## 4 Factors Influencing the Phytochemical Compounds of _Brassica_ Vegetables
### Genetic Factors
#### 4.1.3 Plant Portion and Plant Developmental Stage  
The variation in nutritional and phytochemical content does not differ only among species and varieties of the same species, but also can change during the growth period [6] and based on plant portion [50], as reported below.  
For most of these crops, the more interesting parts of the plant for the nutritional quality are not consumed. For example, seeds seem to possess the highest content ofphytochemical compounds but are not usually consumed and appreciated by consumers; this aspect is confirmed in kale, where seeds possess higher antioxidant capacity than leaves [22]. In turnip, flower buds registered the highest antioxidant content, in respect to leaves, stems and roots [106].  
GLS content also differs based on plant portion. Seeds possess the highest concentration of GLS, followed by infloresences, siliques, leaves, roots, stems and petioles [107]. Indeed, the concentration of aliphatic GLS in kale (_B. oleraca acphala_) leaves increases over time, from seedling to early flowering stages. At that stage, the aliphatic GLS content in leaves of _B. oleraca_ declined drastically over time as the content in the flower buds increased [50].  
A comparison study on turnip tops and turnip greens also reported several and appreciated differences in phytochemicals compounds. Turnip tops gave a higher GLS value (26.02 mol/g dw) than turnip greens (17.78 mol/g dw). The opposite trend was reported for total phenolic, whereby turnip greens showed a higher content (43.81 mol/g dw) than turnip tops (37.53 mol/g dw) [104].  
Several studies confirmed the possibility to detect differences within the same portion of plant. In tronchuda cabbage, the mainly consumed portion are the internal leaves, utilised for salad or cooking; nonetheless, these have an antioxidant capacity lower than the external ones, which are usually discarded [22]. The same results were observed in Chinese cabbage, whereby the variation in bioactive compounds was also evident among different layers of the same head cabbage; phenolic acids and flavonoids were higher in the outer leaves, followed by the mid- and inner leaves. This result could be explained by the higher exposure of outer leaves to sunlight, which stimulates the production of antioxidants [108].  
The stage of growth can influence the content and concentration of phytochemical compounds in _Brassica_, and the knowledge of this aspect is fundamental in choosing the proper harvesting moment for obtaining products with the highest quality. Indeed, the juvenile cabbage possesses more flavonoids than the mature one [26].  
Total GLS content also varies in the function of the stage of growth and increases from vegetative to reproductive stages and maturity. Consequently, the highest content is found either in flower buds, or in leaves harvested at the optimum consumption stage, 180 days after the sowing of kale [50]. In broccoli heads, the highest glucoraphanin content was also observed 180 days after sowing, with a following decline during flowering [109].  
[PERSON] et al. [110] found an increase in ascorbic acid and phenol compounds during the development of the infloresence in three broccoli cultivars.  
Carotenoids are also affected by the plant developmental stage. In kale, the highest content of lutein was registered in 1- to 2-week-old leaves, and the highest content of \(\beta\)-carotene was found in 2- to 3-week-old leaves [111].  
Some of the health-promoting factors may be present 10-times higher in sprouts than in mature vegetables. Sprouting resulted in an overall increase in the total phenolic content and antioxidant capacity and, although germination time was not a discriminating factor, longer germination times resulted in the lower antioxidant capacity of the sprouts [112].