The effect of feed moisture and shear strain on destruction ofBacillus globigii spores during extrusion cooking
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The effects of feed moisture (14–22%), extrusion temperature (80/110/-80/130°C barrel temperature in extruder zone 1/zone 2), residence time, and shear strains on the destruction of spores of Bacillus globigii during processing of corn/soybean (70/30%, w/w) mixtures in a single screw extruder were examined. As expected, higher temperatures increased lethality, while the shear strains in the extruder had no major effect on the destruction of the spores. Reducing the moisture content of the corn/soybean mixture resulted in greater destruction of bacterial spores. Increasing feed moistures (14%,18%, 22%), however, resulted in lower mass temperatures (i.e., 116°C, 110°C, 108°C, respectively, at constant, 80/120°C, extruder barrel temperature). The higher mass temperature at lower moisture contents, which increased spore destruction, appeared to be due to viscous heat generation in the extruder.