Phytochemical composition and antioxidant properties of Portuguese kale and Portuguese tronchuda cabbage produced in a sustainable agriculture production system are affected by climate conditions.

摘要

In this study we evaluated the biological role of Portuguese kale and tronchuda cabbage, based on the determination of average levels of glucosinolates (individual and totals), total phenolics, total flavonoids, L-ascorbic acid (vitamin C), minerals (Fe, Zn and Se) and antioxidant activity, produced in two distinct seasons, spring-summer (SS) and summer-winter (SW) during two consecutive years. Spectrophotometric, spectrometric methods and HPLC methods were used to measure the average contents of the above components. The antioxidant activity was evaluated using the DPPH method and IC₅₀ values were estimated using a curve dose-response. Our results showed that Portuguese kale and Portuguese tronchuda cabbage exhibited high antioxidant activity with 80.6 and 82.2% inhibition of DPPH radicals respectively, and 1.49 and 1.97 mg ml-1 of IC50 average values respectively. These values were very similar to those found for broccoli inflorescences (81.9% of inhibition of DPPH radicals 1.97 mg ml-1 of IC₅₀ average level). Our results showed that the climatic seasons can affect directly (P<0.001) the concentration of the bioactive components and thereby the antioxidant activity. All Brassica showed high antioxidant activity in SS seasons, which seems directly associated to high levels of total flavonoids (P<0.01) and total phenolics (P<0.01). Minor effect was exerted by the climatic seasons on L-ascorbic acid and individual and total glucosinolates and zinc (0.01