Southern Cross University. Australia: It’s known as native spinach, now researchers at Southern Cross
University are trying to determine if Warrigal greens contain similar
levels of oxalic acid as found in spinach and kale. One of the main obstacles to Warrigal greens (Tetragonia tetragoniodes)
being adopted as a mainstream vegetable - and a viable alternative to
spinach - is the perceived high levels of oxalic acid in the leaves. In
rare cases, too much oxalic acid can cause kidney stones.
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Lead researcher is Associate Professor Bronwyn Barkla from Southern
Cross Plant Science. Professor Barkla is being assisted by chemist and
Research Fellow Dr Ben Liu, also from Southern Cross Plant Science, and
2015 SCU Science Summer School student Carolyn Vlasveld, a Bachelor of
Science graduate from Monash University.
“Oxalic acid is a naturally occurring chemical that is found in many
different food sources such as leafy greens, nuts, seeds, most berries,
certain fruits, soy and soy products, as well as meat and dairy
products,” said Professor Barkla.
“High oxalic acid levels in food may constitute a risk to human health
as these compounds readily bind calcium and other mineral nutrients to
form oxalate crystals. This decreases the ability of the body to absorb
these essential nutrients but also, the build-up of calcium oxalate
crystals in the urinary tract is thought to lead to the formation of
kidney stones.
“Studies have shown that soluble oxalate levels in T. tetragonioides can range from 1.5 per cent in leaves of older plants to 12 per cent in leaves of young plants.
“However, these levels are comparable to those reported in some
varieties of spinach including those grown commercially. Yet people
consume spinach on a daily basis.
“In this project we will grow both T. tetragonioides and a
commercial spinach variety under similar growth conditions and directly
compare the levels of oxalate in both young and old leaves of these
plants to perform a direct comparison.”
Tetragonia tetragoniodes, which is high in antioxidants as well
as other minerals, nutrients and vitamins, is a common coastal and
estuarine species of the Pacific region. It is native to New Zealand,
Australia, Japan, Chile and Argentina.
Professor Barkla said Warrigal greens - also known as Botany Bay greens,
tetragon, native spinach or New Zealand spinach – was eaten by both
Indigenous Australians and the early settlers.
“Its use was first mentioned by Captain Cook who ordered that it be eaten by his crew on board the Endeavour to fight scurvy.”
Professor Barkla said Warrigal greens was a hardy crop and could be used to remediate salty soils.
“What makes this plant particularly attractive for cultivation is that
it is significantly salt tolerant, showing the typical response of
halophytes to salinity, with growth enhancement at low salt
concentrations and tolerance of high salt concentrations, unlike most
crop plants where soil salinisation results in unacceptable decreases in
quality and yield.
“The cultivation of this native species would provide more options for
landowners where the salt levels are already moderate to high, allowing
for the increased use of degraded or marginal lands for agricultural
production or the conservation or rejuvenation of ecosystems through the
ability of this plant to bioremediate saline soils through the
hyper-accumulation of salt from the soil into the aerial parts of the
plant.”
Carolyn Vlasveld is assisting Professor Barkla during the month of
January as part of the annual SCU Science Summer School. The Summer
School is designed to give early career scientists experience in
different aspects of research including field work, laboratory based
activities, analysing data and writing up results and conclusions.
“It’s exciting to be part of this project,” said Carolyn, who plans to do post-graduate study focused on plant science.
“There are many Tetragonia plants back home in Melbourne. If I am
able to find out that the levels of oxalic acid are okay then I’ll
definitely be eating them.”