## 3 Results and Discussion
### Miso Fermentation of Cereal Processing By-Products Generates \(\gamma\)-Glutamyl Peptides
oryzae_ also has a notable influence on the volatile aroma profile of the final miso product, which may be influenced by the differences in inherent enzymatic activities of the strain of fungi, as observed in Figure 2C. Nonetheless, we still observe a few aromatic compounds in common, including 2-methoxy-4-vinylphenol, which is often found in soy sauce and is associated with a burnt scent [47], and trimethyl-pyrazine, which is associated with roasted and chocolate aromas [48]. These compounds can likely be attributed to the presence of lignin in wheat bran and provide evidence for koji and miso substrates still contributing towards the final aromatic profile of the fermented miso. In the miso made from wheat bran S1/barley, we also detected other aroma compounds that are found in many fermented products, including red sufu, cacao beans, and soybean products, and are known for their sweet, fruity, and floral notes [49]. In particular, benzaldehyde and \(\alpha\)-ethylidene are formed through the degradation of phenylalanine [49], and menthol creates a menthol aroma [50]. In terms of the other cluster, the miso made up of wheat bran S1/BSG exhibited a high concentration of phenol compounds, including 2,3-dimethyl, which is not typically associated with miso flavour. This phenomenon may be attributed to the breakdown of the high concentration of lignin in cereal bran and BSG, producing phenol compounds [44]. Other phenolic compounds detected include 4-ethyl-2-methoxy, which imparts smoky and spicy notes [51], and 2-phenylpropenal, a compound responsible for the green, honey, alcoholic, sweet, caramel, bread, and coffee aromas found in fermented rice bran [45]. Compounds belonging to the pyrazine group, such as trimethyl-pyrazine, which is associated with a roasted aroma [49], were detected in higher concentrations than in the other two misos made from wheat bran koji (Figure 3). This high concentration of pyrazine compounds may be attributed to the high pH during the fermentation of this miso, which could accelerate the formation of pyrazines through the Maillard reaction between reducing sugars and amino acids [52]. Overall, we observe a strong negative correlation between volatile aroma compounds and \(\gamma\)-glutamyl peptides (Figure 4). This observation may be explained by the cabalism of amino acids; for instance, aldehydes and alcohols are the primary compounds produced through the Ehrlich pathway by various fungal enzymes during fermentation [21] and Strecker degradation [53]. Therefore, the synthesis of kokumi peptides may be hindered as a result of the degradation of amino acids. Figure 4: (**A**) Total abundance of \(\gamma\)-glutamyl peptides in each sample after 12 weeks of fermentation as based on chromatography areas. (**B**) Total concentrations of volatile aroma compounds in each sample after 12 weeks of fermentation. Volatile aroma compounds and kokumi peptides may intensify the experience of the koku sensation, a Japanese term used to describe the presence of kokumi peptides. The link between high levels of fatty acid ethyl esters and kokumi peptides could be a possible explanation for these characteristic associations with the koku sensation, such as aftertaste, lingering, and coating, and remains a question to be further explored.