This Standard applies to virgin olive oil, refined olive oil, refined olivepomace oil, blends of refined olive oil and virgin olive oil and blends of refined olivepomace oil and virgin olive oil.
CODEX STANDARD FOR OLIVE OIL, VIRGIN AND REFINED, AND FOR REFINED OLIVEPOMACE OIL
(Rev. 1-1989)CODEX STAN 33-1981
1. SCOPE
2. DESCRIPTION
2.1 Olive oil is the oil obtained from the fruit of the olive tree (0lea europaea sativa Hoffm. et Link) without having been subjected to manipulation or any treatment not authorized by subsections 2.2 and 2.3 of this Standard.
2.2 Virgin olive oil is the oil obtained from the fruit of the olive tree by mechanical or other physical means under conditions, particularly thermal, which do not lead to alteration of the oil. Virgin olive oil is an oil which is suitable for consumption in the natural state.
2.3 Refined olive oil is the oil obtained from virgin olive oil, the acid content and/or organoleptic characteristics of which render it unsuitable for consumption in the natural state, by means of refining methods which do not lead to alterations in the initial glyceridic structure.
2.4 Refined olivepomace oil is the oil obtained from "
" by extraction by means of solvents and made edible by means of refining methods which do not lead to alteration in the initial glyceridic structure.
olive pomace
3. ESSENTIAL COMPOSITION AND QUALITY FACTORS
3.1
>Identity Characteristics (under normal ecological conditions)
3.1.1
GLC ranges of fatty acid composition (% m/m of methyl esters)
|
Lauric acid
|
(C 12:0)
|
Not present in discernible amounts
|
|
Myristic acid
|
(C 14:0)
|
< 0.1
|
|
Palmitic acid
|
(C 16:0)
|
7.5 – 20.0
|
|
Palmitoleic acid
|
(C 16:1)
|
0.3 - 3.5
|
|
Heptadecanoic acid
|
(C 17:0)
|
< 0.5
|
|
Heptadecenoic acid
|
(C 17:1)
|
< 0.6
|
|
Stearic acid
|
(C 18:0)
|
0.5 - 5.0
|
|
0leic acid
|
(C 18:1)
|
55.0 – 83.0
|
|
Linoleic acid
|
(C 18:2)
|
3.5 – 21.0
|
|
Linolenic acid
|
(C 18:3)
|
< 1.5
|
|
Arachidic acid
|
(C 20:0)
|
< 0.8
|
|
Behenic acid
|
(C 22:0)
|
< 0.3
|
|
Erucic acid
|
(C 22:1)
|
Not present in discernible amounts
|
|
Lignoceric acid
|
(C 24:0)
|
< 1.0
|
3.1.2
Physical and chemical indices3.Relative density (20oC/water at 20oC)
|
Virgin olive oil
|
)
|
|
|
Refined olive oil
|
)
|
0.910 - 0.916
|
|
Refined olive-pomace oil
|
)
|
1.2.2
3.Refractive index (nD20)
|
Virgin olive oil
|
)
|
1.4677 - 1.4705
|
|
Refined olive oil
|
)
|
|
|
Refined olive-pomace oil
|
1.4680 - 1.4707
|
1.2.3
3.Saponification value (mg KOH/g oil)
|
Virgin olive oil
|
)
|
184 – 196
|
|
Refined olive oil
|
)
|
|
|
Refined olive-pomace oil
|
182 – 193
|
1.2.4
3.Iodine value (Wijs)
|
Virgin olive oil
|
)
|
75 – 94
|
|
Refined olive oil
|
)
|
|
|
Refined olive-pomace oil
|
75 – 92
|
1.2.5
3.Unsaponifiable matter (using light petroleum)
|
Virgin olive oil
|
)
|
not more than 15 g/kg
|
|
Refined olive oil
|
)
|
|
|
Refined olive-pomace oil
|
not more than 30 g/kg
|
1.2.6
3.Bellier index
|
