ANTIOXIDANT ACTIVITY IN NETTLE (URTICA DIOICA L.) AND GARDEN ORACHE (ATRIPLEX HORTENSIS L.) LEAVES DURING VEGETATION PERIOD
Different vegetables are a good source of essential components for human food. Consumers are more and more aware of a healthy and balanced diet. Vegetables usually contain natural antioxidants which neutralize free radicals in the human body. The composition of biologically active compounds in plants is depending on the climate and growing conditions, cultivar properties, plant development stage, harvesting time, and other factors. The aim of the research was to evaluate the fluctuation of antioxidant activity in leaves of four common nettle (Urtica dioca L.) clones and three garden orache (Atriplex hortensis L.) varieties during vegetation period in Latvian conditions. Experiments were carried out in open field conditions in the Pūre Horticultural Research Centre during the vegetation period of 2014, in two soil fertility variants for nettle and two sowing periods for garden orache. Antiradical activity was determined using the 2.2-diphenyl-1-picrylhydrazyl radical (DPPH*) method. In nettle leaves, antioxidant activity ranged between 17.31–80.77 %, depending on soil fertility, nettle clone and plant age, and in orache leaves between 17.9–54.0 % depending on variety and sowing time. In nettle leaves, the antioxidant activity at the beginning of the vegetation period ranged between 31.0–62.7 %, the highest activity was observed at the stem elongation stage (75.5–78.5 %). A higher antiradical activity was detected in the control variant (without compost treatment) at the 3–5 and 7–9 leaves stage. In other development stages, better results were obtained in the fertilized variant where compost and peat were used as an organic manure. Differences were found also among clones, especially in the 3–5 leave stage. Significant differences for garden orache leaves were found between sowing times. In the first growing period the antiradical activity ranged between 46.1–54.0 %, in the second it was two times less.