New Research Suggests Olives May Reveal Oil Quality Before Milling

Summary

A new study explores the ​“Lab-on-a-Fruit” approach to pre­dict key aspects of olive oil’s chem­i­cal com­po­si­tion directly from the olive before extrac­tion. The study ana­lyzes the meta­bolic pro­file of olives to iden­tify cor­re­la­tions between the fruit’s com­po­si­tion and the oil obtained after milling, with the goal of under­stand­ing how the olive’s meta­bolic pro­file can pro­vide insight into the final oil’s char­ac­ter­is­tics.

Predicting some of the main char­ac­ter­is­tics of olive oil from the analy­sis of the fruit that pro­duces it may be less dis­tant than once believed. A new study high­lights an approach described as ​“Lab-on-a-Fruit,” a method aimed at eval­u­at­ing key aspects of the future oil’s chem­i­cal com­po­si­tion directly from the olive, before extrac­tion begins.

The study, pub­lished in Food Chemistry, exam­ines the meta­bolic pro­file of the olive to iden­tify cor­re­la­tions between the fruit’s chem­i­cal com­po­si­tion and that of the oil obtained after milling. Researchers ana­lyzed 83 metabo­lites in the olives, divided into three major chem­i­cal fam­i­lies: 21 phe­no­lic com­pounds, 33 volatile com­pounds and 29 metabo­lites asso­ci­ated with the lipid frac­tion and fatty acids.

Among the 21 phe­no­lic com­pounds exam­ined were sev­eral mol­e­cules from the sec­oiri­doid fam­ily and their deriv­a­tives, includ­ing oleu­ropein, oleu­ropein agly­cone, ligstro­side agly­cone, olea­cein, oleo­can­thal and sev­eral hydrox­y­ty­rosol and tyrosol deriv­a­tives. In extra vir­gin olive oil, these com­pounds account for a large share of the oil’s nutri­tional prop­er­ties and some of its defin­ing sen­sory attrib­utes.

The study also con­sid­ered 33 volatile com­pounds, many asso­ci­ated with the lipoxy­ge­nase path­way respon­si­ble for the char­ac­ter­is­tic pos­i­tive aro­mas of olive oil, as well as 29 metabo­lites linked to the lipid frac­tion, includ­ing sev­eral fatty acids.

The goal was not sim­ply to ver­ify whether the same mol­e­cules present in the fruit also appear in the oil, but to under­stand whether the olive’s over­all meta­bolic pro­file already con­tains use­ful infor­ma­tion that could antic­i­pate some of the final oil’s char­ac­ter­is­tics.

In other words, the idea is not to estab­lish a direct cor­re­spon­dence in which a mol­e­cule present in the olive must also be present in the oil. Instead, the premise is that the fruit’s broader meta­bolic pat­tern may already con­tain clues about the oil that will even­tu­ally be pro­duced.

Turning that idea into a tool for real pro­duc­tion set­tings, how­ever, means con­fronting the con­sid­er­able com­plex­ity of the olive-to-oil trans­for­ma­tion.

According to Lorenzo Cecchi, pro­fes­sor of food sci­ence and tech­nol­ogy at the University of Florence’s Dagri depart­ment, who was not involved in the study, the rela­tion­ship between the com­po­si­tion of the fruit and the char­ac­ter­is­tics of the final oil results from the inter­ac­tion of numer­ous chem­i­cal, bio­log­i­cal and tech­no­log­i­cal fac­tors through­out the pro­duc­tion process.

“Knowing how the chem­i­cal com­po­si­tion of the olive cor­re­lates with the chem­i­cal com­po­si­tion of the vir­gin olive oil, and there­fore with its qual­ity, would be very impor­tant,” Cecchi told Olive Oil Times. ​“It would allow pro­duc­ers and mill oper­a­tors to ori­ent the pro­duc­tion objec­tive based on the raw mate­r­ial they are start­ing from.”

“Depending on the com­po­si­tion of the olives, a pro­ducer could decide whether to aim for extrac­tion strate­gies that max­i­mize yield or for strate­gies that empha­size spe­cific qual­ity attrib­utes,” he added. ​“Quality itself can be inter­preted in dif­fer­ent ways: sen­sory qual­ity, nutri­tional or nutraceu­ti­cal qual­ity, or even aspects such as shelf life. Today the most cen­tral aspects are prob­a­bly sen­sory qual­ity and nutri­tional qual­ity.”

