Effect of the year and storage on ascorbic acid content and total polyphenol content in three apple varieties

Ascorbic acid (AA) and total polyphenol content (TP) are important plant antioxidants with many healthy effects, such as "scavengers of free radicals", they inhibit oxidation of low-density lipoproteins, lower cholesterol levels, decrease fragility of blood vessels and increase their permeability, decrease heart coronary risk, etc. One of important sources of these compounds in human nutrition are apples. In two years (1997 and 1998) was investigated ascorbic acid content (AA) and total polyphenol content (TP) in three apple varieties (Idared, Gloster and Ontario) cultivated under equal conditions on the experimental plot of Czech University of Agriculture in Prague-Suchdol. AA content was determined by titration method with 2,6-dichlorphenolindophenol and TP content spectrophotometrically with Folin-Ciocalteau's reagent. In two years' trials AA and TP contents were estimated immediately after harvest in September and then monthly during storage for six months at +5°C. Statistically high significant differences were determined both in AA and TP contents during storage period - there was observed meaningful AA and TP decrease. The highest antioxidant content showed in both years early variety Ontario (in average 12.05 mg/kg AA, 2011.5 mg/kg TP), the lowest semi-early variety Gloster (in average 5.45 mg/kg AA, 1738.0 mg/kg TP). In this context the variety Ontario is the most favourable. The highest decrease of AA content was in variety Ontario (-30.05 %rel), the lowest in variety Gloster (-22.93 %rel ); in TP contents were differences negligible (-27.14 and -27.82 %rel). In spite of this decrease were in Ontario variety both values after six months storage the most favourable (8.45 mg/kg AA, 1466.5 mg/kg TP). Results were statistically evaluated with F-test and t-test. There could be seen differences among varieties and years of cultivation, but these differences were under the level of statistical significance showing only apparent tendencies. While varietal differences in decreasing of AA content during storage were greater (in interval from -22.93 %rel in Gloster variety to -30.05 %rel in Ontario variety), decreasing of TP contents during storage was nearly the same (about -27 %rel of original content