A filtered
sap sample was diluted to 1/3000 with distilled water and
0.2 ml of 5% phenol solution was added to 0.2 ml of the diluted
sample, followed by an addition of 1 ml of sulfuric acid. Then
the solution was vigorously mixed and cooled at room
temperature for 30 min. Absorbance of the solution was
recorded at 480 nm. The calibration was carried out with
glucose as standard.