Effective diffusion coefficients of sodium nitrite and potassium nitrate in pork tissue

A. PINOTTI; N. GRAIVER; A. CALIFANO; N. ZARITZKY

Nueva Orleans, EE.UU

Congreso; Institute of Food Technologist (IFT). 2001 Annuel Meeting; 2001

Institute of Food Technologist (IFT). The society for food science and technology

Smoking, salting, and the addition of additives are diffusion applications that play important roles in meat processing. Curing process utilizes sodium chloride, sodium nitrite and potassium nitrate. The objectives of the work were to: a) determine the diffusion coefficient of NaNO2 and KNO3 in pork tissue (Longissimus dorsi) using brine solutions at 4°C and 20°C; b) establish the effect of NaCl on the diffusion coefficients; c) compare the diffusion coefficients obtained with those calculated by Stefan-Maxwell theory. Cylinders of meat were immersed in the solutions. The concentrations of nitrite and nitrate as a function of immersion time were determined using spectrophotometric techniques. Meat samples were observed by SEM (505, Philips). The unsteady state mathematical formulation was applied considering radial mass transfer. A computer program was used to calculate diffusion coefficients of the salts at different concentrations in the presence of NaCl. The diffusion coefficients were obtained fitting the theoretical curves to experimental data. The effective diffusion coefficients for NaNO2 at 4ºC were: 3.8x10-9 (NaNO2 3 g/l), 4x10-9 (NaNO2 3 g/l + NaCl 10 g/l) and 5.1x10-9 m2/s (NaNO2 3 g/l + NaCl 140 g/l). The corresponding values at 20ºC were: 4.1x10-9, 5.6x10-9 and 8.5x10-9 m2/s. The effective diffusion coefficients for KNO3 at 4ºC were: 4.1x10-9 (KNO3 2.5 g/l), 4x10-9 (KNO3 2.5 g/l + NaCl 10 g/l) and 8.8x10-9 m2/s (KNO3 2.5 g/l + NaCl 140 g/l) and at 20ºC: 4.0x10-9, 4.5x10-9 and 9.5x10-9 m2/s, respectively. The water content in the tissue ranged between 72 and 74 %. An increase of the curing salt diffusivities in the tissue was observed when the diffusion occurred at high NaCl concentrations. This fact could not be explained by the Maxwell-Stefan theory that considers the diffusivity of the ionic species in multicomponent solutions. However, penetration of high NaCl concentration in a tissue affect the cellular structure leading to higher diffusion coefficients. The induced changes, as shown by the micrographs, could explain the rise in the diffusion coefficients of NaNO2 and KNO3 in the presence of NaCl.