Classification and analysis of citrus oils by NIR spectroscopy

A new NIRS method is introduced for the determination of valuable components in various citrus oils. Spectra of grapefruit, orange, mandarin, lemon and lime oils in the range from 1100 to 2500 nm have been registered. Applying principal component analysis to the spectral data a good separation of the different fruit oil types can be achieved. The application of multivariate statistics in conjunction with analytical reference data leads to good NIR calibration results. For the main components (e.g. limonene, γ-terpinene, sabinene) and general chemical–physical parameters (e.g. optical rotation value, aldehyde content) standard errors are in the range of the applied reference method. The multiple coefficients of determination (R2) for components with an amount of more than 1.5% are generally >0.95. Furthermore reliable in-process methods for the determination of the individual nootkatone and aldehyde contents during the isolation and purification process from grapefruit and orange oil are presented.