[Application of wavelet multi-scale orthogonal signal correction in milk components measurement using near-infrared...

Spectral interferences can have a significant impact on the spectral variation and as a consequence can adversely affect the results of calibration model in spectra analysis. Wavelet transform (WT) and orthogonal signal correction (OSC) were both the popular preprocessing algorithms. It was known that the former can effectively eliminate the background and noise and the latter can effectively filter out the interference information irrelevant to analyte concentration during the preprocessing of spectra. According to the different characteristics of analyte information and interference information in near-infrared (NIR) spectra, a new hybrid algorithm (WMOSC) that was the combination of discrete wavelet transform (DWT) and OSC was proposed to eliminate the spectral interferences including background, noise and systemic spectral variation irrelevant to the concentration. First, DWT was used to split the spectral signal into different frequency components, which keep the same data points as the original spectra data, to remove noise and background information by threshold method. Then OSC was applied to each frequency components to remove the information uncorrelated to the concentration independently. Finally, the spectra preprocessed by WMOSC were achieved through the summation of all frequency components. WMOSC was successfully applied to preprocess the NIR spectra data of milk. After elimination of the interference in the NIR spectra data by WMOSC, the partial least squares (PLS) regression was used to develop the calibration models for estimating the contents of main constituents in milk.The prediction ability and robustness of models obtained in subsequent PLS calibration using WMOSC were superior to those obtained using either DWT or OSC alone. The root mean square errors of prediction (RMSEP) of the models for fat, protein and lactose were 0.101 6%, 0.087 1% and 0.110 7%, respectively. The experimental results show that WMOSC is an effective method for eliminating the interferences information in NIR spectra.