Review Article

The Combination of Vibrational Spectroscopy and Chemometrics for Analysis of Milk Products Adulteration

Table 1

The application of vibrational spectroscopy (Raman, near infrared, and mid infrared) combined with chemometrics for milk authentication.

Adulteration issuesType of vibrational spectroscopyChemometricsResultsRef.

Cow milkAddition of sucrose to cow milkNormal mid IR spectra at wavenumbers of 1070–980 cm−1PCA and SIMCA for classification. PCR and PLS for quantificationThe levels of sucrose cold be quantified with Cal: 0.996; Val: 0.993, RMSE (Cal: 0.15% ; Val: 0.20% ), RE% (Cal: 4.9% ; Val: 5.1% ), and RPD (13.40). SIMCA was able to classify test samples with a classification efficiency of 100%[4]
Raw milkDetection of reconstituent milk powder in milkFirst derivative spectra at wavenumbers of 800-1800 cm_1PCA and PLS-DA for classificationFTIR spectroscopy has great potentials in quality control of milk and their related products because the PLS-DA model yielded satisfactory separation of the two spectral fingerprints[12]
Goat milkAdulteration of goat milk with cow milkMIR: 1373, 1454, and 956 cm-1
Raman: 1005, 1154, and 1551 cm-1
SIMCA for classification and PLSR for prediction of milk adulterationSIMCA result showed the β-carotene band at 1373, 1454, and 956 cm-1 (MIR spectra) and 1005, 1154, and 1551 cm-1 (Raman spectra) as a biomarker for classification of cow milk in goat milk
PLSR using MIR and Raman spectra were used to predict goat and cow milk mixtures with 0.32 SECV, 0.98 Cal, 0.57 SEP, and 0.98 Val (MIR) and 0.46 SECV, 0.96 Cal, 0.57 SEP, and 0.94 Val (Raman)
[21]
Mengniu milk, Yili milk, and Haihe milkAddition of melamine in milk2D IR/NIR heterospectra range of 1400-1704 cm-1 and 4200-4800 cm-1NPLS-DA for classification of pure milk and adulterated milkResults showed that, for the samples in the prediction set, the rate of correct classification was 96.2% using synchronous 2D heterospectra IR/NIR correlation spectra versus 88.5% using synchronous 2D homospectral IR/IR and NIR/NIR correlation spectra. Comparison of the results showed that 2D heterospectra IR/NIR correlation spectra and NPLS-DA could give better classification between adulterated milk and pure milk[41]
Raw cow milkAddition of five common adulterants (water, starch, sodium citrate, formaldehyde and sucrose) in raw cow milkMID infrared-ATR spectra range of 4000-600 cm-1PLS-DAThe method was able to detect the presence of the adulterants water, starch, sodium citrate, formaldehyde, and sucrose in milk samples containing from one up to five of these analytes, in the range of 0.5–10% [42]
Raw cow milkAddition of pseudo protein (urea, melamine, and ammonium nitrate) and thickeners (dextrin and starch)First derivative NIR spectra at wavenumbers of 4000-10.000 cm-1Nonlinear supervised pattern recognition methods of improved support vector machine (I-SVM) and improved and simplified K nearest neighbours (IS-KNN)Both methods (I-SVM and IS-KNN) exhibit good adaptability in discriminating adulterated milks from raw cow milks at the concentration of adulteration solutions which equals or exceeds 5%[25]
Nescafe milk powderAddition of melamineNormal NIR spectra at wavenumbers 4000-10.000 cm-1One class partial least square (OCPLS)The combination of NIR spectroscopy and OCPLS can serve as a potential tool for rapid and on-site screening melamine in milk samples with the total accuracy of 89%, the sensitivity of 90%, and the specificity of 88%[26]
Infant formula (powder), milk powder, and milk liquidAddition of melamineNIR spectra range of 9000-4500 cm-1
MIR spectra range of 500-4000 cm-1
Partial least square (PLS), orthogonal projection to latent structures (OPLS), polynomial partial least squares (Poly-PLS), artificial neural networks (ANN), and support vector machine (SVM)Linear calibration methods (PLS and OPLS) show a much larger prediction error, exceeding 1 ppm. The average error of the PLS/OPLS methods is  ppm, while the error of the Poly-PLS, ANN, and SVM-based methods is almost 5 times smaller ()
The relationship between the MIR/NIR spectrum of milk product and melamine content is nonlinear. Thus, nonlinear regression methods, such as Poly-PLS, ANN, SVR, or LS-SVM, are needed to correctly predict the melamine
[27]
Cow milkMilk adulterated with formaldehyde, hydrogen peroxide bicarbonate, carbonate, chloride, citrate, hydroxide, hypochlorite, starch, sucrose, and waterMIR region at wavenumbers of 1000-4000 cm-1Multiplicative scatter correction (MSC) for spectra preprocessing; PCA for visualization of the sample distribution, SIMCA for classification milkIn the first step, a one-class model was developed with unadulterated samples, providing 93.1% sensitivity. Four poorly assigned adulterants were discarded for the following step (multiclass modelling). Then, in the second step, a multiclass model, which considered unadulterated and formaldehyde, hydrogen peroxide, citrate, hydroxide, and starch as adulterated samples, was implemented, providing 82% correct classifications, 17% inconclusive classifications, and 1% misclassifications[43]
