Dry matter
The dry matter of fresh apples was performed by gravimetric
method, according to Polish Norm [19]. Fresh apple
samples (1.5 g) were precisely measured and dried at 70 °C
in a vacuum (3 kPa), until a constant weight. The measurements
were performed in triplicate and expressed as g of
dry weight/100 g of fresh matter.
Total soluble solids
Percentage of total soluble solids was determined refractometrically,
using electronic Pocket Refractometer PAL-1
(Atago, USA). The measurements were taken in triplicate
and expressed in g of soluble solids/100 g of fresh matter.
Titrable acidity
Titratable acidity of samples was determined by using a
pH meter (IQ’s Scientific Instruments), according to Polish
Norm [20]. The chopped apples were transferred to a
volumetric flask (100 ml) and filled with water. Prepared
samples were boiled and filtered after cooling down.
About 10 ml of obtained filtrate was titrated with NaOH
(0.1 mol L−1
) up to pH 8.1. The measurements were performed
in triplicate and expressed in g of malic acid/100 g
of fresh matter.