Thermal inactivation

A recent increase in the number of foodborne illness outbreaks and recalls due to Salmonella in low-moisture foods has resulted in the need for the development and validation of process controls to assure their microbiological safety. Further, the Food Safety Modernization Act rule for Preventive Control for Human Food requires food processors to validate their process controls to ensure food safety. The objective of this study was to develop a response surface model to predict Salmonella inactivation in oat flour, as affected by product composition and extrusion process parameters. Oat flour was adjusted to different moisture (14 to 26% wb) and fat (5 to 15%) contents and was then inoculated with a 5-strain cocktail of Salmonella to attain ca. 8.0 log CFU/g. Inoculated material was extruded through a single-screw extruder running at different screw speeds (75 to 225 rpm) and temperatures (65 to 85oC), without a die. Once steady state conditions were attained, extruded samples were ...

The changes in the heme environment and overall structure occurring during reversible thermal inactivation and in denaturant guanidinium of Euphorbia characias latex peroxidase (ELP) were investigated in the presence and absence of calcium ions. Native active enzyme had an absorption spectrum typical of a quantum-mixed spin ferric heme protein. After 40 min at 60°C ELP was fully inactivated showing the spectroscopic behavior of a pure hexacoordinate low-spin protein. The addition of Ca2+ to the thermally inactivated enzyme restored its native activity and its spectroscopic features, but did not increase the stability of the protein in guanidinium. It is concluded that, in Euphorbia peroxidase, Ca2+ ion play a key role in conferring structural stability to the heme environment and in retaining active site geometry