2.7. Determination of contents of total phenols and flavonoids
The amount of total phenols in pear juice was determined according
to the method described by Singleton, Orthofer, and
Lamuela-Ravent
os (1999) with slight adjustments.
FolineCiocalteu 1.0 mL (10 times dilution, 10 mL/100 mL) was
mixed with 0.5 mL sample and left for 6 min. After adding 2.0 mL
sodium carbonate (20 g/100 mL), the mixture was kept at 30
C for
60 min in dark and the absorbance measured at 760 nm. The
amount of total phenols in pear juice was presented as
mg of gallic
acid equivalents (GAE) per gram of sample.
Total flavonoids content in pear juice sample was measured
using the reported method of Jia, Tang, and Wu (1999) with minor
adjustments. In short, 0.25 mL sample was mixed with 1.25 mL of
de-ionized water and 75
mL solution of sodium nitrite (5 g/100 mL)
and left for 6 min. Later on, 150
mL AlCl
(10 g/100 mL) solution
was added. After 5 min, 0.5 mL of 1 mol/L NaOH was added and
the total volume of the mixture was made 2.5 mL by adding
distilled water. The absorbance at 510 nm was measured and the
results were expressed as
mg of catechin equivalents per gram of
the sample.
3