Detection of fraudulent addition of glucose syrup to mulberry, carob and grape pekmez by Fourier transformed infrared (FTIR) spectroscopy

Pekmez, a traditional food generally produced by concentration of fruit juices, is subjected to fraudulent activities like many other foodstuffs. The aim of this study was to detect the fraudulent addition of glucose syrup to traditional grape, carob and mulberry pekmez. Synthetically adulterated pekmez samples containing glucose in the range of 2,5-50 % (w/w) were produced in laboratory conditions. The color values in terms of L*, a*, b* values, water activity, pH ve °Brix values of pure and adulterated samples were determined. Only differences between the L* values of the pure and adulterated pekmez samples for all pekmez types were found statistically significant (P<0,05). Fourier transform infrared spectroscopy (FTIR) in combination with chemometric methods was used for the detection of fraudulent addition of glucose syrup to traditional grape, carob and mulberry pekmez. FTIR spectra of samples were taken in Mid-infrared (MIR) range of 4000-400 cm-1 using attenuated total reflectance (ATR) sample accessory. Partial least squares-discriminant analysis (PLS-DA) and PLS chemometric methods were used for qualitative and quantitative analysis of pekmez samples, respectively. PLS-DA models were successfully used for the discrimination of pure pekmez samples and the adulterated pekmez samples with glucose syrup. Sensitivity and specificity of 100%, and model efficiency of 100% were obtained in PLS-DA models for all pekmez groups. Detection of the adulteration ratio of pekmez samples was also accomplished using ATR-FTIR spectroscopy in combination with PLS. RMSEC ve REMSEP values of the PLS models generated for the determination of the fraudulent addition of glucose syrup to grape, carob and mulberry pekmez samples were 2,017%, 0,983%, 1,618% and 3,908%, 1,856%, 10,282%, respectively. As a result, it was shown that ATR-FTIR spectroscopy along with chemometric methods had a great potential for determination of pekmez adulteration with glucose syrup.