`Storage Temperature's Big Impact on Shelf Life of High-Phenolic Olive Oils - Olive Oil Times
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Storage Temperature's Big Impact on Shelf Life of High-Phenolic Olive Oils

By Sukhsatej Batra
Feb. 12, 2016 15:09 UTC

The European Union Commission Regulation (EU) No. 432/2012 allows an impor­tant health claim on olive oil that states, ​“Olive oil polyphe­nols con­tribute to the pro­tec­tion of blood lipids from oxida­tive stress.”

For this claim to be valid, 20 grams of the olive oil has to con­tain a min­i­mum of 5 mil­ligrams of hydrox­y­ty­rosol and its deriv­a­tives such as oleu­ropein and tyrosol. Additionally, the label is to spec­ify that 20 grams of the olive oil are to be con­sumed daily to ben­e­fit from this claim.

Providing EVOO that meets the require­ments of the health claim may be as sim­ple as decreas­ing stor­age tem­per­a­tures

While the health claim is jus­ti­fied due to the pres­ence of polyphe­nols in high-qual­ity vir­gin olive oil, one of the biggest hur­dles to the imple­men­ta­tion of this claim is that olive oil polyphe­nol con­tent decreases over time.

Fluctuating phys­i­cal con­di­tions that vir­gin olive oil is sub­jected to dur­ing its jour­ney from the man­u­fac­tur­ing plant until it reaches the con­sumers, such as changes in tem­per­a­ture, oxy­gen and light, cause oxida­tive and hydrolytic dete­ri­o­ra­tion of the olive oil. These chem­i­cal changes shorten the shelf life of vir­gin olive oil as they not only decrease the phe­no­lic con­tent olive oil but also affect the sen­sory qual­ity of olive oil result­ing in loss of taste, fla­vor and appear­ance.

Clearly, there is a need to find ways to extend the shelf life of vir­gin olive oil with­out com­pro­mis­ing its organolep­tic qual­ity or nutri­tional value.

To this end, researchers from the Laboratoire Biotechnologie de l’Olivier in Tunisia and Universidad de Castilla-La Mancha in Spain inves­ti­gated the effect of tem­per­a­ture on sta­bil­ity of phe­no­lic com­pounds in vir­gin olive oil dur­ing long-term stor­age.

The results of the study, pub­lished in the Journal of Agricultural and Food Chemistry, are based on research car­ried out on extra vir­gin olive oil from four com­mon vari­eties of olives, Chemlali, Chetoui, El Hor and Oueslati, found in Northern and Central Tunisia. Olive oil from these olives nat­u­rally dif­fers in the phe­nol, toco­pherol, and antiox­i­dant con­tent.

For the exper­i­ments, iden­ti­cal EVOO sam­ples from the four vari­eties were stored in amber-col­ored glass bot­tles that were either left open to facil­i­tate oxi­da­tion or closed to pre­vent oxi­da­tion. The sam­ples were stored for 18 months at four dif­fer­ent tem­per­a­tures: 5, 15, 25 and 50 degrees Celsius. Every three months, aliquots of the stored EVOOs were ana­lyzed to deter­mine oxi­da­tion rate and polyphe­nol con­tent.

As expected, oxi­da­tion was more rapid in EVOO stored at higher tem­per­a­tures in open bot­tles than in EVOO stored in closed bot­tles at low tem­per­a­tures.

While low tem­per­a­tures increased shelf life of all the vari­eties of EVOO due to low­ered oxi­da­tion rates, the max­i­mum ben­e­fit of low tem­per­a­tures on shelf life was observed for Oueslati EVOO, which increased from 26 weeks at 25 degrees Celsius to 44 weeks at 15 degrees Celsius.

Similarly, lower stor­age tem­per­a­tures and closed bot­tled stor­age increased sta­bil­ity of EVOO phe­nols, although vari­etal dif­fer­ences were observed. Specifically, EVOOs with higher tyrosol sec­oiri­doid com­pounds were found to be more sta­ble than those with higher hydrox­y­ty­rosol com­pounds.

According to the authors, the find­ings of the study could help pro­duc­ers extend the expiry date of vir­gin olive oil based on stor­age tem­per­a­tures and polyphe­no­lic con­tent of olive oil.

Currently, vir­gin olive oil is com­mer­cially stored at 20 to 25 degrees Celsius and the max­i­mum stor­age period of vir­gin olive oil from bot­tling to con­sump­tion is 12 to 18 months.

This stor­age period could be increased and pro­vid­ing cus­tomers with high-qual­ity EVOO that meets the require­ments of the health claim may be as sim­ple as decreas­ing stor­age tem­per­a­tures to 15 degrees Celsius dur­ing pro­duc­tion and in stores.

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