## 2 Bioactive Compounds Commonly Found in Green-Colored Fruits and Vegetables
### Glucosinolates  
#### 2.3.1 Isothiocyanates: Indoles  
General Characteristics, Structure, and Food Sources  
Isothiocyanates (ITCs) are a class of small molecular compounds widely found in cruciferous plants such as broccoli, cabbage, horseradish seed, kale, radish, mustard, and watercress. Their molecular formula is N=C=S, and their structures and varieties in plants are tightly related to the precursors of glucosinolates. ITCs are the main metabolites of glucosinolates hydrolyzed by plant myrosinase in vitro or degraded in human and animal digestive tract by enzymes or microbiota [107]. In general, they exist as oily or low-melting-point solids (Table 1) [108]. Indoles, one of the major unstable ITCs, are planar heteroaromatic molecules. Among indoles, only indole-3-carboniol (I3C) is commercially available as an off-white solid [109]. It is a naturally occurring hydrolysis product of glucobrassicin found in vegetables of the genus Brassica (family Cruciferae), such as broccoli, brussels sprouts, cauliflower, cabbage, kale, mustard greens, bok choy, collar greens, arugula, and kohlrabi, as listed in Table 1[110; 111; 112]. The molecular formula of I3C is C\({}_{9}\)H\({}_{9}\)NO and its chemical structure is shown in Table 2. Under acidic conditions, I3C is unstable and gets converted to a series of oligomeric products in vivo, such as 3,3\({}^{\prime}\)-dindoylmethane (DIM, C\({}_{17}\)H\({}_{14}\)N\({}_{2}\)) [35; 112; 113; 114], a dimer transformed from indole-3-methanol, which belongs to the indoleosinolates family. It is a kind of pharmaceutical intermediate with a white crystalline powder appearance. DIM is also found in many cruciferous plants such as brussels sprouts, broccoli, cabbage, collards, cabbage, shepherd's purse, radish, turnip, and watercress (Table 1). BioavailabilityAfter oral administration, I3C is converted to a series of oligomeric products (mainly DIM) under the acidic conditions of the stomach. It is rapidly absorbed, distributed, and eliminated from the plasma and tissues, and its concentrations are the highest in the liver and the least in the brain [21; 115]. Owing to their lipid solubility characteristic, the concentrations of I3C, DIM, and other derivatives are approximately 6-fold higher in the tissues than in the plasma. Furthermore, the absorption, distribution, metabolism and, elimination of I3C occur more rapidly than its derivatives, such as DIM [21; 115], which is eliminated through the renal system in humans [116]. Interestingly, DIM is the only oligomer found in human plasma. Researchers assume that the production of these oligomers is insufficient or they may not be effectively absorbed in the human gut [112]. Potential Health BenefitsITC has a wide range of biological anti-bacterial, antioxidant, anti-inflammatory, anti-hypertensive, and cardio-protective effects in human and model animals [114; 117]. Dietary supplementation of ITC improved the relaxation of the aorta, reduced the number of infiltrating activated macrophages, and decreased the blood pressure. In an ischemia/reperfusion animal model, feeding broccoli extracts improved postischemic ventricular function, reduced myocardial infarct size, and decreased cardiomyocyte apoptosis [118]. One of the potential mechanisms by which ITC prevents and/or treats cardiovascular and metabolic diseases might be its capacity to remove metabolic waste and ROS [119]. I3C also has various biological anti-inflammatory, immunoregulatory, anti-hypertensive, anti-osteoporosis, and anti-diabetic properties [109; 120; 121]. I3C inhibited NO, TNF-\(\alpha\), and interleukin-10 (IL-10) production in LPS-activated macrophage cells and rat models [122; 123], suggesting its immunoregulatory effects. In addition, I3C immunoregulatory effects on polarization of monocyte-derived macrophages in systemic lupus erythematosus patients were observed as downregulated expression of pro-inflammatory genes and overexpression of anti-inflammatory cytokines [121].