# Flavour Generation during Lactic Acid Fermentation of Brassica Vegetables--Literature Review
## 7 Brassica Fermented Products
### Sauerkraut
However, after two days of fermentation, their content decreased significantly, and the formation of isothiances was favoured [72]. The high presence of GLS breakdown products can partly explain the unique aroma of sauerkraut, since many of them were reported to have an aroma activity, very high dilution factors and low odour thresholds [41; 45]. An interesting study by [PERSON] et al. [100] showed that blanching of cabbage to inactivate autochthonous microbiota in raw material and then fermentation with _Lactobacillus paracasei_ LMG-P22043 can protect GLS from complete degradation. Unfortunately, the authors did not evaluate how this change would affect the flavour of the obtained product. In another study, the sensory properties of sauerkraut obtained with cabbage from organic and conventional farming were compared [101]. Interestingly, the sauerkraut from organic farming was characterized by higher overall acceptance and a better taste and aroma. The biggest difference was obtained for aroma; however, the author evaluated only the overall aroma and not individual attributes. Thus, it is difficult to guess which compounds were responsible. The profile of metabolites responsible for the flavour of sauerkraut gained some attention very recently [30; 54; 69; 102; 103]. [PERSON] et al. [102] evaluated the effect of different cabbage varieties on the chemical composition and sensory properties of sauerkraut. In this study, eight late cabbage varieties fermented spontaneously were compared. The varieties used for fermentation differed with the amount of sugars, specifically glucose, which could affect the properties of the final product. However, even if the initial content of glucose was low while the count of bacteria was high, the efficiency of LA production was also high. In the analyzed sauerkrauts, the presence of 61 volatile compounds was detected, including 5 esters, 15 alcohols, 9 carbonyl compounds, 12 sulfur-containing compounds (among them 4 isothiances), 8 acids, 5 terpen and 6 nitriles and 1,1\({}^{\prime}\)-oxybis-octane. The most abundant compounds were methanol and 3-hydroxybutanone. In general, the concentration of individual compounds differed significantly between the varieties. The sensory analysis showed that the variety did not influence the appearance and texture of sauerkraut, which were suggested to depend on salt concentration [102]. On the contrary, the aroma and taste differed between varieties. The varieties characterized by a higher concentration of isothi cyanates, higher alcohols and volatile organic acids had higher scores for pungent aroma. The analysis of taste descriptors did not reveal any significant differences in saltiness, bitterness and off-tastes. The differences were observed for sauerness; however, surprisingly, they did not correspond to the content of organic acids. Spicy taste correlated with the sourness, and thus the same compounds could be responsible for these sensations. The sweet taste was the highest in the varieties in which the residue sugars were detected. In another, very recent study, the effect of the cultivar of sauerkraut in comparison to commercial sauerkraut was compared [69]. The presence of 32 volatile compounds, including 14 esters, 8 alcohols, 5 sulfur-containing compounds and 4 carbonyl compounds, was determined, and the differences in their abundance were detected among the investigated sauerkrauts. The most numerous and the most abundant in all varieties were esters and a significantly higher level was noted in the traditionally fermented products. Notably, compared to commercial fermentation, spontaneous fermentation can achieve a higher level of ethyl acetate, an ester derived from acetic acid. Likewise, the abundance of alcohols was higher in spontaneously fermented sauerkraut. Interestingly, the level of 2-isothiocyanatobutane and 4-isothiocyanatobut-1-ene was higher in the commercial sauerkrauts, while the abundance of allyl isothi cyanate was higher in traditionally obtained products.