Food fouling deposits

The adhesive strength of a food fouling deposit may be related to the surface free energy of the substrate. Zhao et al. (2004) have developed a theory that gives the minimum adhesion energy between a deposit and a surface ... 

Chemical Reaction Fouling deposit formation on the heat transfer surface by chemical reactions in which the surface material itself is not a reactant (e.g., in petroleum refining, polymer production, food processing). 

Despite the aforementioned efforts, membrane flux decline due to fouling continues to be a major operational issue. Attempts have been made to modify inorganic membranes, mostly their surfaces, to render them less prone to foulant adsorption. One of the frequently encountered fouling problems in biotechnology and food applications is protein adsorption. In membrane reactor applications which are largely associated with hydrocarbons, carbonaceous deposits pose as one of the operational problems. 

FIGURE 22.11 Scanning electron microscopy image of sintered membrane surface fouled with WPC deposits. (From Bird, M.R. and Barttlett, M., J. Food Eng., 53, 143, 2002. With permission.)... 

Belmar-Beiny et al [1994] have also demonstrated differences in deposit morphology dependent on operating conditions. The deposit may vary from a smooth thin film to a dense aggregate structure. The addition of reagents which inhibit the formation of the S-S bonds has been shown to decrease the amount of deposit formed in UHT treatment of milk [Skudder et al 1981]. The addition of chemicals to limit the incidence of fouling in food processing however, would... 

Fryer and Pritchard [1989] emphasise the need to monitor fouling in a food process stream in order that the optimum time for cleaning may be determined so that for instance, a soft otherwise easy to remove deposit, is not converted to a hard intractable form by the action of heat. These authors describe two possible fouling monitors that may be used in a "side stream" fi-om the main process stream. A more detailed discussion of fouling monitors is to be found in Chapter 17. 

Lalande, M., Gallot-Lavallee, T. and Corrieu, G., 1984, Chemical reactions and mass transfer associated with cleaning of heat exchange surfaces fouled by milk deposits, in McKenna. Engineering and Food, Vol. 1. Elsevier Applied Science, London, 59 - 68. 

In practice, a variety of systems contains both amphiphilic molecules and polymers. These are, for instance, found where detergent is used to remove polymeric (proteinaceous) deposits from a fouled surface, for example, in food-processing equipment, teeth, contact lenses, and other biomedical appliances. By aggregation of the amphiphiles at the polymers, the latter ones are solubilized and subsequently released from the surface. This process is schematically depicted in Figure 12.15. 

The main barrier to PI within the sector was that the food industry was innovative in products, but not innovative in processes. As well as institutional barriers in the sector, a number of technical hazards can be identified. Surface deposits (fouling) are perhaps a greater problem in the food and drink sector than elsewhere, as cleanliness is essential. Fouling, of course, leads to inefficiencies due to increased thermal resistance and/or pressure drop. It is therefore important that, in selecting PI plant for applications here, accessibility for cleaning, preferably CIP (cleaning in place), is available. It is sometimes difficult to incorporate CIP in PI plant, however, and care must be taken in selecting appropriate solutions. 

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