## 3 Results and Discussion  
### Changes in the Colour of Flour and Baked Product Crumb as Affected by Additives  
This study investigated the effect of flours obtained from underutilised plant materials, including Oberlander Himbeerapfel apple flour, sweet chestnut flour (_Castanea sativa_), horse chestnut flour (_Aesclus hipprocastanum_), and acorn flours from red, sessile, and pedunculate oaks (_Quercus rubra_, _Q. petraea_, _Q. robur_), on the colour parameters of flour blends and the crumb of the baked products in the CIE L*a*b* colour space. Particular attention was given to changes in lightness (L*) and the chromatic coordinates a* (red-green) and b* (yellow-blue), which reflect the overall colour tone and hue of the samples (Figure 3a-f, Table 1). The additives reduced the lightness of both the flour and the baked products. For wheat flour without additives (L* = 91.9), the addition of apple flour caused moderate darkening, reducing the L* value to 90.9 (5%), 89.6 (10%), and 84.7 (15%) (Table 1). Sweet chestnut flour exhibited a similar but milder effect, with L* reaching 86.8 at a 15% concentration. In contrast, oak flour, particularly from red oak, resulted in a more pronounced reduction in lightness, with L* decreasing to 73.4 at a 15% addition, indicating a significantly darker shade. After baking, a further reduction in lightness was observed due to the intensification of the Maillard reactions and sugar caramelisation. Among the tested samples, the bread enriched with 15% apple flour retained a relatively high L* value of 50.6, compared to 58.7 and 68.4 for the 10% and 5% levels, respectively. This confirms that higher concentrations of apple flour contribute to progressive crumb darkening, although to a lesser extent than oak or chestnut flour. The visual effect of apple flour was therefore the mildest among all tested additives. Figure 3: _Cont._  
Figure 3: (**a**) Changes in the CIE chromatic colour \(\rm a^{*}\) and \(\rm b^{*}\) parameters of flours derived from apple and of the crumb of the baked products prepared from them. (**b**) Changes in the CIE chromatic colour \(\rm a^{*}\) and \(\rm b^{*}\) parameters of horse chestnut and of the crumb of the baked products prepared from them. (**c**) Changes in the CIE chromatic colour \(\rm a^{*}\) and \(\rm b^{*}\) parameters of sweet chestnut and of the crum of the baked products prepared from them. (**d**) Changes in the CIE chromatic colour \(\rm a^{*}\) and \(\rm b^{*}\) parameters of red oak and of the crumb of the baked products prepared from them. (**e**) Changes in the CIE chromatic colour \(\rm a^{*}\) and \(\rm b^{*}\) parameters of pedunculate oak and of the crumb of the baked products prepared from them. (**f**) Changes in the CIE chromatic colour \(\rm a^{*}\) and \(\rm b^{*}\) parameters of sessile oak and of the crumb of the baked products prepared from them. A similar trend was observed in earlier studies using apple pomace as a flour substitute. For instance, [PERSON] et al. [37] reported that increasing the content of apple-derived material led to a clear reduction in the brightness of both the crumb and crust, with lightness values ranging from approximately 62.6 to 47.2. These observations align with our findings, confirming that the addition of apple-based components, although rich in fibre and polyphenols, generally results in darker baked products. This darkening effect is most likely due to enhanced non-enzymatic browning occurring during the baking process, particularly Maillard reactions and caramelisation, which are intensified by the presence of reducing sugars and phenolic compounds. This phenomenon has also been observed in the final baked products by [PERSON] et al. [28], [PERSON] et al. [38], and [PERSON] et al. [29], especially in gluten-free and fibre-enriched breads, where darker crumb and crust colours were reported as a result of such reactions. Chromatic coordinates (a* and b*) were measured in wheat flour blends enriched with alternative flours and in the crumb of the corresponding baked products.