Ingredients other than oregano made up between 50% and 90% of the adulterated samples, according to Choice, a sister organisation of the UK-based watchdog Which?, which published similar findings last year.
Choice said findings show food fraud is occurring in the supply chain and has referred the matter to the Australian Competition and Consumer Commission (ACCC), which has started an investigation.
‘You shouldn't need a lab test to tell what herb you're buying’
In August and September 2015, Choice bought 12 different dried oregano products.
- Coles Oregano Leaves
- G Fresh Oregano Leaves "Mediterranean"
- Herbie’s Spices Oregano Leaves
- Hoyt's Oregano Leaves Rubbed
- Master of Spices Oregano Leaves
- MasterFoods Oregano Leaves
- McCormick Oregano Leaves
- Menora Oregano
- Spencers Oregano
- Spice & Co. Oregano Leaves
- Stonemill (Aldi) Oregano
- Woolworths Select Oregano Leaves
A sample from a single batch of each was tested using Fourier Transform Infrared (FT-IR) spectroscopy and chemometric modelling.
Products were a mixture of major brands sold in supermarkets and smaller ones sold through independent delis and grocers in Sydney, Melbourne and Perth.
Five were 100% oregano but the other seven – from brands Master of Spices, Hoyt's, Stonemill (Aldi), Spice & Co, Menora, Spencers and G Fresh – contained ingredients including olive leaves (in all seven samples) and sumac leaves (in two samples).
Choice said it tested just one sample of a single batch from each brand, so results might not be indicative of individual brands and companies' whole range of oregano products. Brands found to be affected by adulteration in the spot check may be selling other batches that are fine.
However, it also couldn’t guarantee the authenticity of all batches from brands found to be 100% oregano.
"To find that we have been supplied a product that is not as per provided paperwork nor our own product specification is extremely shocking and disappointing," Spice & Co told Choice.
The firm notified its retailers and advised it would hold and not re-supply its product until it had ‘absolute assurance’ of the integrity of the oregano.
Spice & Co told the watchdog the supplier was doing further tests on the item and additional "authenticity/botanical" testing in future.
Aldi has signs in stores advising that "in the approximate period between January 2015 and March 2016 the Stonemill Oregano and Stonemill Mixed Herbs did not meet Aldi's product specifications", and requesting that customers return the products for a full refund, according to Choice.
Consumers should be able to trust labels
Choice said consumers need to have confidence in food labels.
“At the end of the day all entities along the supply chain are responsible for the authenticity and traceability of the product being sold to consumers.
“Choice would like to see retailers, suppliers, producers and enforcement agencies increase and improve checks to ensure that all oregano products – and indeed all packaged herbs and spices – are what they say they are on the label.”
In the Which? investigation 19 of 78 samples contained other ingredients, mostly olive and myrtle leaves but also cistus. They were found to make up 30% - 70% of the product.
Tests by mass spectrometry were by Professor Chris Elliott, director of the Institute for Global Food Security at Queen’s University in Belfast.
Results were shared with the Food Standards Agency (FSA) who said it would look into the issue but did not put a timeline on any investigation.