EFFECT OF PROCESSING AND STORAGE CONDITIONS ON THE MICROFLORA OF CLOSTRIDIUM PERFRINGENS-INOCULATED FRANKFURTERS

Predictive model for growth of Clostridium perfringens during cooling of cooked pork supplemented with sodium chloride and sodium pyrophosphate

A dynamic model was developed to predict growth of Clostridium perfringens in cooked ground pork supplemented with salt (0-3% wt/wt) and sodium pyrophosphate (0-0.3% wt/wt) under varying temperatures. C. perfringens (NCTC 8238, NCTC 8239, and NCTC 10240) spores were heat shocked, cooled, and inoculated into ground pork. Isothermal bacterial growth was quantified with variable salt and phosphate concentrations at temperatures ranging from 15 to 51 °C. The primary Baranyi model was fitted to all C. perfringens growth profiles and gave a satisfactory fit (R² ≥ 0.85). A quadratic polynomial secondary model was developed (P < 0.0001) to predict the maximum specific growth rate as a function of temperature, salt, and phosphate concentrations (R² = 0.93). A dynamic model was developed and validated using growth data retrieved from 7 published studies. Thirty three out of 44 predictions were within the acceptable prediction zone (-0.5 ≤ prediction error ≤ 1.0). The developed predictive model can be used to minimize the risk of C. perfringens in pork products supplemented with additives during cooling.

Risk assessment for Clostridium perfringens in ready-to-eat and partially cooked meat and poultry products

An assessment of the risk of illness associated with Clostridium perfringens in ready-to-eat and partially cooked meat and poultry products was completed to estimate the effect on the annual frequency of illnesses of changing the allowed maximal 1-log growth of C. perfringens during stabilization (cooling after the manufacturing heat step). The exposure assessment modeled stabilization, storage, and consumer preparation such as reheating and hot-holding. The model predicted that assuming a 10- or 100-fold increase from the assumed 1-log (maximal allowable) growth of C. perfringens results in a 1.2- or 1.6-fold increase of C. perfringens-caused illnesses, respectively, at the median of the uncertainty distribution. Improper retail and consumer refrigeration accounted for approximately 90% of the 79,000 C. perfringens illnesses predicted by the model at 1-log growth during stabilization. Improper hot-holding accounted for 8% of predicted illnesses, although model limitations imply that this is an underestimate. Stabilization accounted for less than 1% of illnesses. Efforts to reduce illnesses from C. perfringens in ready-to-eat and partially cooked meat and poultry products should focus on retail and consumer storage and preparation methods.

Behavior of Clostridium perfringens at low temperatures

Refrigerated storage is an important step in the preparation of foods and inadequate storage is one of the main causes of food poisoning outbreaks of Clostridium perfringens. Therefore, growth and germination characteristics of C. perfringens in a temperature range of 3-42 degrees C were determined in fluid thioglycollate broth (FTG) and Dutch pea soup. To study the effect of adaptation, cells were either inoculated from a 37 degrees C pre-culture or from a temperature-adapted pre-culture. Membrane fatty acid patterns were determined at all temperatures to examine the effect of temperature on membrane composition. Spores were either inoculated with and without heat treatment. Adaptation of cells did not influence growth rate nor lag phase. Growth in pea soup, however, was slower and lag phases tended to be more extended compared to FTG. No growth was observed at temperatures < or =10 degrees C and death rates in pea soup were higher than those in FTG at these low temperatures. Cells preserved the membrane fluidity by reducing the arachidic acid content and increasing the lauric acid content when the temperature dropped. This resulted in a net reduction in chain length. Microscopic analysis of cells grown at 15 degrees C revealed a morphological change: cells were elongated compared to those grown at 37 degrees C. These data demonstrate the ability of C. perfringens to adapt to lower temperatures. However, this did not influence growth characteristics compared to non-adapted cells. Spores of C. perfringens did germinate at all temperatures with and without heat-activation. Combining this fact with the extended survival at low temperatures emphasizes the need for adequate heating of refrigerated foods before consumption to eliminate health risks due to C. perfringens.