## 3 Results
### Carbohydrates and Acids in Fermented Samples
#### 3.5.1 Major Contributors to Fermented Dairy Flavor  
The targeted VOCs were those that were related to dairy flavor. Fermented soy, oat, and coconut bases were screened for their presence by FID and the results are shown in Table 12. When all fermented bases were compared, diacetyl, acetoin, acetaldehyde, acetone, and ethanol levels were significantly different in all three bases. Ethyl acetate, an ester that is found in lactobacillus!I fermented products [93] and in dairy cheese [94], was targeted but not identified in any of them. Diacetyl, acetoin, and acetaldehyde play a key role in dairy flavor perception [95] and are products of pyruvate degradation. pyruvate can be metabolized through two main pathways. The first one converts pyruvate into a-acetolacetate, which is decarboxylated to diacetyl in aerobic conditions without any enzymatic activity. Diacetyl can then be reduced to acetoin and acetoin to 2-3-butanediol. The second one transforms pyruvate into acetaldehyde through acetyl-coenzyme A (acetyl-CoA) [96]. The effect LGG can cause on the levels of these pyruvate breakdown products can be relevant for the sensory perception of fermented samples. Acetoin and diacetyl provide buttery odors that are responsible for caramel and sweet flavors, respectively [49]. Acetoin is generally produced in higher amounts than diacetyl through citrate metabolism, which was reflected in all three fermented bases. Both compounds were significantly higher in fermented oat samples, followed by coconut and soy. This could be explained by a higher fermentable carbohydrate content in oat samples. Citrate levels in the plant bases was unknown; therefore, it was not possible to confirm that a higher citrate content in oat base was responsible for these results. LGG-containing samples reflected higher acetoin levels in all three bases in comparison to samples that were fermented with culture combinations without LGG. Consequently, it could be assumed that LGG has a high diacetyl-reductase activity to transform diacetyl into acetoin. Acetoin was produced in lower quantities in soy samples by BY-01+LGG and YF-L01+LGG in comparison to YF-L02+LGG. LGG increased diacetyl levels in oat and coconut when it was combined with YF-L01 and BY-01. In contrast, it decreased them in combination with YF-L02 in all three bases. [PERSON] et al. reported a relationship between excessive amounts of diacetyl and unpleasant odors [96]. This suggests that YF-L02 without LGG would not be an appropriate candidate to ferment oat samples due to the high diacetyl levels that were identified in this sample. One of the main principal components of fermentation aroma in yoghurt is acetaldehyde [96]. Samples that were fermented with LGG-containing culture combinations showed significantly lower acetaldehyde content in all three bases. This could be due to a low ability  
\begin{table}
\begin{tabular}{c c c c c c c} \hline \hline
**Base** & **Culture Combination** & **Acetaldehyde** & **Diacetyl** & **Acetoin** & **Acetone** & **3-Methyl-Butanal** & **Ethanol** \\ \hline \multirow{4}{*}{Soy} & YF-L01 & 2.73 \(\pm\) 0.06 \({}^{\mathit{All}}\) & 4.05 \(\pm\) 0.17 \({}^{\mathit{All}}\) & 15.38 \(\pm\) 0.13 \({}^{\mathit{All}}\) & 1.47 \(\pm\) 0.02 \({}^{\mathit{All}}\) & 0.71 \(\pm\) 0.09 \({}^{\mathit{All}}\) \\  & YF-L02 & 2.52 \(\pm\) 0.08 \({}^{\mathit{All}}\) & 7.06 \(\pm\) 0.48 \({}^{\mathit{All}}\) & 15.35 \(\pm\) 11.11 \({}^{\mathit{All}}\) & 1.46 \(\pm\) 0.08 \({}^{\mathit{of _L. rhamnus_ to produce it from carbohydrate, protein or nucleic acid sources, or due to a high enzymatic activity to convert it into ethanol. Acetaldehyde is a product of pyruvate degradation by acetyl-coenzyme A, but it can also be produced through other metabolic pathways from citrate by _S. thermophilus_ (strain present in YF-L01, YF-L02, and BY-01). Acetone content was significantly higher in soy samples. It is a compound that confers apple and solvent flavor and has been identified in dairy products such as kefir [93].