🍎 Determination of milk fat purity (detection of vegetable and animal fats, e.g. beef tallow and lard) by gas chromatographic analysis of triglycerides with a flame ionization detector — fat is isolated from butter by melting and filtering through sodium sulfate at 50 °C, from milk on a silica gel column, by the Röse–Gottlieb method or from cheese according to ISO 14156; a 5 % solution (packed column) or ≤ 1 % (short capillary column) separates triglycerides by carbon number C24–C54, and S-values calculated from their fractions are compared with the limits for pure milk fat; reference method, PN-EN ISO 17678

Food chemistry PN-EN ISO 17678

Overview

WHAT THE STANDARD COVERS. We read the text of the standard in the iTeh sample of ISO 17678:2019 | IDF 202:2019 (English text): title page, contents, ISO and IDF forewords, Clauses 1–7 and Clause 8 up to the beginning of 8.3.3.1 (calibration) — the sample ends on page 6. Parts of the text are missing in the sample: the end of 8.1.2 (note 1) and 8.3.1 on baseline drift (truncated sentences), and 5.6 (n-heptane) is known only from the reference in 8.2. The rest — chromatographic conditions, integration, calculation of S-values, detection of foreign fat, precision, test report and Annexes A–D — we do not read; we know the titles from the contents.

ACCORDING TO THE TEXT OF ISO 17678:2019. The second edition of June 2019 was prepared by ISO/TC 34 “Food products”, Subcommittee SC 5 “Milk and milk products”, jointly with the International Dairy Federation (IDF); it replaces the first edition ISO 17678 | IDF 202:2010. Changes according to the foreword: the scope was restricted to exclude milk fat from special feeding practices and from whey, extended to include milk fat from cheese with low lipolysis, a method for fat extraction from cheese was added, and the bibliography was expanded. Contents: 8 Procedure (8.1 preparation of test samples: from butter or butteroil, by the Röse–Gottlieb method, from milk on silica gel columns, from cheese; 8.2 fat sample solution; 8.3 chromatographic triglyceride determination: baseline drift, injection technique, calibration, chromatographic conditions), 9 Integration, evaluation and control of analytical performance, 10 Calculation and expression of results (10.1 triglyceride composition, 10.2 S-values, 10.3 detection of foreign fat), 11 Precision (interlaboratory test, repeatability, reproducibility), 12 Test report, Annex A (normative) “Preparation of the packed column”, Annex B (informative) “Quantification of the foreign fat content”, Annex C (informative) “Uncertainty of measurement”, Annex D (informative) “Interlaboratory test”. Scope (1): reference method for determining milk fat purity by GC analysis of triglycerides; it uses differences between the triglyceride fingerprint of milk fat and those of other fats and oils, via defined formulae based on a normalized weighted sum of triglyceride peaks; the result is compared with values observed for a range of pure milk fat samples; both vegetable fats and animal fats, e.g. beef tallow and lard, can be detected. The method applies to bulk milk and products made thereof, irrespective of common feeding practices, breed or lactation, in particular to fat from products supposed to contain pure milk fat of unchanged composition — butter, cream, milk and milk powder. Because a false-positive result can occur, the method does not apply to milk fat: a) from bovine milk other than cow’s milk; b) from single cows; c) from cows whose diet contained a particularly high proportion of vegetable oils (rapeseed, cotton, palm oil, etc.); d) from cows suffering from serious underfeeding (strong energy deficit); e) from colostrum; f) subjected to technological treatment, e.g. removal of cholesterol or fractionation; g) from skim milk, buttermilk or whey; h) from cheeses showing increased lipolysis; i) extracted by the Gerber, Weibull–Berntrop or Schmid–Bondzynski–Ratzlaff methods or isolated with detergents (e.g. the Bureau of Dairy Industries method) — with these methods substantial quantities of partial glycerides or phospholipids pass into the fat phase. Notes: butyric acid (C4) occurs in nature exclusively in milk fat and allows quantitative estimation of low to moderate amounts of milk fat in vegetable and animal fats, but with its variation (about 3.1–3.8 % of fat mass) it is difficult to give qualitative and quantitative information for foreign fat to pure milk fat ratios