Chlorogenic acid (3-O-ceffeoyl-D-quinic acid), an ester of caffeic acid with quinic acid, is one of the phenolic compounds from the group of hydroxycinnamic acids found in lettuce. It has many properties beneficial to health, among other things antioxidant, antimutagenic and anticarcinogenic. In this work the effect of calcium ions on the content of chlorogenic acid in fresh and storaged leaves of lettuce were studied. The changes of total phenoloc compounds expressed as chlorogenic acid equivalents and antioxidant activity were also evaluated in this research.

The plants from pot experiment were treated with 0,1 M CaCl₂ solution as spray on leaves and then divided into three parts one of that was processed directly after harvest and others were being storeged for 7 and 14 days at 5^oC. In this studies lyophilized samples of lettuce “Omega” cultivar were used from whitch chlorogenic acid was extracted with 70% (v/v) aqueous methanol solution. After evaporation to dryness the residues were dissolved in water and cleaned by means of SPE extraction using SepPak C₁₈ column. Sampling fraction containing phenolic compounds was eluted with 60% (v/v) aqueous methanol solution and next was separated on individual components by HPLC, Eurosil Bioselect 300-5 C₁₈ Column (300 x 4 mm) with gradient elution: A-5% formic acid in water, B-methanol. The content of chlorogenic acid was calculated with the use of calibration curve. Total phenolic compounds of isolated fraction was determinated according to the Folin-Ciocalteu procedure. Antioxidant activity was determined by DPPH assay.

Results from our experiment indicated that calcium ions used in our research have beneficial effect on formation of chlorogenic acid and dicaffeoyl tartaric acid in the leaves of lettuce. There was found approximately threefold increase of the level of chlorogenic acid and 30% increase of the level of diceffeoyl tartaric acid in compare to control. High correlation coefficient between antioxidant activity of isolated fraction, the level of chlorogenic acid and calcium ions indicates on high contribution of this ions in biosynthesis of phenolic acids.

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