Abstract
Oxalic and phytic acid are phytochemicals considered to be anti-nutritional factors as they are predominantly found as oxalates and phytates bound to minerals like calcium and potassium. Studies have associated excessive oxalate consumption with increased urinary excretion of oxalate (hyperoxaluria) and calcium oxalate kidney stone formation, and excessive phytate consumption with decreased bioaccessibility and bioavailability of certain minerals and reduced utilization of dietary protein. However, other studies suggest that dietary consumption of phytate may be beneficial and inhibit formation of calcium oxalate kidney stones. In light of these conflicting reports, dietary intake of oxalate and phytate enriched plants should be considered in relation to potential health outcomes following consumption. Terminalia ferdinandiana is one such plant and is investigated here with respect to oxalate, phytate, and mineral contents. Assessment of oxalate and phytate contents in T. ferdinandiana fruit, leaf, and seedcoat tissues through hydrolysis into acid forms revealed oxalic acid contents ranging from 327 to 1,420 mg/100 g on a dry weight (DW) basis whilst phytic acid contents ranged from 8.44 to 121.72 mg/100 g DW. Calcium content in the different tissues ranged from 131 to 1,343 mg/100 g. There was no correlation between oxalic acid and calcium, however a significant, positive correlation was observed between phytic acid and calcium (r = 0.9917; p < 0.001), indicating that tissues rich in phytic acid also contain higher levels of calcium. The high content of phytic acid in comparison to oxalic acid in T. ferdinandiana fruit found in this study and the dietary significance of this in terms of calcium bioavailability, needs to be investigated further.
Highlights
Terminalia ferdinandiana (Kakadu plum) is a native Australian fruit consumed by Indigenous communities for centuries
Study on the proximate composition of the kernels of T. ferdinandiana showed that kernels contain 32% protein, 35% fat and is a good source of minerals and nutrients (17)
Studies on the proximate composition of T. ferdinandiana fruits, leaves and seedcoats are scarce and no values are available for comparison
Summary
Terminalia ferdinandiana (Kakadu plum) is a native Australian fruit consumed by Indigenous communities for centuries. Commercial demand for T. ferdinandiana fruit continues to increase because of its high vitamin C content (2). A variety of T. ferdinandiana food products are available in the market such as juices, sauces, jam and whey product isolates. A number of T. ferdinandiana nutraceutical products such as energy bar (with quandong), probiotic (with manuka honey), probiotic punch (with cranberry), analgesic spray, dietary supplements (tablet and liquid format) and freeze dried powder are available. A report on the high levels of oxalate (2) present in T. ferdinandiana fruits has raised concerns regarding the potential risk of kidney stone formation following fruit consumption. Normal dietary intake is reported to be in the range of 50–200 mg oxalate per day but can exceed 1,000 mg per day if foods rich in oxalate are consumed
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