Formation of zinc-chlorophyll-derivative complexes in thermally processed green pears (Pyrus communis L.)

The formation of zinc-chlorophyll-derivative complexes was investigated in peels-on green D'Anjou pears when subjected to blanching in zinc ion solution (1300, 2600, and 0 ppm) at 94 degrees C for 6, 12, or 18 min and then canning at 94 degrees C for 20 min. The peels removed from the pears were freeze-dried and ground into powders in liquid nitrogen for pigment extraction using ethyl ether. The visual absorption of the extracts was measured using a spectrophotometer along with identification and quantification of chlorophyll derivatives using reverse-phase HPLC method. Furthermore, pears with or without the peels were blanched in 2600 ppm of zinc solution for 12 min following the canning process in 10 degree Brix syrup solution. Total antioxidant (TA) and total phenolic content (TPC) of the pear flesh and peels were evaluated using Folin-Ciocalteu's phenol and 1,1-diphenyl-2-picrylhydrazyl assays. Thermal processing destroyed chlorophylls on pear peels, in which pheophytins were found to be the major degraded compounds while an insignificant amount of pyropheophytins was also formed. In zinc blanched peels, Zn pheophytins a was the dominant green compound, and its amount increased about 100% and 144.4% in peels blanched in 1300 ppm zinc solution for 6 and 12 min, respectively. When blanching peels in 2600 ppm zinc solution for 6 and 12 min, the pigment increased about 118% and 242%, respectively. Significant reductions in TA and TPC were found on the peels of zinc treated pears, but the overall TA and TPC of whole fruits were not significantly affected by the treatments.