Evaluation of the antioxidant potential of cauliflower (Brassica oleracea) from a glucosinolate content perspective

Glucosinolates (GLSs) are of great interest for their potential as antioxidant and anticancer agents. Our aim was to assess in vitro antioxidant activity of cauliflower GLSs and their derivatives, as well as to evaluate their contribution to the overall antioxidant capacity of cauliflower extracts using four different in vitro assays, 2,2′-azino-bis-(3-ethyl-benzothiazoline-6-sulphonic acid) radical cation (ABTS+), 2,2-diphenyl-1-picrylhydrazyl assay (DPPH), oxygen radical absorbance capacity assay (ORAC) and superoxide radical scavenging activity assay (SRSA). The antioxidant activities of GLSs determined using ABTS+ and DPPH assays were weak. In contrast, ORAC and SRSA assays showed significant antioxidant activity for GLSs. This activity was particularly important for glucobrassicin, which was the most effective GLS, and for glucoiberin and gluconapin. Mixtures of GLSs did not show either synergy or antagonism in general. Interestingly, the breakdown products, i.e. enzymatic hydrolysis-derived products (EHDP) of GLSs, were far more active than the native GLSs. The highest increases in antioxidant activity were obtained for EHDPs from progoitrin, sinigrin and glucoraphanin; progoitrin EHDP being the second most active derivative behind glucobrassicin EHDP. Antioxidant activities and GLS composition of different cauliflower by-product extracts were also determined. The contribution of different GLSs on measured antioxidant activity of cauliflower extracts was also discussed.