Page 162 - Breeding and regulatory opportunities, Renaud

Chapter 5

Broccoli is an abundant source of nutrients, including provitamin A (β-carotene),

vitamin C (ascorbate), and vitamin E (tocopherol) (USDA Nutrient Database,

2011). It is also a source of phytochemicals associated with health beneits and

these include glucosinolates, carotenoids, tocopherols, and lavonoids (Brown et

al., 2002; Kushad et al., 1999; Farnham et al., 2009). Verhoeven et al. (1996), Keck

and Finley (2004) and Here and Büchler (2010), reported that diets rich in broccoli

reduce cancer incidence in humans. Strong associations between consumption

level and disease risk reduction exists for glucosinolates (anti-cancer), tocopherols

(cardiovascular), and the carotenoids (eye-health) (Higdon et al., 2007).

Sulfur containing glucosinolates are found in the tissues of many species of the

Brassicaceae family. When glucosinolates are consumed, they are hydrolyzed

into isothiocyanates (ITC) and other products that up-regulate genes associated

with carcinogen detoxiication and elimination. Aliphatic glucoraphanin (up to

50% of total glucosinolates) and the indolylic glucosinolates, glucobrassicin and

neoglucobrassicin are abundant in broccoli lorets (Kushad et al., 1999; Brown

et al., 2002; Schonhof et al., 2004). Glucoraphanin is hydrolyzed either by the

endogenous plant enzyme myrosinase (Fenwick et al., 1983; Juge et al., 2007) or

by gut microbes to produce sulforaphane, an ITC. The indole glucosinolates are

tryptophan-derived in a similar but alternate biosynthetic pathway (Mithen et al.,

2000). The health promoting efects of the indolyl glucosinolates are attributed

to indole-3-carbinol, a hydrolysis product of glucobrassicin, N-methoxyindole-

3-carbinol and neoascorbigen, hydrolysis products from neoglucobrassicin,

and the catabolic products derived from alkyl glucosinolates. Clinical studies

have shown that the glucosinolate hydrolysis products reduce the incidence

of certain forms of cancer (e.g., prostate, intestinal, liver, lung, breast, bladder)

(Wang et al., 2004; Hsu et al., 2007; Kirsh et al., 2007; Lam et al., 2010; Bosetti et al.,

2012; Wu et al., 2012). The lipophilic phytonutrients found in broccoli include the

carotenoids lutein, zeaxanthin, ß-carotene, and tocopherols (forms of vitamin

E) (Kopsell and Kopsell, 2006; Ibrahim and Juvik, 2009). In addition to their role

as vitamins, these compounds are powerful antioxidants (Kurilich et al., 1999;

Kurilich and Juvik, 1999). Consumption of vegetables high in tocopherols and

carotenoids has decreased the incidence of certain forms of cancer (Mayne,

1996). Lutein and zeaxanthin protect against development of cataracts and

age-related macular degeneration (Krinsky et al., 2003). Tocopherols have also

been associated with reduced risk of cardiovascular disease by preventing

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