Detection of adulteration of raspberry purees using infrared spectroscopy and chemometrics

Fourier transform infrared (FTIR) spectroscopy and attenuated total reflection (ATR) sampling have been used to detect adulteration of raspberry purees. A database of 871 spectra of pure and adulterated fruit purees was collected between 1993 and 1994. Partial least-squares (PLS) regression of the spectra onto a dummy variable representing sample type was performed. A 95% confidence interval for the prediction values for pure raspberries was defined: within this region, spectra were accepted as pure raspberry; outside this region, spectra were rejected. Using this criterion, 95% of pure raspberries were accepted as such. Adulteration with apple and plum could be detected at minimum levels of ∼20% w/w, with sucrose at ∼4% w/w. Spectra of 150 additional samples harvested during 1995 served as further validation samples: comparable classification success rates were obtained. The speed of FTIR spectroscopy makes this technique a rapid method for screening raspberry purees for adulterants.