for polygalacturonase (PG, EC 3.2.1.15) extraction, the same
procedure was used as for PME but with 0.5 M NaCl and 2% PEG
(polyethylene glycol). The procedure of Lohani, Trivedi, and Nath
(2004), adapted to grapes, was used for the assay: 0.4 ml of extract
were incubated with 1.2 ml of 0.2 M sodium acetate (pH 4.5) buffer,
to which 1.2 ml of 0.5% polygalacturonic acid was added. The
sample was incubated at 37 C for 1 h, then boiled (100 C for
5 min) after the addition of 400 ll of 0.1% DNS (3,5 dinitrosalicylate)
prepared in 30% potassium sodium tartrate and 0.4 M
NaOH. PG reading was taken at 540 nm. Enzyme activity is
expressed in lmol/min gdw.