Sodium polyphosphate (NaPP) salts are widely used in the dairy industry. In processed cheese manufacture, these salts lead to hydration and partial dispersion of casein improving the protein emulsification. The effect of NaPP salts over physicochemical properties of processed cheese is well-established. However, the interactions between NaPP’s and casein are not fully understood. Raman spectroscopy has been used for molecule identification and structural characterization, but low sensitivity in highly concentrated samples is the main drawback. Surface-enhanced Raman spectroscopy (SERS) is a combination of Raman spectroscopy and nanotechnology that can enhance the weak Raman signals improving its structural information. In this contribution, Raman Spectroscopy and SERS were used to investigate the interactions between NaPP salts and casein by comparing the signals in a casein control solution with the signals in model solutions and processed cheese. For the model solutions, three different polyphosphate salts – disodium pyrophosphate (DSP), tetrasodium pyrophosphate (TSPP), and pentasodium triphosphate (STP) – were mixed with calcium caseinate (10.5 wt% in water) in a dry matter (DM) content of 2.3% at pH 6.5, before and after heat treatment (90C). The processed cheeses were made with calcium caseinate (10.5 wt%), 65% of humidity, butter oil (23 wt%) and one NaPP salt mentioned above at 2.3% DM at pH 6.5. The samples were analyzed by Raman and SERS, being silver nanoparticles (AgNP) the SERS substrate. As expected, SERS enhanced the peak intensities when compared to the conventional Raman. Our results suggest that the heat treatment affects the interactions between casein and phosphates. The band at 900 cm-1 assigned to phosphate was more intense in caseinate solutions before heat treatment than in samples submitted to heat treatment or in the processed cheese. TSPP presented the most distinct behavior in the caseinate solutions. The processed cheeses made with TSPP and STP showed peaks between 1300 to 1500 cm-1 that were not observed in processed cheese made with DSP. These results suggest that TSPP and TSP may interact with casein via hydroxyl (OH) groups. Changes in peaks intensities at 1505, 1440 and 533 cm-1 are assigned to other conformational changes of the protein backbone. We demonstrated that SERS is a powerful technique to explore structural changes in proteins that help to understand the function of specific ingredients in food processing.

Interactions between casein and sodium phosphate salts in processed cheese using surface-enhanced Raman spectroscopy

2019 Fall National Meeting

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