Method for detecting the rancidity of oilseeds, seeds and nuts

A process for establishing a rancidity index table and allocating a rancidity index value to an absorption or reflection spectrum of oil fruits, nuts and seeds, comprising the steps of:

• irradiating a sample of an oil fruit, a nut or a seed with a light source,
• projecting the reflected and/or transmitted light onto a photosensor,
• detecting the absorption or reflection spectrum in a wavelength range from 900 to 2500 nm, by means of the photosensor,
• extracting ingredients of the sample by sample preparation techniques based on a determination of volatile compounds from a vapour space above the sample,
• separating volatile components of the sample by applying gas-chromatographic techniques,
• identifying separated volatile components of the sample by mass spectroscopic detection of constituents of the volatile components which are relevant for lipid oxidation,
• determining a rancidity index value of the sample from identified volatile components of the sample,
• allocating at least individual characteristic wavelengths or wavelength ranges of the detected absorption or reflection spectrum of the sample to the rancidity index value,
• repeating the previous steps for a representative number of samples and forming a rancidity table from the determined rancidity index values and allocated absorption or reflection spectra or, respectively, characteristic wavelengths or wavelength ranges of the detected absorption or reflection spectra.