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 degrees 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, Ente rococci, Staphylococci, heterotrophic, and non-specific anaerobic/facu ltative bacteria using standard culturing techniques. Bacterial concen trations 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 sample s indicated that extrusion techniques used in this study did not consi stently sterilize animal feed. Results suggested that a single-screw, dry-extrusion process can reduce concentrations of potentially pathoge nic bacteria, but that modification of extrusion techniques used in th is study may be necessary for consistent optimal reduction of bacteria l concentrations in food waste-amended animal feed. (C) 1998 Elsevier Science Ltd. All rights reserved.