טכניון מכון טכנולוגי לישראל
הטכניון מכון טכנולוגי לישראל - בית הספר ללימודי מוסמכים  
M.Sc Thesis
M.Sc StudentEtzion Cohen Yael
SubjectAnalysis of Protein Components in Milk by MIR Spectroscopy
DepartmentDepartment of Biotechnology
Supervisors Professor Emeritus Itzhak Shmulevich
Professor Emeritus Uri Cogan


Abstract

This study investigates the potential use of attenuated total reflectance spectroscopy in the mid-infrared range for determining protein concentration in raw cow’s milk. The determination of protein concentration is based on characteristic absorbance of milk proteins, which includes two absorbance bands in the 1500-1700cm-1 range, known as the Amide I and Amide II bands, and absorbance in the 1060-1100cm-1 range, that is associated with phosphate groups covalently bound to casein proteins. In order to minimize the influence of the strong water band (centered around 1640cm-1) that overlaps with the Amide I and Amide II bands, an optimized automatic procedure for accurate water subtraction was applied. Following water subtraction, the spectra were analyzed by three methods, namely, by simple band integration, by partial least squares (PLS) and by neural networks. For the neural network models, the spectra were first decomposed by principal component analysis (PCA), and the neural network inputs were the spectra principal components scores. In addition, the concentrations of two constituents expected to interact with the protein, i.e., fat and lactose, are also used as inputs. These approaches were tested with 235 spectra of standardized raw milk samples, corresponding to 26 protein concentrations in the 2.47-3.90% (weight per volume) range. The simple integration method led to very poor results, while PLS resulted in prediction errors of about 0.22% protein. The neural network approach led to prediction errors of 0.20% protein, when based on PCA scores only, and 0.08% protein when lactose and fat concentrations were also included in the model. These results indicate the potential usefulness of FTIR/ATR spectroscopy for rapid (possibly on-line) determination of protein concentration in raw milk