## 4 Factors Influencing the Phytochemical Compounds of _Brassica_ Vegetables
### Environmental and Agricultural Factors  
Seasonal variation, light exposure, temperature, water availability [113], phytosanitary measures, sowing date and harvesting period [114] are all factors linked to environmental conditions that can influence the quality, in particular nutritional content and profile, of _Brassica_ vegetables [6]. Different responses to seasonal variations were reported in several _Brassica_ crops, such as broccoli, kale, and turnip [115]; this effect is determined mainly by temperatures and day length during the period before harvest. Countless studies agree that spring season crops, growing at intermediate temperatures, high light intensity, during longer days and in dry conditions (or low average of rainfall) during their vegetative period, contain an increased total GLS and phytochemicals concentration [50; 104; 114]. For example, in canola (_Brassica napus_), it was found that GLSconcentration increased when a temperature of 40 \({}^{\circ}\)C was maintained for 4 h on five successive days, giving a total of 15-degree days of stress (15 DD/40 \({}^{\circ}\)C) [116]. Some authors reported that higher and lower temperatures, rather than intermediate temperatures, brought about an increase in GLS concentration, e.g., growing temperatures between 7 \({}^{\circ}\)C and 13 \({}^{\circ}\)C brought about an increase in glucoraphanin and lutein in broccoli; furthermore, they acted as a trigger for biosynthetic pathways [117]. Moreover, broccoli sprouts grown at constant high (29-33 \({}^{\circ}\)C) or low (11-16 \({}^{\circ}\)C) temperatures had higher antioxidant content than sprouts grown at intermediate temperature (21.5 \({}^{\circ}\)C) [118]. The same authors confirm that the main antioxidant content is observed in sprouts that grow with a strong temperature range of 30/15 \({}^{\circ}\)C day/night. Autumn/winter season crops, grown at lower temperature, lower light intensity, shorter days, and higher water availability, tend to have the lowest total GLS and other phytochemicals concentration [119; 120]. An exception is represented by a turnip that produces higher flavonoids and vitamin C content in the autumn/winter season; this crop accumulates and produces the main phytochemicals with low/moderate temperature and considerable radiation, mainly in turnip tops [121]. More precisely, in _Brassica rapa_, the correlation with temperature is also bound to the plant portion; indeed, the number of days with a minimum temperature below 0 \({}^{\circ}\)C was negatively correlated with total GLS content in turnip greens. In turnip tops, GLS content was positively correlated with the number of days with a maximum temperature above 20 \({}^{\circ}\)C. In the case of phenolics, no correlation was found between climatic factors and turnip greens, while in turnip tops, total flavonoids and total phenolics content seemed to be correlated with the number of days with a minimum temperature below 0 and 10 \({}^{\circ}\)C, respectively [104]. In broccoli, freezing temperature can positively influence the concentration of sulforaphane [122]. The biotic and abiotic factors that characterize the surrounding environment can influence the quality of _Brassicaceae_. With respect to biotic sphere, aphid infestation brought about an increased production of primary metabolites, including amino acids, as well as some secondary metabolites, as a plant defence mechanism against these pathogens. Concerning abiotic factors, the water stress condition and metal exposure produce an initial increase in photosynthetic pigments, proteins, free amino acids and sugar content, followed by a subsequent decrease [123]. In detail, a relation between copper stress and the production of amino acids was found as free amino acid production takes part in the detoxification from excess copper [124]. In _Brassica juncae_, the accumulation of metals produces a 35% increase in oil content [123].