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

Importance of the Topic

Milk adulteration poses health risks and economic losses across the dairy supply chain. Rapid detection and quantification of common contaminants such as water, whey, urea, synthetic milk, synthetic urine and hydrogen peroxide are essential for quality assurance, regulatory compliance and consumer safety.

Objectives and Study Overview

This study evaluated two mid infrared Fourier transform infrared spectroscopy based methods for on site screening and measurement of adulterant levels in bovine milk. The first method provides a fast dilution screen, while the second identifies and quantifies specific contaminants using simple sample preparation.

Methodology

The screening approach measures milk directly with no preparation using a 30 micrometer DialPath transmission accessory. A partial least squares regression model correlates spectral features in the 1300 to 950 inverse centimeter region with overall dilution levels down to 3 percent by volume.

For specific contaminant analysis, spiked milk samples are mixed with chloroform to remove fat, and the water soluble fraction is vacuum dried on a diamond attenuated total reflection crystal to form a thin film. Mid infrared spectra are acquired in the 4000 to 1000 inverse centimeter range with 64 co added scans at 4 inverse centimeter resolution.

Instrumentation Used

Two ultra compact FTIR systems were employed:

• An Agilent Cary 630 FTIR spectrometer with a DialPath 30 micrometer liquid transmission accessory for rapid screening.
• An Agilent 5500 FTIR analyzer equipped with single reflection diamond ATR sampling for specific adulterant identification and quantification.

Spectral acquisition parameters included 64 co added interferograms per spectrum, 4 inverse centimeter resolution and approximately 30 seconds per measurement.

Main Results and Discussion

Partial least squares models achieved excellent performance:

• Screening model for overall dilution yielded R2 values of 0.98 and standard error of prediction below 0.83 percent by volume.
• Quantification of individual adulterants in dried films produced R2val above 0.94 and SEP values of 1.18 g/L for whey, 0.232 g/L for urea, 0.412 g/L for synthetic urine, 0.028 g/L for synthetic milk and 0.009 g/L for hydrogen peroxide.

The spectral fingerprint region captured unique absorbance bands for each contaminant, enabling reliable discrimination and quantitation.

Benefits and Practical Application of the Method

The combined approach offers a time and cost efficient alternative to classical analytical assays. Key advantages include:

• On site screening by non specialist operators in under two minutes.
• Minimal sample preparation with simple cleaning of sampling accessories.
• Rapid quantification of specific contaminants with high correlation to reference values.

Future Trends and Opportunities

Emerging directions include integrating compact FTIR analyzers with digital quality management platforms, extending methods to other dairy products and food matrices, further miniaturization of hardware and application of advanced chemometric and machine learning algorithms to enhance detection sensitivity and multicomponent analysis.

Conclusion

Compact mid infrared FTIR systems equipped with DialPath and diamond ATR sampling provide an efficient workflow for screening and quantifying common milk adulterants at production sites. These methods deliver rapid results, high accuracy and operational simplicity compared to traditional laboratory assays, supporting improved dairy quality control.

References

1. Santos PM, Pereira Filho ER, Rodriguez Saona LE. Application of handheld and portable infrared spectrometers in bovine milk analysis. Journal of Agricultural and Food Chemistry. 2013;61(6):1205 1211.
2. Agilent Technologies Inc. Agilent FTIR family lab results anywhere you want. Publication number 5991 1405EN. 2013.