Olive oil is well known for its health benefits. The star of the Mediterranean diet, it is rich in good fats and beneficial bioactive compounds with antioxidant and anti-inflammatory properties and is linked to improved cardiovascular and metabolic health.
The process of making olive oil produces waste, but when science and tradition unite a new, potentially useful product emerges – olive mill wastewater.
Admittedly, ‘olive mill wastewater’ or OMW, the name typically used by scientists, is not a particularly appetising name for a new superfood candidate. As the name suggests, it is one of many byproducts created when olives are milled and the oil separated and filtered.
To improve economic returns, manufacturers often look for ways to reuse, recycle or compost waste materials and convert them into more useful products.
For example, the solid waste products from olive oil production, olive pomace, olive oil sediment, olive pit residue and spent olive cake can all be used as animal feed, compost, or biomass fuel.
OMW is the liquid waste produced during the olive oil extraction process. It is a dark, cloudy, bitter and slightly acidic liquid, and millions of litres of it are generated each year.
Oddly enough, given its recent emergence as a potential superfood, it is considered to be the most harmful byproduct created during olive oil production. It contains large amounts of organic and phenolic compounds, which can make it toxic to plants and animals through contamination of soil and waterways if it’s not properly treated and managed before release.
However, one family-run farm in Tuscany, Italy has found alternative uses for OMW and are using it to create health supplement shots and a biodynamic cosmetics range called OliPhenolia. The jars of shots come in natural bitter and sweetened forms and are based on the traditional consumption of ‘aqua mora’, an old Italian name meaning ‘dark water’, as a health tonic.
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Scientists have also been looking into the contents of OMW and how it might be used. The high level of organic compounds known as phytochemicals or phytonutrients, the very thing that makes it harmful to the environment, has many potential health benefits for humans.
Phytochemicals are compounds produced by plants as natural defences against environmental stressors and predators. Although they aren’t essential nutrients needed for survival, they can have a positive impact on human health, earning them the broader name of bioactive compounds or bioactives.
What beneficial compounds are found in OMW?
The bioactives in OMW include 30 or more phenolic compounds such as tannins and flavanols, plus dietary fibres such as mucilage and pectin. These compounds have antioxidant, anti-inflammatory, antimicrobial, and anticarcinogenic properties and can also lower blood sugar and cholesterol and benefit the gut microbiome.
These compounds are thought to be part of the reason why plant foods are good for our health, above and beyond the essential nutrients they contain. High consumption of bioactives is linked to a reduced risk of cardiovascular diseases, metabolic disease, diabetes, cancer and more.
Because many of these phenolic compounds are water soluble, the concentration can be up to 10 times higher in OMW than in regular olive oil, with levels varying depending on pressing methods, storage and olive type.
This health-giving wastewater could be consumed as a drink, tonic or elixir, and there are also methods of extraction that can concentrate the bioactives and nutrients, allowing them to be used in other products.
However, to be successful, these techniques need to be cheap enough to produce products that are valuable enough to outweigh the costs associated with the treatment and discharge of waste.
Most of the research on OMW is centred around its potential use as a source of ‘nutraceuticals’. Nutraceutical is a portmanteau combining the words ‘nutrient’ and ‘pharmaceutical’ and is used to describe products derived from food and plant sources that have significant health benefits.
Nutraceuticals are complex mixes of nutrients and bioactives, which can combine to have greater effects. They can be used as supplements or added to foods to boost their bioactive health benefits. They can be used in food production as natural preservatives.
In 2021, at least five companies around the world were known to be extracting phenolic compounds from OMW for use as natural preservatives or bioactives to be added to food products or supplements.
So, can we expect OMW to become the next wheatgrass or apple cider vinegar shot? Maybe. History shows that we humans love a superfood with a great origin story, and we love the idea of supplements and tonics that feel like especially healthy silver bullets.
A bias called the ‘unhealthy-tasty intuition’ also means we often believe that foods or drinks that taste bad are more likely to be healthy, compared to tasty foods, which we are more likely to believe are unhealthy.
Human trials are next up
It’s important to note that while multiple studies have been conducted by testing OMW directly in cell cultures and on microbes, no studies have yet been conducted in actual humans to assess any direct health benefits.
Conversely, multiple studies have been conducted on the health benefits of olive oil.
Whole olives contain all the nutrients and bioactives of both the olive oil and OMW as well as the dietary fibre that is lost during oil production. But olives can’t actually be eaten fresh – they need to be processed by pickling or curing to make them edible.
This means they need to be soaked for a long time and can lose many of the beneficial compounds during processing. This can also make the resulting products high in salt and so could negate some of the benefits. However, compared to olive oil, the health benefits of olives as a food are not actually very well studied.
Phytochemicals are plentiful in all plant foods, so can be readily accessed in a diet high in fruits, vegetables and whole grains. Bioactive compounds are also many and varied, with more than 10,000 currently identified.
This means consuming a specific bitter drink or extracting the bioactives for functional foods or other nutraceutical products for repeat consumption isn’t likely to be more beneficial than the combinations found in a healthy balanced diet.
Eating whole plant foods also has the added benefit of displacing less healthy foods from the diet, which doesn’t occur with tonics and supplements as these are typically just added on top of the existing diet.
But, since most people are not eating plant foods at the levels recommended by national dietary guidelines and the World Health Organisation, novel products may help them boost their intake of bioactives and nutrients, while simultaneously creating a valuable use for a common waste product.
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