3.1 Composition of yeast extract
GC-MS detected 205 peaks from trimethylsilylated compounds associated with yeast extract. The compounds included 50 amino acids and their derivatives, 17 saccharides, 7 sugar alcohols, 20 organic acids, 6 nucleotides, 7 fatty acids, 66 miscellaneous compounds, and 32 unknown compounds, as annotated by the NIST14 database. Figure 1indicates the score plots for the compositions of yeast extracts based on PCA. The contribution ratios of PC1 and PC2 were 14.0% and 9.0%, respectively. Extract samples E1, E2, E3, and E4 were plotted right-down on the score plot. M1 and M2 were plotted right-up, and M3 and M4 were left side. Therefore, the sole yeast extract samples were separated into at least three clusters. Each mixed yeast extract sample was plotted at intermediated places. The data were summarized in a data matrix that was used for the machine learning analyses.