up to 20 %; quantitative results cannot be derived from the sterol content, and qualitative detection of foreign fat by sterols is ambiguous; false-positive results have been reported for milk from certain Asian regions and with grass-only diets (mountain and highland pasture), which can be substantiated by a content of conjugated linoleic acid C18:2 c9t11 ≥ 1.3 % of fatty acid mass — nevertheless, results conforming to the purity criteria are accepted for such samples too; if a positive result is suspected to be caused by cases c) or d), it can be confirmed by fatty acid or sterol analysis, but a negative result of another method does not confirm purity. References (2): ISO 1211 | IDF 1 (fat in milk), ISO 1740 | IDF 6 (fat acidity), ISO 1736 | IDF 9 (fat in dried milk), ISO 2450 | IDF 16 (fat in cream), ISO 3696 (water), ISO 7328 | IDF 116 (fat in edible ices), ISO 14156 | IDF 172 (lipid extraction). Definition (3.1): milk fat purity — absence of vegetable and animal fats determined by the procedure of this standard, determined from S-values calculated from triglyceride contents (in percent by mass). Principle (4): fat from milk or milk products is analysed by GC on a packed or a short capillary column, separating triglycerides by total carbon number; the fractions of molecules C24–C54 (even numbers only) are inserted into formulae to calculate S-values — sums of weighted triglyceride fractions; exceeding the limits established with pure milk fat means detection of foreign fat; the suitability and equivalence of both column types have been demonstrated previously. Reagents (5): water of grade 2 according to ISO 3696; carrier gas nitrogen or helium or hydrogen (≥ 99.995 %); saturated triglyceride and cholesterol standards (≥ 99 %) for standardizing the milk fat standard; methanol (≤ 0.05 % water); n-hexane; hydrogen and synthetic air free from organic impurities (< 1 µl/l); anhydrous sodium sulfate. Apparatus (6): high-temperature gas chromatograph (at least 400 °C) with FID; for capillary GC an on-column or programmed-temperature vaporization injector — a split injector is unsuitable; high-temperature septa, graphite seals; glass packed column 2 mm × 500 mm with 3 % OV-1 on a 125–150 µm support (preparation in Annex A) or a short capillary column (e.g. 5 m) with a non-polar phase resistant to ≥ 400 °C — conditioned by 20 analyses of a fat solution within no more than two days, with response factors close to 1 and not higher than 1.250 0 (more is accepted for C24 because of overlap with cholesterol); column length is limited by the required resolution; Extrelut column 1–3 ml with silica gel (only for 8.1.4); water bath (50 ± 2) °C; oven 50 and 100 °C; syringe whose plunger does not reach into the needle tip (packed column — better repeatability); balance readable to 0.1 mg. Sampling (7): not part of the method, recommended method in ISO 707 | IDF 50. Preparation (8.1): from butter or butteroil — melt 50–100 g at 50 °C and filter the fat layer through a filter with 0.5–1.0 g of sodium sulfate in a preheated funnel, in the oven, without transferring serum (a smaller sample increases the risk of non-representativeness); the fat so obtained is almost free of phospholipids; by the Röse–Gottlieb method according to ISO 1211, 1736, 2450 or 7328; from milk — 0.7 ml of milk at 20 °C onto an Extrelut column, after about 5 min 1.5 ml of methanol to denature protein–lipid complexes, extraction with 20 ml of n-hexane, evaporation at 40–50 °C and weighing (several extractions combined if needed); from cheese — according to ISO 14156 | IDF 172, and for cheeses with strong lipolysis (often mould-ripened and long-ripened) the fat acidity is determined according to ISO 1740 — above 8 mmol/100 g of fat the standard is not applicable. Solution (8.2): 5 % (V/V) of melted fat in n-hexane or n-heptane for a packed column, 1 % or less for on-column injection on a 0.53 mm capillary column; 0.5–1 ml into an ampoule. Determination (8.3): the column is conditioned to minimize baseline rise, to which high-temperature triglyceride analysis is particularly susceptible in the high carbon-number range; packed column — hot-needle technique (needle heated about 3 s before rapid injection); cool on-column capillary injection — immediate injection and needle dwell time typically about 3 s; calibration — two to three analyses of standardized milk fat at the beginning of each working day (continuation outside the sample).

