Lab Tests Explained

Harvest time is a busy time for all growers and processors alike.  However, as we get caught up in the haste of the season, the way in which olives have been handled pre through to post-production will certainly show up in chemical testing results.  I know we always harp on improving quality, however, ensuring you are keeping to quality parameters at all times is not just something you need to keep in mind but practice day-to-day.  Don’t worry if your results aren’t the shining light you hoped for this season, but think of this as an opportunity to improve your processes.  Sometimes there are circumstances that you have no control over but can certainly have an impact on quality.

 

In the industry, at the moment there seems to be confusion about olive oil testing.  What tests are required and what does all the terminology mean?

 

I have listed the range of most tests available in accredited Australian Laboratories:

TEST NAME IOC Range Description
FFA

Free Fatty Acid

0.0-0.8% is a common test for trade classification.  Free fatty acid is expressed as percent of oleic acid (the predominant fatty acid in olive oil).

 

When high values are present this test indicates poor fruit handling or delayed time from fruit removal to milling.    The main factors in reducing high FFA levels you must process as soon as possible or within 24 hours.  Ensure that the fruit handling process is not subjecting the fruit to heat.

PV

Peroxide Value

0-20meq O2/kg is a primary measurement of oxidation in oil.  Oils which present higher values are not as stable and certainly have a much-reduced shelf life.  Higher values could indicate improper handling of oil and/or fruit.   PV’s of 13 or more are said to be rejected by the buyer.
FAP

Fatty Acids Profile

Fatty acid composition as determined by gas chromatography
(% m/m methyl esters):
– Myristic acid < 0.05
– Palmitic acid 7.5 – 20.0
– Palmitoleic acid 0.3 – 3.5
– Heptadecanoic acid < 0.3
– Heptadecenoic acid < 0.3
– Stearic acid 0.5 – 5.0
– Oleic acid 55.0 – 83.0
– Linoleic acid 3.5 – 21.0
– Linolenic acid < 1.0
– Arachidic acid < 0.6
– Gadoleic acid (eicosenoic) < 0.4
– Behenic acid < 0.2*- Lignoceric acid < 0.2
is a test performed to detect adulteration with other oils and also determines the monounsaturated (the best type of fat), polyunsaturated (lower levels desired) & saturated (lower levels desired) profile of your oil.  A vast range of fatty acids are tested  from Myristic acid to Lignoceric Acid.   This test shows the allowable range for the scope of fatty acids including Linoleic acid (or Omega 6) &  Palmitic acid (which can be in higher concentrations in warmer areas and you may find higher levels of this acid during warmer seasons).

 

PP

Total Polyphenols

Expressed as mg caffeic acid/kg oil. This test is useful in determining the stability of olive oil, however, there is a correlation between the amount of total polyphenols and the resistance to oxidation over time.  Polyphenol content decreases with prolonged storage.

 

This test can also be used to optimise the milling process because the amount of polyphenols decreases during the extraction process.  (Remember a processing system doesn’t make good oil you are essentially trying to uphold as close to the oil quality originally in the fruit).   In a “Robust oil” you might have your polyphenol level at say 430ppm to be palatable and some consumers would still find this level to be too overpowering.  However it has been noted over the years that some oils are achieving levels of over 1400ppm.

Rancimat – Induction Time is used as a primary measure of stability.  The analysis gives an indication of shelf life of your oil.
UV absorption a secondary indicator of oxidation and is used to test old oils or refined oils.  Refined oils have higher values.  Higher values could also indicate adulteration.
Sterols – Cholesterol < 0.5%
– Brassicasterol < 0.1%
– Campesterol < 4.0%
– Stigmasterol < campesterol in edible oils
– Delta-7-stigmastenol < 0.5%
– Beta-sitosterol +
delta-5-avenasterol +
delta-5-23-stigmastadienol +
clerosterol + sitostanol +
delta 5-24-stigmastadienol > 93.0% 

Total sterol content (mg/kg)

– Virgin olive oils

– Refined olive oil > 1000

 

this test is used in detecting adulteration.  Olive oil has a fairly stable sterol composition.  This test is normally needed if you are exporting.

 

Campesterol levels in certain varieties have been found to be higher in some varieties in some growing regions.   So not all measures of sterols are a true indicator of authenticity.

