Spectrophotometer ageing and prediction of fruit attributes

Deterioration of lamp output quality over time and degradation of detector signal to noise ratio are issues associated with ageing of a spectrophotometer. To document the effect of instrument ageing on short wavelength near infrared spectroscopy-based assessment of internal attributes of fruit quality prediction (total soluble solids, TSS, of juice), an assessment was conducted of several handheld PDA based spectrophotometers over several years, with repeated spectra of a reference Teflon (PFTE) tile and spectra of 20 apple fruit acquired at yearly intervals. The repeatability of each instrument was assessed as the standard deviation of absorbance of repeated measures of a reference, typically around 0.2mAbs. Instrument changes were identified in performance and in principal components analysis plots, but performance (apple TSS model) was not related to instrument repeatability. A piecewise direct standardisation method is recommended to maintain a multivariate calibration model across spectrometers.