Análise multivariada aplicada a espectroscopia Raman e absorção óptica em fraude de leite caprino e efeito SERS em leite bovino

Abstract

Due to the important nutritional and economic value of bovine and caprine milks, they are constant targets of fraud. In the present work, two studies were developed. The first study characterizes the components present in bovine and caprine milks through Raman and infrared vibrational spectroscopy (MIR and NIR). Then, it was sought the evaluation of chemometric techniques Principal Component Analysis (PCA) and regression by partial least squares (PLS), associated with vibrational spectroscopy techniques as alternative methods of tampering detecting in adulterated raw caprine milk with the addition of raw bovine milk. The PCA models generated with Raman and MIR spectra showed satisfactory results in discrimination samples of 90-100% goat milk, adulterated with steps of 2% bovine milk. In the PLS analysis of the samples with 60-100% goat milk, adulterated with steps of 2% bovine milk, the calibration curves were obtained with a value of 𝑅 2 ≥ 0.995. In the second study, was sought to obtain the amplification of the Raman signal of pasteurized bovine milk using SERS active substrates. In this study, the SERS substrates were produced in borophosphate glass matrices containing determined concentrations of silver nitrate (AgNO3 ) as a precursor agent. The metallic silver nanostructures were grown on the surface of the SERS substrates using the bottom-up method, with a controlled hydrogen atmosphere and times of 1, 3, 5, 8 and 11 minutes of annealing heat treatment at 300 ºC. Using a 488 nm laser line, all active SERS substrates showed SERS activity and amplified the Raman signal from pasteurized bovine milk. It is noteworthy the SERS substrates doped with 1% and 6% silver ions and annealing time of 3 and 11 minutes, which presented SERS efficiency factors of 9.1 and 16.2 respectively.