STATUS (as of 03.10.2026). In the PKN search (query “17678”, 03.10.2026) PN-EN ISO 17678:2019-07 in the Polish and English versions (“Wprowadza: EN ISO 17678:2019 [IDT], ISO 17678:2019 [IDT]”) carries no withdrawal note; PN-EN ISO 17678:2011 (Polish version) — “Wycofana i zastąpiona przez PN-EN ISO 17678:2019-07 – wersja angielska”, and PN-EN ISO 17678:2010 (English version) — withdrawn and replaced by PN-EN ISO 17678:2011; the other results (PN-EN 17678-1 and -2) concern post-tensioning of concrete structures. Card of the English version: publication date 30.07.2019, 38 pages, KT 35 Mleka i Przetworów Mlecznych, “Zastępuje PN-EN ISO 17678:2011 – wersja polska”, among additional elements the amendment PN-EN ISO 17678:2019-07/Ap1:2020-10E (with the note “Tytuł zmieniony poprawką” — we have not read the content of the amendment). Card of the Polish version: publication date 10.02.2021, 30 pages, no withdrawal note. In the iTeh catalogue (read 03.10.2026) ISO 17678:2019 has the status “Published”, stage 90.93 (International Standard confirmed).

HOW MANY LABORATORIES AND IN WHAT FORM (copy of the accreditation scope database, data up to 17.09.2026, read 03.10.2026). The number 17678 appears in 6 records at 4 laboratories: AB 285, AB 370, AB 433 (2), AB 705 (2). In the current PCA documents (read 03.10.2026; AB 285 issue no. 28 of 13.01.2026, AB 705 issue no. 21 of 06.05.2026, AB 433 issue no. 26 of 11.06.2026, AB 370 issue no. 25 of 04.08.2026) the number appears in 8 lines at the same 4 laboratories — at AB 433 the number occurs twice in each of the two records (standard and amendment), hence 4 lines with the number for 2 records; in each document the number of page markers equals the number of PDF pages, without repetitions; a search of all PCA documents downloaded from the BIP on 03.10.2026 found no laboratories outside the database copy. Form “PN-EN ISO 17678:2019-07” (AB 370, AB 705), “PN-EN ISO 17678:2019-07” with “PN-EN ISO 17678:2019-07/Ap1:2020-10” (AB 433) and “PN-EN ISO 17678:2019” (AB 285). None of these items is suspended. The “Laboratories” tab (query “PN-EN ISO 17678”) shows all 4 laboratories — checked by a tab query on the labcoda.pl production server on 03.10.2026.

WHAT THE LABORATORIES TEST (items in PCA). Object: dairy products (AB 285); dairy products — processed cheeses, ripened cheeses, creams, curd cheeses, butter, dairy spreads (AB 370); dairy products excluding long-ripened and mould cheeses (AB 433); butter and cream (AB 705). Characteristic: presence of foreign fats (AB 285, AB 370, AB 705), presence of foreign fat in milk fat — “from 4.00 %” (AB 433) and content of foreign fat in milk fat (5.01–95.0) % (AB 433); AB 370 gives “from 2 %”. Technique: gas chromatography with flame ionization detection (GC-FID) at all.

