Characterization of the white dots defect (PIPS) in Doce de leite

Doce de leite is a typical concentrated dairy product, widely consumed in Brazil and Argentina. It is common to find white dots (PIPS-coined from dots on dominoes tiles) in the mass of commercial samples, considered as a defect. The present work aimed to characterize PIPS in samples of pasty dulce de leche using different analytical techniques. Through microscopy techniques, it was possible to observe spherical aggregates whereby the surface of the PIPS is composed of a material needle-shaped. Using the energy dispersive X-ray spectroscopy (EDS) technique, calcium was found to be its major constituent. Applying infrared and Raman spectroscopy, it was possible to identify calcium associated with citrate. Moreover, with the aid of powder X-ray diffraction (PXRD) the structure of calcium citrate hexahydrate (CCH) was identified as the main component of PIPS. High performance liquid chromatography (HPLC) of PIPS hydrolysates used for aminoacids profiling (aminogram) revealed that about 4% of PIPS was made by aminoacids, and highlighted higher concentrations for Glu, Pro, Leu and Asp. Solid state nuclear magnetic resonance (NMR) spectrum of C-13 showed carbon chain signals of Glu, Asp and Leu. The P-31 spectrum showed characteristic signals of inorganic orthophosphates. Thus, it was possible to conclude that PIPS have a crystalline structure composed mostly of CCH, but also by aminoacids and a small amount of phosphates that could be related to the presence of alpha(s1)-casein, suggesting the latter as the site surface for heterogeneous nucleation and crystal growth.

Automated summary

This study characterized the white dots in doce de leite using various analytical techniques. Results showed that the white dots were composed mainly of calcium citrate hexahydrate (CCH), amino acids, and a small amount of phosphates. The study also identified the formation mechanism of the white dots, suggesting the role of alpha(s1)-casein in heterogeneous nucleation and crystal growth.