## 3 Results and Discussion
### The Volatile Compound Profile of Cream and Sour Cream Samples  
Some fermented foods are a rich source of bioactive components which may have beneficial effects on health. LAB used as starter cultures may allow the transformation of lactic acid and citrate, lactate, protein, and fats into volatile compounds which, along with amino acids and other products, may play a critical role in the flavor of the resulting products [71]. In our work, volatile compounds in cream samples enriched with essential oils from the lemon peel, clove bud, and juniper berry that was fermented with _B. animals_ subsp. _lactis_ Bb-12 were identified by SPME-GC-TOF-MS and the data are presented in Table 4. The results are presented as the average relative peak area of three replicates (the peak area of the compound divided by the peak area of internal standard naphthalene d8). These did not correspond with the absolute amount of a compound identified in the studied samples, but were calculated and used only for evaluating the differences between the analyzed samples. The use of the SPME-GC-TOF-MS method allowed us to identify 22 volatile compounds belonging to the classes of aldehydes, ketones, acids, sulfur compounds, terpen, and phenolic constituents. Two sulfur compounds, five ketones, and one aldehyde were found in the cream samples not treated with LAB. The ketones were represented by the following compounds: 2-butanone, 2-pentanone, 2-hexanone, 2-heptanone, and 2-nonanone. They were identified as the most important aroma components of cheeses with mold growth [72]. Among them, 2-pentanone, 2-heptanone, and 2-nonanone are characterized by a fruity floral fragrance, while 2-butanone and 2-hexanone have a sharp sweet smell. This class of carbonyl compounds is formed by the enzymatic oxidation of free fatty acids to \(\beta\)-keto acids and their decarboxylation, although 2-butanone is formed from diacetyl (2,3-butanedione), which is a product of lactose fermentation and citrate transformation. Only the content of 2-heptanone and 2-nonanone was found to be changed in the cream samples fermented with _B. animals_ subsp. _lactis_ Bb-12, while the level of the remaining ketones was comparable to the nonfermented cream samples. In general, except for the stored sour cream samples containing the highest concentration of clove bud essential oils, all stored sour cream samples showed no increase in the identified ketones compared to the samples at the initial day. Moreover, 2,3-butanedione (diacetyl), a diketone responsible for the buttery flavor of the dairy product, was present in a lower amount in stored sour cream samples compared to unstored sour cream samples. However, the sour cream samples enriched with 12.5% essential oils contained a similar amount of 2,3-butanedione as that of unstored sour cream. It should be noted that diacetyl is produced by some species of the LAB family, including _Streptococcus_, _Leuconostoc_, _Lactobacillus_, and _Pediococcus_. [PERSON] et al. [73] found higher diacetyl production in lactobacilli compared to bifidobacteria. The strain _L. casei_ BT 1268 contained higher amounts of diacetyl in both intracellular and extracellular extracts, while _B. animals_ subsp. _lactis_ Bb 12 and _B. longum_ BL 8643 showed a lower concentration in both fractions. In addition, the content of diacetyl in a product may increase or decrease during fermentation. Such changes can be explained by the fact that diacetyl is highly volatile and can evaporate at low temperatures, as well as from dry products. Among the volatile compounds identified in all tested samples, there were two sulfur compounds, namely, hexanal (aldehyde) and dimethyl sulfide. Dimethyl sulfide determines the flavor of cheese and may be present in yogurts [74] in varying amounts depending on the technique used for yoghurt-making and whether skim milk or full-fat milk is used for yogurt production. Sulfur compounds can be formed from the degradation of methionine by enzymes released by LAB.