Alpha Tocopherols are polyphenols and are the principle form of vitamin E. It is used as a measure of quality and stability.
Moisture Content Virgin oils exhibit a certain percentage of moisture in suspension of oil and should not exceed 0.2%.  If this test shows a higher result this can lead to storage problems and the source of the moisture should be determined.  Usually the source of the moisture indicates a malfunctioning vertical separator.
Stigmastadienes Stigmastadiene content (mg/kg)

– Edible virgin olive oils < 0.10

– Lampante virgin olive oil < 0.50

 

this is a test that detects bleaching during a refining process.  When sterol components are exposed to high temperatures stigmastadienes are formed.  High levels are a good indicator of  the presence of refined oil(s).
Trans fatty acids – Edible virgin olive oils < 0.05 Trans fats occur when an oil is hydrogenated means to add hydrogen and turn a product into a solid (which you would find in the spreadable olive oil/margarine section of your supermarket).
TAG’s: Tri acyl glycerides Composition & ECN42 (Equivalent Carbon Number 42) Maximum difference between the actual and theoretical ECN 42 triacylglycerol content:

– Edible virgin olive oils 0.2

– Lampante virgin olive oil 0.3

– Refined olive oil 0.3

– Olive oil 0.3

– Crude olive-pomace oil 0.6

– Refined olive-pomace oil 0.5

– Olive-pomace oil 0.5

 

When other vegetable oils have a similar fatty acid (like sunflower, rapeseed and grape seed) to olive oil, this test is used to detect adulteration.  (See also DAG)
Unsaponifiable matter Unsaponifiable matter (g/kg)

– Olive oils < 15

– Olive-pomace oils < 30

 

The fraction of substances in oil & fat which is not saponified by caustic alkali, but is soluble in ordinary fat solvent is called unsaponifiable matter.  A characteristic feature of unsaponifiable matter in olive oil is its content of squalene, which is higher than that of other vegetable oils.
Waxes Wax content C40 + C42 + C44 + C46 (mg/kg)
– Edible virgin olive oils < 250
– Lampante virgin olive oil < 3001/
– Refined olive oil < 350
– Olive oil < 350
– Crude olive-pomace oil > 3502/
– Refined olive-pomace oil > 350
– Olive-pomace oil > 350
the levels of waxes and diols (erthrodiol and uvaol) are found in higher levels of solvent-extracted (or refined) olive oils.

 

When the oil has a wax content between 300 mg/kg and 350 mg/kg it is considered a lampante virgin olive oil if the total aliphatic alcohol content is < 350 mg/kg or the erythrodiol + uvaol content is < 3.5%.

Oil & moisture by cold press extraction, solvent extraction or NIR Cold press or Partial Extraction:

NIR:

Solvent Extraction:

In order to take out some of the guesswork when the optimal harvest time should be, these tests can be carried out in one of three ways.  This test shows the level of oil accumlation and indicates that when oil accumulation is around its peak, the harvest should be conducted.
DAG: Di-acyl Glycerides Fresh extra virgin olive oil contains a high proportion of 1,2-diacylglycerols  to 1,2- and 1,3-diacylglycerols, while olive oil from poor quality fruits and refined olive oil have elevated levels of 1,3-

diacylglycerols.

is a test that is required to determine adulteration and authenticity.  An elevated level of DAGs indicates oxidized of

poor quality, and/or adulterated with cheaper refined oils.

 

During the breakdown of triacylglycerols, diacylglycerols are formed.

Pyropheophytin a PPP “Pyro” meaning heat and “pheophytin” meaning chlorophyll. Pyropheophytins occur when oil has been subjected to heat or age-related degradation.
Heavy Metals & Pesticide Residues Maximum permissible concentration
Lead (Pb) 0.1 mg/kg
Arsenic (As) 0.1 mg/kg
these tests are required for export and wholesaler determination of olive oils.  The limits are set by Codex Alimentarius Commission.

 

Sensory Tests

Organoleptic test Positive descriptors are; fruity, green,

citrus, spicy, fragrant, tropical, soft, over-ripe, bitter

and pungent, and they are determined by the

quality of fruit produced on the tree.

 

Negative descriptors are caused by human error and

include; fusty, musty, muddy, winey, metallic,

rancid, burnt and others.

 

The sensory characteristics are the primary indicators of EVOO.  However, even the most sensitive palate cannot detect every case of adulteration.  All EVOO oils must be free of defects.  The sensory components of olive oil are; Aroma, Flavour Profile, Fruitiness, Pungency & Bitterness.

EXPORTING:  Determining authenticity of oils may require a number of tests.   The laboratories normally have packages which include IOC and adulteration tests to ensure that oils meet IOC standards.  Depending on where you are exporting to there may be further requirements than the standard tests.

 

CODE OF PRACTICE:  As the new standards have just been adopted, you may need to consult your laboratory on the tests now required..

 

Contacting a Laboratory:

 

Author

Amanda Bailey, Director of The Olive Centre.  Contact 07 4696 9845 or email: sales@theolivecentre.com.au

 

References

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