*4.2. Cabbage and Kale*

Among the *Brassica* species, cabbage (*Brassica oleracea* L. var. *capitata*) and Savoy cabbage (*B. oleracea* L. var. *sabauda* L.) are other two popular cole crops grown all over the world for their "heavy" heads constituted by leaves surrounding the terminal buds and that can be green or red-purple [246]. As for broccoli and cauliflower, the pigmentation of red cabbage genotypes is due to the accumulation of anthocyanins. Comparing four green and four red cabbage genotypes, Yuan et al. [247] observed that the structural genes involved in the biosynthesis of anthocyanins (CHS, F3H, F30H, DFR, LDOX, and GST), were steadily up-regulated in red genotypes for the entire growing period. The same authors observed that the expression of the structural genes responsible for the biosynthesis of anthocyanins was up-regulated in correspondence of nitrogen and phosphorous deficiency. Consistently with the mechanism of transcriptional regulation observed in purple cauliflower, in correspondence of the structural gene up-regulation it was observed a simultaneous increase of the transcript levels of the bHLH gene BoTT8, and of the MYB transcription factor BoMYB2. In a recent study analyzing the gene associated with the purple pigmentation of ornamental cabbage characterized by green external leaves and inner purple leaves, Jin et al. [109] found that phytoregulators such as abscisic acid (ABA) and ethylene (ET) play a key role in promoting the biosynthesis of anthocyanins. The same study identified 14 and 19 putative candidate genes involved in the biosynthesis of ABA and ET, respectively, and among those two ABA-biosynthesis related genes (BoNCED2.1, BoNCED2.2) and two ET-biosynthesis related genes (BoACS11, BoACO4) were expressed significantly more in purple leaves than in green leaves and were strongly correlated with the total anthocyanin content of the purple inner leaves.

Analyzing the anthocyanin profile of red cabbage using HPLC/DAD-ESI/Qtrap MS, Arapitsas et al. [248] separated and identified up to 24 anthocyanins all characterized by cyanidin as aglycon, mono- and/or di-glycoside, non-acylated, or acylated with aromatic and aliphatic acids. Similarly, using HPLC-DAD-MS/MS, Wiczkowski et al. [249] identified twenty cyanidin derivatives, with cyanidin-3-diglucoside-5-glucoside as the base structure, and cyanidin-3-diglucoside-5-glucoside, cyanidin-3-(sinapoyl)(sinapoyl)-diglucoside-5-glucoside, and cyanidin-3-(*p*-coumaroyl)-diglucoside-5-glucoside were the most abundant non-acylated anthocyanins. Moreover, Koss-Mikołajczyk et al. [250] identified nineteen different cyanidin derivatives, with cyanidin-3-(feruloyl)-diglucoside-5-glucoside and cyanidin-3-(sinapoyl)(sinapoyl)-diglucoside-5glucoside having been the most predominant. Similar results were obtained by other authors, who however using different analytical procedures and equipment identified a lower number of anthocyanins [19,251].

Analyzing raw and pickled red cabbage, consistently with other studies McDougall et al. [252] identified eighteen anthocyanin structures, most of which had cyanidin-3-diglucoside-5-glucoside as the core structure non-acylated, mono-acylated or di-acylated with *p*-coumaric, caffeic, ferulic and sinapic acids, but pelargonidin-3-glucoside and new cyanidin-3-*O*-triglucoside-5-*O*-glucoside di-acylated with hydroxycinnamic acids were also identified. The same authors examining the stability of anthocyanins after simulated gastrointestinal digestion found that anthocyanin structures were quite stable, and acylated structures were markedly more stable than non-acylated anthocyanins, nevertheless the after-digestion total recovery of anthocyanins was about 25%.

Feeding twelve volunteers with increasing doses (100, 200, and 300 g) of steamed red cabbage containing 1.38 μmol of anthocyanins/g (containing 30 acylated and 6 non-acylated anthocyanins), Charron et al. [253] evaluated the red cabbage anthocyanin bioavailability analyzing the excretion of intact and metabolized anthocyanin compounds in the urine. After 24 h, from the excreted urine were recovered 3 non-acylated and 8 acylated intact anthocyanins and 4 glucuronidated and methylated anthocyanin metabolites. Overall, the recovery of anthocyanins in excreted urine was four times higher for non-acylated compared to the acylated anthocyanins.

Comparing the biological activities (antioxidant, cytotoxic, anti-genotoxic, and influence on enzymatic activities) of the extract of green and red cabbage Koss-Mikołajczyk et al. [250] found that the anthocyanin content and profile was highly correlated with the antioxidant capacity of tested plant extracts measured through different spectrophotometric assays (ABTS, FC, DPPH, and FRAP), and by testing the cellular antioxidant activity. Instead, all the other biological activities tested were not correlated with the content of neither anthocyanins nor glucosinolate derivatives, suggesting that the food matrix effect may be more relevant than the biological activity of the single compound. This aspect should be further examined considering that other cabbage-like vegetables may be subject to different processing and anthocyanins and glucosinolates may have different levels of stability depending on the type of thermal or non-thermal processing and even the effect of the food matrix may change [19,254].