Virgin olive oil
|
not more than 17
|
|
Refined olive oil
|
|
|
Refined olive-pomace oil
|
not applicable
|
1.2.7
3.Semisiccative oil test
|
Virgin olive oil
|
)
|
|
|
Refined olive oil
|
)
|
negative
|
|
Refined olive-pomace oil
|
)
|
1.2.8
3.0livepomace oil test
|
Virgin olive oil
|
)
|
negative
|
|
Refined olive oil
|
)
|
|
|
Refined olive-pomace oil
|
not relevant
|
1.2.9
3.Cottonseed oil test
|
Virgin olive oil
|
)
|
|
|
Refined olive oil
|
)
|
negative
|
|
Refined olive-pomace oil
|
)
|
3.1.2.10 Teaseed oil test
|
Virgin olive oil
|
)
|
|
|
Refined olive oil
|
)
|
negative
|
|
Refined olive-pomace oil
|
)
|
3 .1.2.11 Sesameseed oil tests
|
Virgin olive oil
|
)
|
|
|
Refined olive oil
|
)
|
negative
|
|
Refined olive-pomace oil
|
)
|
3.1.2.12 Sterol content (% of the sum of betasitosterol, campesterol and stigmasterol)
|
Virgin olive oil
|
)
|
|
|
Refined olive oil
|
)
|
negative
|
|
Refined olive-pomace oil
|
)
|
|
Virgin olive oil
|
)
|
|
|
Refined olive oil
|
)
|
negative
|
|
Refined olive-pomace oil
|
)
|
|
Virgin olive oil
|
)
|
|
|
Refined olive oil
|
)
|
negative
|
|
Refined olive-pomace oil
|
)
|
|
Beta-sitosterol
|
Campesterol
|
Cholesterol
|
||
|
Virgin olive oil
|
)
|
|||
|
Refined olive oil
|
)
|
≥ 93
|
≤ 4.0
|
≤ 0.5
|
|
Refined olive-pomace oil
|
)
|
3.1.2.10 Teaseed oil test
|
Virgin olive oil
|
)
|
|
|
Refined olive oil
|
)
|
negative
|
|
Refined olive-pomace oil
|
)
|
3.1.2.11 Sesameseed oil tests
|
Virgin olive oil
|
)
|
|
|
Refined olive oil
|
)
|
negative
|
|
Refined olive-pomace oil
|
)
|
3.1.2.12 Sterol content (% of the sum of betasitosterol, campesterol and stigmasterol)
|
Beta-sitosterol
|
Campesterol
|
Cholesterol
|
||
|
Virgin olive oil
|
)
|
|||
|
Refined olive oil
|
)
|
≥ 93
|
≤ 4.0
|
≤ 0.5
|
|
Refined olive-pomace oil
|
)
|
3.1.2.13 Saturated fatty acids at position 2
Maximum level
|
Virgin olive oil
|
1.5% m/m
|
|
Refined olive oil
|
1.8% m/m
|
|
Blends of refined olive oil and virgin olive oil
|
1.8% m/m
|
|
Refined olive-pomace oil
|
2.2% m/m
|
|
Blends of refined olive-pomace oil and virgin olive oil
|
2.0% m/m
|
0) and stearic (18:0) acids expressed as a percentage (m/m) of the total fatty acids at position 2.
The saturated fatty acids at position 2 means the sum of the palmitic (16:
3.2.1
Quality CharacteristicsColour, odour and tasteVirgin olive oil: Clear oil, of a yellow to green colour, with specific odour and taste, free from odours or tastes indicating alteration or pollution of oil.Refined olive oil: Clear oil, limpid without sediment, of clear yellow colour without specific odour or taste and free from odours or tastes indicating alteration or pollution of the oil.Refined olivepomace oil: Clear oil, limpid, without sediment, of a yellow to yellowbrown colour, without specific odour or taste and free from odours or tastes indicating alteration or pollution of the oil.Blends: The colour, odour and taste shall be intermediate between those of two types blended.
