Bacterial concentration reduction of food waste amended animal feed using a single-screw dry-extrusion process

Institutional food waste was collected, pulped, mixed with ground corn and soybean hulls and dry-extruded at temperatures of 110–135°C for no more than 30 s to produce animal feed. Raw food waste, pre- and post-extrusion animal feed, and commercial swine feed samples were collected aseptically and analyzed for total and fecal coliform, Enterococci, Staphylococci, heterotrophic, and non-specific anaerobic/facultative bacteria using standard culturing techniques. Bacterial concentrations recovered from post-extrusion animal feed were substantially reduced from all other sample types. Survival of heterotrophic and non-specific anaerobic/facultative bacteria in some post-extrusion samples indicated that extrusion techniques used in this study did not consistently sterilize animal feed. Results suggested that a single-screw, dry-extrusion process can reduce concentrations of potentially pathogenic bacteria, but that modification of extrusion techniques used in this study may be necessary for consistent optimal reduction of bacterial concentrations in food waste-amended animal feed.