Scatter-based quantitative spectroscopic analysis of milk fat and total protein in the region 400–1100 nm in the presence of fat globule size variability

Accurate prediction models for fat and total protein content in raw milk have been built on visible and short-wave near infrared spectra (400–1100 nm) of a designed sample set with systematically varied nutrient composition and homogenization degree. Unlike the conventional approach to the spectroscopic milk analysis, exploiting the components' absorbance, the present method basically relies on the phenomenon of light scatter by fat globules and protein micelles.It has been shown that partial least-squares (PLS) regression on raw spectral data results in higher prediction accuracies of fat and total protein content compared to scatter-corrected spectra. Interpretation given to individual PLS factors confirms a dominating role of scatter in the modeling and aids in general understanding of quantitative multivariate analysis based on complex optical responses resulting from multiple scattering by different particles at significantly varying size distributions. This new approach can be used in the raw milk laboratory or field analysis as well as for in-line monitoring of various milk transfer and production stages.Practical modeling issues, i.e. experimental design of the sample set, model validation and refinement, have been also elaborated in this study. Variable selection by interval PLS (iPLS) regression essentially improved the model performance. Selected intervals can be utilized for technical simplification of suggested method of milk analysis.

• Fat and total protein in raw milk are accurately determined from Vis/SW-NIR spectra.
• The method is resistant against large variability of fat globule sizes.
• PLS calibration is based on light multiple scatter by fat and protein particles.
• Experimental design for milk component calibration based on mixing standard samples