New Research Reveals Impact of Malaxation on Olive Oil Phenolic Profile

Summary

New research sug­gests that the malax­a­tion phase dur­ing olive oil pro­duc­tion plays a sig­nif­i­cant role in deter­min­ing the phe­no­lic pro­file of the oil, espe­cially sec­oiri­doids. Factors such as tem­per­a­ture, time, oxy­gen expo­sure, and water addi­tion dur­ing malax­a­tion impact the con­tent and pro­file of phe­no­lic com­pounds, which are linked to the sen­sory and health prop­er­ties of olive oil. The study empha­sizes the impor­tance of con­sid­er­ing the olive cul­ti­var, envi­ron­ment, and pro­cess­ing meth­ods to opti­mize phe­no­lic con­tent and over­all qual­ity of extra vir­gin olive oil.

The slow, con­trolled mix­ing of the crushed olives dur­ing the milling process – the malax­a­tion phase – might have a larger role in deter­min­ing olive oil’s phe­no­lic pro­file than pre­vi­ously thought.

New research pub­lished in Food Chemistry com­piled years of stud­ies on how malax­a­tion tem­per­a­ture, time, oxy­gen expo­sure, and the addi­tion of water impact the con­tent and pro­file of polar phe­no­lic com­pounds, espe­cially sec­oiri­doids, a sub­class of phe­nols.

“These are the most rep­re­sen­ta­tive phe­no­lic class in olive oil, and they’re the ones most trans­formed dur­ing malax­a­tion,” Ítala Marx, a post­doc­toral researcher at the University of Córdoba and co-author of the research, told Olive Oil Times.

During malax­a­tion, larger pre­cur­sor mol­e­cules, such as oleu­ropein and ligstro­side, nat­u­rally pro­duced by the fruits, are con­verted – bio­trans­formed – by enzymes.

Those con­vey smaller, highly bioac­tive com­pounds such as oleo­can­thal and olea­cein, which are linked to olive oil’s pun­gency, bit­ter­ness and antiox­i­dant power.

Decades of research have shown that daily con­sump­tion of olive oil rich in phe­nols pro­duces sig­nif­i­cant health ben­e­fits.

Furthermore, the com­plete phe­no­lic pro­file of extra vir­gin olive oil is deeply inter­twined with its aro­mas and fla­vors.

“Phenolics are respon­si­ble for bit­ter­ness and pun­gency. So if you increase them, you nat­u­rally improve sen­sory com­plex­ity,” Marx said. ​“The con­sumer wants that ​‘green’ fla­vor, that bit­ter­ness. These are linked to the phe­no­lic pro­file.” 

“That’s why we focused on sec­oiri­doids,” she explained.“They’re at the core of both the sen­sory expe­ri­ence and the health-related value of extra vir­gin olive oil.”

“I started this work dur­ing my PhD,” Marx added. ​“My pro­gram was com­pletely devel­oped in indus­trial olive oil mills. All cam­paigns, from 2019 to 2022, were focused on how to opti­mize extrac­tion to improve oil’s phe­no­lic con­tent, and malax­a­tion was the core of my research.”

The review paper focused on how the enzy­matic bio­trans­for­ma­tion hap­pens dur­ing malax­a­tion and how sen­si­tive the process is to malax­a­tion con­di­tions.

“Everything depends on the olive cul­ti­var. You can’t apply the same tem­per­a­ture and time and expect the same result from dif­fer­ent olives,” Marx remarked.

The influ­ence of cul­ti­var, or geno­type, is per­haps the strongest vari­able. ​“Genotype is the main fac­tor that impacts olive oil’s phe­no­lic com­po­si­tion,” Marx said.

This was made evi­dent by stud­ies in which dozens of olive cul­ti­vars were grown under iden­ti­cal con­di­tions and extracted using the same tech­nol­ogy and pro­ce­dure.

“They showed wide vari­a­tion in phe­no­lic pro­files,” Marx said. 

“Even Arbequina, usu­ally con­sid­ered low in phe­no­lics, can sur­prise you,” she added, hint­ing at the pro­found impact that dif­fer­ent farm­ing envi­ron­ments can con­vey.

“If you extract oil from Arbequina in an inten­sive orchard, or from Arbequina in a tra­di­tional setup, the result will be com­pletely dif­fer­ent,” she explained.

Marx intro­duced research con­ducted in the Almeria desert, in Andalusia, where Arbequina and Picual olive vari­eties were cul­ti­vated in the same desert con­di­tions.

“It’s a com­mer­cial brand. When we ana­lyzed the olive oils, the Arbequina had over 1,000 mil­ligrams per kilo­gram of phe­nols. That’s not typ­i­cal,” she said.

According to Marx, the highly stress­ful envi­ron­ment of the desert boosted the phe­no­lic syn­the­sis.

“We saw the same hap­pen­ing with Arbequina cul­ti­vated in Brazil, amounts of phe­no­lics higher than you’d expect,” she said.

Even more inter­est­ing than the total amount of phe­nols, it was the phe­no­lic pro­file of the olive oils.

