**3. Glucosinolates**

Glucosinolates are sulfur and nitrogen-containing compounds predominantly occurring in brassica vegetables (see **Table 2**). Depending on their structure, these compounds are further divided into three subclasses, aliphatic, aromatic, and indole glucosinolates [43]. Glucosinolates, well-known cancer-preventing bioactive compounds, and isothiocyanates (**Figure 2**) provide characteristic flavors to brassica vegetables [44]. Turnip is an excellent source of glucosinolates with 100–130 mg /100 g FW total glucosinolate content [45]. When compared with other Chinese leafy vegetables (cabbage, pakchoi, cai-Tai, choy-sum) of the brassica family, the turnip has shown the highest glucosinolate content, with gluconapin being the highest accumulated glucosinolate (65.84 mg/100 g FW) [45]. UPLC/MS analysis has indicated progoitrin as another high accumulated glucosinolate in turnip [38]. Rutabaga is a hybrid plant of cabbage and turnip with a considerable amount of glucosinolates (7.34 μmol/g DW), with progoitrin as major glucosinolate; however,


#### **Table 2.**

*Glucosinolates of root vegetables of the Brassicaceae family.*

*Bioactive Components of Root Vegetables DOI: http://dx.doi.org/10.5772/intechopen.105961*

**Figure 2.**

*Glucosinolate conversion into isothiocayanate by the action of myrosinase.*

total glucosinolate content is reduced upon cooking(6.86 μmol/g DW) [46]. Boiling and high-pressure cooking can reduce glucosinolate content by three times [31].

Glucosinolate content of radish varies depending upon the radish cultivar; however, glucoraphanin is a major constituent of the glucosinolate profile of all radish cultivars. Red radish has reported glucosinolate content of 163.91 mg sinigrin equivalent/100 g FW [47]. 4-methylthio-3-butenyl glucosinolate is prominent in white radish, which is converted into 4-methylthio-3-butenyl isothiocyanate by the action of myrosinase enzyme. The resulting metabolite is responsible for the specific pungent flavor of radish. 4-methylthio-3-butenyl glucosinolate comprises 90% of the total glucosinolate profile in Japanese varieties [48]. Spanish black radish also has identified radish-specified glucosinolates, which induce detoxification enzymes in HepG2 cell lines. However, the glucoraphanin (4-methylthio-3-butenyl glucosinolate), a major glucosinolate of radish, is not preserved in black radish-based dietary supplements [35, 36]. Tissue damage during cutting, chewing, cooking, and fermentation leads to glucosinolate degradation into isothiocyanates, thiocyanates, and cyanides. The major degradation product of radish glucosinolates other than erucin is 5-(methylthio)- 4-pentenenitrile [49]. Mustard is also reported in the literature for high glucosinolates levels and isothiocyanate byproducts. A study on mustard seeds has indicated higher levels of aliphatic glucosidase in all mustard varieties, with total glucosidase content ranging from 51.96 to 64.36 umol/g FW in root mustard [50]. Glucosinolates are highly sensitive to extraction techniques and pre-extraction treatments. A study conducted on brassica vegetables has indicated cold methanolic extraction with conventional wet tissue freeing is suitable for glucosinolate recovery compared to hot methanolic extraction. Also, freeze-drying was found to be avoidable for short time storage [51].
