🍎 Alkalinity of animal and vegetable fats and oils without distinguishing between alkaline constituents (e.g. sodium soaps in imperfectly refined oils, calcium soaps from bones) — test portion of up to 40 g depending on colour and expected result, dissolved in 100 ml of aqueous acetone with bromophenol blue at 40 °C and titrated warm (30–40 °C) with 0.01 mol/l hydrochloric acid until the colour changes from blue to yellowish green; result as mg sodium oleate per kg (S = 304 000·V·c/m) or % NaOH (A = 4·V·c/m), mean of two determinations; not for dry melted animal fats or fats with acidity above 60 %; PN-EN ISO 10539:2002

Food chemistry PN-EN ISO 10539

Overview

WHAT THE STANDARD COVERS. We read the text of the standard in the iTeh sample of ISO 10539:2002 (first edition of 15.03.2002, English text) — PN-EN ISO 10539:2002 adopts EN ISO 10539:2002 and ISO 10539:2002 as identical (PKN search). The sample covers the whole text: foreword, clauses 1–12 and Annex A (results of an interlaboratory trial) up to page 5.

ACCORDING TO THE TEXT OF ISO 10539:2002. The standard was prepared by ISO/TC 34 "Food products", Subcommittee SC 11 "Animal and vegetable fats and oils". Scope (1): determination of the alkalinity of animal and vegetable fats and oils without distinguishing between the various constituents; the method is not applicable to dry melted animal fats, nor to oils and fats with an acidity greater than 60 % (mass fraction) determined according to ISO 660. Note to the scope: alkaline constituents may be natural (e.g. calcium soaps from bones) or accidental (e.g. sodium soaps in imperfectly refined fats and oils). References (2): ISO 660:1996 (acid value and acidity), ISO 661:1989 (preparation of test sample), ISO 3696:1987 (water for laboratory use). Definition (3.1): alkalinity — proportion of alkali in a fat or oil determined by titration with hydrochloric acid by the method of this standard. Principle (4): a test portion is dissolved in warm aqueous acetone and titrated with hydrochloric acid. Reagents (5): water of grade 3 according to ISO 3696; aqueous acetone — 970 ml acetone, 20 ml water and 10 ml bromophenol blue solution (2 g/l in acetone), brought to a blue colour with 0.1 mol/l NaOH and then to the appearance of a yellowish green colour with 0.1 mol/l hydrochloric acid; standard volumetric hydrochloric acid solution c(HCl) = 0.01 mol/l, standardized not more than 7 days before use. Apparatus (6): borosilicate glass apparatus for aqueous acetone; wide-necked conical flasks of 400–500 ml. Sampling (7) is not part of the method — ISO 5555 is recommended; the test sample is prepared according to ISO 661 (8). Preparation of apparatus (9.1): each flask and stirrer is rinsed with successive 20 ml portions of aqueous acetone until the acetone no longer changes colour, and dried. Test portion (9.2, Table 1): up to 40 g weighed to 0.1 g, depending on the expected result and the colour of the sample — light samples: up to 500 mg sodium oleate/kg — 40 g, over 500 to 1000 — 10 g, over 1000 — 4 g; dark — 2 g; very dark — 1 g; for test portions below 10 g replicate portions totalling at least 5 g are taken and masses and titres are summed as one determination; a solid portion is melted below the boiling point of acetone, 100 ml of aqueous acetone at 40 °C is added, stirred and left until it separates into two layers — in the presence of soap the upper layer is blue. Determination (9.3): the warm (30–40 °C) solution is titrated with 0.01 mol/l hydrochloric acid while stirring until the indicator changes from blue (or blue-green) to the yellowish green of the acetone added; the mixture is allowed to settle to observe the colour clearly; note: an explosion-resistant hotplate with a magnetic stirrer and burette support is particularly useful. Two determinations on the same sample (9.4). Results (10): alkalinity as NaOH, A (% by mass) = 4·V·c/m, or as sodium oleate, S (mg/kg) = 304 000·V·c/m, where m — mass of the test portion in g, c — concentration of HCl in mol/l, V — volume of HCl in ml; the result is the mean of two determinations if the repeatability requirement is met. Test report (12): identification of the sample, sampling method (if known), test method with reference to the standard, conditions not specified in the standard and incidents that may have influenced the result, the result. Annex A: interlaboratory trial organized by AFNOR — 15 laboratories from 6 countries, statistics according to ISO 5725-2 (Table A.1): sample D — 14 laboratories after eliminating outliers, mean 8.3 mg/kg, sr 0.7, r 1.9, sR 2.3, R 6.4 mg/kg, CVR 27.1 %; sample E — 11 laboratories, 216.3 mg/kg, sr 0.6, r 1.8, sR 8.4, R 23.7 mg/kg, CVR 3.9 %; sample H — 12 laboratories, 12.5 mg/kg, sr 0.5, r 1.3, sR 9.5, R 27.0 mg/kg, CVR 76.1 %.

