By Giorgia Marino, Renewable Matter / Renewable Matter
As with so many other aspects of Mediterranean civilization, we have to say thanks to the ancient Romans for the entry of olive oil into our gastronomic culture. It was they who spread olive cultivation throughout the territories of the empire to northern Europe, improved oil production and classified it according to pressing methods and seasonality. They were such devotees ofliquid gold, as they called it, that they went so far as to demand it as a form of tax payment.
Oil, however, is not the only valuable product that can be obtained from olive trees. While paying taxes in pomace or hazelnuts would have seemed at least inconvenient to an ancient Roman citizen, today the value of these by-products of olive processing is widely recognized, both from a scientific and industrial perspective. The question is, how to exploit it?
The phenolic compounds-rich in antioxidant, anti-inflammatory, and antimicrobial properties-contained in olive pomace and leaves could become valuable raw materials for the pharmaceutical and nutraceutical industries, cosmetics, and animal feed. The challenge will be to ferry an industry still very much anchored in tradition to a future of circular innovation, transforming mills into true multiproduct biorefineries.
Oil extraction between tradition and innovation
Before delving into the future vision of a perfectly circular and integrated olive industry, it is necessary to take a step back to understand how oil production works, what are the critical points to be overcome and what is the potential to be exploited.
The first thing to point out is that, from the point of view of circularity, there is a very wide margin for improvement: the oil obtained from the olives represents no more than 10-20% of the fruit, and what remains after extraction (the pomace and the stones) is still very little exploited. How to use these byproducts also depends on processing technologies. “The methods of oil extraction have changed somewhat in recent years,” explains Luca Sebastiani, professor of horticultural science at the Scuola Superiore Sant’Anna in Pisa and one of Italy’s leading experts in olive growing. Traditionally, after harvesting and washing, the olives were processed using a pressure crushing process. “The virgin pomace that remained after extraction,” Sebastiani continues, “was still rich in oils and had a relatively low moisture content. It could therefore be sent to pomace factories, which extracted the residual oil and put it on the market.”
However, this system produces large amounts of wastewater, the so-called “vegetation water,” which the mills must take care to dispose of somehow. “To reduce wastewater, we then turned to decanters, which are centrifuges that extract the oil particles, and finally to the latest generation of methods called ‘two-stage,’ which generate virtually no wastewater.” On the other hand, eliminating the wastes led to an increase in the moisture content of the pomace. “With traditional pressurized systems it was around 20-30%,” Sebastiani explains, “while with the decanter we get up to 48-50% moisture content. Finally, with the latest two-stage methods, the water content of the pomace is up to 70 percent.”
But if new extraction technologies have improved the quality of the oil (richer in polyphenols because it is not processed with water, which instead dissolves them) and solved the problem of disposing of vegetation water for olive mills, they have on the other hand complicated life for pomace producers. “A product that, for the same weight, contains much more water makes the extraction of residual oils more expensive. And pomace factories have thus begun to stop taking pomace that is too wet. What to do with it then?” The issue, Sebastiani concludes, actually paved the way for thecircular economy in the olive sector.
Pomace and hazelnut, where the circular economy of olives begins
The simplest thing that can be done with the pomace that remains at the mills is to use it as fertilizer. “You take it as it is, stone and all, dry it a bit and then spread it on the soils,” Professor Sebastiani says. “But surely this is not the best way to exploit its value.” You can also make high-quality compost from it, which is completely plant-based and, unlike compost from municipal waste, has no impurities. “The nursery industry is experimenting with using this compost as a substrate to replace peat, which today has very significant restrictions at the European level because it is not a renewable material.”
However, a major push toward circular valorization of oil by-products came from the introduction of technologies to separate the olive kernel, which was previously pressed and ended up in pomace. “The peanut can then be dried and sold as fuel for boilers,” Sebastiani explains. What remains is an even more water-rich pomace called “pulp.” “The pulpino is recovered and can have several uses,” he continues. “The most immediate one is energy transformation: it is sent to the biodigester and becomes biogas, while the residue can still be used as fertilizer.”
But while the utility of biogas is undoubted, the phenolic molecules concentrated in the pulp could certainly find better uses. “Studies in animal husbandry,” Sebastiani explains, “have shown that adding dried pulpino to feed has positive effects on the health of the animals and consequently on the products that are made from it.” Effects that, of course, could be exploited for products intended for human consumption. Extracting bioactive molecules from virgin pomace (but also from vegetable water) is thus the new frontier on which studies on the circular oil economy are now focusing.
Precious molecules and biorefineries
One of the leading experts on “molecular” upcycling in olive growing is Professor Maurizio Servili of the University of Perugia, who, in order to emphasize the value that could be derived from a smarter exploitation of olives, prefers to speak of “co-products” instead of oil by-products. Servili is credited with numerous studies on secoiridoids, i.e., phenolic molecules derived exclusively from the olive-oil chain. They have tongue-twister-like names, such as oleuropein, demethyloleuropein, ligustroside, and nüzhenide, and boast important antioxidant and anti-inflammatory properties. That is why, as Servili himself explained in a webinar at theNational Olive and Oil Academy, they are now receiving a great deal of attention from the pharmaceutical and nutraceutical industries.
“From the purified extracts of these molecules, various products can be obtained,” Sebastiani further explains. “For example, they can be added to foods such as yoghurt, meats and cold cuts as natural preservatives, or used as supplements, to produce enriched foods and beverages. Some people have tried to make a bitter aperitif with it, but I don’t think it has entered the market.”
In short, the clearance from the scientific point of view is there, the processes are tested, and these are things that are already feasible. The issue now is scalability. “It’s a matter of understanding what the market is and who will be able to invest in process innovation,” Sebastiani notes. “It would be necessary to transform the traditional oil mill into a newly developed company that, in addition to oil, would produce various things, from biogas to hazelnuts to purified compounds. This is quite a difficult transition, which requires radical reorganization.”
There are those, however, who are not frightened and have already started down this road, perhaps taking advantage of the boost of some bioeconomy funds made available by theEuropean Union , which, in any case, let us remember, with a global share of 67 percent is the world’s leading olive oil producer. This is the case of the Up4Health project, which, thanks to funding from the Circular Bio-based Europe program, aims precisely to create a biorefinery where by-products of olive and wine growing (oil and wine pomace, olive stones and residues of other nuts) are recovered to make molecules for the nutraceutical and cosmetic industries.
They are pioneers, but soon, according to Luca Sebastiani, they will be in good company. “It is a necessary path and the numbers say so: using 98 percent of an olive is obviously better than using only 10 to 20 percent and then having to pay for the disposal of the waste. In the future,” he concludes, “we will move more and more toward recovering everything: circularity is an inevitable transformation to keep the supply chain alive.”
