface area and uniformity of the particles, which improves color perception [97]. Furthermore, the shift in hue angle (h\({}^{\circ}\)) reflects a subtle balance between red and yellow pigments, which is influenced by drying kinetics and oxygen exposure during processing [98]. Overall, the visualization of the CIELAB color space allows a clear distinction between the tested samples and supports the use of instrumental color measurement for the objective evaluation of color and quality of tomato powders.