Cow milkTetracycline’s residue (tetracycline, chlortetracycline, and oxytetracycline)MID FTIR spectra at wavenumber of 4000-550 cm-1SIMCA for classification, PLS and PCR for quantification of tetracycline residueSIMCA could be used for classification of pure milk and milk adulterated with the confidence level of 99%. The calibration models developed with three algorithms (PLS1, PLS2 and PCR) to predict tetracycline, chlortetracycline, and oxytetracycline concentrations in milk revealed values of of 0.999, 0.998, and 0.997, respectively[44]
Raw milkAddition of tetracyclineFT-MIR spectra at wavenumber of 1550-1725 and 2800-2981 cm-1, while FT-NIR used raw and first derivative spectra at the region of 3500-8000 cm-1PLS for quantification of tetracycline hydrochloride in milkFT-MIR: the optimum number of factors using PLS method was 15, and the between the predicted and actual values was 0.89, the SEC value was 385 ppb, and the repeatability value was 163
FT-NIR: PLS-first derivative calibration method gave an value of 0.76, SEC value of 431 ppb, and the repeatability value of 73 ppb
Results indicated that FT-MIR spectroscopy could be used for rapid detection of tetracycline hydrochloride residues in milk
[45]
Pasteurized milkAddition of sweet whey in milkRaman spectra in range from 800-1800 cm-1ANN for quantification and PLS for corrected predictionA high-capacity prediction model was obtained using ANN, with of 0.9999. Alternatively, ANN can be replaced by a linear model adjusted using PLS, which also exhibited reasonable results for the prediction of percentage of whey added ()[46]
Cow milkAddition of water, urea, starch, and goat milkNIR spectra in region of 950-1650 nmPCA and the data driven soft independent modeling of class analogy (DD-SIMCA) for classification, PLS for quantificationPreliminary PCA performed on the whole data revealed that both big similarities and differences between pure and adulterated milk samples were collected from a variety of dairy farms
The DD-SIMCA approach achieved satisfactory classification. By the PLSR model, standard error of prediction (SEP) values of 4.35, 0.34, 4.74, and 5.56 g/L and Val value of 0.94, 0.87, 0.93, and 0.89 were obtained for water, urea, starch, and goat milk, respectively
[47]
Cow milkReal time prediction of fat, protein, and lactoseNIR spectra in region 950-1690 nmPLSR for quantification of fat, protein, and lactoseThe obtained prediction models were thoroughly tested on all the remaining samples not included in the calibration sets (, respectively, 846 and 857). For the post hoc prediction models, this resulted in an overall prediction error (RMSEP) smaller than 0.08% (all % are in ) for milk fat (range 1.5-6.3%), protein (2.6-4.3%), and lactose (4-5.1%), while for the real-time prediction models, the RMSEP was smaller than 0.09% for milk fat and lactose and smaller than 0.11% for protein[48]
Cow milkAdulteration with water or wheySecond derivative NIR spectra (whole region, 1100-1850, 2048-2500, and combination of 1100-1850, 2048-2500 nm)DPLS and SIMCA for classification, PLSR for quantificationThe best DPLS classification model for natural milk, milk adulterated with water and milk adulterated with whey was developed using the MSC and second derivative spectra in the whole region of 1100–2500 nm with a PLS factor of 7 and classification performance of 100%
The best prediction result is obtained for water adulterated in natural milk, when the model is developed by using the MSC spectra over the whole region of 1100–2500 nm. Its statistical results are the lowest value of the root mean square error of prediction (RMSEP) of 2.159% () with a PLS factor of 4, while the best calibration model for milk adulteration by mixing whey yields the prediction result with a RMSEP value of 0.244% () by a PLS factor of 4. This model was built using the MSC pretreated spectra of the combination regions of 1100–1850 and 2048–2500 nm
[49]
Commercial milk samplesAdulteration with waterNIR spectra at 400-2500 nmPCA for classification and PLS for quantificationPCA perfectly classified between pure milk and milk adulterated with water. PLS was successfully used to predict the concentration of water in milk samples with more than 0.9 and RMSEC lower than 0.04[50]
Cow milkHydrogen peroxideFTIR spectra at 4000-600 cm-1Artificial neural network (ANN) for classification and multiple linear regression (MLR) for quantificationChemometrics of ANN could classify pure and adulterated milk samples with hydrogen peroxide with high accuracy. Quantification of hydrogen peroxide could be obtained using MLR with of calibration 0.80 and RMSEC value of 0.15[51]
Raw milkSodium hypochloriteFTIR spectra at 4000-650 cm-1SIMCA for classificationSIMCA could classify pure raw milk and adulterated raw milk with sodium hypochlorite with a specificity of 56.7%[43]