Food contacts many inert surfaces that direct flow or induce turbulence during processing. These surfaces could be modified to provide additional capabilities. The feed spacer material of spiral-wound membranes used in dairy applications is one such surface that could be functionalized to mitigate bacterial growth.
Controlling bacteria is critical to a safe food supply. However, it has become more difficult as consumers demand lower levels of preservatives, such as salt (1). The dairy industry is seeking technologies to eliminate or mitigate the growth of bacteria, such as Listeria monocytogenes (LM), while meeting consumer demands (2). LM is of particular concern because it is especially lethal — in many cases, the mortality rate of LM infection is 25–30%. For example, raw milk cheeses contaminated with LM from Vulto Creamery in upstate New York infected eight people, including a newborn, and caused two deaths. The affected products were recalled, and the manufacturer was shut down (3).
Raw milk is pasteurized prior to further processing because it may contain LM and other microbial contaminants. However, the pasteurization process only destroys LM if it is properly applied. LM that remains or is reintroduced by contamination can be adsorbed or destroyed during downstream processing of milk using spiral-wound membrane elements that incorporate functionalized feed spacer materials. The feed spacer is composed of a temperature-resistant polymer mesh. The surface is chemically modified to promote LM adsorption, enabling antimicrobial agents immobilized on the surface to kill LM. Standard membrane cleaning methods can also kill adsorbed LM.
Functionalized meshes can be applied broadly in dairy plants for a range of milk and milk-based streams, including brine streams used in cheese making. The feed spacer mesh is an integral part of all spiral-wound membrane elements, and it can be applied with any membrane process, such as in ultrafiltration (UF) of raw milk. The mesh can also be used in the absence of a membrane in recirculating systems to inhibit LM growth. The modified material may be used in temperature-stable sanitary elements, and it may be steam-sterilized after LM adsorption and material saturation...
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