## 3 Results
### Crumb and Crust Color of Bread  
Figure 2 shows how the color parameters of the crumb and crust of the bread samples (\(L^{\star}\), \(a^{\star}\), and \(b^{\star}\)) changed depending on the PHP, FPH, GSP, and FGS addition levels in the wheat flour. Since the color of bread correlates with its quality and consumer acceptance, the evaluation of color parameters is essential [29]. The \(L^{\star}\) value of the crumb for all breads was higher than those of the crust. This was due to the fact that the color change of the bread crust was mainly influenced by the Maillard reaction. As a result of the Maillard reaction, brown melanoidins were formed, which darkened the crust. Furthermore, the color of the crumb was influenced by the color of the components added to the wheat flour, especially polyphenols and dietary fiber. Furthermore, statistically significant correlations (\(p<0.01\)) were found between the crumb \(L^{\star}\) and the total phenolic content and antioxidant activity (r = \(-0.944\) and r = \(-0.925\), respectively). The Maillard reaction had no effect on the formation of the crumb color. The reason for this was that the inside of the bread could not reach the same temperature as the crust [33]. The highest crumb \(L^{\star}\) value was obtained in the control bread, and the presence of all additives (except the breads with the 0.5% and 1.38% addition of FGS) resulted in a significant reduction (\(p<0.05\)) (Figure 2a). Similarly, the crust \(L^{\star}\) value of the control bread was different from that of all the enriched breads (\(p<0.05\)) (Figure 2d). The \(L^{\star}\) value of the crumb and crust of the breads decreased with an increasing level of enrichment (Figure 2a,d). The results from the ANOVA also showed that the level and type of additives had an effect on the \(L^{\star}\) value of the crumb and crust. In addition, the enrichment of the bread with PHP decreased the lightness of the crumb from 70.01 to 54.30 (bread with the 4% addition of PHP). The bread samples with the addition of pistachio hulls (both dry and fresh) had lower brightness in both the crust and crumb due to the color effects caused by the higher amount of phenolic compounds in pistachio hulls (Table 1). The \(a^{\star}\) values of the crumb and crust increased with the increasing levels of additives (Figure 2b,e). The most striking change in the crumb and crust \(a^{\star}\) values was observed in the breads with PHP. The \(a^{\star}\) values of the crumbs and crusts ranged from 1.84 and 5.43 (control bread) to 6.92 and 16.61 (for bread with the 4% addition of PHP), respectively. The increase in the redness of the crumb color of bread with PHP was probably due to the phenolic content and the natural color of the pistachio hull powder, which is red to light yellow and affects the color of the bread. In addition, statistically significant correlations (\(p<0.01\)) were found between the crumb \(a^{\star}\) value and the total phenolic content and antioxidant activity (r = 0.834 and r = 0.898, respectively). Moreover, both enzymatic and non-enzymatic browning could be the reason for higher redness values in the crust color of breads with pistachio hulls than in breads with grape seeds. Similarly, statistically significant correlations (\(p<0.01\)) were found between the crust \(a^{\star}\) value and the total phenolic content and antioxidant activity (r = 0.737 and r = 0.833, respectively). The \(a^{\star}\) values of the crumb and crust of the control bread were significantly different from those of the enriched breads,except for the crumb \(a^{*}\) value of the breads with 0.5% and 1.38% FGS additions. The \(b^{*}\) value of the crumb and crust of all the enriched breads decreased with increasing levels of additives. The crumb \(b^{*}\) values decreased from 14.05 in the control bread to 8.87, 8.98, 8.20, and 8.36 when 4% of wheat flour was replaced with PHP, FPH, GSP, and FGS, respectively (Figure 2c,f). In addition, the breads containing pistachio hulls had lower crust \(b^{*}\) values than the breads with grape seeds.