Wheat starch was processed in a 19 mm diameter, single screw extruder to study the physical and structural modifications that occur during extrusion cooking. Structural modification of the starch polymers was investigated using gel permeation chromatography (GPC), enzymatic digestions and dilute solution viscometry. Both the GPC and intrinsic viscosity results showed that the average molecular size significantly decreased as a result of extrusion processing. The relative amount of material excluded by Bio-Gel A150m was considerably lower for extruded samples than for unprocessed wheat starch and this size reduction of the amylopectin fraction was attributed to mechanical rupture of covalent bonds. The characterization of the structural modifications of the starch polymers is reported.

The effect of extrusion cooking in a single screw extrude1 on the molecular weight distribution of wheat starch was correlated to the starch melt rheology. A simple fist-order model has been developed which defines the extent of mechanical degradation of the amylopectin component as a function of nominal shear stress and residence time in the extruder. A limited set of experimental observations were used to test the model. Iso-shear stress curves were calculated for the experimental range of conditions. The curves can be used, in conjunction with estimates of the residence time, to calculate equivalent processing conditions, and to predict the extent of amylopectin degradation. The model may allow the use of small extruders to determine fundamental process parameters for full scale extrusion.

We develop a prioritization framework for foodborne risks that considers public health impact as well as three other factors (market impact, consumer risk acceptance and perception, and social sensitivity). Canadian case studies are presented for six pathogen-food combinations: Campylobacter spp. in chicken; Salmonella spp. in chicken and spinach; Escherichia coli O157 in spinach and beef; and Listeria monocytogenes in ready-to-eat meats. Public health impact is measured by disability-adjusted life years and the cost of illness. Market impact is quantified by the economic importance of the domestic market. Likert-type scales are used to capture consumer perception and acceptance of risk and social sensitivity to impacts on vulnerable consumer groups and industries. Risk ranking is facilitated through the development of a knowledge database presented in the format of info cards and the use of multicriteria decision analysis (MCDA) to aggregate the four factors. Three scenarios representing different stakeholders illustrate the use of MCDA to arrive at rankings of pathogen-food combinations that reflect different criteria weights. The framework provides a flexible instrument to support policymakers in complex risk prioritization decision making when different stakeholder groups are involved and when multiple pathogen-food combinations are compared.

The study used a structured expert elicitation survey to derive estimates of the foodborne attributable proportion for nine illnesses caused by enteric pathogens in Canada. It was based on a similar study conducted in the United States and focused on Campylobacter, Escherichia coli O157:H7, Listeria monocytogenes, nontyphoidal Salmonella enterica, Shigella spp., Vibrio spp., Yersinia enterocolitica, Cryptosporidium parvum, and Norwalk-like virus. For each pathogen, experts were asked to provide their best estimate and low and high limits for the proportion of foodborne illness relative to total cases. In addition, they provided background information with regard to food safety experience, including self-evaluated expertise for each pathogen on a 5-point scale. A snowball approach was used to identify 152 experts within Canada. The experts' background details were summarized using descriptive statistics. Factor analysis was used to determine whether the variability in best estimates was related to self-assessed level of expertise or other background information. Cluster analysis followed by beta function fitting was undertaken on best estimates from experts who self-evaluated their expertise 3 or higher. In parallel, Monte Carlo resampling was run using triangular distributions based on each expert's best estimate and its limits. Sixty-six experts encompassing various academic backgrounds, fields of expertise, and experiences relevant to food safety provided usable data. Considerable variation between experts in their estimated foodborne attributable proportions was observed over all diseases, without any relationship to the expert's background. Uncertainty about their estimate (measured by the low and high limits) varied between experts and between pathogens as well. Both cluster analysis and Monte Carlo resampling clearly indicated disagreement between experts for Campylobacter, E. coli O157, L. monocytogenes, Salmonella, Vibrio, and Y. enterocolitica. In the absence of more reliable estimates, the observed discrepancy between experts must be explored and understood before one can judge which opinion is the best.

Residence time distributions for wheat starch in a single screw exnuder were measured for different operating conditions using a manganese dioxide tracer. Two flow models which differed in the definition of dead space were used to represent the flow pattern in the extruder. The parameters for each model were fitted using the experimental residence time distributions. Screw speed and the moisture level of the feed showed the strongest effects on the average residence time. A small fraction of the flow, 5-20%, was held up in the dead space region. The remainder passed directly through the active region with a residence time distribution close to plug flow. An apparent power law index for the starch melt was calculated and over the experimental range of extrusion conditions it varied from 0.2 to 1.0.