## 4 Discussion
[37] noted, due to their low olfactory threshold, volatile compounds derived from lipid autooxidation are considered essential contributors to the characteristic aroma of dry fermented sausages. According to [PERSON] et al. [38], the main fraction of lipids responsible for the formation of specific volatiles includes phospholipids, and to a lesser extent triacylglycereros. This specificity is due to the fact that phospholipids contain more unsaturated fatty acids compared to the acids occurring in triacylglycereros. As described by [PERSON] et al. [39], phospholipids contain relatively high amounts of linolenic and arachidonic acids that are subject to auto-oxidation processes, which result in the formation of: 2,4-decadienal, 2-nonenal, 1-octen-3-one, and 2,4-nonadien. The lipid oxidation-derived volatile compounds in current studies on fermented sausages include compounds such as alkenals, aldehydes, and ketones, similar to the study by [PERSON] et al. [40]. Concerning the type of meat, beef sausages were characterized by a higher amount of hexanal, which gives a green, grassy odor [41] compared to fallow deer sausages. Hexanal is a typical volatile compound of oxidizing linoleic acid similar to pentanal and octanal [24]. The results of the research carried out by [PERSON] et al. [42] showed that dry cured ham was characterized by the highest content of aldehydes (pentanal, hexanal, octanal) among the various fermented meat products. As shown by the results of the analysis of the fatty acid profile, beef sausages had a lower content of linoleic acid compared to the fallow deer product, which may indicate the ongoing oxidation processes. The content of all volatile compounds derived from fat oxidation did not differ significantly between the samples with and without the addition of nitrite (C and S). On the contrary, the results obtained by [PERSON] et al. [41] showed higher amounts of propanal, butanal, 1-penten-3-one, pentanal, heptanal, pentanoic acid, 2-pentyl-furan, 1-octen-3-one, octanal, hexanoic acid, 2-octenal, and 1-octanol in samples with added nitrite. Similarly, research by [PERSON] et al. [43] indicated that 25% nitrate reduction increased the heptanal content in dry sausages. Another group of volatile compounds present in beef and fallow deer fermented sausages are those derived from bacterial metabolism. Lactic acid bacteria and staphylococci generate volatile compounds from amino acid degradation and carbohydrate fermentation while staphylococci additionally generate ethyl esters through their esterase activity [17; 22; 44; 45]. Carbohydrate fermentation-derived volatiles were the most abundant group of bacterial metabolism-derived volatile compounds in the experimental fermented sausages. These results are in accordance with those reported by [PERSON] et al. [43]; however, they found that among this group of compounds (acetic acid and ethanol) were the most abundant compounds, whereas in the present study, the most abundant compound in the group of carbohydrate fermentation-derived volatiles was 2,3-Butanediol, [R-(R*,R*)]-. Similar to our findings, 2,3-butanediol was quantified as the dominant alcohol in Turkish sausages obtained from beef [46]. As reported by [PERSON] et al. [46], 2,3-Butanediol is formed by the reduction of methyl ketones from the \(\alpha\)-oxidation of fatty acids and is often detected in fermented jerky. Volatile compounds derived from esterase activity in the current study included seven compounds. Ethyl butanoate and ethyl 3-methyl-butanoate were the most abundant in both beef and fallow deer fermented sausages. Elimination of nitrite had no impact on the production of these volatile compounds; however, the addition of freeze-dried whey powder to uncured sausages resulted in increasing ethyl (S)--(-)-lactate, ethyl butanoate, and ethyl hexanoate during the production of fallow deer fermented sausage. The origin of ester compounds in traditional fermented sausages can be due to different microbial groups including lactic acid bacteria, coagulase-negative cocci, yeast, and mold.