An Australian woman now knows why her supermaket-bought orange turned purple hours after it had been cut open.
Photo via @ABCscienceGreat to see a 'public health scare' clarified by science! https://t.co/SdK4wkF9W5
— Arwen Nugteren (@ArwenNugteren) September 26, 2018
Following multiple tests, these have been deemed by scientists as not a risk to human health.
But why did it turn purple in the first place?
It turns out that natural occurring anthocyanins in the orange reacted with the iron particles found on the knife that had been recently sharpened and used to cut it, caused it to turn purple.
Scientists from Queensland Government collected samples from the woman's home and also took the knife that was used to cut it, alongside the steel that had been used by her husband to sharpen the knife.
The results were highly anticipated and were finally released to ABC News this week.
Here's what the report from scientists said:
- Purple pigment from affected oranges was extracted using a mixture of water and ethanol
- When the pH of the extract was increased the colour changed from pink — blue — green/yellow which is characteristic of anthocyanins
- The extract had a maximum absorbance at approximately 573nm which is also characteristic of anthocyanins and different to many other natural colours
- Anthocyanins occur more in blood oranges, but the content can increase following a period of cold storage
- The regions of blue/purple discolouration were found to contain elevated concentrations of iron [and other metallic elements] compared to regions with a normal appearance
- When a piece of unaffected orange was treated with iron it produced an intense blue colour similar to that in the complaint samples
Speaking to ABC News following the results, the woman, Ms Moffitt, said that she was feeling amazement after the results.
"I'm glad we could find an answer, that would've been a real headscratcher otherwise", she added.
