Olive Leaves Can Improve Oil Quality, Researchers Find

A new study con­firmed that under cer­tain con­di­tions, the addi­tion of olive leaves in the olive extrac­tion process might enhance the over­all polyphe­nol con­tent and sen­sory pro­file of the result­ing extra vir­gin olive oil.

According to the research pub­lished in Food Chemistry, the com­bined extrac­tion of olives and olive leaves in a lab­o­ra­tory envi­ron­ment intro­duced chem­i­cal and organolep­tic changes to the extra vir­gin olive oil, which are dif­fer­ent from those pre­vi­ously observed in an indus­trial set­ting.

“We began work­ing by mod­i­fy­ing spe­cific para­me­ters of the extrac­tion process, such as tem­per­a­ture, time, addi­tion or not of water,” Ítala Marx, a researcher at the Instituto Politécnico de Bragança and University of Porto and co-author of the research, told Olive Oil Times.

“The fol­low­ing step was to co-extract olive oil with nat­ural sources of phe­no­lic com­pounds,” she added. ​“In this study, we ana­lyzed the impact of the addi­tion of 1 per­cent fresh olive leaves, co-extracted with Arbequina olives.”

The researchers decided on adding 1 per­cent of fresh olive leaves after observ­ing that a small but unde­fined quan­tity of leaves ends up in the extrac­tion process in most large-vol­ume milling oper­a­tions.

“From there, our team wanted to inves­ti­gate what actu­ally hap­pens to the olive oil when such incor­po­ra­tion hap­pens, in terms of sen­sory attrib­utes, qual­ity para­me­ters, phe­no­lic con­tents, volatile com­pounds,” Marx said.

The results of the exper­i­ment, which was con­ducted using a small-scale Abencor sys­tem, show that the result­ing olive oil offers a sig­nif­i­cant improve­ment in sen­sory attrib­utes — but reduced polyphe­no­lic con­tents and volatiles — com­pared to olive oil pro­duced solely from olives with­out the pres­ence of any leaves.

However, pre­vi­ous research from the same aca­d­e­mic team in an indus­trial set­ting demon­strated an improve­ment in sen­sory attrib­utes and an increase in polyphe­nols, com­pared to olive oil pro­duced solely from olives with­out the pres­ence of any leaves.

“We attribute such dif­fer­ent results to the dif­fer­ent con­di­tions of the two stud­ies,” Marx said. ​“In an indus­trial set­ting, for instance, we were able to con­trol oper­at­ing tem­per­a­ture dur­ing the malax­a­tion process, set at 22 ºC for 45 min­utes, while in the lab set­ting, we had a 30 °C tem­per­a­ture dur­ing the malax­a­tion process. And we also had dif­fer­ent oper­a­tional times.”

“In the indus­trial-scale research, with the same per­cent­age of fresh leaves added to the process, we obtained olive oil which is rich both in phe­no­lic con­tents than in volatile com­pounds,” she added. ​“In the Abencor lab­o­ra­tory-scale research, we have seen that olive oils extracted with­out leaves would have main­tained a higher amount of the main phe­no­lic con­tents, which did not hap­pen on the indus­trial scale research.”

In the indus­trial scale exper­i­ment, recently pub­lished in the European Food Research and Technology jour­nal, the researchers incor­po­rated the 1 per­cent fresh leaves before the crush­ing process so that the con­tents were crushed together, obtain­ing par­ti­cles of equal dimen­sions.

That did not hap­pen in the Abencor sys­tem exper­i­ment, where the processed con­tents were reduced to smaller sizes using a small chop­ping machine.

“In such case, the sur­face con­tact is wider because the dimen­sion is smaller,” Marx said. ​“The inter­ac­tion among con­tents is there­fore higher. Plus, the leaves were added before the malax­a­tion process. So we believe that this is the most rel­e­vant dif­fer­ence between the two exper­i­ments.”

According to the researchers, the improve­ment to the olive oil derived from adding leaves is prob­a­bly due to their chem­i­cal com­po­si­tion. They have not only a rich phe­no­lic pro­file but also present enzymes des­tined to affect final qual­ity.

Although, in the lab set­ting, with the Abencor sys­tem, the leaves did not increase the polyphe­nols and the volatile com­po­si­tion of the result­ing olive oil. Both were higher in olive oils processed with­out leaves.

The researchers found that Abencor sys­tems, widely used in research set­tings because they are smaller, cheaper and more prac­ti­cal, might not pro­vide the com­plete pic­ture.

“During the exper­i­ment with the Abencor sys­tem, we deter­mined the enzyme path­ways involved in the for­ma­tion of the main phe­no­lic ele­ments, such as oleu­ropein, hydrox­y­ty­rosol, oleo­can­thal,” Marx said. ​“We also focused on the lipoxy­ge­nases path­way, which is respon­si­ble for form­ing the main volatile com­pounds.”

“We focused on both these path­ways find­ing how the inte­gra­tion of the olive leaves pro­duced an inter­ac­tion with these path­ways but did not con­tribute to them, affect­ing them neg­a­tively instead,” she added. ​“So, our find­ings prove that the Abencor sys­tem, widely used in research for its acces­si­bil­ity and small scale, can not mimic the indus­trial-scale con­di­tions.”

The Portuguese researcher also noted that pre­vi­ous research exper­i­ment­ing with the Abencor sys­tem and com­par­ing the results with indus­trial con­di­tions often found dif­fer­ent results even when rel­e­vant fac­tors, such as oper­at­ing time or tem­per­a­ture, were the same in both set­tings.

“Many fac­tors must be con­sid­ered, such as oxy­gen expo­sure, super­fi­cial con­tact, size of ham­mer mills and even more, such as the sep­a­ra­tion dur­ing the cen­trifu­ga­tion and decanta­tion and more,” Marx said.

In the indus­trial scale exper­i­ment, the result­ing extra vir­gin olive oil pro­file sat­is­fied the most strin­gent qual­ity para­me­ters, while in the Abencor sys­tem, those results were not matched.

“It is inter­est­ing to note that in both set­tings, we obtained improved sen­sory attrib­utes,” Marx said.

She added that the research team is already study­ing the impact on the olive oil pro­file deriv­ing from adding olive leaf micro-organ­isms into the olive trans­for­ma­tion process.

• Food Chemistry
• European Food Research and Technology