Why does near infrared transmittance spectroscopy discriminate Quark-type cheese manufactured in the presence or absence of aflatoxin M1 (AFM1)?

Many studies on milk have demonstrated that aflatoxin M1 (AFM1) binds to milk proteins and, in particular, to casein and that it was concentrated in the curd during the manufacture of cheese. Investigations on the affinity of AFM1 towards different proteins in milk are very limited, even if this aspect appears to be particularly important due to its influence in quantitative toxin recovery in cheese. The aim of this work was a better comprehension of why near infrared (NIR) transmittance spectral analysis in the range 850–1050 nm, could discriminate Quark type cheese manufactured using milk at different levels of AFM1 contamination (control < 50 ppt 100 ppt and 200 ppt). Cheese-making was carried out at the experimental pilot plant of the Dairy Science Institute in Lodi under strictly controlled conditions. Each cheese production was repeated twice (six tests, 20 L each). Cheese samples were analysed for fat, protein, dry matter and AFM1 content at time 0 and during storage for 19 days (every three days) for a total of 42 samples. Capillary electrophoresis (CE) profiles and (NIR) transmittance spectra, were also collected. Spectra, corrected for scattering, were processed by multivariate curve resolution classical least squares using the estimation of individual constituents (fat, protein, water) for signal interpretation in the investigated region. Partial least squares regression (PLSR) results showed a good NIR transmittance discrimination power between contaminated and uncontaminated samples. Comparable results were obtained by applying PLSR to CE data using the peak area of as 1–I–casein as the variable. The regressors obtained by the two PLSR were very similar, with the highest significance at 950 nm. This work demonstrated that the indirect spectroscopic detection of AFM1 is strongly related to the cheese proteolytic trend.