The extract for the assay of PAL was generated by the method of
Zheng et al. (2012), with some modifications. A 5-g sample of mixed
tissue from the peel or pulp of each replicate was homogenized in
20 mL of 50 mM sodium borate buffer, pH 8.8, containing 0.3 g
polyvinyl polypyrrolidone (PVPP) and 5 mM b-mercaptoethanol.
.