# Flavour Generation during Lactic Acid Fermentation of Brassica Vegetables--Literature Review
## 7 Brassica Fermented Products
### Kimchi  
Kimchi is a product originating from Korea, made by the fermentation of vegetables, such as Chinese cabbage, radish or cucumber with multiple seasonings, such as salts, red pepper, ginger, garlic and leek [104]. There are more than 50 different types of kimchi, depending on the raw ingredients and preparation methods. Traditionally, fermented and salted kimchi was prepared to preserve fresh plants during the winter months in Korea. Although nowadays there is no problem with vegetable supplies during the winter season, kimchi is still consumed daily by Koreans and is gaining popularity in other parts of the world [105]. The major microbial group involved in the fermentation of kimchi are LAB. LAB present in the raw materials mediates the fermentation and is a key indicator of kimchi quality [106]. The flavour of kimchi is a result of the composition and content of microbiotar-related metabolites, such as organic acids and free sugars, which affect the acidity and sweetness, the two most important taste attributes of kimchi. The degradation of carbohydrates, which are major components of cabbage, results in the formation of multiple organic acids, which are responsible for the unique sour taste of kimchi [107]. It was observed that the optimum pH range for the most desirable flavour of kimchi is 4.0-4.5 [108]. pH values can be affected by multiple factors, such as type of cabbage, additives, storage conditions, or the amount of initial inoculated cells [109]. Five organic acids were identified in fermented cabbage: LA, citric acid, malic acid, acetic acid, and succininic [110]. It was reported that in the early stages of fermentation, the content of citric acid, malic acid and succininic acid increased, then later decreased with a simultaneous rise in LA and acetic acid [107]. The composition of organic acids in kimchi might be affected by different changes in the ferentation process, such as the salinity [111] or the type of starter culture [110]. Some of the major sugars detected in this kimchi were mannose, fructose, glucose, and galactose. Their concentration is reduced with fermentation time, whereas mannitol appeared in the middle stage of fermentation and is reduced slowly. Mannitol is produced through the reductive action of glucose, fructose, and sucrose and it influences the sharp umami taste of kimchi [112]. [PERSON] et al. [110] studied the effects of combining two LABs as a starter culture on model kimchi fermentation. The authors described in detail how this affected the final composition of volatile and non-volatile metabolites. Based on the obtained results it was concluded that a combination of different LAB starter cultures might help modulate the composition of kimchi significantly. Therefore, the flavour formed mainly by metabolites can also be changed by using appropriate LAB strains. The sensory profile of kimchi is described as heat burn, fermented, and related to the seasoning (fishy, garlic, red peppers) [113]. The terminology regarding kimchi flavour is large and reflects ingredients, processing, fundamental tastes, and trigeminal sensations. The most intense odorants in kimchi have included diallyl disulfide, diallyl trisulfide, dimethyl trisulfide, and methyll disulphide. Less intense examples presented in the samples were 3-(methylthio)propanal, (_E_,_Z_)-2,6-nonnadien, phenylacetaldehyde, linalool, (_E_,_E_)-2,_A_-decadien and 2,3-butanedione [114]. Sulfur compounds are known to be the most important volatile substances that determine the aroma of kimchi and are formed during the fermentation process of the kimchi ingredients [115]. The specific flavour of kimchi may affect consumers' liking, especially non-Koreans who are not used to its sharp, specific notes. It is challenging for food industries to launch this kind of product into foreign markets since the acceptability of the quality might differ across cultures. [PERSON] et al. [116] analyzed the influence of the fermentation stage on sensory perception.