## 3 Discussion
### Effect of Various Heat Treatment Methods on the Color of Basil Leaf Infusions  
The color of the basil varies depending on the part it comes from: leaf, stem, flower, or spike [56]. This study used only basil leaves.  
The color of basil infusions measured shortly after their preparation became darker, redder, and yellower along with increasing steeping time. This is in accordance with the results of [PERSON] et al. [57], who found that samples of feverfew (_Tanactum parhenium_) aqueous infusions prepared at a temperature of 20-70 \({}^{\circ}\)C were darker and had a higher hue angle than those prepared at higher temperatures (80-100 \({}^{\circ}\)C). As they concluded, this was not related to the content of bioactive compounds because significant increases in the total phenols content were seen at temperatures above 75 \({}^{\circ}\)C. Similarly, in a study by [PERSON] et al. [58], most of the antioxidant substances in Matcha green tea were observed in infusions prepared at a higher temperature of 90 \({}^{\circ}\)C.  
In this study, basil infusions after 2 h of storage under atmospheric conditions became darker, redder, and usually yellower, unlike infusions made at 85 \({}^{\circ}\)C. All the above-mentioned results suggest that the darker color of samples processed at lower temperatures results from the oxidation of polyphenic compounds under the influence of polyphenyl oxidase (PPO) to o-quinones [59]. These react with other quinones, phenolic compounds, proteins, and amino acids to form brown complexes. PPO activity decreased with increasing temperature and showed very low activity at 75 \({}^{\circ}\)C [59; 60].  
The sous-vide method (\(p\leq 0.05\)) resulted in darker, less green, and less yellow basil leaves than fresh and traditional steeping. The total color difference (\(\Delta\)E) of sous-vide treated leaves was higher than for conventional treatments. The discussion on green vegetable color is a complex issue as many parameters and culinary procedures are applied by researchers. The less green color of sous-vide processed plants in comparison to traditionally treated plants was also reported by [PERSON] et al. [61] in their study on broccoli, and in [PERSON] et al. [62] who studied Brussels sprouts. Moreover, in the case of sous-vide green vegetables, reduction in cooking temperature from 100 \({}^{\circ}\)C to 90 \({}^{\circ}\)C resulted in a decreased value of the parameter a* [63].  
Cooking and storage also reduced the degree of green kale, which decreased with increasing cooking time [64]. This may be related to the degradation of chlorophyll during storage and the leaching of the color substances into the water during cooking. The study also found a lower color intensity of cooked kale than raw kale. [PERSON] et al. [65] showed that the a */b * ratio, which is a validated indicator of the green color intensity in broccoli, increased in the initial phase of the process with the set temperature, probably because of the higher rate of water evaporation from the raw material. Further treatment leads to the loss of chlorophyll and its transformation into derivative compounds depending on temperature and pH. [PERSON] et al. [64] also found a high correlation between greenness (a* value) and total chlorophyll content.  
Vacuum conditions, no-water environment, and mild temperature of the sous-vide samples (60 \({}^{\circ}\)C) favored a lower transformation of chlorophyll (green color) to pheophytin (olive green color), through the magnesium substitution of the chlorophyll by hydrogen [66]. The highest amounts of pheophytin were found in samples cooked in boiling water (100 \({}^{\circ}\)C), cooked in water at a temperature of 85-90 \({}^{\circ}\)C, and in sous-vide samples [63].  
Different conclusions were reached by [PERSON] et al. [67; 68], who reported no differences between the color of sous-vide and steamed broccoli, as well as [PERSON] et al. [69; 70], who did not observe any color difference between boiled, cook-vide, and sous-vide green beans pods.