“We observed more olea­cein and more oleo­can­thal in Arbequina com­pared to Picual. Meanwhile, Picual was richer in glu­co­sides like oleu­ropein and ligstro­side,” Marx said.

“The total amount may be sim­i­lar, but the pro­file is dif­fer­ent. And that impacts both sen­sory traits and oxida­tive sta­bil­ity,” she added.

The phe­no­lic pro­file is essen­tial. ​“Take oxida­tive sta­bil­ity. It is not just about how many phe­no­lics are present, but which ones,” Marx said.

“Oleacein and oleo­can­thal, which Arbequina has more of, don’t sta­bi­lize oil as well as oleu­ropein glu­co­side, which is more com­mon in Picual,” she added.

When it comes to milling the olives, these dif­fer­ences should be care­fully con­sid­ered.

“If you have Arbequina in an inten­sive orchard, and you know its usual phe­no­lic weak­ness, you might invest in tech­nolo­gies like pulsed elec­tric fields or oxy­gen con­trol to improve it,” Marx said. 

“But if you’re work­ing with Arbequina from a tra­di­tional, stressed envi­ron­ment, you may already be start­ing with a higher phe­no­lic base­line,” she added.

These nuanced dif­fer­ences point towards a future of tai­lored extrac­tion strate­gies.

“It’s not just about the cul­ti­var any­more. It’s about cul­ti­var, plus envi­ron­ment, plus pro­cess­ing,” Marx said. ​“And if you want to make excel­lent extra vir­gin olive oil, you need to take into account all three.”

The paper exam­ined how malax­a­tion tem­per­a­ture and time impact phe­no­lic con­tent.

Studies have shown that mod­er­ate tem­per­a­tures between 20°C and 30°C gen­er­ally pro­mote bet­ter extrac­tion of phe­no­lics, while exces­sive heat leads to degra­da­tion.

“The effect fol­lows a bell shape. We reach an opti­mal point, often around 20 to 30 min­utes of malax­a­tion, and then phe­no­lic con­tent starts to drop,” Marx said. ​“Longer malax­a­tion pro­motes oxi­da­tion, degra­da­tion and enzy­matic break­down of phe­no­lics.”

Still, the olive cul­ti­var is always worth con­sid­er­ing.

“You can’t say 25 °C and 30 min­utes is always best. For some cul­ti­vars, like Arbequina, 45 min­utes at 25 °C may work bet­ter,” she explained, hint­ing at the spe­cific analy­ses on spe­cific cul­ti­vars cited in the review paper.

One of the most trans­for­ma­tive find­ings was related to oxy­gen. ​“Oxygen pro­motes phe­no­lic degra­da­tion,” Marx noted.

“So when we elim­i­nate it, by using vac­uum sys­tems or even con­trol­ling the oxy­gen atmos­phere, we can retain more phe­no­lics in olive oil,” she added.

More specif­i­cally, some indus­trial-scale tests using high vac­uum dur­ing malax­a­tion showed increases of 25 to 48 per­cent in phe­no­lic con­tent, espe­cially in sec­oiri­doid deriv­a­tives.

Even par­tial oxy­gen con­trol can help.

“Just reduc­ing the head­space oxy­gen in the malaxer cham­ber can make a dif­fer­ence. And cul­ti­vars respond dif­fer­ently, some are more sen­si­tive than oth­ers,” she remarked.

Many milling processes are car­ried out by adding water. It is a com­mon way to con­trol the con­sis­tency of olive paste, which is what results from crush­ing olives, and an easy way to improve yield.

But research con­firmed that it comes with a hid­den cost.

“We tested dif­fer­ent amounts of water in indus­trial mills, again with Arbequina,” Marx said. ​“And with­out water, we obtained olive oils with higher phe­no­lic con­tent.”

The rea­son is chem­i­cal. Phenols are hydrophilic. When water is added to the olive oil paste in the malaxer, the water takes the phe­no­lic com­pounds from the paste.

“If we don’t add water, we have the chance to retain them, to have them stay with the olive oil,” Marx explained.

The research demon­strated the promise of recent, non-ther­mal extrac­tion tech­nolo­gies.

“Pulsed elec­tric fields, ultra­sound and microwaves. All of these can increase both phe­no­lic con­tent and olive oil yield. And unlike tra­di­tional meth­ods, they don’t degrade the sen­sory pro­file,” Marx said.

Adding tem­per­a­ture, time, or water to improve yields is a well-estab­lished prac­tice at many olive oil mills.

“Yes, that worked for yield, but destroyed the phe­no­lics and the taste,” Marx said. ​“Now, with these new tech­nolo­gies, we can have both: higher phe­no­lics and bet­ter sen­sory attrib­utes.”

Overall, the phe­no­lic pro­file and total phe­nols com­bine to deter­mine an olive oil’s sta­bil­ity, taste and health ben­e­fits. Marx pointed out that the research will con­tinue.

“We need to move toward cul­ti­var-spe­cific guide­lines,” she con­cluded. ​“With the data we have now, and the tech­nol­ogy avail­able, it’s pos­si­ble to pro­duce excel­lent olive oils, even from cul­ti­vars not tra­di­tion­ally known for phe­no­lics.”