Antioxidant capacity and nitrosation inhibition of cruciferous vegetable extracts

Cruciferous vegetables belong to the mustard family of plants such as Brussels sprouts, kale, broccoli, cabbage and cauliflower. They are well known for their cancer prevention properties which are due to high content of bioactive compounds, isothiocyanates (ITCs). This study was aimed to investigate nitrosation inhibition ability of the cruciferous vegetables commonly consumed with meat products namely, broccoli, cauliflower and cabbage. Aqueous extracts of fresh and steamed (2 and 4 min) vegetables were subjected to determination of antioxidant capacity (DPPH and FRAP assay) and chemical composition i.e. total phenolic and isothiocyanate (ITC) content. It was found that TPC, DPPH and FRAP values of raw vegetables were different in each vegetable and ranged from 17.12-38.91 mg GAE/100 ml, 44.09-63.31% and 1.36-6.81 mg TE/100 ml, respectively. Among three types of cruciferous vegetable, broccoli had the highest PEITC content being 0.21 mmol/100 g compared to cauliflower (0.15 mmol/100 g) and cabbage (0.06 mmol/100 g). Moreover, it was found that steaming process significantly enhanced antioxidant activity, TPC as well as PEITC content in a timedependent manner up to 4 min (p<0.05). Nitrosation reaction was stimulated in vitro at Ph 3.0 and spectrophotometric method was used to determine formation of nitrosodimethylamine (NDMA) in the presence and absence of cruciferous vegetable extracts. The highest NDMA inhibition was found in broccoli and steaming could promote the effect in all vegetables. Prevention of DNMA was believed to be a result of PEITC content in the vegetables because when anti-nitrosation ability of synthesized isothiocyanates was determined, PEITC acted as a potent inhibitor with 89.28% inhibition whereas that of ascorbic acid (positive control) was 88.57% and allyl isothiocyanate had the least effect (53.21%) at the same concentration. This study infers that the concomitant consumption of cruciferous vegetables may possess toxicity reduction of nitrosamine and these effects can be enhanced by a common heating process of the vegetables.