The content of glucose increased in completely ripe strawberry fruits. The increase was the highest in the cvs. ‘Fern’ and ‘Kent’. The cvs. ‘Elsanta’ and ‘Pegasus’ were exceptions. Their fruits exhibited lower amounts of glucose in completely mature fruits. The highest contents of glucose measured in this stage were in the cvs. ‘Fern’ (28.2 g/kg) and ‘Northaester’ (27.1 g/kg), while the fruits of cvs. ‘Marmolada’ (16.3 g/kg) and ‘Elsanta’ (16.9 g/kg) contained the lowest amounts of glucose.
The content of fructose increased at the transition between the stage of early ripeness and the stage of complete ripeness of strawberries. During this time the highest increase in the fructose content was measured in the cv. ‘Fern’ (by 9.5 g/kg), which also contained the most fructose of all (33.0 g/kg). A slightly lower increase was measured in the cvs. ‘Kent’ (by 5.8 g/kg) and ‘Evita’ (by 5.6 g/kg). During the two stages of maturity the smallest differences in the contents of fructose were calculated in the cvs. ‘Elsanta’ and ‘Pegasus’, namely 0.4 g/kg. On average, less ripe fruit contained 22.3 g/kg of fructose, while more ripe ones had 26.2 g of fructose per kg of fresh fruits.
The highest content of xylose, which however, presents a small share among the sugars even in highly ripe fruits, was measured in the fruits of the cvs. ‘Northeaster’ and ‘Simphony’ (1.4 and 1.2 g/kg, respectively). The lowest amounts were in the cvs. ‘Miss’ (0.5 g/kg) and ‘Selena’ (0.6 g/kg). The results point to the fact that there are very small differences in the xylose contents among the technologically and completely ripe fruits of the treated cultivars. The mean xylose content is the same in all the varieties (0.9 g/kg).
The highest share of total acids (approximately 90%) was exhibited by citric acid (Table 2). Its content decreased with the maturity of fruits in the majority of cultivars. But in the cvs. ‘Kent’ and ‘Northaester’ the content of citric acid increased. The mean content of citric acid in the fruits during the stage of technological maturity (column 1) extended from 4.4 g/kg in the cv. ‘Miss’ to 10.4 and 10.5 g/kg in the cvs. ‘Evita’ and ‘Fern’, respectively. During the stage of complete ripeness (column 2) the strawberry fruits of the cv. ‘Fern’ contained the highest amount of citric acid, namely 10.3 g/kg, while the cv. ‘Miss’ fruits exhibited only 4.5 g/kg. On average, the content of citric acid in the strawberry fruits reached 8.4 and 8.2 g/kg, and it did not differ statistically significantly among the cultivars with regard to the stage of ripeness.