3.2.2
Free acidity
|
Acidity maximum % m/m expressed as oleic acid
|
Acid value maximum mg KOH/g oil
|
|
|
Virgin olive oil
|
3.3
|
6.6
|
|
Refined olive oil
|
0.3
|
0.6
|
|
Refined olive-pomace oil
|
0.3
|
0.6
|
|
Blends
|
l.5
|
3.0
|
3.2.3
Peroxide value (in milliequivalents peroxide oxygen/kg oil)
|
Virgin olive oil
|
≤ 20
|
|
Refined olive oil
|
≤ 10
|
|
Refined olive-pomace oil
|
≤ 10
|
|
Blends
|
≤ 20
|
3.2.4
Specific extinction in ultraviolet
|
Extinction (E)maximum at 232 nm
|
Extinction (E)maximum at 270 nm
|
Emaximum variation at near 270 nm
|
|
|
Virgin olive oil
|
3.50
|
0.30
|
|
|
Refined olive oil
|
-
|
1.10
|
0.16
|
|
Refined olive-pomace oil
|
6.00
|
2.00
|
0.20
|
|
Blends of refined olive oil and virgin olive oil
|
-
|
0.90
|
0.15
|
|
Blends of refined olive-pomace oil and virgin olive oil
|
5.50
|
1.70
|
0.18
|
4. FOOD ADDITIVES
|
Extinction (E)maximum at 232 nm
|
Extinction (E)maximum at 270 nm
|
Emaximum variation at near 270 nm
|
|
|
Virgin olive oil
|
3.50
|
0.30
|
|
|
Refined olive oil
|
-
|
1.10
|
0.16
|
|
Refined olive-pomace oil
|
6.00
|
2.00
|
0.20
|
|
Blends of refined olive oil and virgin olive oil
|
-
|
0.90
|
0.15
|
|
Blends of refined olive-pomace oil and virgin olive oil
|
5.50
|
1.70
|
0.18
|
|
Maximum level
|
||||
|
4.1
|
Virgin olive oil
|
None permitted
|
||
|
4.2
|
Refined olive oil
|
)
|
Alpha-tocopherol for the purpose of restoring natural tocopherol lost in processing
|
200 mg/kg total alpha-tocopherol in the final product
|
|
Refined olive-pomace oil
|
)
|
|||
|
Blends
|
)
|
4. FOOD ADDITIVES
|
Maximum level
|
||||
|
4.1
|
Virgin olive oil
|
None permitted
|
||
|
4.2
|
Refined olive oil
|
)
|
Alpha-tocopherol for the purpose of restoring natural tocopherol lost in processing
|
200 mg/kg total alpha-tocopherol in the final product
|
|
Refined olive-pomace oil
|
)
|
|||
|
Blends
|
)
|
5. CONTAMINANTS
5.1
|
Matter volatile at 105oC
|
||
|
Virgin olive oil
|
0.2% m/m
|
|
|
Refined olive oil
|
0.1% m/m
|
|
|
Refined olive-pomace oil
|
0.1% m/m
|
|
|
Blends
|
0.1% m/m
|
|
|
5.2
|
Insoluble impurities
|
|
|
Virgin olive oil
|
0.1% m/m
|
|
|
Refined olive oil
|
0.05% m/m
|
|
|
Refined olive-pomace oil
|
0.05% m/m
|
|
|
Blends
|
0.05% m/m
|
|
|
5.3
|
Soap Test
|
|
|
Refined olive oil
|
)
|
|
|
Refined olive-pomace oil
|
)
|
negative
|
|
Virgin olive oil
|
)
|
|
|
Virgin olive oil
|
)
|
not applicable
|
|
Blends
|
)
|
6. HYGIENE
It is recommended that the product covered by the provisions of this Standard be prepared in accordance with the appropriate Sections of the General Principle of Food Hygiene recommended by the Codex Alimentarius Commission (CAC/RCP 1 1969, Rev. 3-1997).
7. LABELLING
In addition to the provisions of the General Standard for the Labelling of Prepackaged Foods (CODEX STAN 1 1985, Rev. 11991), the following provisions shall apply.
