Mid-infrared Fiber Optic Solutions for Dairy Product Analysis

Milk and dairy products are a widely produced and traded source of nutrition globally. The main goal of the quality control is to provide accurate and reproducible information about the product quality and safety in real time during industrial preparation process.  Spectroscopic methods including Infrared spectroscopy, Raman, reflectance, and fluorescence, are attractive alternatives for traditional analytical methods due to the non-destructive nature, little sample preparation, rapid analysis, minimizing of the use of hazardous solvents. 

In the dairy industry, main parameters that give information about quality include fat, protein, and lactose. Infrared spectroscopy including Mid infrared (MIR) and Near infrared (NIR) is commonly applied to milk and dairy products for authentication and quality control.  MIR spectra provide information arising from the fundamental molecular vibrational frequencies while NIR spectra contain information from the overtones and combination of such vibrations. Unlike NIR, MIR are much more sensitive and provide much clearer chemical structure information.   The understanding of measurement of fat, protein and lactose using MIR is well developed and accepted in official methods for milk (AOAC International, 2016, method number 972.16).  Analysis of milk by IR is based on absorption of IR energy at specific wave numbers by CH groups in fatty acid chains of fat molecules (3000-2850cm-1), by carbonyl groups in ester linkages of fat molecules (1730 cm-1), by peptide linkages between amino acids of protein molecules( 1550cm-1), and by OH groups in lactose molecules  (1040cm-1) ( Figure 1).  

Figure 1 ATR spectra of milk products measured with fiber probes ( left) and the ATR fiber probe setup (right)

Bench top MIR milk analyzer has been widely used for off-line and on-line analysis. But it does not meet the increasing need for in-line analysis in the milk production process.  Fiber optic techniques provide an attractive solution.  The use of flexible optical probe allows the separation of sampling from the spectrometer.  It requires no sample preparation and is ideal for both on-line and in-line analysis in hazard environment or in sterile conditions. 

Mid-infrared fiber solution uses attenuated total reflection (ATR) probe configuration. The working principle is illustrated in Figure 2. Regardless of the fiber probe, light from FT-IR analyzer is guided by the optical fiber probe on the surface of solid sample or diving into the fluid sample. The light with sample spectra is captured by a fiber optical detection line and returned to the analyzer where the data is analyzed and post-processed. Incorporating the ATR probe into the milk production line can provide continuous real time analysis of product compositions. With more precise control and understanding of the production process it is possible to make timely adjustments and ensure optimum yield without overusing expensive raw materials, and effectively reduce the variations in the final products. 

Figure 2 ATR fiber optic probe System

As shown in Figure 1, the ATR spectra measured with the fiber probes clear differentiate different milk products in the content of fat, sugar.  By combining appropriate chemometrics model, it has huge potential to pick up even more subtle changes. 

ATR probe can also combine with other fiber probes such as Raman, NIR reflection, fluorescence to provide complimentary information in real time on milk products composition & quality. Figure 3 shows a Multi-spectra fiber optic system for monitoring the dissolution process for milk powder.  Four different fiber probes were inserted in the reactor and in-situ spectra of ATR, Raman, NIR and Fluorescence were collected simultaneously in the dissolution process of milk powder.   

Figure 3 Multi-spectra fiber optical system for milk dissolution analysis

Aurora Pro Scientific offers full solution for fiber optic probes and analytical services. Should you have any questions about our products, please visit our website, and contact us at sales@auroraprosci.com.