Ultrasound Can Improve EVOO Extraction

Researchers have developed an affordable extraction system using ultrasound that can improve quality and increase yield.

Maria Lisa Clodoveo
Mar. 21, 2017
By Ylenia Granitto
Maria Lisa Clodoveo

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A research team from the University of Bari has been focus­ing on opti­miz­ing the malax­a­tion stage in olive oil pro­duc­tion. Malaxation is the step when the olive paste is stirred before it is sep­a­rated in a cen­trifuge.

The main objec­tives of research in the field of extrac­tion are essen­tially three con­cern­ing the malax­ing phase: to reduce the length of this step, to improve the heat exchange and to increase the oil extrac­tion yields with­out neg­a­tive effects on the phe­nol con­tent,” Maria Lisa Amirante Clodoveo from the University of Bari Aldo Moro explained.

The reduc­tion of pro­ce­dure and resource con­sump­tion, cou­pled with the main­te­nance of qual­ity, con­tributes to guar­an­tee­ing bet­ter prof­its.- Maria Lisa Amirante Clodoveo

The tra­di­tional sys­tems, such as warm­ing up the olive paste, adding water and pro­long­ing the dura­tion of malax­a­tion have been stressed out to the point that it appeared nec­es­sary to intro­duce some­thing new to ben­e­fit more in terms of yield and effi­ciency,” Clodoveo said.

In this sense, the first objec­tive of the researchers coor­di­nated by Clodoveo was to find a solu­tion to improve this oper­a­tion. The malaxer is a batch machine which works between two con­tin­u­ous devices (the crusher and decanter), and it is an inad­e­quate heat exchanger, due to the unfa­vor­able ratio between its small sur­face com­pared to the big vol­ume of olive paste withi it.


Worldwide, emerg­ing tech­nolo­gies from microwaves to pulsed elec­tric fields have been tested and used, but the group of Italian researchers focused on ultra­sound. In addi­tion to their effect on mod­u­lat­ing the chem­i­cal, phys­i­cal and bio­chem­i­cal reac­tions within the crushed olive paste, ultra­sound offers low-cost devices, easy scal­a­bil­ity and high sus­tain­abil­ity of the process from an ener­get­i­cal point of view.

Hence, researchers wanted to present a tech­ni­cal solu­tion that would be afford­able for a wide range of pro­duc­ers to increase yields and qual­ity with­out addi­tional energy costs.

Maria Lisa Clodoveo

We believed that ultra­sound could be very promis­ing since it exerts a bland ther­mal action com­bined with a con­sid­er­able mechan­i­cal action,” Clodoveo explained. The mechan­i­cal action is due to the cav­i­ta­tion which, in sim­ple terms, con­sists in the for­ma­tion of micro­scopic vapor bub­bles caused by the oscil­la­tions in pres­sure val­ues.

The bub­bles reach a crit­i­cal diam­e­ter until they vio­lently implode, gen­er­at­ing fluid jets that break up those cells which have passed through the crusher intact. However, not all ultra­sound fre­quen­cies are able to gen­er­ate the effec­tive cav­i­ta­tion inside the olive paste. During sim­u­la­tion tests, the researchers ver­i­fied that only a low-fre­quency ultra­sonic range (20 – 50 kHz) is use­ful to reach the goal.

Essentially, many cells pass through the crusher with­out break­ing until they end up in the malaxer. Thanks to ultra­sound, cav­i­ta­tion instan­ta­neously causes the rup­ture of these cells, releas­ing oily droplets and minor com­pounds,” the researcher explained. This has a twofold effect con­sist­ing in a higher release of olive oil, and a higher con­cen­tra­tion of polyphe­nols and antiox­i­dants like carotenoids and toco­pherols.”

By apply­ing ultra­sound in a con­tin­u­ous-cycle mill, the researchers observed an evi­dent increase in yield, from approx­i­mately 14.5 per­cent with a con­ven­tional process to 16.5 per­cent with ultra­sound.

Additionally, they assessed an increase of more than 20 per­cent of the polyphe­nols in the sam­ples treated with an ultra­sound sys­tem. The con­tent of mol­e­cules with healthy action, eval­u­ated by Filomena Corbo, resulted higher than in tra­di­tional olive oil,” Clodoveo pointed out.

Also, the pro­file of chem­i­cal and organolep­tic prop­er­ties used for the clas­si­fi­ca­tion of the prod­uct has not been affected, and there were no sig­nif­i­cant dif­fer­ences com­pared to the tra­di­tional sys­tem.

Moreover, the head­space analy­sis of the sam­ples con­ducted with gas chro­matog­ra­phy by Antonello Paduano revealed that the volatile com­pounds did not suf­fer any dam­age. This under­lined that the del­i­cate enzyme lipoxy­ge­nase path­way was not com­pro­mised by the ther­mal action of ultra­sound.

In order to meet the chang­ing needs of the mar­ket, millers need plants with high effi­ciency, capa­ble of lim­it­ing invest­ment and man­age­ment costs, reduc­ing the pro­cess­ing time and max­i­miz­ing the work­ing capac­ity,” Clodoveo explained. The reduc­tion of pro­ce­dure and resource con­sump­tion, cou­pled with the main­te­nance of qual­ity, con­tributes to guar­an­tee­ing bet­ter prof­its,” she remarked.

The final step of the research required the col­lab­o­ra­tion with the Polytechnic University of Bari. Thanks to the mechan­i­cal engi­neer­ing skills of Riccardo Amirante we reached the indus­trial scale,” Clodoveo added, spec­i­fy­ing that with the fund­ing PerformTech from the Apulia Region, the machine reached a high level of tech­no­log­i­cal matu­rity and it is now ready for release to the mar­ket.

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