7.1 Name of the Food
7.1.1
All products designated as "
" shall conform to the provisions of this Standard for virgin olive or refined olive oil and shall be either virgin olive oil, refined olive oil or a blend of refined olive oil and virgin olive oil.
olive oil
7.1.2
All products designated as "
" shall conform to the provisions for virgin olive oil.
virgin olive oil
7.1.3
All products designated as "
" shall conform to the provisions for refined olive oil.
refined olive oil
7.1.4
All products designated as "
" shall conform to the provisions for refinedpomace oil.
refined olivepomace oil
7.1.5
Refined olivepomace oil shall in no case be described as "
" but shall always be designated as "
".
olive oil
refined olivepomace oil
7.1.6
Blends of refined olivepomace oil and virgin olive oil shall be described as "
".
olivepomace oil
7.2 Labelling of Nonretail ContainersIn addition to the provisions of the General Standard for the Labelling of Prepackaged Foods (CODEX STAN 11985, Rev. 11991), the following provisions shall apply to outer containers of a number of prepackaged containers of the products covered by the Standard.Information on the above labelling requirements shall be given either on the container or in accompanying documents, except that the name of the food, lot identification and the name and address of the manufacturer or packer shall appear on the container.However, lot identification and the name and address of the manufacturer or packer may be replaced by an identification mark, provided that such a mark is clearly identifiable with the accompanying documents.
8. METHODS OF ANALYSIS AND SAMPLING
8.1 Determination of Fatty Acid CompositionAccording to IUPAC 2.301, 2.302 and 2.304 or ISO 5508: 1990/5509: 1999.
8.2 Determination of Relative DensityAccording to IUPAC 2.101, with the appropriate conversion factor. Results are expressed as relative density at 20oC/water at 20oC.
8.3 Determination of Refractive IndexAccording to IUPAC 2.102.Results are expressed as the refractive index relative to the sodium D-line at 20ºC.
8.4 Determination of Saponification Value According to IUPAC 2.202.Results are expressed in mg KOH/g oil.
8.5 Determination of Iodine ValueAccording to IUPAC 2.205/1, Wijs method, or ISO 3961:1996Results are expressed as % m / m absorbed iodine.
8.6 Determination of Unsaponifiable MatterAccording to IUPAC 2.401 (part 1-5). Results are expressed as g unsaponifiable matter/kg oil.
8.7 Determination of Bellier Index (CAC/RM 20-1970) DefinitionThe Bellier Index of an oil is the temperature at which precipitation of salts of the fatty acids of this oil commences, when the oil has been saponified and made into solution as described under Procedure.ReagentsThe reagents used shall be of recognized analytical reagent quality.
Aqueous ethanolic potassium hydroxide solution.
42.5 g of pure KOH is dissolved in 72 ml of distilled water and adjusted to 500 ml with 95% v/v ethanol.
70% v/v ethanol solution (use pure ethanol or rectified spirit).
Aqueous acetic acid solution 1+2 (by volume) so adjusted that 1.5 ml exactly neutralizes (phenolphthalein indicator) 5 ml of the aqueous ethanolic potassium hydroxide solution (8.7.2.1).Apparatus
220 mm x 2627 mm test tubes.
Condenser consisting of a glass tube with stopper.
Thermometer graduated in 1/4 from 8 to 25C, fixed in a stopper.
Preparation of SampleTo remove water, the oil is decanted and filtered through paper at a temperature slightly above the melting point of certain solid constituents which could separate from the fluid fatty matter.ProcedurePlace 1 ml of oil and 5 ml of the aqueous ethanolic KOH solution into a test tube. Connect to condenser and heat moderately, agitating by rotation from time to time until saponification is completed, i.e. until a perfectly clear solution in obtained. Allow to cool, disconnect condenser and add 1.5 ml of the aqueous acetic acid solution and 50 ml of the ethanol solution. Attach thermometer and homogenize. Place test tube in a beaker of water at 2325C. If a flocculent precipitate forms, leave standing for an hour at the same temperature and filter into a test tube. Attach thermometer to the test tube containing the clear solution. Place for a moment in a beaker of water at about 10°C less than the estimated Bellier index. Withdraw and ensure even temperature by inverting a number of times (cooling should be at the rate of about 1C per minute). Repeat this operation until cloudiness appears. Note temperature. Allow the temperature to increase a few degrees to dissolve the precipitate. Homogenize by inverting test tube over and cool. The cooling should be slow and shaking more frequent as the temperature approaches that noted the first time.Expression of ResultsThe Bellier index is the temperature C at which the cloudiness reappears.RepeatabilityTwo parallel determinations may not differ by more than 0.25C.
