Adulteration detection of soymilk based on near-infrared spectroscopy

Abstract: In order to rapidly detect the internal nutritive index and discriminate adulteration soymilk, the near infrared transmission spectrometer such as Purespect was used to obtain spectrums for 83 unadulterated and adulterated soymilk samples. The spectral scanning procedure was conducted in dark room, 643.26-954.15 nm wavelength range was chosen, scanning wavelength interval was 1.29 nm. Each soymilk sample was scanned three times. Pure soymilks were made according to the regulations in soymilk products industry standard SB/T 10633-2011. A lot of water, essence, thickening agent, food sunset yellow pigment were added to unadulterated soymilk samples in order to obtain adulterated soymilk samples. In this study, 31 adulteration samples and 62 unadulterated samples were prepared in the processing laboratories. 14 soymilk samples were gathered from the market. All samples were used to scan the spectrum and determining chemical composition. The experimental results indicated that smooth lines and clear spectrogram were obtained using Savitzky-Golay and the second derivative method. Chemometrics method of partial least squares (PLS) was used to the model calibration for protein and total solid content in samples. The correlation coefficient of predicted value and measured value of protein and total solid content for soymilk calibration samples were 0.9756 and 0.9489 respectively. The correction of root mean square error for soymilk calibration samples were 0.186 and 0.175 respectively. 12 and 14 was selected for principal component number respectively. 24 prediction samples were prepared for analyzing predictive capability. The results indicated that the residual values of predicted value and measured value for soymilk prediction samples were small and close to zero. The distribution of residual was uniform for both sides of zero line. The residual sums between predicted and measured protein and total solid content values were -0.074 and -1.191 respectively. The results verified that the calibration models could accurately predict the protein and total solid content for soymilk samples. According to the standard of soymilk industry, the internal nutrition of sample was satisfied and the sample was disqualified when the protein mass fraction in soymilk samples was less than 2%, the total solids mass fraction in soymilk samples was less than 6%. Through comparing the predicted values of prediction samples with the regulation values by soymilk industry standard, No. 6-22 samples were disqualified. The resolution of individually adulterated soymilk from all prediction samples was 100% based on the practical sample collection conditions and measured value by chemical methods,. The results verified that the protein and total solid content calibration models were capable of discriminating the adulteration soymilk. This experiment indicated that rapidly detect the major quality index and discriminate adulteration soymilk were achieved based on NIR spectra. This detection method can be used to support for the healthy and abidingly development of soymilk industry.