In the study – published in the journal Food Control – Dr Selena Wang and Hilary Green from UC Davis tested 22 samples from retail and online stores from all the major domestic and imported brands and oil types (eg. refined, extra virgin etc) and found six were adulterated with other oils (soybean, sunflower, safflower), while 15 were rancid (oxidized before the expiration date), degrading the oils’ flavor and health benefits.
‘When the oil becomes rancid, it loses the natural antioxidants and vitamin E over time’
The fact that stale avocado oil appears to be the rule, rather than the exception, suggests there’s an urgent need to develop standards, not only to ensure that consumers receive high quality products but to establish a level playing field in the industry, said Dr Wang, associate specialist in Cooperative Extension at the Department of Food Science and Technology at UC Davis.
“When the oil becomes rancid, it loses the natural antioxidants and vitamin E over time,” she told FoodNavigator-USA.
“And second, there’s some research that suggests that oxidized lipids have negative health effects and increase the risk of neurodegenerative diseases. As the antioxidant level goes down, the smoke point also decreases, so it impacts performance as well.”
‘Rancid oil tends to have a greasier mouthfeel’
From a sensory perspective, meanwhile, a lot of consumers are “so familiar with the smell of rancid oil that they think that’s what oil should smell like,” claimed Dr Wang.
“If you want to know what rancid oil smells like, open a bag of walnuts that’s been sitting in the cupboard for months; walnuts go rancid super-fast [as they are high in healthy polyunsaturated fatty acids, which are less stable]. Rancid oil also tends to have a greasier mouthfeel.”
But how badly oxidized were the sample avocado oils tested, and were most that UC Davis classified as ‘rancid’ just starting to go stale, or were they well past their prime?
“Because we don’t have any rules on this, you can’t say for sure what the threshold is, which is why we need standards,” said Dr Wang.
“Some were on the border, and some were very oxidized, and bear in mind that some of the oils that were quite oxidized based on several different oxidation markers still had a year of shelf-life remaining.”
When it comes to best before dates, meanwhile, there is no standard practice, added Gabriel Perez-Krieb, chairman and CEO at Chosen Foods, the only brand in the study (along with Marianne’s) with products that were pure (unadulterated) and non-oxidized (not rancid/stale).
“In our case, we code the best before date as 18 months from the date of production, and that’s on the label,” he told FoodNavigator-USA. “But some companies put it three years out, and you don’t know when it was produced.”
Storage and packaging
But why are the oils going rancid?
A combination of factors from using damaged or rotten fruits as source material (some of the products were “probably rancid almost from the…