## 2 Nutritional Quality
### Antioxidant Compounds
#### 2.1.1 Water-Soluble Antioxidants  
* Phenolic compounds  
Phenolic compounds are the most widespread antioxidant family present in vegetables. This large group of compounds is particularly present in _Brassica_ vegetables and constitutes the main source of antioxidants in these plants [14; 17]. These plants produce them as secondary metabolites for protection from pest and insect attack. Their importance in human health is related to antioxidant and anti-inflammatory properties that could have preventive and/or therapeutic effects against obesity, cancer, and neurodegenerative and cardiovascular diseases [18]. Among _Brassica_ species, kale and broccoli have the highest quantity of total polyphenols with about 13 mg gallic acid/g of dry weight [19; 20]. Flavonoids represent common phenolic compounds in _Brassica_; they possess a lot of biological properties, e.g., antioxidant activity, a capillary protective effect, and an inhibitory effect elicited in various stages of tumours [14; 21]. They are characterized by numerous subclasses, but the most important in _Brassica_ are the following:  
1. Flavonols: together with anthocyanins, they are the main represented flavonoids in _Brassica_ species; they can be found in internal and external parts of leaves, seeds, shoots and sprouts leaves [22; 23]. The most represented flavonoids in _Brassica_ vegetables are quercetin (up to 23 mg/100 g fresh product in kale), kaempferol (up to 47 mg/100 g fresh product in kale) and isorhamtein (up to 24 mg/100 g fresh product in kale) [24]. Quercetin, found mainly in kale, is characterized by a strong antioxidant power (higher than vitamin C); it exerts its activity against free oxygen radicals and acts on the prevention of cardiovascular diseases and cancer, atherosclerosis and chronic inflammation, and the induction of enzymes that detoxify carcinogens [25; 26]. Kaempferol 3-O-sophoroside is the main represented flavonoid in broccoli florets; its high intake is linked with a lower risk of coronary heart disease [27]. Kaempferol and quercetin, and in less amounts, myricetin, are the main represented flavonoids in _B. rapa_ subsp. _sylvestris_. 2. Flavones: Apigenin and luteolin are the only flavones detected in hydrolys extracts of different _Brassica_ vegetables (up to 45 and 12 mg/g of fresh weight in Chinese cabbage, respectively), excluding broccoli, where they were not detected [28]. 3. Anthocyanins were detected in _Brassica_ vegetables and described by several authors [13; 29]. They are present only in bright coloured species and varieties with red, orange and purple pigmentation, such as some kales, purple broccoli, and red and black cabbage. These compounds show an interesting antioxidant activity. The 80% of anthocyanins present in _Brassica_ species are in the acylated form, more stable and easily absorbable by the organism. The main represented anthocyanins in cruciferous are cyanidin derivatives. In particular, red cabbage possesses eight main types of anthocyanins (for a total of up to 190 mg Cyanin\(-\)3-Glucoside equivalents/100 g of fresh weight) [30]; cyanidin\(-\)3-diglucoside is the most represented [31]. In broccoli, more than 17 anthocyanins were detected [29]. Among phenolic compounds, even if they are not hydro-soluble, it is worth mentioning the lignans, diphenolic compounds that possess several biological activities, through their antioxidant and oestrogenic properties. Lignans may reduce the risk of certain cancers and cardiovascular diseases [16]. Some studies reported that lignans are mainly present in the kale family, broccoli and Brussel sprouts with lariciresinol (972, 599 and 493 mg/100 g fresh edible weight of Broccoli, Curly kale and Brussel sprouts, respectively) and pinoresinol (315, 1691 and 220 mg/100 g fresh edible weight of Broccoli, Curly kale and Brussel sprouts, respectively) being the most abundant [15; 32].