WHERE A SEEMINGLY CORRECT RESULT IS EASY TO GET. Positive result: the standard lists nine cases in which pure fat may give a false-positive result (1 a–i) — including goat, sheep or buffalo milk (other than cow’s milk), milk from single cows, colostrum, fat after cholesterol removal or fractionation, fat from buttermilk and whey; confirmation by another method works only one way — a negative result of another method does not prove purity (note 4). Cheeses: with fat acidity above 8 mmol/100 g the standard does not apply (8.1.5) — AB 433 excludes long-ripened and mould cheeses, AB 370 includes ripened cheeses without such an exclusion in the entry. Extraction: fat from the Gerber, Weibull–Berntrop, Schmid–Bondzynski–Ratzlaff methods or isolated with detergents is unsuitable (1 i) — partial glycerides and phospholipids change the profile. Chromatograph: a split injector is unsuitable (6.1), and a capillary column requires conditioning and response factors ≤ 1.250 0 (6.3). Quantitative result: the principle of the method is detection (4); quantification of foreign fat is described in the informative Annex B, which we have not read — AB 433 has a separate item “content of foreign fat” (5.01–95.0) %. Lower limit: AB 370 (“from 2 %”) and AB 433 (“from 4.00 %”) give different detection thresholds; the standard gives no such threshold in the part of the sample.

WHAT WE DO NOT GIVE. Chromatographic conditions, formulae for S-values and their limits, precision, rules for quantifying foreign fat from Annex B or the preparation of the packed column from Annex A are not quoted — they lie outside the sample. We do not give regulations on the labelling of butter and dairy products.

Method principle

Fat is isolated from butter (melting and filtering through sodium sulfate at 50 °C), from milk (silica gel column, methanol and n-hexane), by the Röse–Gottlieb method or from cheese according to ISO 14156. A solution of the fat in n-hexane or n-heptane is separated by high-temperature gas chromatography with FID on a packed (3 % OV-1) or short capillary column, giving fractions of triglycerides C24–C54 by carbon number. S-values (weighted sums) are calculated from the fractions; a value outside the limits for pure milk fat indicates foreign fat — vegetable or animal.

Applications

• Detection of vegetable and animal fats (e.g. tallow, lard) in fat from bulk milk and products that should contain pure milk fat — butter, cream, milk, milk powder, cheese with low lipolysis (1)
• Not applicable to, among others, milk other than cow’s milk, milk from single cows, colostrum, buttermilk, whey and cheeses with strong lipolysis (1, 8.1.5)
• Dairy products, butter, cream — presence, and at one laboratory also content of foreign fat: items in the accreditation scopes of 4 laboratories in PCA

Key parameters

Standard

Standard number

PN-EN ISO 17678:2019-07

Title (PL)

Mleko i przetwory mleczne — Oznaczanie czystości tłuszczu mlecznego przez analizę triglicerydów za pomocą chromatografii gazowej

Title (EN)

Milk and milk products — Determination of milk fat purity by gas chromatographic analysis of triglycerides

Step-by-step procedure

1. Isolation of fat

   Butter: melt 50–100 g at 50 °C, filter through sodium sulfate; milk: Extrelut with methanol and n-hexane; Röse–Gottlieb or cheese according to ISO 14156 (8.1). PN-EN ISO 17678:2019-07 with no withdrawal note in PKN (03.10.2026).

2. Cheese check

   For cheeses with strong lipolysis, fat acidity according to ISO 1740; > 8 mmol/100 g — the standard does not apply (8.1.5).

3. Solution

   5 % in n-hexane or n-heptane (packed column) or ≤ 1 % (0.53 mm capillary), 0.5–1 ml into an ampoule (8.2).

4. Chromatography

   Conditioned column; hot needle about 3 s (packed) or cool on-column injection; daily calibration with 2–3 analyses of standardized milk fat (8.3).

5. Evaluation

   Fractions of triglycerides C24–C54 → S-values → comparison with limits for pure milk fat (4; formulae in Clause 10, outside the sample).

Required equipment and apparatus

Reagents, media and consumables

Health and safety (OHS)

• n-Hexane and methanol — flammable and harmful; work under a fume hood
• Hydrogen as carrier or FID gas — flammable; tightness of the gas installation

Frequently asked questions