Enhancement of Health Promoting Bioactivity in Broccoli Florets by Increasing Levels of Selenium and Indolyl Glucosinolates

Broccoli (Brassica oleracea L. ssp. Italica) is a rich source of glucosinolates, phytochemicals that are hydrolyzed into isothiocyanates with known human anti-carcinogenic bioactivity. Increasing dietary intake of the element selenium (Se) also has been shown to reduce the risk of cancer. Previous research reported that Se fertilization at high concentrations reduces the concentration of glucoraphanin, the glucosinolate precursor of sulforaphane, an isothiocynate known to upregulate genes in mammals associated with detoxification of dietary carcinogens.

This research reports on simultaneous enhancement of both Se and glucosinolate concentrations in broccoli floret tissue. Methly jasmonate (MeJA) is known elicitor, active in increasing concentrations of indolyl glucosinolates and phenolic compounds in Brassica species. Five broccoli genotypes were subjected to root fertilization with solutions of Na₂SeO₄ and MeJA sprays to aerial portions of the plants at floral initiation and 4 days prior to harvest of the head, respectively. Two different levels of Se fertilization (32 and 982 mg/L of Na₂SeO₄) increased the concentration of Se in floret tissues across five genotypes from 3.0 (control) to 36.0 μg/g and to 520.3 μg/g, respectively. The low level of Se fertilization (32 mg/L of Na₂SeO₄) did not influence concentrations of glucoraphanin and total glucosinolates significantly, whereas the Se treatment (982 mg/L Na₂SeO₄) decreased concentrations of the aliphatic glucosinolate, glucoraphanin and total glucosinolates by 34 and 8%, respectively. The low level of Se fertilization with MeJA treatment displayed no significant change of glucoraphanin concentrations with a 90 and 50% increase in indolyl and total glucosinolates concentrations, respectively. These results suggest that selenium- and glucosinolate-enriched broccoli with improved health-promoting properties can be generated by this combined treatment.