8.8 Semi-siccative Oil Tests (CAC/RM 211970)Principle of MethodBased on the reaction between semisiccative (unsaturated) oils and bromine yielding substances which form an insoluble precipitate at 0C.ReagentsThe reagents shall be of recognized analytical reagent quality.
Hexane, or, if not available, light petroleum with distillation point between 40 and 60C and bromine value less than 1, free of residues.
Bromine reagent obtained by adding drop by drop while shaking 4 ml of chemically pure bromine (the presence of chlorine prevents the reaction) into 100 ml of hexane or light petroleum, chilled to 0C and kept in the melting ice bath until required.
Apparatus
Stoppered 50ml Erlenmeyer flask.
Bath of melting ice.
ProcedureThe oil to be tested is filtered and dried. Place 1 ml of the oil in the previously dried Erlenmeyer flask and dissolve in 10 ml of hexane. Place the stoppered Erlenmeyer flask in the melting ice bath. After 5 min add 10 ml of bromine reagent in small quantities at a time, while shaking and maintaining the temperature at 0C. The colour of the solution must clearly indicate excess bromine. Leave the Erlenmeyer flask in the melting ice bath for one hour, after which note appearance of solution. If semisiccative oil is present, a flocculent precipitate will form varying in quantity according to the percentage of adulteration and the nature of the adulterating oil. The solution remains clear and transparent in the case of genuine olive oils.Expression of ResultsThe result is expressed as positive or negative.
8.9 OlivePomace Oil Test (CAC/RM 221970) Principle of MethodBased on the temperature of precipitation of salts of the fatty acids after saponification.ReagentsThe reagents used shall be of recognized analytical reagent quality.
Aqueous ethanolic potassium hydroxide solution. 42.5 g of pure KOH is dissolved in 72 ml of distilled water and adjusted to 500 ml with 95% v/v ethanol.
70% v/v ethanol solution (use pure ethanol or rectified spirit).
Aqueous acetic acid solution 1+2 (by volume) so adjusted that 1.5 ml exactly neutralizes (phenolphthalein indicator) 5 ml of the aqueous ethanolic potassium hydroxide solution.
Apparatus
100 m1 balloonflask equipped with reflux condenser.
50 ml test tubes.
Heating arrangement to keep balloonflask at about 80°C.
Thermometer graduated from 15° to 60°C.
Preparation of SampleTo remove water, the oil is decanted and filtered through paper at a temperature slightly above the melting point of certain solid constituents which could separate from the fluid fatty matter.ProcedurePlace about 1 g of the oil, prepared as above, into the balloonflask. Add 5 ml of aqueous ethanol potassium hydroxide solution. Attach condenser and bring to boil holding at this temperature for 10 minutes, shaking from time to time. Allow to cool at ambient temperature. Add 1.5 ml of acetic acid solution and 50 ml of ethanol solution previously heated to 50C. Mix by shaking, introduce thermometer and allow to cool, noting the appearance of the solution once 45C in reached. If a flocculent precipitate forms at a temperature above 40C, the test is positive. Allow to cool to ambient temperature (not lower than 18C) over at least 12 hours. Observe solution again; the formation of a flocculent precipitate, floating in the middle of the liquid also indicates that the test is positive. A cloudiness not forming into flakes does not indicate the presence of olive pomace oil. Expression of Results The result is expressed as positive or negative. NOTE : On rare occasions some virgin olive oils, obtained by second pressing, yield a positive result.8.10 Cottonseed Oil Test (CAC/RM 231970) Principle of Method Based on red colour developed by cyclopropenoic acids under the operating conditions in the presence of sulphur. ReagentsThe reagents used shall be of recognized analytical quality.Sulphur reagents : Mix equal volumes of amyl alcohol and a solution of 1 g of sulphur in 100 ml of carbon disulphide. Apparatus
250 mm x 25 mm test tubes.
Water bath with constant temperature control.
Heating apparatus to keep the test tubes at 110o120o C.
