(342b) Membrane Separation and Functionalized Membrane Feed Spacers to Reduce or Eliminate Pathogenic Bacteria in Dairy Processing

Pathogenic bacteria are a serious concern in dairy processing. Downstream contamination after pasteurization is the primary source of Listeria monocytogenes (LM). Repasteurization is expensive and may not be feasible for all streams and products. Membranes and functional surfaces in membrane elements are alternatives to thermal processing of these streams. Two different approaches will be discussed, including sterile filtration and solid-phase anti-microbials, to reduce or eliminate pathogens from dairy streams.

Dairy streams include various milk streams (whole, skim, etc.), fractions of those streams to produce cream, protein, and permeate, as well as the brine used to flavor cheese. LM is found in all these streams and can be treated through size exclusion and adsorption. We have found size exclusion to be exceptionally effective for treating brine, with a complete removal of Listeria Innocua in a single stage. Other dairy streams are more challenging to treat because of the complex composition of milk, including fat, protein, lactose, and salts.

We have developed a functionalized feed spacer mesh that can be applied in all spiral wound membrane elements. This is regardless of the membrane being used, including microfiltration, ultrafiltration, nanofiltration, or reverse osmosis. The feed spacer is required to provide turbulence and reduced fouling but is otherwise inert. We have functionalized the feed spacer mesh with polymer grafts containing multiple quaternary amine groups. These groups enhance pathogen adsorption to the feed spacer. The polymer grafts also disrupt the cell wall, resulting in cell death. Adsorbed bacteria are also destroyed during normal membrane clean-in-place conditions. We will share results confirming surface adsorption, reduced growth, and cell death using functionalized feed spacer. We will also share extensive results from plating studies to better understand the anti-microbial mechanism and the dosing required for various growth media.