# Flavour Generation during Lactic Acid Fermentation of Brassica Vegetables--Literature Review
## 7 Brassica Fermented Products
### Sauerkraut  
Sauerkraut is a product that is obtained from fermented white cabbage (_Brassica oleraca_ var. _capita_), commonly consumed in Central and Eastern Europe. The word \"sauerkraut\" originated in the German language and means \"sour cabbage\". To produce sauerkraut, the cabbage is shredded, mixed with salt brine and sometimes also with shredded carrot as an additional source of sugars. Salt is necessary for the development of anaerobic conditions during fermentation and for inhibiting the growth of spoilage microbes and the activity of endogenous pectinolytic enzymes responsible for cabbage softening [90]. Importantly, the amount of salt added influences the population and profile of LAB and the sensory quality of sauerkraut. Considering the WHO recommendations to reduce the consumption of salt, the attempts to replace sodium chloride with other minerals without compromising the sensory quality were conducted [91,92]. When the fermentation mixture is prepared, it is placed in fermentation vessels and kept from one week to several months for fermentation. After that, sauerkraut is packed in metal cans or glass jars, and is consumed as a fresh product or is pasteurized to extend its shelf-life [90]. Notably, even the type of package can affect the sauerkraut quality, as reported by [PERSON] et al. [93,94]  
From a microbiological point of view, in the course of fermentation, cabbage undergoes a sequential fermentation that is initiated by heterofermatterative bacteria and is finished by homofermatterative LAB [95]. The fermentation by LAB is crucial to obtain the unique sauerkraut flavour because a study on the acidification of cabbage without the microbial fermentation did not result in a similar flavour to sauerkraut [96]. Notably, the study by [PERSON] et al. [97] showed that the sensory perception is similar for sauerkrauts obtained via spontaneous LA fermentation and starter cultures. However, although insignificant, the highest overall acceptability was obtained for cabbage fermented with _Lactobacillus plantarum_ and 1.5% of sodium chloride. Interestingly, this product had the highest score for an attribute described as raw cabbage-like, which was associated with green, immature sauerkraut [97]. In this study, the commercial sauerkrauts were characterized by the highest acid flavour and saltiness. In the same sauerkrauts, the authors analyzed the profile of breakdown products of GLS [98]. They found that fermentation induced the formation of iberin, iberin nitrile, allyl cyanide, allyl isothiamate and sulforaphane, which are derived from glucoiberin, sinigrin and glucoraphanine, respectively. Notably, in commercial sauerkrauts, the products derived from sinigrin, the main GLS in cabbage, were not detected. Interestingly, the salt concentration was found to influence the isothiamate and nitrile formation [98]. The products fermented with a higher concentration of salt (1.5%) were characterized by a higher content of isothiances when fermented with _Lactobacillus plantarum_ for iberin and with _Leuconstoc mesenteroides_ for allyl isothiamate. LA fermentation was reported to completely degrade GLS in sauerkraut, irrespective of the cabbage cultivation season, salt concentration and fermentation type [99]. The most comprehensive profile of GLS breakdown products was provided by [PERSON] et al. [72] The authors detected the presence of 16 degradation products of GLS, including four derived from indole GLS (glucuronissicin), one from aromatic GLS (glucuroninstuttin) and 11 from aliphatic GLS. Glucoiberin, glucoiberverin, glucoerucin and glucoraphanin were hydrolysed to both isothiances and nitriles; gluconapin and gluconasturtin hydrolysed only to isothiances; progoitrin degraded with the formation of 5-vinyloxazolidine-2-thione, the cyclisation product of the unstable isothiamate; and sinigrin hydrolysed to allyl isothianate, which partly underwent cyclisation to epithelocyanate, 1-cyano-2,3-epithiopropane. In this study, at the beginning of fermentation, the formation of nitriles dominated.