Agrobiodiversity in organic Brassica crops: relationship between pigment composition and antioxidant activity

Within the framework to increase the sustainability in agriculture, the BRESOV H2020 project (http://bresov.eu) is working for implementing Brassica oleracea organic breeding and farming through the evaluation of agrobiodiversity. We evaluated the main quality parameters of the produce of Brassica genotypes obtained from breeding activities among accessions of B. oleracea L. var. botrytis and B. oleracea L. var. italica, aimed to increase the adaptation for organic farming. Eighteen genotypes (parental and hybridized lines) were evaluated for dry matter, soluble solid contents (SSC), ascorbic acid (AsA) content, pigment composition, as well as antioxidant activity (Folin-Ciocalteu, FC, and DPPH scavenging index). The main objectives of this work were to: a) establish the variability of each quality parameter; and b) determine possible relationships between pigment composition and antioxidant activity. The considered pigments, total anthocyanins (ATH), chlorophylls (Chl a and Chl b) and total carotenoids (CAR), were measured using spectrophotometric methods. The antioxidant activity was measured using protocols previously validated for Brassica extracts. The results indicated a great variability of pigment composition, particularly for Chl b, with the highest coefficient of variation (CV=173%), while, unexpectedly, the Folin-Ciocalteu index showed the lowest CV (19%). Ascorbic acid content ranged from 4.2 to 414.3 mg 100 g-1 dw (CV=47%), while total anthocyanin content ranged from 15.2 to 113.5 mg 100 g-1 dw (CV=68%). The antioxidant assays were reciprocally well correlated (r=0.679, P=0.002). The correlation between chemical measurements and antioxidant activity highlighted the contribution of ATH to DPPH scavenging index (r=0.854, P=<0.0001). The FC index was similarly correlated to both ATH (r=0.499, P=0.035) and CAR (r=0.486, P=0.041). Unexpectedly, no significant correlations were found between AsA content and DPPH index. These results indicate the key role of anthocyanins as antioxidant compounds in Brassica genotypes.