## 2 Results and Discussion
### The Composition of Volatile Compounds
Terpenes, such as alpha-limonene (citrus peel), 3-carene (raisin, sweet, terpene), alpha-terpinolene (sweet and pine), linalool (floral, lavender, citrus), terpinen-4-ol (pine), alpha-terpineol (floral, lilac), beta-elemene (herbal, spicy), beta-caryophyllene (clove, turpentine), and alpha-caryophyllene (orange, pepper), may have contributed to the aroma of the fermented sausages. In the case of the control sausages, the contents of alpha-terpinolene, linalool, terpinen-4-ol, and alpha-terpineol were higher than those in the sausages with probiotics. Owing to the large group of terpenes found in the study sausages, it is difficult to unequivocally assess their influence on the quality and sensory characteristics. In addition, the presence of terpenes results from the additives and spices used, affecting the perception of positive sensory features, such as fruity, herbal, pine, and spicy odour (2019, 2020). In the sausages with probiotics, the total level of aldehydes increased during the 12 weeks of storage and was significantly higher than that in the control sausages. The highest content at week 12 was found for the hexanal, octanal, and nonanal formed as a result of the oxidation of unsaturated fatty acids. Lipid oxidation processes take place in dry fermented meat products due to the participation of bacteria, including _Lactobacillus_ spp., which leads to the formation of aldehydes, which, in turn, positively affect the sensory characteristics of the product (16; 28). The major contributors to the typical aroma of meat products during the ripening or dry-curing stages are the compounds of lipid oxidation (29). [PERSON] et al. (2020) found a similar high content of hexanal in traditional Italian sausages. [PERSON] et al. (2020) observed a significant increase in the hexanal content in Cantonese sausage (raw maturing sausages) during 30 days of storage. Octanal is characterised by meat, citrus, herbal, and floral odours. Nonanal is characterised by the rancid, soap, fat, plastic, and hexanal odours of green leaves (17; 27; 31; 32). Moreover, hexanal is considered an indicator of the proper course of the oxidation processes in the meat fermentation process (18). The content of benzaldehyde in the samples with probiotics was higher after fermentation and during the entire storage period. The presence of benzaldehyde in fermented sausages may be derived from phenylalanine by bacterial activity (16). The odour of benzaldehyde is considered characteristic of fermented meat products and is described as cherry-marzipan, burnt sugar, and almond (4; 33). In a study of probiotic sausages during the 6 th week of storage, a statistically higher score of dried meat odour was recorded, and this could have been due to the higher aldehyde content. Aldehydes are among the compounds that have a significant impact on the odour of the product as they have a low perception threshold (30; 34). In a study of probiotic sausages, the levels of esters, mainly those of ethyl acetate (fruity aroma) and ethyl butanoate (pineapple aroma), were significantly higher after fermentation and in the 6 th week of storage. In contrast, the ethyl lactate and ethyl octanoate (fruity, apple, and floral aromas) levels were higher at each stage of the study in probiotic sausages. The higher ester concentrations in fermented sausages can be attributed to LAB esterase activity (35; 36). Esters are the aromatic compounds responsible for the fruity odour of dry fermented sausages (37). Esters, due to their low sensory threshold, are believed to have a significant influence on the odour of meat products. In dry fermented sausages with and without probiotic starter cultures, the effect of esters during storage could mask the perception of negative sensory factors, which resulted in low scores for bitter, storage, and other flavours, as well as spicy and other odours. In addition, the fruity odour may mask the rancid odour of meat fat (24; 37; 38).