A fast and cost-effective GC-FID method for the determination of adulterated milk fat

Importance of the topic

An accurate and cost-effective method for verifying milk fat authenticity is essential to prevent economic fraud and guarantee product quality. Adulteration with lower-cost vegetable oils or other animal fats compromises nutritional value, regulatory compliance, and consumer trust. Fast and reliable triglyceride fingerprinting supports quality control in dairy production and secures supply chains against fraudulent practices.

Objectives and study overview

This study evaluates a gas chromatography–flame ionization detection (GC-FID) approach, following ISO 17678:2019, to determine purity of milk fat. The main goals were:

• Demonstrate chromatographic separation of triglycerides (C24–C56) in clarified butter.
• Establish response factors using certified reference materials (CRMs).
• Apply S-value equations to detect various adulterants (vegetable oils, coconut/palm kernel fat, beef tallow, lard).
• Assess method precision, repeatability, and suitability for routine QC testing.

Methodology

Sample preparation involved melting commercial clarified butter and diluting it to 1% (w/v) in heptane. Two CRMs—pure butter fat (BCR-632A) and butter adulterated with coconut oil (BCR-632B)—were similarly prepared. Pure CRM injections (n=3) established response factors for each triglyceride and cholesterol peak. Clarified butter (n=9) and adulterated fat (n=5) replicates were analyzed to evaluate precision and S-value calculations.

Instrumentation

• Thermo Scientific TRACE 1610 GC with Instant Connect PTV injector (simulated on-column mode).
• Thermo Scientific iConnect FID with wide-bore jet.
• TraceGOLD TG-1MT metal capillary column (6 m × 0.53 mm × 0.15 µm).
• Thermo Scientific AS 1610 liquid autosampler (capacity 155 vials).
• Carrier gas: nitrogen at 5 mL/min.
• Chromeleon CDS 7.3 for instrument control, data acquisition, and compliant reporting.

Key results and discussion

Triglyceride peaks from C24 to C56 were baseline-integrated and normalized using response factors, all <1.25. Clarified butter S-values for four adulteration models consistently fell within specified ISO limits (RSD ≤0.3%). The adulterated sample exceeded the limit for coconut/palm kernel fat, confirming method specificity. Absolute peak area RSDs averaged 1.1% over nine injections, and customized Chromeleon reports enabled efficient review of triglyceride profiles and S-value outcomes.

Benefits and practical applications

• Fast analysis (<38 min run time) with single-platform data handling.
• Cost reduction by using lab-generated nitrogen as carrier gas.
• High sensitivity to detect low-level adulterants in dairy fats.
• Compliance with ISO/IDF reference methods and regulatory requirements.
• Automated reporting and traceability under 21 CFR Part 11.

Future trends and potential applications

Advances may include coupling GC-FID profiling with chemometric pattern recognition to automate fraud detection. Integration with high-throughput sampling systems can further enhance laboratory productivity. Expanding this approach to other dairy matrices and plant-based analogs could broaden monitoring capabilities in the evolving food industry.

Conclusion

The TRACE 1600 series GC-FID system with PTV on-column injection and inexpensive nitrogen carrier gas offers a robust, precise, and ISO-compliant solution for milk fat authenticity testing. The method reliably distinguishes pure milk fat from various adulterants, ensuring quality control and regulatory adherence in dairy processing.

References

1. IDF guidance on milkfat purity determination, 2019.
2. ISO 17678:2010(E)/IDF 202:2010(E) on milk fat purity by triglyceride GC analysis.
3. ISO 17678:2019/IDF 202:2019 revision of milk fat purity method.
4. IDF Bulletin 499: Practical application of milkfat purity standards, 2019.
5. Thermo Fisher Scientific, Chromeleon CDS Enterprise, BR72617-EN0718S.
6. European Commission JRC Report EUR 21316 EN: Certification of triglyceride reference materials, 2005.