## 3 Results
### Color  
Color is a very important feature of a product, which affects its positive or negative perception by the consumer. Currently, two methods of color measurement are used, instrumental and sensory. The instrumental method is considered to be objective, but the measurement is performed on a limited sample area, which is a disadvantage [46]. The _sous-vide_ heat treatment method had an effect on reducing the lightness (\(L^{*}\)) of broccoli, green beans and beetroot comparing to the raw sample (Table 1). However, for cooked broccoli and beetroot, the differences obtained were not significant (\(p>0.05\)). The results correlate with those of [PERSON] et al. [47], [PERSON] et al. [39], and [PERSON] et al. [34] who also noticed a lower L* value for broccoli after cooking. For green beans, however, the \(L^{*}\) value (30 and 60 min) remained at a similar level compared with the raw sample, and significant (\(p<0.05\)) changes in lightness were recorded only in the longest-cooked sample (90 min). As the cooking time increased, green color intensity (-\(a^{*}\)) of broccoli and green beans decreased, but in most cases these changes were not significant (\(p>0.05\)). Broccoli cooked for the shortest time (15 min) showed very similar green color intensity to the raw sample. The intensity (\(a^{*}\)) of red color of beetroot decreased during cooking, but the values of this  
Figure 3: Results of sensory evaluation of _sous-vide_ processed beetroots. parameter remained similar regardless of cooking time (45, 90, 180 min). Green vegetables color mainly relates to chlorophyll, whose degradation to isomers leads to color changes. As the effect of heat treatment, the transitions of chlorophyll into pheophytins and then degrades to pyrophenophytes. The color changes can also be a result of the activity of enzyme, which alters the light reflecting properties of the surface which is due to the air removal from plant tissue and its replacement with water and cell juice because of cell membrane disruption [34; 39; 48; 49]. Yellowness (\(b^{\star}\)) of broccoli increased along with cooking time and significant differences (\(p<0.05\)) were reported after 30 and 45 min of cooking. Chlorophyll degradation reduces the green color intensity and leads to yellowing. The yellowish of broccoli has been associated with enzyme peroxidase and lipoxygenase [50]. Heat treatment of green beans and betroot caused a significant decrease (\(p<0.05\)) yellowness in comparison with raw vegetable. The yellowness (\(b^{\star}\)) of green beans significantly (\(p<0.05\)) decreased during the longest (90 min) heat treatment, and in beet it was reported at a comparable level regardless of the length of cooking time (45-180 min). With the use of the measured values of the \(L^{\star}a^{\star}b^{\star}\) parameters, color saturation (\(C^{\star}\)), hue angle (\(h^{\circ}\)) and the total color difference (\(\Delta E^{\star}\)) were calculated (Table 1). The color saturation (\(C^{\star}\)) of all samples after _sous-vide_ cooking differed significantly (\(p<0.05\)) from the raw sample. While the color saturation of broccoli significantly (\(p<0.05\)) increased, it significantly (\(p<0.05\)) decreased in green beans and betroot. The values of color saturation for individual vegetables, regardless of cooking time, remained at similar levels and no significant differences were found between them (\(p>0.05\)). The values of color tone (\(h^{\circ}\)) in all heat-treated samples (broccoli, green beans, beetroot) significantly (\(p<0.05\)) decreased in comparison to raw material, and their values remained at a similar level regardless of cooking time (\(p>0.05\)). A decrease in the value of the \(h^{\circ}\) parameter resulted in a less intense hue of green and red. Similar results presented [PERSON] et al. [51] and [PERSON] et al. [34], who observed that the hue angle (\(h^{\circ}\)) values of broccoli decreased after steaming.