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:The maceration of potato tuber (Solanum tuberosum cv Bintje) by technical enzyme preparations was examined with the aid of ýuorescence microscopy using ýuorescein diacetate as a dye. Treatment with Pectinex Ultra-SP-L from Aspergillus aculeatus resulted in a higher release of single viable cells and smaller clumps of cells than treatment with Rohament P from Aspergillus niger. Fractions with high pectin lyase and low polygalacturonase activity obtained by anion exchange chromatography of Pectinex Ultra SP-L showed the highest degree of maceration. When two diþerent cloned polygalacturonases (PG1 and PG2) and a cloned pectin lyase (PL1) from A aculeatus were examined, the highest degree of maceration was observed with PL1. In conclusion, pectin lyase is probably the main enzyme in Pectinex Ultra-SP-L responsible for the maceration of potato tuber.

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When bacteria attach to the walls of pipelines, they can form biofilms, which can cause the recontamination of food products. In order to quantify such recontamination, a one-dimensional biofilm model was developed taking into account adsorption, desorption, and the growth of cells. The model consisted of two mass balances describing increases in biofilm formation at the wall and the accumulation of cells in the liquid phase. The necessary parameters for the model were obtained in laboratory biofilm experiments. These experiments involved a flowing system and the use of Staphylococcus aureus as a model pathogen and silicon tubing as a testing material. S. aureus was inoculated into the system for 2 h, and then the system was changed to a sterile medium. Both biofilm formation and the release of cells into the flowing liquid were measured until steady-state conditions were reached (for up to 9 days). The experiments were performed in duplicate for different flow conditions (i.e., for Reynolds numbers of 3.2, 32, and 170). It was shown that at higher Reynolds numbers, the biofilm developed faster, probably owing to an increase in the transfer of nutrients to the surface. The proposed biofilm model was capable of describing the data obtained for the three different flow conditions with the use of the specific growth rate in the biofilm and the desorption coefficient as fit parameters. The specific growth rates were 0.16, 0.27, and 0.49 h−1 for Reynolds numbers of 3.2, 32, and 170, respectively, and the desorption coefficients were about 1% of these values.

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Purifying and recycling process water is a way to minimize the use of potable water and the production of wastewater in the food industry. Water recycling should, however, never affect the quality of the final products. Therefore, a model has been developed to investigate the possibilities of water recycling in a potato factory. One problem that could arise in a water recycling system is the accumulation of dissolved components, such as salts, in the process water loop, which would affect the product quality. Therefore, the quality of the potato products can be related to the amount of chloride ions present in the final product. The model described in this article is based on mass balances and transient diffusion theory is used to calculate the amount of chloride ions present in the process water and in the final product. The calculations show that chloride ions do accumulate in the water and in the potatoes during recycling, because of the addition of salts to the system. The approach used proved to be useful to obtain quantitative information on the process and to find critical points in the system.