## 4 Discussion
However, this phenomenon did not change the yellowish color (\(b^{*}\)-values); the \(\Delta\)E parameter showed higher values than the Just Noticeable Difference Values of 2.3 [42], indicating there were noticeable visual differences between beer samples when wheat flakes were substituted by wasted bread. The instrumental data from color measurements and sensory analysis disagreed, in contrast with previous findings [9]. This indicates the importance of both instrumental- and sensory-based data in evaluating foodstuff appearance, along with the further exploration of these contrasting evaluations. [PERSON] et al. [43], when analyzing the color of Pilsen-style craft beers with adjuncts, observed lighter colors when compared to pure malt beers, and they pointed out that adjuncts can cause a color reduction and are associated with a lower concentration of amino acids and carbohydrates derived from malt in the word. Considering beer flavors, the types of adjuncts used can interfere with the flavor profile. It has been previously shown that, in Pilsen-style craft beers, the addition of corn as an adjunct contributes to the increase in the bitterness of beer, while the use of rice as an adjunct has the opposite effect [43]. Meanwhile, [PERSON] et al. [10] prepared a pale ale beer with stale bread and, in their sensory analysis, found that the participants were not able to detect a noticeable difference in the beer with the addition of bread and the incorporation of stale bread in a 50:50 ratio did not affect the overall character of the beer. A similar result was found in the descriptive analysis of the present study: WB beer did not present off-flavors and aromas, or a marked difference, when replaced by wheat flakes. It is worth noting that the produced WB peers included bread made with wheat flour. This may be the reason why the trained panel did not detect significant differences between the WB and control beers. In fermented beverages, volatile acids and alcohols are derived from the microbial fermentation of sugars, and, overall, these compounds were identified in a higher concentration in the control beer. However, alcohols can be also formed by the microbial decarboxylation of ketoacids, lipid oxidation, or the degradation of the iso-\(\alpha\)-acids of hops during the oxidation of beer [44; 45], and acids from lipid hydrolysis or Strecker aldehydes [46]. Volatile acids are important aromatic compounds in fermented beverages, as they can contribute to off-flavors [24; 25], and, in the present work, the addition of wasted bread instead of wheat flakes reduced octanoic acid, which presents a sweat/cheesy aroma. On the other hand, volatile alcohols are the most abundant components in beer samples and an important source of flavor [45], and, in the produced beers, could contribute to the beverage aroma bouquet, since the compounds herein were shown to present flower, green, fruit, and malt whiskey aroma. Aldehydes and ketones are off-flavors in Pilsen, ale, and wheat beers, since they contribute to grass/tallow and herb/butter/resin odors, respectively [25; 45]. Acetaldehyde, which contributes to green/apple notes [27], is formed as a metabolic branch point in the pathway from carbohydrate to ethanol and has levels directly related to the ethanol content [47]. Methyl ketones can form through Maillard reactions [48] and may be derived from the drying procedure of barley to turn them into malt and by the baking and toasting process of WB. These formation pathways are in line with the results from aldehydes and ketones found in the present work. Esters are critical indicators of quality because they are key compounds for composing the fruity and floral notes of the final product, and, for all esters identified, the addition of wasted bread led to lower amounts of the compounds. Their formation is closely related to fatty acids' and amino acids' intracellular metabolism of fermenting yeast cells, and, due to the ethyl esters apolar features, they can diffuse through the cellular membrane into the fermenting medium [49].