One of the first com­pli­ca­tions con­cerns phe­no­lic com­pounds, which play a key role in both the nutri­tional and sen­sory prop­er­ties of extra vir­gin olive oil.

“The trans­fer of phe­no­lic com­pounds from olives to oil is actu­ally very small,” Cecchi said. ​“In the lit­er­a­ture you some­times find fig­ures around two per­cent, but in our own stud­ies we have mea­sured val­ues closer to 0.4 per­cent under real milling con­di­tions.”

This means that even if the fruit con­tains high con­cen­tra­tions of phe­nols, only a small frac­tion may ulti­mately appear in the oil, depend­ing in part on how the extrac­tion process unfolds.

Another major chal­lenge is that the fruit’s chem­i­cal com­po­si­tion becomes highly unsta­ble once the olive is bro­ken.

“In a freshly har­vested olive still intact on the tree, about 70 per­cent of the phe­no­lic frac­tion may con­sist of oleu­ropein in its gly­co­sy­lated form,” Cecchi said. ​“But as soon as the fruit is dam­aged or crushed, even within sec­onds, that pro­file changes dra­mat­i­cally because enzy­matic reac­tions begin imme­di­ately.”

Because of this rapid trans­for­ma­tion, mea­sur­ing the phe­no­lic com­po­si­tion of olives in a way that accu­rately reflects their orig­i­nal state is itself a tech­ni­cal chal­lenge.

“If we sim­ply crush the olive and extract the phe­nols for analy­sis, we are already mea­sur­ing some­thing that has changed,” Cecchi noted. ​“To obtain a more real­is­tic pic­ture, researchers some­times freeze the whole olives in liq­uid nitro­gen and then imme­di­ately freeze-dry them before analy­sis to stop the enzy­matic reac­tions.”

Beyond the fruit’s chem­istry, the extrac­tion process intro­duces addi­tional lay­ers of vari­abil­ity.

“The process plays a deci­sive role,” Cecchi said. ​“The time and tem­per­a­ture of malax­a­tion, the expo­sure to oxy­gen and even the design of the malaxer can sig­nif­i­cantly influ­ence how phe­nols and volatile com­pounds evolve dur­ing extrac­tion.”

At the same time, the sen­sory pro­file of olive oil depends not only on phe­no­lic com­pounds but also on volatile mol­e­cules gen­er­ated dur­ing pro­cess­ing.

“The pos­i­tive aro­matic notes of olive oil largely come from com­pounds pro­duced through the lipoxy­ge­nase path­way,” Cecchi explained. ​“These reac­tions gen­er­ate the mol­e­cules respon­si­ble for the green sen­sory notes typ­i­cally asso­ci­ated with fresh extra vir­gin olive oil.”

According to Cecchi, some of these trans­for­ma­tions depend strongly on pro­cess­ing con­di­tions, while oth­ers are intrin­sic to the fruit.

“Some aspects are strongly influ­enced by para­me­ters such as tem­per­a­ture dur­ing pro­cess­ing,” he said. ​“But oth­ers, such as the ter­pene pro­file, appear to depend much more on the cul­ti­var and on char­ac­ter­is­tics of the fruit itself, for exam­ple the mat­u­ra­tion level.”

Despite these com­plex­i­ties, Cecchi said the direc­tion out­lined by the research reflects a broader evo­lu­tion in how olive oil pro­duc­tion may be stud­ied and man­aged in the future.

“What researchers are imag­in­ing is a sys­tem capa­ble of col­lect­ing in real time large amounts of data across the entire pro­duc­tion chain,” he said. ​“From the cli­matic con­di­tions dur­ing the grow­ing sea­son, to the char­ac­ter­is­tics of the olives at har­vest, to the para­me­ters of the milling process and finally the prop­er­ties of the oil pro­duced.”

By inte­grat­ing these datasets, it may even­tu­ally be pos­si­ble to build pre­dic­tive mod­els that link fruit char­ac­ter­is­tics, pro­cess­ing vari­ables, and vir­gin olive oil com­po­si­tion.

“To develop pre­dic­tive sys­tems, you need very large datasets,” Cecchi added. ​“You need to train ana­lyt­i­cal tools using thou­sands of obser­va­tions so that they can rec­og­nize pat­terns and antic­i­pate the char­ac­ter­is­tics of the final prod­uct.”

Such sys­tems could one day allow pro­duc­ers not only to pre­dict the oil yield from a given batch of olives, but also to adjust pro­cess­ing para­me­ters to steer pro­duc­tion toward spe­cific sen­sory or nutri­tional pro­files.