The effects of temperature and pH on the extraction of oxalate and pectin from green kiwifruit (Actinidia deliciosa L.), golden kiwifruit (Actinidia chinensis L.), kiwiberry (Actinidia arguta) and persimmon (Diospyros kaki)

摘要

Oxalates and pectin were extracted from four locally grown fruits at three different pH levels, 6.9, 0.6 and -0.3, at two different temperatures, 21 and 80 ℃. Green kiwifruit (Actinidia deliciosa L. Hayward), golden kiwifruit (Actinidia chinensis L. Hort 16A Zespri), kiwiberry (Actinidia arguta, CV. Takaka Green) and persimmon (Diospyros kaki) contained moderate levels of oxalates. Total and soluble oxalates were more efficiently extracted at 21 ℃ using 2 m HCL, while the highest amounts of pectin were extracted from the fruits at 80 ℃ using 0.2 m HCL. Extraction using 0.2 and 2 m HCL gave the highest yields of total oxalates, which ranged from 47.1 to 220.4 mg total oxalates per 100 g dry matter (DM) for persimmon and kiwiberry, respectively. Extraction using water at 21 ℃ gave soluble oxalate contents ranging from 21.2 mg 100 g~(-1) DM, for persimmon, to 105.0 mg 100~(-1) DM, for kiwiberry fruits. Extraction of pectin was not achieved efficiently using water at either temperature, while extraction using 2 m HCL gave lower values; optimal extractions of pectin were achieved at 80 ℃ using 0.2 m HCL.