## 3 Discussion
Chemometric techniques are extremely important and widely used for solving flavour chemistry problems. Amongst these, heatmaps and PCA are commonly used to interpret chromatographic data involving a large number of compounds and a large number of variables. Heatmaps are a clustering technique that complement PCA by grouping data sets according to their similarity or dissimilarity [47]. For example, [PERSON] et al. used heatmap analysis and PCA to characterise the volatile profiles of milk fermented using different \begin{table}
\begin{tabular}{c c c c c c c c c c} \hline \hline \multirow{2}{*}{**No.**} & **Volatile** & **Odour Threshold** & \multicolumn{6}{c}{**OAV**} & \multirow{2}{*}{**References**} \\ \cline{3-3} \cline{5-10}  & **Compound** & **(ug/L)** & & & & & & & & \\ \hline \(1\) & Acetaldehyde & 8.7 & 0.68 & - & 0.32 & 2.57 & - & - & [PERSON] et al., 2011 [42] \\ \(2\) & Benzaldehyde & 24 & 0.10 & 0.03 & 0.005 & 0.05 & 0.01 & [PERSON] et al., 2014 [43] \\ \(3\) & \(3\)-Methyl-butanal & 5.4 & 0.18 & - & - & 0.18 & 0.19 & - & [PERSON] et al., 2003 [44] \\ \(4\) & Decanal & 3 & - & 0.09 & 0.05 & 0.40 & 0.24 & 0.03 & [PERSON] et al., 2002 [45] \\ \(5\) & Nonanal & 1 & 0.21 & 0.49 & 0.25 & 2.02 & 1.22 & 0.19 & [PERSON], 2003 [46] \\ \(6\) & \(2\),\(3\)-Butanedione & 10 & - & 0.47 & 0.24 & - & - & 0.12 & [PERSON] et al., 2003 [44] \\ \(7\) & \(2\)-Nonanone & 5 & 1.99 & 0.60 & 0.93 & 1.93 & 1.73 & 0.47 & [PERSON] et al., 2002 [45] \\ \(8\) & Acetoin & 55 & 0.08 & 0.30 & 0.05 & 0.39 & 0.14 & 0.08 & [PERSON] et al., 2003 [44] \\ \(9\) & \(1\)-Nonanol & 45.5 & - & - & - & 0.07 & 0.04 & 0.001 & [PERSON] et al., 2002 [45] \\ \(10\) & Formic acid & 9 & - & - & 1.41 & - & - & - & [PERSON], 2003 [46] \\ \(10\) & ethyl ester & & & & & & & & & \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Odour activity values (OAVs) of the volatile flavour compounds produced in yogurts following fermentation with different ratios of _L. delbrueckii_ subsp. _bulgaricus_ IMAU20312 and _S. thermophilus_ IMAU80809 in starter cultures compared with the commercial starter culture. starter cultures [48]. We evaluated the relationship between volatile aroma compounds in different samples using PCA and heatmaps and found that the composition of the volatile aroma compounds in the A3 sample was the closest to that of the commercial control group. Sensory evaluation is a powerful tool that can aid communication amongst consumers and producer groups in the fermented dairy industry. Although the flavour characteristics of products are influenced by some key volatile flavour compounds, the final quality of the products is determined by texture attributes [49]. In order to confirm the effects of these compounds on the sensory attributes and general taste for consumers, sensory evaluations were made. In our study, the results of the sensory evaluation of five ratios of _L. delbrueckii_ subsp. _bulgaricus_ and _S. thermophilus_ in the starter cultures and the control showed that the A3 sample had significantly better characteristics than the other combinations and was close to the control (Table 3). This result was consistent with the PCA and heatmap (Figures 2 and 3). In addition, fermentation characteristics such as pH, TA, viscosity and WHC were important in determining consumer acceptance [50].