Endive plants were hydroponically grown in greenhouse control conditions. The aim of this investigation was to assess the biological quality of endive cultivated in three different growing media. Organic media: coconut fiber and wood fiber, were compared to rockwool, commonly used as a standard horticultural medium in greenhouse vegetable production. Three crispum leaf endive cultivars: ‘Galanti’, ‘Perceval’ and ‘Barundi’ and one latifolium leaf cultivar (escarole chicory): ‘Kethel’ were examined during the spring time. At about 10 days before harvest the plants were covered with low tunnel made from double-sided black and white foil to bleach the leaves and at 5–7 days before the end of the experiment nutrient solution was replaced by water to reduce the nitrate concentration in the leaves of endive. The content of dry matter, ascorbic acid, total soluble solids (TSS), total sugars (TS), phenolic acids and nitrates (NO₃), P, K and Ca was determined in leaves of both bleached and not bleached plants. Also the antioxidant activity was measured by two assays DPPH and FRAP. The effect of cultivation substrate, cultivar, and bleaching treatment on the quality of endive appeared diversed. The unbleached endive showed a higher content of dry mass, higher concentrations of sugars, TSS, potassium, and calcium than the bleached plants. The bleached plants had significantly lower fresh mass of plants (by 33% in average), but in turn were characterized by higher concentrations of phosphorus and polyphenolic acids. Plants cultivated on wood fiber contained the smallest amount of nitrates, comparing to plants grown either on rockwool or coconut fiber. None of the investigated plants contained more nitrates than the acceptable level of nitrates for lettuce grown under cover. The antioxidant activity of endive plants measured by FRAP method was higher in not bleached endive plants than in the bleached ones. The antioxidant impact of endive plants expressed as DPPH was not reduced in response to bleaching. The highest antioxidant activity was observed in plants of ‘Kethel’.

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