`Researchers Develop Easier, Cheaper Method for Measuring Free Acidity - Olive Oil Times

Researchers Develop Easier, Cheaper Method for Measuring Free Acidity

By Paolo DeAndreis
Mar. 9, 2024 02:04 UTC

Brazilian researchers have devel­oped a new method for cal­cu­lat­ing the free acid­ity of olive oil and other edi­ble oils.

The find­ings, pub­lished in Food Chemistry, indi­cate that imple­ment­ing this new tech­nique uses 90 per­cent fewer chem­i­cals, is more cost-effec­tive and may be more accu­rate and sim­ple to exe­cute.

This approach sig­ni­fies a move toward devel­op­ing cleaner, quicker meth­ods, offer­ing ben­e­fits for both pro­duc­ers and con­sumers.- Cleiton Antônio Nunes, researcher, Federal University of Lavras

Free acid­ity mea­sure­ment is essen­tial in the olive oil sec­tor. The International Olive Council’s (IOC) trade stan­dards set the upper limit of acid­ity for extra vir­gin olive oil at 0.8 per­cent. Virgin olive oils must have an acid­ity of no more than two per­cent.

Olive oils from high-qual­ity, well-pre­served olives tend to have lower acid­ity, but they will not nec­es­sar­ily have good sen­sory attrib­utes,” Cleiton Antônio Nunes, co-author of the study and a food sci­ence researcher at the Federal University of Lavras in Brazil, told Olive Oil Times.

See Also:The Categories of Olive Oil

Low acid­ity alone does not con­firm the qual­ity of a good veg­etable oil,” he added. Acidity does not con­sti­tute a sen­sory char­ac­ter­is­tic of the prod­uct but is instead a chem­i­cal indi­ca­tor.”

The researchers set out to val­i­date and refine the new method by com­par­ing its results with those obtained from the same edi­ble oil sam­ples via vol­u­met­ric alka­line titra­tion, the tra­di­tional method used by the IOC. The pro­ce­dure is straight­for­ward and involves a chem­i­cal reac­tion with the fatty acids that cause acid­ity.

The reac­tion’s com­ple­tion is indi­cated by the mix­ture’s tran­si­tion from col­or­less to pink upon adding a reagent,” Nunes said. The vol­ume of this reagent con­sumed until the color changes is then used to deter­mine free acid­ity.”

The con­ven­tional method, con­ducted in lab­o­ra­to­ries, typ­i­cally requires about 20 min­utes per sam­ple.

The advan­tage of the tra­di­tional method is that it presents low ana­lyt­i­cal com­plex­ity, mean­ing it does not require expen­sive and sophis­ti­cated equip­ment nor a large lab­o­ra­tory struc­ture,” Nunes said.

On the other hand, the ana­lyst’s expe­ri­ence in deter­min­ing the point at which the mix­ture changes color, the end point of titra­tion and the vol­ume of reagent con­sumed to reach this point is cru­cial for the analy­sis to be reli­able,” he added. Therefore, it is impor­tant to have well-trained ana­lysts.”

According to Nunes, the tra­di­tional method’s sig­nif­i­cant demand for chem­i­cals ele­vates costs and gen­er­ates sub­stan­tial chem­i­cal waste, pos­ing poten­tial envi­ron­men­tal haz­ards.

The alter­na­tive method pro­posed in the study employs a reagent that changes color upon react­ing with the oil’s free acids. The higher the free acid con­tent, the more intense the result­ing color,” Nunes said.

Subsequently, the col­ored solu­tions are pho­tographed using a smart­phone, and an appli­ca­tion ana­lyzes the color inten­sity, trans­lat­ing it into numer­i­cal data.

This data is then applied in math­e­mat­i­cal mod­els to cal­cu­late the oil’s free acid­ity, thus employ­ing dig­i­tal image col­orime­try as the foun­da­tional method­ol­ogy,” Nunes said.

Digital image col­orime­try is an ana­lyt­i­cal tech­nique that derives numer­i­cal color infor­ma­tion from dig­i­tal images. This infor­ma­tion can then be cor­re­lated with spe­cific val­ues of inter­est via math­e­mat­i­cal mod­els.

See Also:Researchers Develop Simplified Way to Determine Polyphenol Contents of Olive Oil

Contrary to titra­tion, which relies on human visual judg­ment, our pro­posed method dig­i­tally mea­sures color using an app, enhanc­ing the pre­ci­sion of mea­sure­ments,” Nunes said.

When jux­ta­posed with the out­comes from the tra­di­tional method, the new approach’s results showed excel­lent con­cor­dance. We noted a remark­able cor­re­la­tion between the data acquired through the dig­i­tal image col­orime­try method and that from the titri­met­ric analy­sis,” Nunes said.


The amount of sam­ples and reagents needed in the method we devel­oped is about 90 per­cent less than the tra­di­tional method, but we believe it is pos­si­ble to reduce it even fur­ther,” he added.

The new study lays the ground­work for devel­op­ing a prac­ti­cal appli­ca­tion. Our goal is to stream­line analy­ses by uti­liz­ing a smart­phone cam­era and appli­ca­tions to cap­ture and process color data,” Nunes said, empha­siz­ing that min­i­mal lab­o­ra­tory infra­struc­ture and a skilled ana­lyst are still pre­req­ui­sites for sam­ple prepa­ra­tion and result inter­pre­ta­tion.

Nunes envi­sions the pos­si­bil­ity of pro­vid­ing a user-friendly kit con­tain­ing the nec­es­sary reagents for ana­lysts to con­duct tests and obtain results through a ded­i­cated app shortly.

The research team has also applied dig­i­tal image col­orime­try tech­niques to other crit­i­cal analy­ses of olive oil and other edi­ble oils, such as deter­min­ing per­ox­ide val­ues.

Nunes noted the impor­tance of such val­ues in eval­u­at­ing oil qual­ity and the matu­rity of olives, bananas, and other fruits.

This approach [dig­i­tal image col­orime­try-related] sig­ni­fies a move toward devel­op­ing cleaner, quicker meth­ods, offer­ing ben­e­fits for both pro­duc­ers and con­sumers,” Nunes said

Future research aims to assess the new free acid­ity mea­sure­ment method’s robust­ness across var­i­ous con­di­tions, includ­ing dif­fer­ent smart­phone brands, set­tings and cam­era qual­i­ties.

For some dig­i­tal image col­orime­try-based meth­ods, cre­at­ing a spe­cific app could sim­plify and fur­ther auto­mate analy­ses,” Nunes said. Collaboration with inter­dis­ci­pli­nary teams would be cru­cial for deliv­er­ing a high-qual­ity final prod­uct.”


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