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Reusing Olive Waste | Ask the Expert

Over 3 million tonnes of olive oil is produced each year. This generates a massive amount of leftover solid waste, which is challenging to dispose of, as it is high in antimicrobial chemicals, salt, and fats. If untreated, this waste can disrupt soils and pollute waterways - but could we use it as a valuable raw material?

Laura Nystrom, a professor of food biochemistry at ETH Zurich, is part of the European Food Innovation and Technology (EIT) Food project Phenoliva, which aims to turn olive waste into useful products. We asked Laura about what valuable components she can extract from olive waste, how they do it and how the components they recover can be put to good use.

Why is olive waste - or pomace - a problem? 

Well, olive waste - known as pomace - is a problem because it contains a high level of phenolic antioxidants. It’s generally known that antioxidants are beneficial for our health, and we want to eat foods that have high levels of antioxidants. That's also partly why olives are deemed healthy, as they contain health-promoting elements like antioxidants.

However, these phenolic antioxidants can also be problematic because they inhibit the growth of microbes. So the pulp or the pomace that is produced as the side stream from olive mills producing olive oil cannot just be composted, because the soil microbiota can’t break it down. This means it is essentially dumped in landfills, which can cause problems for nearby aquatic life.

Is there a better use for olive waste?

We saw this olive waste as having valuable components for value-added ingredients for food. The next question was how can we efficiently extract the olive antioxidants and utilize those rather than just consider them to be waste?

Most of the antioxidants we extract from the pomace could be used as extracts for foods, cosmetics, and other products. Our extracts have been well received by the food industry: they are all-natural extracts obviously, because it's an extract made from food-grade raw materials, and nothing synthetic. It's essentially a natural antioxidant.

They can also be used to improve soil since the absorbent material we use to extract compounds from the olive waste ends up containing a substantial amount of antioxidants, too. This allows us to use it as a “biochar” - a material similar to charcoal which is porous and improves the physical structure of the soil but can also inhibit the growth of certain pathogens that affect olive trees. So, it's both a chemical and physical improvement of the soil.

One of the things we are also working on is using the colour compounds that we can extract from olive waste. These extracts are quite intensely coloured, so we’re hoping to find an additional use for those colour pigments, perhaps as food colourings.

Is all olive waste the same, or do you have to separate waste streams?

Different kinds of olives are chemically different and contain different amounts of antioxidants and chemical components. We are focusing largely now on black olives, but there are even differences between varieties and where they’re grown. It’s one of the current hurdles - how can we standardize the end product when working with different raw materials?

Have you faced challenges finding new uses for pomace?

One of the challenges of our extracts is that phenolic antioxidants are typically associated with a quite bitter taste. This means it can be tricky to find a good balance between adding enough antioxidants to give effective health benefits, but so much that we compromise the sensory quality of the foods we’re adding them to.

Another major hurdle is with European legislation. Since this type of extract has not been used in food before, it will require either special approval from the European Food Safety Authority (EFSA) as a novel food ingredient, or to be treated as a food additive. Typically, consumers do not want additional additives in their food, so we’re trying to avoid that. Even though our extract is a natural compound, it might still appear as an E-number on the ingredients list and be perceived negatively.

Why is now the right time for olive waste reuse to become successful?

I think the overall concept of circularity in food systems and agriculture is definitely gaining a lot more attention, but people are still not willing to compromise a great deal of their enjoyment of food. I think it is key that we are offering two solutions for diminishing food waste: we're working with the sidestream material from olive oil mills and utilizing that waste better, but we can also use our extracted antioxidants to extend the shelf life of different types of food products. This helps reduce food waste because those products can be used over a longer time and, therefore, don't necessarily need to be thrown into the garbage bin so soon.

Are industries and policymakers becoming more interested in recycling olive waste? 

I would say that it has gained a lot of positive attention. The issues caused by the waste from olive oil mill side streams are well-acknowledged problems in olive-growing countries and areas. We work mostly in collaboration with partners in Andalucia, Spain, and also in Italy and other Mediterranean areas, such as Greece, all of whom face the same problems and so are showing a lot of interest in putting this approach into practice. 

Why isn't this technology more widely adopted yet?

Well, there are a few challenges to overcome. First, there is the bitter taste of phenolic antioxidants, but another hurdle is ensuring the cost of producing the extracts is reasonably low. To be financially beneficial and sustainable, we need to process large amounts of the pomace. Then, there are the challenges of working with natural materials and adjusting to seasonal changes while still producing a consistently reproducible extract that can be brought to market.

Could you use the same approach for making use of waste from other products?

We’ve also discussed using a similar approach with date fruit pits with some collaborators in the United Arab Emirates, so yes - I think a similar philosophy and approach can be utilized for other types of foods or food production streams. But the volumes and types of compounds to extract, what materials to use, and which type of processes to combine are all dependent on the raw material you start with. 

So, what’s next for Phenoliva

We definitely want to bring our olive-based antioxidants to the market! That still has some legislative hurdles, and we also need to demonstrate the safety and consistency of our extract. Then, we need to scale up to be able to produce larger amounts to make it available to the food industry and the different companies that want to actually use the extracts in their products.

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