Experimental study and modeling of nisin diffusion in agarose gels
ABSTRACT Research in safety of processed food has focused on the use of anti-microbial compounds to suppress pathogenic bacteria growth such as Listeria monocytogenes and Staphylococcus aureus. Previous studies developed an anti-microbial edible film, incorporating the bacteriocin nisin. Nisin effectiveness was based on both nisin desorption from the film and its diffusion in the food product. In this present work, and as a preliminary study, nisin diffusion in agarose gel was investigated. The apparent diffusion coefficients were calculated, taking into account factors influencing the diffusion rates such as nisin concentration, diffusion time and temperature. Influence of agarose content on nisin diffusion was also evaluated. As a result, Fick’s second law well represented nisin diffusion in agarose gel. In 3% (w/w) gel, the diffusion coefficient values varied between 1.92 × 10−11 and 8.14 × 10−11 m2 s−1 for temperatures ranged between 5.4 and 22.3 °C. Diffusion phenomena satisfied Arrhenius relationship. Agarose content from 3% to 6% did not have any effect on nisin diffusion. However, agarose content of 8% significantly reduced nisin diffusion in agarose gel cylinders.
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ABSTRACT: The microbial and enzyme activity in different points within cheese and quality of final product are determined by local concentrations of salt and moisture in aqueous phase. To predict the evolution of moisture content in different layers of the Iranian white cheese during brining, constant and variable moisture diffusion coefficients were determined using experimental moisture time–dependent concentration-distance profiles. These experimental profiles for Iranian white cheese were obtained in rectangular samples, ensuring semi-infinite unidirectional mass transfer within saturated solution of sodium chloride at different temperatures (6, 14, 19, 24 °C) and brining times (6, 24, 48 h). Results showed that moisture diffusivity increases with increasing temperature and moisture content in cheese aqueous phase. The variation of the moisture effective diffusivity as a function of temperature was represented by the Arrhenius’s relation. Finally, the relation of diffusivity with moisture content and temperature was developed. The predicted diffusivity values using the developed model showed a good agreement with the experimental values by using Boltzman variable method.Journal of Science and Technology of Agriculture and Natural Resources. 01/2009;