STATUS (as of 03.10.2026). The PKN search engine (query "PN-EN ISO 10539", 03.10.2026) returns one result: PN-EN ISO 10539:2002 — Polish version, "Introduces: EN ISO 10539:2002 [IDT], ISO 10539:2002 [IDT]", without a withdrawal note.

HOW MANY LABORATORIES AND IN WHAT FORM (copy of the accreditation scope database, load up to 17.09.2026, read 03.10.2026). The number 10539 appears in 2 records at 2 laboratories: AB 285 and AB 370. In the current PCA documents (read 03.10.2026; AB 285 issue no. 28 of 13.01.2026, AB 370 issue no. 25 of 04.08.2026) the number appears at the same 2 laboratories; in each document the number of page markers equals the number of PDF pages, without duplicates; searching all PCA documents downloaded from the BIP on 03.10.2026 found no laboratories outside the database copy. Form at both: "PN-EN ISO 10539:2002". None of these items is suspended. The "Laboratories" tab (query "PN-EN ISO 10539") shows both laboratories — checked by a tab query on the labcoda.pl production server on 03.10.2026.

WHAT THE LABORATORIES TEST (PCA items). AB 285: vegetable and animal oils and fats — alkalinity (soap content) (1.5–15.0) mg sodium oleate/kg, titrimetric method. AB 370: vegetable oils — alkalinity (soap content) (0.76–15.30) mg sodium oleate/kg, (0.00001–0.00020) % and (0.06–1.20) mg sodium/kg (calculated), titrimetric method.

WHERE A SEEMINGLY CORRECT RESULT IS EASY TO GET. Scope: the method does not cover dry melted animal fats or samples with acidity above 60 % according to ISO 660 (1) — acidity must be known before the determination. Glassware: flasks and stirrer are rinsed with aqueous acetone until it no longer changes colour (9.1) — alkaline residues on the glass give alkalinity that is not in the oil. Test portion: its mass depends on colour and expected result (Table 1); below 10 g replicates are summed to at least 5 g (9.2). Titrant: 0.01 mol/l acid standardized not more than 7 days before use (5.3). End point: the solution is titrated warm (30–40 °C) and the colour judged after the layers have separated (9.3). Unit: the same result may be given as mg sodium oleate/kg or % NaOH (10) — AB 370 additionally gives % and mg sodium/kg (calculated), so comparisons must check which quantity is reported. Low levels: in the interlaboratory trial reproducibility R was 6.4 mg/kg at a mean of 8.3 mg/kg and 27.0 mg/kg at 12.5 mg/kg (Table A.1); the ranges of both laboratories start below 2 mg sodium oleate/kg.

WHAT WE DO NOT GIVE. We do not summarize ISO 660, ISO 661 or ISO 5555 in this entry. We do not give requirements for the soap content of refined oils.

Method principle

Soaps and other alkaline constituents of a fat are determined together by acid–base titration. The test portion is dissolved in warm acetone with a little water and bromophenol blue, previously neutralized to a yellowish green colour; in the presence of soap the upper layer turns blue. The solution is titrated warm with 0.01 mol/l hydrochloric acid until the yellowish green colour returns, and the acid consumed is converted to sodium oleate (mg/kg) or sodium hydroxide (%).

Applications

• Animal and vegetable oils and fats — sodium soaps in imperfectly refined oils and fats (1, note)
• Animal fats containing natural alkaline constituents, e.g. calcium soaps from bones (1, note) — except dry melted fats
• Vegetable and animal oils and fats and vegetable oils — alkalinity (soap content) — 2 accreditation scope records of 2 laboratories in PCA

Key parameters

Standard

Standard number

PN-EN ISO 10539:2002

Title (PL)

Oleje i tłuszcze roślinne oraz zwierzęce — Oznaczanie alkaliczności

Title (EN)

Animal and vegetable fats and oils — Determination of alkalinity

Step-by-step procedure

1. Preparation of glassware

   Rinsing flasks and stirrer with 20 ml portions of aqueous acetone until no colour change, drying (9.1). PN-EN ISO 10539:2002 — no withdrawal note (PKN, 03.10.2026).

2. Test portion

   Up to 40 g to 0.1 g according to Table 1; below 10 g — replicates totalling ≥ 5 g (9.2).

3. Dissolution

   Melting below the boiling point of acetone, 100 ml aqueous acetone at 40 °C, stirring, separation of layers (9.2).

4. Titration

   Warm (30–40 °C) with 0.01 mol/l HCl from blue to yellowish green; judged after the layers separate (9.3).

5. Result

   S (mg sodium oleate/kg) or A (% NaOH); mean of two determinations when repeatability is met (9.4, 10).

Required equipment and apparatus

Reagents, media and consumables

Health and safety (OHS)

• Acetone is flammable — the standard names an explosion-resistant hotplate with stirrer as particularly useful (note to 9.3); a solid test portion is melted below the boiling point of acetone (9.2)

Frequently asked questions