# Functional Characterization of _Saccharomyces_ Yeasts from Cider Produced in Hardanger
## 3 Results and Discussion
### Correlations of AAs and Physico-Chemical Parameters with Aroma Compound Formation  
Data Analysis and Data Configuration  
As described in previous sections, we determined 54 different compounds (Table 1 (measured H\({}_{2}\)S production), Table 2, Tables S6 and S7) in the resulting ciders. Strain _S. cerevisiae_ 2303 was identified as an outlier and omitted in further statistical analyses (see Appendix A). All 54 continuous variables (summarized in Table 1 (measured H\({}_{2}\)S production), Table 2, Tables S6 and S7) associated with 19 different yeast strains were selected to draw a heat map (Figure 3). In Figure 3, the rows represent the measured compounds (and the corresponding clusters), and the columns represent the different yeast strains (and the resulting clusters) used for the single-strain fermentations in the fermentation experiment. Before generating the heat map, the data were standardized to a value between 0 and 100 using the following equation:  
\[\mathrm{new\ score}=(\mathrm{score}-\mathrm{min}(\mathrm{x}))/(\mathrm{max}( \mathrm{x})-\mathrm{min}(\mathrm{x}))^{*}100, \tag{1}\]  
The dendrograms on the top and left side of the heatmap show how the variables and the rows are clustered independently (they indicate the degree of similarity between the variables or yeast strains). Color coding is used to show the values of each variable in the dataset and also to show clusters of variables or samples that have similar expression patterns. The color scale indicates the range of values for each variable, with low values represented by dark colors and high values represented by light colors. Variables and/or samples (i.e., yeast strains) that are more similar to each other are grouped in the same cluster/block. The height of the dendrogram branches represents the degree of similarity between the variables or samples, with lower heights indicating a higher degree of similarity. Although all patterns in the heat map may indicate a relationship between rows and columns, we look for rectangular areas that are approximately the same color. This indicates a group of rows correlated with the corresponding group of columns. According to the results of the heatmap analysis, the total of 54 variables associated with the 19 yeasts used for fermentation can be divided into four main classes, shown on the left side of the heatmap. In addition, the yeast strains are also divided into four main groups, shown in the upper part of the heatmap (Figure 3). The first class of variables (i.e., the first class on the upper left) consists mainly of aromatic compounds (hexyl acetate, Z-3-hexenyl acetate, isoamyl acetate, butyl acetate, octyl acetate, propyl acetate, E-2-hexenyl acetate, octyl acetate); in this class are the amino acids glutamic acid and lysine and the biogenic amines putrescine and glucose. The second class of variables (i.e., the second class on the upper left) includes malic acid, 4-ethyl guaiocal, 4-ethyl valerate and ethyl butyrate. The third class of variables (i.e., the third class at the top left) includes H\({}_{2}\)S, the amino acid valine, and the aromatic compounds ethyl phenyl acetate and 4-ethyl phenol. The fourth class of variables (i.e., the fourth class at the top left) consists of CO\({}_{2}\) release, glutamine, methionine, and serine. Figure 3: The heatmap and cluster analysis of a total of 54 continuous variables: 26 aroma compounds (i.e., the response variables grouped into 5 chemical classes/groups in Y-block data used in PLS regression) and 28 variables including amino acids, sugars, ethanol, organic acids, etc. (i.e., the predictor variables which made the X-block data used in PLS regression) of 19 _Saccharomyces_ strains used in the fermentation trial. It was found that the compounds of the first class of variables on the upper left in cider fermented with _S. uvarum_ strains 2046, 2071, and 2061 (i.e., the first group of yeast strains on the upper left) had the lowest content. The highest levels of the same class of variables/compounds were found in cider fermented with _S.