ProcedurePlace approximately 10 ml of the oil under examination into a test tubes add the same volume of sulphur reagent; shake and keep in water bath at 70° 80°C, shaking until the carbon disulphide has completely evaporated (generally 5 minutes are enough), which is confirmed by the appearance of slight fuming above the liquid. Transfer the test tube to the heating apparatus and keep at 110° 120°C for 2.hours. A red, or pink colour indicates the presence of cottonseed oil. However, the appearance of an orange colour must not be interpreted as being proof of the presence of cottonseed oil.Expression of ResultsThe result in expressed as positive or negative.NOTE: The heating of the cottonseed oil to a temperature above 170°C brings about a progressive destruction of the cyclopropenoic acid responsible for the coloration. This destruction in practically complete at 200°C.8.11 Teaseed Oil Test (CAC/RM 24-1970) Principle of MethodBased on Fitelson (modified Lieberman-Burchard) tests i.e. red colour developed by acetic anhydride in the presence of sulphuric acid in chloroform solution of the oil.ReagentsThe reagents used shall be of recognised analytical quality.
Chloroform
Concentrated sulphuric acid (d = 1.84)
Acetic anhydride
Diethyl oxide
Apparatus
150 mm x 15 mm test tubes.
2 ml pipette, graduated in tenths.
Dropper so calibrated that 7 drops of oil weigh approximately 0.22 g.
Water bath at 5oC.
ProcedureUsing the graduated pipette, place 0.8 ml of acetic anhydride, 1.5 ml of chloroform and 0.2 ml of sulphuric acid in a test tube. Cool to 5C, then add approximately 0.22 g of oil. If cloudiness appears add acetic anhydride drop by drop with shaking until the solution becomes clear. Keep at 5C for 5 minutes. Add 10 ml of diethyl oxide previously cooled to 5C. Stopper the test tube and mix immediately by inverting it twice. Return the test tube to the bath at 5C and observe the colour. After about one minute a red colour will appear if tea oil is present.Expression of ResultsThe result is expressed as positive or negative. NOTE: A pink colour shall be regarded as negative, since some olive oils yield this colour.8.12 Sesameseed Oil Tests (CAC/RM 251970)Principle of MethodBased on the detection of sesamoline, a glycoside, and sesamine, a complex cyclic ether, which are present in small amounts in sesameseed oil.8.12.1 Detection of SesamolineReagentsThe reagents used shall be of recognized analytical quality.
Concentrated hydrochloric acid (d = 1.18).
Solution of 2% v/v freshly distilled furfural in 95% v/v ethanol.
ApparatusGraduated 50m1 stoppered test tube.ProcedurePlace 10 ml of the oil and 10 ml of conc. hydrochloric acid in the graduated test tube. Stopper and shake vigorously for 30 seconds. Allow to stand. Add 0.5 ml of the solution of furfural. Stopper and shake again. Allow to stand until decantation. If the lower layer does not turn red, the test is negative. If a red coloration appears, add 10 ml of water and shake gently and allow the liquid to settle. If the coloration disappears, the test is negative. If the coloration remains, the test is positive. Refined sesame oils do not always give a positive reaction by this method.Expression of ResultsThe result is expressed as positive or negative.8.12.2 Detection of SesamineReagentsThe reagents used shall be of recognized analytical quality.
Concentrated sulphuric acid (d = 1.84).
Solution of freshly distilled furfural in acetic anhydride, 0.35/ml v/v.
Apparatus
25-ml, stoppered graduated test tube.
Decanting beaker approximately 50-ml.
Flatbottomed porcelain dish approximately 60 mm in diameter.
ProcedurePlace 10 ml of the oil and 5 ml of the solution of furfural in the test tube. Stopper and shake vigorously for approximately one minute. Pour the mixture into the decanting beaker and allow to settle. Transfer a portion of the deposit into the dish and add 6 or 7 drops of sulphuric acid. Mix by shaking the dish gently. The test is positive if a greenishblue colour appears. Sesame oils, even when refined, give a positive reaction.Expression of ResultsThe result is expressed as positive or negative.8.13 Determination of the Sterol Content According to IUPAC 2.403.Results expressed as % of the sum of betasitosterol, campesterol and stigmasterol. 8.14 Determination of the Fatty Acids in the 2 Position According to the IUPAC method (1979, 6th edition) no. 2.210. "
".
Determination of the Fatty Acids in the 2position in the Triglycerides of Oils and Fats
0) and stearic (18 :0) acids expressed as a percentage m/m of the total fatty acids at position 2.
