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Modelling inward diffusion of salt in model cheese matrix using time-lapse confocal laser scanning microscopy.

P. Sharma




Modelling inward diffusion of salt in model cheese matrix using time-lapse confocal laser scanning microscopy.
P. Sharma*1,3, J. Sheehan1, J. Floury2. 1Teagasc Food Research Centre Moorepark, Fermoy, Co. Cork, Ireland, 2STLO, INRAE Agrocampus Ouest, Rennes, France, 3Utah State University Logan, UT.

Salt dissolved in the aqueous phase of cheese, diffuses slowly through the dense protein network and influences structure, texture and flavor development. Although, cheeses may have similar gross composition, a hypothesis exists that differences in microstructure will result in different rates of salt migration. The objective of this study was to determine the influence of varying pH (5.4 vs 6.8) on the diffusion rate for salt in a model cheese system, i.e., renneted casein gels. Model cheese systems were prepared by adding rennet to a Micellar Casein Concentrate (~15% casein) after pH adjustment with glucono-δ-lactone and addition of protein (Fast Green; 1% wt/wt) and sodium (CoroNa green; 100μM) sensitive fluorescent dyes. Gels were formed in specialized slides (IBIDI) followed by brine addition (NaCl 23%). Salt diffusion was tracked using an inverted confocal laser scanning microscope (laser excitation at 488 nm). Microstructural parameters of both protein gels were quantified from confocal imaging (laser excitation for Fast Green at 633 nm) using the high-resolution detection unit (Airyscan). The effective diffusion coefficients for salt obtained after fitting data on Fick's second law were slower than previous reports. This was attributed to the absence of structural irregularities such as free water and fat channels in the isotropic dense hydrated protein (15%) network. Diffusion coefficients at pH 6.8 (6.44 � 2.33 �m2/s) were significantly (P < 0.05) lower than at pH 5.4 (18.64 � 4.45 �m2/s) and were attributed to a less porous gel structure at pH 6.8 (median pore size = 2.92 �m) compared with pH 5.4 (median pore size = 4.45 �m). Microstructural heterogeneity at the lower pH was attributed to a greater phase separation between protein and water as observed by CLSM. This novel salt tracking system suggests that varying cheese physico-chemistry influences salt diffusion rates. This technique will support further research particularly on diffusion behavior of salt in reduced moisture cheeses.

Keywords: model cheese, salt diffusion, confocal laser scanning microscopy.

Biography: Dr. Prateek Sharma is a new faculty member in the Department of Nutrition, Dietetics, and Food Sciences at Utah State University, USA. He is an experienced dairy and cheese researcher. He obtained his PhD from Massey University (New Zealand) while working on an industry-sponsored research project studying “Shear work induced changes in structure, rheology of Mozzarella type cheeses.” At Teagasc Food Research Centre (Moorepark, Ireland), Dr. Sharma, was leading projects in the area of diffusion of small solutes in model cheese networks. Dr. Sharma has a strong interest in the material side of the foods, especially dairy foods.