Melanoidins, the brown-colored compounds formed through the Maillard reaction, are responsible for color development in dulce de leche (DL), a popular confectionary dairy product in the Río de la Plata region, particularly in Uruguay and Argentina. Color is a critical quality parameter that strongly influences consumer preference. This work aimed to develop a method to perform preliminary structural characterization of the chromophores produced by the Maillard reaction. Melanoidins are present in a water-insoluble fraction, linked to a protein backbone, conforming melanoproteins of high molecular weight. The insoluble melanoprotein fraction (10% total solids) was isolated, and the chromophores released by proteolysis and isolated by gel-permeation chromatography. The analysis of the products revealed that they present a high degree of molecular weight (MW) polydispersity, in a range of 300 to 2000 Da, where the compounds of higher molecular weight contributed the most to the color of the product. The isolated fractions were further analyzed by RP-HPLC using a diode array detector (DAD) detector. These results, together with H-NMR data, suggested that the chromophores isolated belonged to a relatively simple mixture of aromatic products with higher hydrophobic character relative to other products of the melanoprotein digestion.

The supply of relevant immunological components is stable throughout the colostrum stage. The effects of pasteurization on antibodies depend on isotype, subclass, and specificity. This information is relevant to improving the immunological quality of colostrum, especially for preterm newborns.

Browning and gelation kinetics of a sheep milk and sucrose model system with 70% total solids (simulating dulce de leche) and the influence of temperature and sucrose content on this process were studied. The Kubelka-Munk index and subjective heat stability tests were used to monitor nonenzymatic browning and to determine gelation time. Browning and gelation processes showed different kinetics where gelation was shown to occur much faster than browning. Both independent variables (temperature and sucrose content) had a significant influence in both processes, where temperature had the higher impact.

The effect on color of the initial pH employed in dulce de leche (DL) production was evaluated through physicochemical and spectroscopical characterization of the melanoidins formed in the process. Melanoidins originated at pH values of 6.5, 7.0, and 7.5, and they were released by the enzymatic hydrolysis of the protein backbone and purified by gel filtration. They showed a significant degree of polydispersity, in general, with molecular weights (MWs) below 1,800 Da. DL produced at a higher pH released melanoidins with higher average MW after the enzymatic hydrolysis. They also presented darker colors (dE*ab, C*), more closely resembling those typical of the commercial product. Analysis of the fractions isolated by gel filtration using HPLC-DAD and multinuclear NMR showed an heterogeneous and complex composition. Even though structurally related, the 1H NMR spectra of melanoidins showed a higher degree of aromaticity at higher pH values. In conclusion, the pH employed in DL production affects the amount and structure of the colored products originated by MR reactions, and thus the color of the final product.

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