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.
2.10. Colour density, polymeric colour and percentage polymeric
colour
The colour density (CD) of the water treated samples, polymeric
colour (an index of anthocyanin degradation) (PC) of the bisulfite
bleached samples and the percentage of polymeric colour were
analysed in triplicate using method proposed by Giusti and
Wrolstad (2001) with a slight modification.
Colour density (CD) was calculated using the control sample
according to the following formula:
CD ¼ ½ðA420 nm A700 nmÞþðA512 nm A700 nmÞ
dilution factor ð4Þ
Polymeric colour (PC) was determined using the bisulfide –
bleached sample using the following formula:
PC ¼ ½ðA420 nm A700 nmÞþðA512 nm A700 nmÞ
dilution factor ð5Þ
Percentage polymeric colour (% PC) was calculated using the
following formula:
%PC ¼ ðPolymeric Colour=Colour DensityÞ 100 ð6Þ
2.11. CI