• Detection and quantification of apple adulteration in diluted and sulphited strawberry and raspberry purées using visible and near infrared spectroscopy

      Downey, Gerard; Kelly, J. Daniel; Department of Agriculture, Food and the Marine (American Chemical Society, 2003)
      Adulteration of sulphited strawberry and raspberry purées by apple is a commercial problem. Strawberry (n=31) and raspberry (n=30) purées were prepared from Irish-grown fruit and adulterated at levels of 10-75% w/w using cooking apples. Visible and near infrared transflectance spectra were recorded using a 0.1 mm sample thickness. Classification and quantification models were developed using raw and scatter-corrected and/or derivatised spectral data. Classification as pure strawberry or raspberry was attempted using soft independent modelling of class analogy (SIMCA). The best models used spectral data in the wavelength ranges 400-1098 nm (strawberry) and 750-1098 nm (raspberry) and produced total correct classification rates of 75% (strawberry) and 95% (raspberry). Quantification of apple content was performed using partial least squares (PLS) regression. Lowest predictive errors obtained were 11.3% (raspberry) and 9.0% (strawberry). These results were obtained using spectral data in the wavelength ranges 400-1880 and 1100-1880 nm respectively. These results suggest minimum detection levels of apple in soft fruit purées of approximately 25% and 20% w/w for raspberry and strawberry respectively.