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 13 C showed carbon chain signals of Glu, Asp and Leu. The 31 P 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 α s1 -casein, suggesting the latter as the site surface for heterogeneous nucleation and crystal growth.