2.2.4.3. Sample preparation for HPLC. The HPLC system was used to
measure the ascorbic acid concentration and the peptide fraction
concentration in orange juice. To prepare the samples for HPLC,
they were centrifuged at 7000 g for 5 min. The supernatant was
then filtered through 25 mm syringe filter into the sample holders.
The concentration of ascorbic acid remained the same after
centrifugation and filtration; this was tested by comparing the
concentration added and HPLC peak areas.