The saturated fatty acids at position 2 means the sum of palmitic (16 :8.15 Determination of Free AcidityAccording to IUPAC 2.201.Results are expressed as % m/m oleic acid and/or as the number of mg KOH required to neutralize 1 g oil.8.16 Determination of Peroxide ValueAccording to IUPAC 2.501 or ISO 3960 :1998Results expressed as milliequivalents active oxygen/kg.8.17 Determination of Specific Extinction in UltraViolet (CAC/RM 261970)Principle of MethodThe degree of oxidation of olive oil is reflected by its specific extinction at 232 nm and 270 nm. In fact, virgin olive oils, of good quality and correctly stored, contain very few products of oxidation; these mainly peroxidic in nature, have a maximum absorption at approximately 232 nm. The values of E λ, at 232 and 270 nm in such olive oils are below the maximum provided for in the standard. On the other hand, when the oil is treated with a decolourising agent (i.e. an absorbent earth) during the refining process, conjugated trienoic compounds are formed. These compounds have a maximum absorption situated at approximately 270 nm; this means that refined oils have higher values of E λ at 270 nm.NOTE: Measurement of specific extinction in ultra-violet is essentially a measurement of the state of alteration of the oil. It is not specifically a measurement of the refining. In some particular cases, abnormally altered virgin oils can show spectral characteristics close to those of refined oils. Reagents
Spectrophotometrically pure cyclohexane: Minimum transmittance at 220 nm: 40% and minimum transmittance at 250 nm: 95% by comparison with distilled water.
Basic alumina of known grade
Basic alumina of Brockmann grade 1 (0% water) is obtained by heating for 3 hours at 380-400ºC basic alumina (chromatographic quality) of particle size 30μ to 130 μ (mean 80 μ). To 100g of this product add 5 ml of distilled water to produce basic alumina of Brockmann grade close to IV.NOTE: Method used to check the activity index of the alumina.Place 30 g of the basic alumina (as obtained above) in a chromatographic column, 450 mm long with a diameter of 35mm; through this column pass, under the conditions laid down in the method, a mixture of 95% virgin olive oil, having a specific extinction coefficient below 0.18 at 270 nm, and of 5% arachis oil previously treated, during the refining process, with decolourising agent (absorbent earth) and having a specific extinction coefficient equal to or above 4 at 270 nm. If this mixture shows a specific extinction coefficient greater than 0.11, the activity of the alumina is acceptable. Should the elution of conjugated trienes not have taken place using this alumina, an alumina at a higher hydration should be used after verifying that it agrees with the preceding test.Apparatusv
Ultra-violet spectrophotometer for measurements between 210 and 300 nm.
Quartz cells of 1cm thickness.
50-ml and 500-ml volumetric flasks.
Chromatographic column, 450 mm long with a diameter of 35 mm.
Adjustment of Spectrophotometer: dissolve 0.2 g of dry potassium chromate in exactly 1 litre of a 0.05 N solution of potassium hydroxide. Place exactly 25 ml of this solution in a 500-ml flask and bring up to the 500-ml mark with the 0.05 N solution of potassium hydroxide. Determine the optical density of this latter solution by comparison with the 0.05 N solution of potassium hydroxide as a reference solution, in a 1 cm cell. This, at 275 nm should be 0.200 0.005.ProcedureIf the oil is not completely clear at ambient temperature, filter before attempting measurements. Place approximately 0.5 g, weighed accurately, of the oil in the 50-ml flask. Add the cyclohexane up to the mark and shake. Fill a cell with this solution and measure the optical density using the cyclohexane as a reference solution. Make determinations at 232 and 270 nm. Determine, in the region of 270 nm, the wavelength of the maximum absorption λm and determine the optical density at λ m nm, λ m-4 nm and λ m +4 nm. Calculation and Expression of ResultsCalculation of Specific Extinction at 232 and 270 nmwhere:E λ = specific extinction at wavelength λ nmA λ = optical density at wavelength λ nmc = concentration of the test solution in g/100 mll = thickness of the cell in cmNOTE: If the optical density is less than 0.2, re-measure with a more concentrated solution. If it is more than 0.8, re-measure with a weaker solution.