Content of ascorbic acid, quercetin, kaempferol and total phenolics in commercial broccoli

A total of 80 commercial broccoli samples were collected over a two-year period to determine seasonal variation in the levels of ascorbic acid (AA), vitamin C (the sum of AA and dehydroascorbic acid [DHAA]), the predominant flavonoids quercetin and kaempferol, and total phenolics at the consumer level. Levels of AA and vitamin C varied between 13.37–110.30 and 57.35–131.35 mg/100 g fresh weight (FW), respectively. The levels of quercetin and kaempferol ranged from 0.03 to 10.85 and 0.24 to 13.20 mg/100 g FW, respectively. Total phenolic activity ranged from 48.15 to 157.77 mg/100 g FW. Significant seasonal variation and year-to-year variability were observed in the content of all phytochemicals examined. Total phenolic levels correlated positively with levels of vitamin C, quercetin, and kaempferol. Based upon the USDA/ERS 2007 database for consumption based upon sales, and the data reported herein, the daily availability of vitamin C from broccoli was estimated at 8.99 mg; accounting for 15% of Reference Daily Intake (RDI). The average daily availability of quercetin, kaempferol and total phenolics from broccoli was estimated as 0.23, 0.32 and 5.50 mg, respectively.