## 3 Results and Discussion
### The Volatile Compounds Related to the Aroma Profiles of the Fermented Samples
In addition, while 2-heptanone, ethanol, 2-nonanone, and nonyl methyl ketone compounds also support the formation of the aroma profile of this product, especially acetoin and 2,3-pentanedione that impart a butter, strawberry, caramel, fruit, rum flavor, 1-butanol that has a fermented-type odor and a fruity-type flavor, and 3-methyl-2-butanone that has a creamy, dairy sweet oily, milky buttery odor, [55] compounds have high effects on the aroma of the ST-p sample, both in terms of their amounts and with significant differences (\(p<0.05\)) from the amounts in the other samples. Of these compounds, especially the hexanoic acid, then hexanol, and in addition, the acetoin, 2,3-pentanedione, 1-butanol, and 3-methyl-2-butanone compounds can be associated with the _S. termophilus_ strain in this study. Some studies have been conducted on the contribution of LAB strains to aroma profiles, which has been an important topic in the literature in recent years. For example, in a study by [PERSON] et al. [56], two different dairy products were obtained, fermented and unfermented, after inoculation with _L. casei_ culture, and the volatile compound profile of these samples were analyzed by headspace solid phase microextraction-gas chromatography-mass spectrometry. The peak area values of the milk sample fermented with _L. casei_ culture on day 0 were found as 2-butanone 1.49%, 2-pentanone 4.68%, 2-heptanone 6.84%, 2-nonanone 1.45%, acetoin 0.32%, and ethanol 3.00%. In a study conducted by [PERSON] et al. [57], volatile compounds of the fermented dairy product produced with _L. bulgaricus_ culture were determined by SPME-GC-MS method. A total of 86 volatile flavor compounds were identified in the fermented milk product, including 17 carboxylic acids, 14 aldehydes, 13 ketones, 29 alcohols, 8 esters, and 5 aromatic hydrocarbon compounds. Various volatile flavor compounds (acetaldehyde, 3-methyl-butanal, 2-pentenal, hexanal, 2-octenal, nonanal, 2,3-butanedione, acetoin, 2-heptanone, 2-nonanone, and formic acid ethenyl ester) were identified due to their high odor activity values. On the other hand, in a study conducted by [PERSON] et al. [58], volatile components of fermented milk prepared with various culture combinations of _S. thermophilus_ and _L. plantarum_ or _B. animalis_ were analyzed using SPME-GC-MS. In the fermented beverage produced with _S. thermophilus_ culture, 2.3 butanedione was determined as 0.52%, acetylbenzene as 0.46%, benzaldehyde as 2.08%, nonanal as 0.29%, ethanol as 0.39%, 1-hexanol, 2-ethyl as 4.82%, benzylalcohol as 2.20%, 3-pentanol, 2-methyl as 0.99%, and total hydrocarbon as 3.06%. Finally, in a study conducted by [PERSON] et al. [47], volatile aroma compounds were determined in yogurts produced by adding _L. heleticus_ culture using SPME-GC-MS. It was observed that yogurt with _L. heleticus_ added had butanoic acid, 3-methylhexadecanoic acid, n-decanoic acid, propylene glycol, 1-hexanol, succindialdehydedehyde, 2,3-butanedione, methyl isobutyl ketone, benzaldehyde, formic acid heptyl ester, delta-nonalactone, hexanedamide, and N, N\({}^{\prime}\)-di-benzoylyloxy and its derivatives. In the present study, according to the principal component analysis (PCA) (Figure 4), the relationship between the samples and the volatile aroma components was examined. According to these results, the BB-p sample was clearly separated from the others. As explained above, this result shows that the effect of the _B. bifidum_ on the volatile aroma profile of the product is different from the others. In Figure 4, it is seen that the _B. bifidum_ is correlated with the phenethyl alcohol, 3-methyl-1 butanol, and ethanol compounds. On the other hand, the LC-p sample also shows separation from the group, albeit with a small difference. It is seen that _L. casei_, which is effective in the production of this sample, is correlated with the compounds hexanol, 2-methylbutanal, 2-nonanone, 2-heptanone, the acetoin, and d-limonene.