2.5. Moisture content
The moisture content of blueberries was measured using hot
air-oven (FED53 127 Binder, USA) according to the standard
method (AOAC, 1975) (105 C, 24 h). The results were presented
as an average of three measurements.
2.6. Extraction procedure for total polyphenols and antioxidant
capacity
Extraction of blueberries (5 g/25 mL) was performed in triplicate
in acidified 80% methanol (0.1% HCl; v/v) according to
Zheng, Wang, Wang, and Zheng (2003). Supernatants obtained
were subjected to analyses of total phenolic compounds (TPC),
total monomeric anthocyanins (TMA), measurement of percentage
polymeric colour, determination of pigment degradation and
measurements of antioxidant capacity by TEAC ABTS assay.
2.7. Total polyphenolic compounds (TPC)
The modified method of Horszwald and Andlauer (2011) was
applied to evaluate the content of TPC in blueberries samples.
The analysis was performed on microplate reader (Tecan Infinite
M1000 Pro, Tecan Group, Mannedorf, Switzerland). The results
obtained were expressed as g gallic acid equivalent (GAE)
100 g1 DM.
2.8. Total monomeric anthocyanins (TMA)
TMA were quantified by pH-differential method according to
Giusti and Wrolstad (2001) with the use of above-mentioned
equipment. Extracts of blueberries (n = 3) were diluted with two
buffer solutions at pH 1 and 4.5. Cyanidin-3-glucoside (Cy-3-G)
(MW = 449.2 g mol1) was used as a standard with a molar
absorptivity coefficient of 26,900 L mol1 cm1. The results were
expressed as g Cy-3-G 100 g1 DM.
2.9. Trolox equivalent antioxidant capacity (TEAC) by ABTS
TEAC assay was performed as described by Horszwald and
Andlauer (2011) with the above-mentioned equipment. The results
obtained were expressed as mmol Trolox Equivalents (TE)
100 g1 DM. Three replicates per treatment were done.