A new approach for quantitative analysis of melamine in milk was proposed based on two-dimensional (2D) correlation
near-infrared spectroscopy and multi-way partial least squares (N-PLS) in this paper. 40 pure milk samples and 40 milk
samples adulterated with different contents of melamine were prepared. The near-infrared transmittance spectra of all
samples were measured at room temperature. Then 2D NIR-NIR correlation spectroscopy under the perturbation of
adulterant concentration was calculated and N-PLS model for the melamine concentration was established with 2D
correlation spectra (28x51x51). For the prediction set, the root mean square errors of prediction (RMSEP) for melamine
concentration was 0.067 g/L and the coefficient correlation between actual reference values and predicted values was
0.999, which means the model has good predictive ability. For comparison purpose, partial least squares (PLS) model
was also built using the conventional one-dimensional near-infrared spectra (28x51), where the RMSEP and the
coefficient correlation were 0.079 g/L and 0.998, respectively. The average relative prediction error was 22.9% for
N-PLS model; whereas it was 122.4% for PLS model. The N-PLS models yielded relatively low RMSEP and average
relative prediction error as compared to PLS model. Therefore, N-PLS method was more robust than PLS method for
accurate quantification of the concentration of melamine in milk.
The adulteration of milk with harmful substances is a threat to public health and beyond question a serious crime. In
order to develop a rapid, cost-effective, high-throughput analysis method for detecting of adulterants in milk, the
discriminative analysis of melamine is established in milk based on the two-dimensional (2D) correlation infrared
spectroscopy in present paper. Pure milk samples and adulterated milk samples with different content of melamine were
prepared. Then the Fourier Transform Infrared spectra of all samples were measured at room temperature. The
characteristics of pure milk and adulterated milk were studied by one-dimensional spectra. The 2D NIR and 2D IR
correlation spectroscopy were calculated under the perturbation of adulteration concentration. In the range from 1400 to
1800 cm-1, two strong autopeaks were aroused by melamine in milk at 1464 cm-1 and 1560 cm-1 in synchronous
spectrum. At the same time, the 1560 cm-1 band does not share cross peak with the 1464 cm-1 band, which further
confirm that the two bands have the same origin. Also in the range from 4200 to 4800 cm-1, the autopeak was shown at
4648 cm-1 in synchronous spectrum of melamine in milk. 2D NIR-IR hetero-spectral correlation analysis confirmed that
the bands at 1464, 1560 and 4648 cm-1 had the same origin. The results demonstrated that the adulterant can be discriminated correctly by 2D correlation infrared spectroscopy.
Adulteration of milk and dairy products has brought serious threats to human health as well as enormous economic
losses to the food industry. Considering the diversity of adulterants possibly mixed in milk, such as melamine, urea,
tetracycline, sugar/salt and so forth, a rapid, widely available, high-throughput, cost-effective method is needed for
detecting each of the components in milk at once. In this paper, a method using Fourier Transform Infrared spectroscopy
(FTIR) combined with two-dimensional (2D) correlation spectroscopy is established for the discriminative analysis of
adulteration in milk. Firstly, the characteristic peaks of the raw milk are found in the 4000-400 cm-1 region by its original
spectra. Secondly, the adulterant samples are respectively detected with the same method to establish a spectral database
for subsequent comparison. Then, 2D correlation spectra of the samples are obtained which have high time resolution
and can provide information about concentration-dependent intensity changes not readily accessible from
one-dimensional spectra. And the characteristic peaks in the synchronous 2D correlation spectra of the suspected samples
are compared with those of raw milk. The differences among their synchronous spectra imply that the suspected milk
sample must contain some kinds of adulterants. Melamine, urea, tetracycline and glucose adulterants in milk are
identified respectively. This nondestructive method can be used for a correct discrimination on whether the milk and
dairy products are adulterated with deleterious substances and it provides a new simple and cost-effective alternative to
test the components of milk.
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