## 3 Results and Discussion
### Color Parameters  
An important aspect of the quality of apples subjected to VI is color. Apple flesh color and its susceptibility to the browning process are cultivar-specific. The tendency to darken the flesh of apples is related to its chemical composition, mainly the content of polyphenols and the activity of ascorbic acid and PPO [4; 35]. The brightness (L*) of fresh apple flesh is significantly higher (for most cultivars) compared to apples after the impregnation process. The values of the initial and after VI color parameters are in the range of 54.4-67.8 and 33.4-48.3, respectively (Table 2). A similar relationship was found for the chromatic color parameters a* and b*. However, a statistically significant reduction was only observed for the b* value. The decrease in the value of the L* and b* parameters is due to the increase in the glassiness and translucency of the fruit flesh after the VI process as a result of introducing the solution into the tissue. This gives the effect of a lesser light reflection from the measured surface. The decrease in brightness and b* value of the apple cubes after the vacuum impregnation process was also noted by [PERSON] et al. [36] and [PERSON] et al. [37]. The a* parameter assumed both positive values (red color direction) and negative values (green color direction), depending on the cultivar. Its changes after impregnation tended to achieve zero, i. e. an increase in the case of negative values and a decrease in the case of positive values. This is due to the loss of a distinct color tone of the tissue after introducing the solution. [PERSON] et al. [38]  
Figure 1: Relationship between mass gain and firmness of apple cubes before VI. points to the possibility of improving the color and its uniformity in the case of VI of apples by using a very high vacuum (pressure of about 7 kPa). However, such treatment may cause deterioration in the texture of the fruit and impede the impregnation of the tissue by solution. The calculated values of the color difference (\(\Delta\)E) between the L*, a*, and b* values of the samples, before and after impregnation, assume lower values for cultivars with rapidly darkening flesh, such as Idared, Lobo, Pinova, Gala Must, which result from the immediate browning of the samples and reduction in the L* value at the time of dicing. Components of the impregnation solution, ascorbic and citric acid, are compounds that inhibit the enzymatic browning process, which contributes to less differentiation of color parameters after VI. Based on the results obtained from the color measurement, it can be stated that the VI process with a solution of 0.5% ascorbic acid, 0.5% citric acid, and 10% sucrose effectively inhibited the browning process of various cultivar apple cubes, regardless of their susceptibility to this process. However, differences in the color of the samples were noted. The obtained values of L*, a*, and b* were used to calculate the browning index (BI) of fresh and vacuum-impregnated apple cubes. These values had a significantly higher range for fresh apple cubes (21.5-61.1) compared to cubes subjected to impregnation (16.5-45.0). [PERSON] et al. [37] recorded BI values for apples after vacuum impregnation in the range of 28 to 37. The most important distinguishing feature affecting the BI values was the positive values of the b* parameter, which indicated the share of yellow. A high correlation (r = 0.92) was found between the BI and b* values of the vacuum-impregnated apple cubes. In the case of the sample before impregnation, this correlation was lower (r = 0.73). The correlation between BI and a* values was noted only for fresh samples before impregnation (r = 0.69). There was no correlation between BI and L* values. Among the cultivars tested, the lowest BI values were found in Cortland and Ligol. These cultivars were characterized by light flesh (L* = 62 and 65.2, respectively) and low susceptibility to tissue browning.