## 3 Results and Discussion
### Amino Acid Profile of Shoyu Sauces  
Glutamic acid was the dominant amino acid in all tested samples (Figure 1). The highest content of glutamic acid was found in TS_O (over 23%), and the lowest in KS_O (18.09%). The average share of aspartic acid ranged from 8.49% for TS_C to 14.46% for TS_O. Samples of the same sauce were characterized by an average high content of lysine (7.63%), and the lowest content of arginine (2.04%), compared to other sauces (where the range was 5.47-7.37%). The organic koikuchi sauces were distinguished by a higher content of proline (over 7.5%) compared to an average of 5.5% for tamari sauces, and the lowest content of lysine (5.21%). TS_C was characterized by a significantly higher proportion of Ala (9.12%), while the average contents were less than 5% for the rest of the sauces. In all samples of all sauces, the lowest content of tyrosine was observed (approx. 0.93 \(\div\) 1.21%). Principal component analysis (PCA) was performed on amino acid content to obtain a small number of factors that accounted for variance in the observed variables. Two principal components (PC1 and PC2) were considered meaningful and together accounted for 95.08% of the total variance in the dataset (Figure 2). Component 1 explained 66.2% of the variance in the dataset and presented meaningful loadings for the variables. It is visible that TS_O and TS_C differed the most in the shares of arginine, aspartic acid, and serine, and KS_O and KS_C were impossible to distinguish according to PC1. Component 2 explained 28.88% of the variance and revealed the differences between KS_O and both TS_O and TS_C, mainly due to proline, arginine, and aspartic acid. Factor scores for PC1 and PC2 were obtained from the statistical output for each of the soy sauce samples and plotted together with the significant variable loadings. The flavor of soy sauce is characterized by a distinct strong umami taste, accompanied by complex salty, sweet, and sour flavors [25]. The type and number of amino acids have a strong effect on the taste, and both aspartic and glutamic acids are responsible for the umami taste [38]. Serine, proline, glycine, threonine, and alanine are associated with a sweet taste, and valine, methionine, isoleucine, phenylalanine, lysine, leucine, arginine, histidine, and tyrosine give a rather bitter taste [26; 38]. According to this, we mapped the quality characteristic (taste) of individual amino acids and analyzed the principal components  
Figure 1: Average share (%) of individual amino acids in soy sauce. Figure 2: Principal component analysis (PCA) of soy sauce using contents of amino acid and their impact on taste (umami, sweet, bitter). The diameter of the dots is correlated with the av. content of amino acids in all samples. once again (Figure 3). The analysis revealed that tamari sauces (both conventional and organic) could be distinguished from koikuchi sauces by variables relating to a richer umami and sweet taste, which was the consequence of the elevated content of glutamic acid and alanine, respectively. However, organic shoyu sauces are characterized by a higher content of umami taste carried by amino acids such as aspartic and glutamic acids. In practice, the consumer might perceive tamari sauces as sweeter and organic sauces as having a more intense umami flavor. Apart from amino acids, a large number of compounds have been reported to be linked to taste attributes in soy sauces. The taste of soy sauces is influenced by the presence of peptides, some of which give bitterness and astringency. Acidic peptides and organic acids' presence have an impact on the sour taste. Kokumi peptides are known to act with specific receptors in the mouth, (calcium-sensing receptor--CaSR) [1], leaving a kokumi taste, described as complex, mouthful, long-lasting, and enhancing the intensity of other basic tastes, such as umami.