At-Site Screening and Measurement of Adulterant Levels in Bovine Milk by Mid FTIR Spectroscopy

Significance of the Topic

Milk adulteration, such as dilution with water or addition of whey, urea, melamine and other substances, poses economic, quality and safety concerns for producers and consumers.
Rapid, on-site analytical methods capable of detecting and quantifying adulterants are critical for effective quality control in the dairy industry.

Study Objectives and Overview

This application note demonstrates two mid-infrared (MIR) FTIR-based approaches for bovine milk analysis: a direct screening method to detect overall dilution and a targeted measurement method to identify and quantify specific adulterants.
Both methods employ compact Agilent FTIR instruments designed for easy use at production sites by non-specialist operators.

Methodology and Instrumentation

Screening Method:

• Instrument: Agilent Cary 630 or 5500 FTIR analyzer with DialPath 30 µm transmission sampling.
• Spectral range: 1300–950 cm⁻¹ (fingerprint region).
• Acquisition: 64 co-added interferograms, 4 cm⁻¹ resolution, ~30 s per sample.
• Sample handling: direct milk measurement, no preparation; windows simply wiped between samples.

Identification and Quantification Method:

• Instrument: Agilent 5500 FTIR analyzer with single-reflection diamond ATR.
• Sample preparation: equal-volume extraction of spiked milk with chloroform to remove fat, vacuum-drying of the aqueous supernatant on ATR crystal.
• Spectral acquisition: same parameters as screening method.
• Adulterants studied: whey (1.87–30 g/L), urea and synthetic urine (0.78–12.5 g/L), synthetic milk urea (0.05–0.8 g/L), hydrogen peroxide (0.009–0.15 g/L); overall dilution 3–50% v/v across six milk lots.

Main Results and Discussion

Screening Performance:

• Partial least squares (PLS) model correlating MIR fingerprint spectra with dilution achieved R² = 0.98 for calibration and validation.
• Standard error of calibration (SEC) 0.74% v/v, standard error of prediction (SEP) 0.83% v/v.

Specific Adulterant Quantification:

• Whey: SEP 1.18 g/L, R² = 0.98; characteristic Amide I (1635 cm⁻¹) and Amide II (1530 cm⁻¹) bands.
• Hydrogen peroxide: SEP 0.009 g/L, R² ≈ 0.95.
• Synthetic milk: SEP 0.028 g/L, R² = 0.98.
• Synthetic urine: SEP 0.412 g/L, R² = 0.98; Urea: SEP 0.232 g/L, R² = 0.98; key bands at 1615 cm⁻¹ (C=O) and 1454 cm⁻¹ (NH₄⁺).

The strong water absorbance at 3300 cm⁻¹ is fully opaque, but the fingerprint region remains accessible and informative for both models.

Benefits and Practical Applications

The screening approach delivers a complete analysis cycle in under two minutes and detects dilution to as low as 3% v/v.
Color-coded alerts guide operators in real time, enabling immediate decision-making at delivery points.
The targeted ATR method provides rapid, reliable quantification of multiple common adulterants without the need for extensive laboratory infrastructure.

Future Trends and Opportunities

Integration of portable FTIR analyzers into routine dairy quality control workflows can enhance product safety and traceability.
Advances in chemometric algorithms and machine learning may improve model robustness and expand the range of detectable contaminants.
Cloud connectivity and automated data management will facilitate remote monitoring and centralized compliance reporting.
Miniaturization and multi-sampling accessories may broaden applications to other food matrices and process monitoring.

Conclusion

Compact FTIR analyzers equipped with DialPath transmission sampling and diamond ATR modules offer a fast, user-friendly solution for on-site screening and quantification of milk adulterants.
These methods deliver high accuracy (R² ≈ 0.98), low detection limits and significant time and cost savings compared to conventional laboratory techniques.

Used Instrumentation

• Agilent Cary 630 FTIR spectrometer with DialPath 30 µm transmission cell.
• Agilent 5500 FTIR analyzer with single-reflection diamond ATR accessory.
• Acquisition settings: 64 scans, 4 cm⁻¹ resolution, ~30 s per measurement.
• Agilent Microlab software for data acquisition and PLS analysis.

References

• P. M. Santos, E. R. Pereira-Filho, L. E. Rodriguez-Saona, “Application of handheld and portable infrared spectrometers in bovine milk analysis,” Journal of Agricultural and Food Chemistry, 61(6), 1205–1211 (2013).
• Agilent Technologies, “Agilent’s FTIR family – lab results, anywhere you want,” PN 5991-1405EN.