A Calibration Method, Based on Piecewise Ridge Ls Estimator Designed for Determination of Olive Oil Mixtures on the Basis of Nir Spectral Data

− The spectrophotometric analysis of oil mixtures, containing olive oil, is the subject of this paper. Its objective is to propose and evaluate a new methodology for determination of a selected component of such a mixture. According to this methodology, the space of concentration values to be estimated is partitioned into subspaces and the calibration is performed separately for each subspace by means of a new piecewise ridge least-squares estimator. The estimation of concentrations is carried out, using the results of calibration, in two cycles: first, rough estimates of concentrations are found and a corresponding subspace is identified; next, the results of calibration, obtained for this subspace, are used for refining the estimates of concentrations. The performance of the proposed methodology is assessed using a criterion related to measurement uncertainty.