Ascorbic acid concentration was determined according to
Rapisarda (1996), by liquid chromatography HPLC (PerkinElmer,
Australia), using an injector (Rheodyne with 20 mL loop), a
photodiode detector, a Knauer Eurospher II 100-5C18 column
250 mm 4.6 mm I.D. (Berlin, Germany) and a similarly packed pre-
column. The elution was performed with a buffer solution
consisting of KH2PO4/H3PO4 at pH 2.3, at a
flow rate of 16.7 mL s1,
the wavelength was at 260 nm. An aliquot of freshly prepared pulp
(5 g) was homogenised with 25 mL of 3% metaphosphoric acid,
centrifuged,
filtered through a 0.45 mm Whatman Puradisc and
HPLC injected. The concentration of ascorbic acid was calculated
from the experimental peak area by analytical interpolation in a
standard calibration curve, and was expressed as mg kg1 of fresh
weight. Total polyphenol analysis was determined according to the
Singleton and Rossi (1965) method, using the Folin–Ciocalteau
reagent (FC) and the gallic acid as a standard. The FC reagent relies
on the transfer of electrons in alkaline medium from phenolic
compounds to phosphomolybdic/phosphotungstic acid complexes,
which are determined spectrophotometrically at 700 nm.
Thirty grams of peach fresh tissue for each replication was
homogenised with methanol (1:10, w/v). After
filtration through a
Whatman grade N. 1
filter paper, methanolic extracts were
concentrated under reduced pressure and the residue was
suspended in 50% (v/v) aqueous methanol and used for phenolic
content assay. Results were expressed as mass of gallic acid
equivalents (mg kg1 fresh weight).