Antioxidative and antimutagenic activities and polyphenol content of pesticide-free and organically cultivated green vegetables using water-soluble chitosan as a soil modifier and leaf surface spray

Five green vegetables (qing-gen-cai, Chinese Cabbage, spinach, Welsh onion and green pepper) commonly used in our daily diet were analysed to determine their antioxidative and antimutagenic activities and chemical content of polyphenols. We obtained pesticide-free and organically cultivated (O) vegetables using water-soluble chitosan as a soil modifier and leaf surface spray (as an alternative natural insecticide) in order to investigate biofunctions induced or enhanced by such specialised cultivation practices. In addition, we purchased the same varieties of vegetables cultivated on an adjacent farm in the conventional manner (C) using pesticides and chemical fertilisers in order to examine the differences in biological activities and distribution of constituents responsible for such activities. The antioxidative activity shown by O vegetables was 120% times higher than that shown by C vegetables in the case of spinach and 20–50% higher in the case of Welsh onion, Chinese cabbage and qing-gen-cai. In comparison with C vegetables, the antimutagenic activity shown by O vegetables was higher against 4-nitroquinoline oxide (4NQO) in qing-gen-cai, Chinese cabbage and Welsh onion, against benzo[a]pyrene (BaP) in all five vegetables, against 2-amino-3-methylimidazo[4,5-f]quinoline (IQ) in qing-gen-cai, Chinese cabbage and green pepper and against 3-amino-1-methyl-5H-pyrido[4,3-b]indole acetate (Trp-P-2) in spinach only. Among all green vegetable juices tested for flavonoid composition, quercitrin, caffeic acid and baicalein in O vegetables were detected in concentrations 1.3–10.4 times higher than those found in C vegetables, suggesting the influence of different cultivation practices.