## 3 Results and Discussion
### Evaluation of Colour Parameters of Bread Crumb  
The colour of bread crumb is an important quality attribute that influences consumer perception and product appeal. The lightness (\(L^{\star}\)) value of breads containing millet and spelt beverages, at substitution levels up to 75%, did not differ significantly from the control sample (Table 5). This suggests that these beverages had no considerable effect on crumb brightness. In contrast, even a 25% substitution with oat beverage resulted in a noticeable darkening of the crumb. According to [PERSON] et al. [49], such colour changes may be positively perceived by consumers, as darker bread is often associated with higher fibre content and greater nutritional value. No significant changes were observed in the \(a^{\star}\) parameter (red-green axis) across any of the samples, indicating that cereal-based beverages did not influence red or green tones in the crumb. However, the \(b^{\star}\) parameter, corresponding to yellowish, increased proportionally with the level of plant-based beverage substitution. This indicates a direct relationship between yellowish intensity and beverage concentration. Nonetheless, the \(b^{*}\) values observed in this study were lower than those reported by [PERSON] et al. (2019) in gluten-free breads supplemented with cereal beverages, likely due to differences in matrix composition and ingredient interactions. The most noticeable changes in crumb colour were recorded in samples made with oat beverage, particularly BO75 and BO100. In these variants, the total colour difference (\(\Delta\)E) exceeded 5 units--a threshold considered visually perceptible--confirming that oat beverage had the strongest effect on crumb colour among all beverages tested. This effect may be attributed to the natural composition of oat beverages, which often contain higher levels of pigments such as carotenoids and phenolic compounds. These compounds can contribute to darker and more yellow crumb coloration upon baking, due to their inherent colour and their participation in Maillard-type reactions. Moreover, the fiber content in oat beverages might also play a role in modulating water activity and heat transfer, thereby influencing browning reactions during baking. Analysis of the whiteness index (_WI_) revealed the lowest values in breads containing oat beverage, corresponding with the observed reduction in \(L^{*}\) values. In contrast, the browning index (BI) increased with higher levels of water substitution, regardless of beverage type. This trend may be attributed to the presence of simple sugars in cereal-based beverages, which promote Maillard reactions and caramelization during baking (2015, 2016). In this study, the occurrence of these reactions is supported by significant changes in crust color detected through colorimetric analysis. In addition, the yellowness index (YI) also increased with beverage addition, reflecting the natural beige-yellow hue of the cereal-based drinks. This finding is consistent with the upward trend in \(b^{*}\) values observed in samples with higher substitution levels. Overall, oat beverage had the most pronounced influence on crumb colour parameters, especially in terms of reducing brightness and enhancing yellowness. This tendency may result from the specific raw materials used in oat beverage formulations, which often include whole grain extracts rich in natural pigments and reactive compounds. Although detailed compositional analysis of the beverages was beyond the scope of this study, their known biochemical profile suggests they may promote both non-enzymatic browning and pigment transfer during baking. Spelt and millet beverages had a much milder effect, maintaining crumb colour properties closer to those of the control bread.