Fruit were
homogenized for 1 min at medium speed in a blender. The
homogenate (25 g) was added to 75 mL of 6% metaphosphoric acid
with a homogenizer (Heidolph Silent Crusher M Homogeniser P/N-
595-06000-00, Germany) at medium speed for 1 min. Extracts
were centrifuged at 20,000
g for 15 min at 4 C and the
supernatant was collected into a 100 mL volumetric
flask. One
milliliter of the extract was
filtered through a membrane
filter
(0.45 mm, Macherey Nagel, Germany) and a 20 mL sample was used
for HPLC analysis of ascorbic acid. Extracts were analyzed using a
liquid chromatograph equipped with a diode array detector
monitoring at 254 nm. Separations were achieved on a Luna C18
(2) column (4.6
150 mm, 5 mm)
fitted with a guard column
(4
3.0 mm, 5 mm) of the same material (Phenomenex, CA). HPLC
elution was carried out at 30 C using 20 mM KH2PO4 pH 3.0/
acetonitrile (95:5) as the mobile phase at a
flow rate of 0.7 mL
min1. Results were expressed as mg ascorbic acid 100 g1 of fresh
weight.