Salt release monitoring with specific sensors in "in vitro" oral and digestive environments from soft cheeses

The objective of the present work is to demonstrate the interest and the feasibility of the measurement of NaCl concentrations in soft cheeses and in particular an in vitro digestion process by the use of chemical sensors. The analyzed matrices were the commercial Italian mozzarella cheeses and domestic cheese base models. The classification of mozzarellas was performed according to their salinity, while the breakdown of cheese base models has been followed both at initial steps of digestion in artificial mouth dispositive mimicking the oral sphere and in a gut-imitating digester (TIM-1). During the breakdown of soft cheese in the digester, the estimated values for Na(+) concentration using mono-Na-ISEs showed correlation coefficients values about 0.907 and 0.832 compared to Ionic Chromatography (IC) reference values, with an important relative error (about 30-40%). The use of ISE array system combining several electrodes, in particular electrodes showing more selectivity to Cl(-) and Na(+) ions, showed the best results for Na(+) concentration estimation, with good correlations both in calibration (R=0.962) and in validation (R=0.952) steps. For cheese digestion in the artificial mouth, good correlations for Na(+) concentration were observed using single Na-ISE compared to IC with coefficients ranking between 0.93 and 0.96 for both the calibration and validation steps. Moreover, a fair correlation between chloride ions measured with Cl-ISE2 and Na(+) (R=0.96) was found. The best results were obtained with the use of ISEs array combining, in particular, Cl(-) and Na(+) detections. The salinity of commercial mozzarella cheese samples, as far as originally utilized milk type (cow or buffalo), were also satisfactory determined with developed ISE array.