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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 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. 

“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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