A comparative study of phenolic compounds and antioxidant and antiproliferative activities in frequently consumed raw vegetables

The aim of this study was to assess the antioxidant value and antiproliferative activity of some vegetables such as raw garlic (Allium sativum L), white and yellow, and red onions (Allium cepa L), red and green peppers (Capsicum annuum L.), and white cabbage (Brassica oleracea var. capitata f. alba), which were harvested in the same year and in the same geographical and climatic conditions. It was found that the highest content of some bioactive compounds (25.19 ± 2.2 mg GAE/g, 3.84 ± 0.3 mg CE/g, 4.88 ± 0.3 mg CE/g, 59.20 ± 0.8 μg CE/g, 1992 ± 99.8 μg AA/g, 452.7 ± 26.1 mg CGE/kg DW for polyphenols, flavonoids, tannins, flavanols, ascorbic acid, and anthocyanins, respectively) and the antioxidant activity (41.32 ± 3.9, 31.05 ± 2.7, 59.17 ± 5.2 and 58.94 ± 5.1 μM TE/g for DPPH, FRAP, CUPRAC and ABTS, respectively) was in red onion. Methanol extracts in concentration of 1,000 μg ml⁻¹ of garlic and red onion exhibited antiproliferative activity (83.1 ± 2.1 and 85.0 ± 3.2% of viability, respectively). In spite of relatively high antioxidant activity in methanol extracts of yellow onion, red and green pepper, no antiproliferative activity on both tumor cell lines was registered. In conclusion, among the studied vegetables raw red onion was the preferable. The interrelationship was in the following order: red onion > white onion = yellow onion > red pepper > garlic = green pepper > white cabbage. The antiproliferative activities of these vegetables were different: some samples reacted only on Calu-6 and the others—on SNU-601. Thus, vegetables from the same cultivation place were examined for their antioxidant and antiproliferative activities with four different methods. Based on obtained data a direct comparison between these vegetables was possible for the first time.