` How Heat, Light and Oxygen Harm Olive Oil

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How Heat, Light and Oxygen Harm Olive Oil

May. 22, 2012
By Julie Butler

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Researcher Jamie Ayton at the Aus­tralian Oils Research Lab­o­ra­tory

A three-year study by Aus­tralian sci­en­tists con­firms that oxy­gen, light and heat are indeed among extra vir­gin olive oil’s worst ene­mies.

The study also pro­vides the best avail­able guid­ance for gaug­ing the shelf life and use-by date for olive oils, Jamie Ayton, Rod­ney J. Mailer and Ker­rie Gra­ham state in their report.

The bot­tom line in The Effect of Stor­age Con­di­tions on Extra Vir­gin Olive Oil Qual­ity (PDF)” is that olive oil should be stored at cool tem­per­a­tures, away from light and with­out expo­sure to oxy­gen.

Not just in the short term, but through­out the life of the oil, which includes dur­ing the trans­port, stor­age and mar­ket­ing of the oil, as well as when the oil has reached its final destination…the con­sumer” they say.

Oth­er­wise, the olive oil can dete­ri­o­rate so much that it can no longer be clas­si­fied as extra vir­gin olive oil, at a huge expense to grow­ers.”

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Test results

The study found that high stor­age tem­per­a­ture and oxy­gen expo­sure neg­a­tively affect the sen­sory pro­file of olive oils. Over time at higher tem­per­a­tures, the com­pounds that cause pleas­ant flavours and aro­mas in olive oil change and instead cause unpleas­ant ones. Ran­cid­ity devel­ops sooner and free fatty acid lev­els rise faster.

Sim­i­larly, when exposed to oxy­gen, ran­cid­ity starts to develop and olive oil’s sen­sory prop­er­ties quickly and sig­nif­i­cantly decline.

Expo­sure to light causes a sub­stan­tial loss of antiox­i­dants, espe­cially toco­pherols, and an increase in ran­cid­ity com­pared to oil stored in the dark.

Mean­while, all three affect — though to dif­fer­ent degrees — an oil’s colour. This is impor­tant as the first sen­sory’ assess­ment a con­sumer makes is by assess­ing the colour of the oil they are going to pur­chase” the report says..

Study method

Funded by Australia’s Rural Indus­tries Research and Devel­op­ment Cor­po­ra­tion (RIRDC) and the Aus­tralian Olive Asso­ci­a­tion, the inten­sive research tracked nine Aus­tralian EVOOs over three years, using 882 bot­tles of olive oil.

  • To test the effect of tem­per­a­ture, sam­ples were stored at 15°C, 22°C and 37°C.
  • To test for oxy­gen expo­sure, some were stored with the bot­tle lid only loosely attached and 10 mL of oil was removed each month to ensure the head space in the bot­tle con­tained oxy­gen.
  • To test for light expo­sure, sam­ples were stored in clear bot­tles exposed to sun­light and flu­o­res­cent light.
  • Chem­i­cal para­me­ters for oxi­da­tion and age­ing, and the sen­sory char­ac­ter­is­tics of the oils, were analysed every three months.

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Lead researcher Jamie Ayton, an edi­ble oils chemist at the New South Wales Depart­ment of Pri­mary Indus­tries Aus­tralian Oils Research Lab­o­ra­tory, in Wagga Wagga, spoke to Olive Oil Times about the project.

Is there any aver­age shelf life for olive oil? Tak­ing your research into account, how could a pro­ducer cal­cu­late a best-before or use-by date for their olive oil?

Many fac­tors affect the shelf life of an olive oil, such as the ini­tial oil matrix as well as the con­di­tions the oils are stored under. Oils which have low total polyphe­nols lev­els and high lev­els of polyun­sat­u­rated fatty acids will have a shorter shelf life than those which are more robust (i.e. high polyphe­nols and low polyun­sat­u­rated fatty acid con­tent).

As you can see from the results in our report, there is no blan­ket” state­ment which can apply to all oils. The gen­eral indus­try view is that oils which are more than 18 – 24 months old are reach­ing the outer lim­its of their shelf life. Hav­ing said that, some of the oils in our project were still clas­si­fied as EVOO after 36 months under rea­son­able” stor­age con­di­tions.

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After the oil has dete­ri­o­rated, there are no health impli­ca­tions with using it, it is just that it may no longer be clas­si­fied as EVOO accord­ing to stan­dards cri­te­ria (IOC or AS5264-2011).

What should shops and con­sumers do?

Retail­ers should ensure that tem­per­a­ture is reg­u­lated suf­fi­ciently. I would sug­gest less than 25 degrees C would be prefer­able. Oils should also have min­i­mal expo­sure to light and radi­ant heat from lights in super­mar­kets.

Prior to this, ware­hous­ing and trans­port con­di­tions should be man­aged in order to have the min­i­mum impact on the oil.

Con­sumers should fol­low sim­i­lar advice. The oil should be stored in the dark at cool tem­per­a­tures, for exam­ple at the back of a kitchen cup­board — not on the win­dowsill or near the stove top. Once the bot­tle is opened, expo­sure to oxy­gen will occur, there­fore the oil should be used quickly, while still fresh.



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