Antioxidant potential in broccoli and observations on flavor in a segregating broccoli population (Brassica oleracea)

Epidemiological studies indicate that broccoli consumption is inversely association with cardiovascular disease and cancer risk. Broccoli contains a number of bioactive compounds including glucosinolates, S-methyl cysteine sulfoxide (SMCSO) and many antioxidants that may be responsible for this protective effect. However, glucosinolates and SMCSO are also thought to negatively impact flavor and consumer acceptance of the vegetable, therefore increasing the level of these compounds in broccoli could be deleterious to its consumption. The antioxidant capacity of broccoli cultivars was investigated using the oxygen radical absorbance capacity (ORAL) assay and the dichlorofluorescin-diacetate (DCFH-DA) assay. The DCFH-DA assay was used to examine the antioxidant effects of broccoli extracts in HepG2 cells. The relationship between content of glucosinolates and SMCSO was also characterized in a broccoli population. ORAL assay findings indicated that water fractions of broccoli extracts had higher antioxidant capacity than lipid fractions and that cultivars varied in their antioxidant capacity. This variability was not associated with ascorbic acid or flavonoid content of the water fractions but was correlated with two carotenoids (lutein r = 0.57; zeaxanthin r = 0.81; p < 0.05) in the lipid fractions. DCFH-DA assay results showed that both water and lipid extracts of broccoli could significantly inhibit production of free radicals in HepG2 cells and that the effect was not correlated with ascorbic acid, flavonoid, carotenoid or tocopherol content. Correlation analysis between antioxidant capacity of broccoli extracts determined by ORAC or DCFH-DA showed that antioxidant capacity of water extracts from the ORAL assay correlated with antioxidant activity from DCFH-DA assay, but that for lipid extracts the ORAC assay could not predict antioxidant activity in cell culture. Results from the characterization of the relationship between glucosinolates, SMCSO and flavor indicated that glucosinolate content may have an impact on several flavor attributes, but SMCSO content did not affect broccoli flavor.