Environmental Temperatures Influence Antioxidant Properties and Mineral Content in Broccoli Cultivars Grown Organically and Conventionally

Broccoli (Brassica oleracea L.) is a widely consumed cool-season crop that is well-known for its health benefits and high nutritional content. With a growing consumer interest in local and organic foods, it would be helpful to determine if farmers can improve the nutrient and antioxidant content of broccoli through cultivar selection and to gain insight into environmental effects on nutritional properties. This study evaluated total phenolic content (TPC), antioxidant capacity (ABTS.+ assay), and ascorbic acid (AA), as well as the levels of ten nutrients (N, P, K, S, Ca, Mg, Zn, Fe, Mn, and Cu) in six broccoli cultivars (‘Arcadia,’ ‘Emerald Pride,’ ‘Gypsy,’ ‘Packman,’ ‘Premium Crop,’ and ‘SBC8410’). Six cultivars were grown in Northern Colorado for two years using conventional and certified organic practices. Production year had a significant effect (p<0.05) on both antioxidant levels and nutrient levels, perhaps a result of warmer temperatures reflected by quite different weather patterns between the two growing years. Nutrient levels were higher in 2005, a cool production season, while antioxidant levels were higher in 2006 in a warm season (p<0.0001). Organic broccoli had overall higher levels for TPC, antioxidant capacity, P, K, and Ca, while conventional broccoli was higher in Fe (p<0.05). Significant cultivar differences were found in most tests. All three antioxidant tests were positively correlated (p<0.05) with each other and negatively correlated with N, P, K, S, Ca, Mg, Zn, Mn, and Cu levels, indicating an inverse relationship between antioxidant levels and mineral content. This study suggests that choice of cultivar provides a viable option for local farmers who may wish to market more nutritious broccoli. Additional work is needed to confirm the preliminary indication that warm temperatures may trigger elevated antioxidant properties, but lower mineral uptake.