Quantification of Factors Which Influence Nisin's Inhibition of CIostridium botulinum 56A in a Model Food System

We modeled nisin's anticlostridial activity and assessed the antagonistic or potentiating influences of food ingredients. The model systems contained yeast extract, proteose peptone, and glucose; were supplemented with protein (0.075, 0.75, 7.5% w/v), phospholipid (0.075, 0.75, 7.5% w/v), or soluble starch (5, 17.5, 30% w/v); and were adjusted to pH 5.5, 6.0, or 6.5. Samples inoculated with 10⁴/mL spores were incubated at 15, 25, or 35°C. Statistical analysis developed an equation (r²= 0.76) that modeled the response and identified temperature as the most significant (α 0.001) variable. Nisin lost effectiveness with increasing temperature. Nisin concentration had significant positive and phospholipid negative, linear effects. Many interactive effects were significant (α 0.20). Nisin inhibited C. botulinum until its residual level dropped below a threshold, which decreased from 154 IU/mL at 35°C to 12 IU/mL at 15°C.     

MODELING THE BEHAVIOR OF LISTERIA MONOCYTOGENES IN pH-MODIFIED CHICKEN SALAD DURING COLD STORAGE AND TEMPERATURE ABUSE CONDITIONS

Listeria monocytogenes grows at refrigeration temperatures (5C or below) and tolerates various environmental stressors. The Food and Drug Administration specifies a zero tolerance for this pathogen in certain ready‐to‐eat processed foods. Modeling its dynamic behavior to fluctuation in temperature at various pH levels is critical to the safety of food. This study presents linear and nonlinear models to predict the behavior of L. monocytogenes in pH‐modified chicken salad at various cold storage and temperature abuse conditions. A linear model of the kinetics accounting for simple and interactive effects of storage time, temperature and pH was developed. Predictions of the linear model were inconsistent with laboratory observations. The limitations of the linear model were reflected in the poor correlation of model predictions to the observed values (r² = 0.58). A proposed nonlinear model was therefore used to model the observed data. The four model parameters (N(0), C_c(0), k_max and N_res ) were optimized for each of the nine treatments. Correlation coefficient (r²) values ranged from 0.70 (pH 5.2, 7.2C) to 0.99 (pH 4.0, 21.1C), indicating an improved accuracy. Developing a functional and validated microbial predictive model for chicken salad requires further analyses and collection of data at additional pH and temperature values to determine a single set of parameter values that would represent the microbial behavior at the full range of pH and temperatures observed under storage conditions. Future experiments should address the adaptive nature of L. monocytogenes, as the response to environmental stressors affects the survival of the organism in food systems.     

USE OF THE BIRD-LEIDER EQUATION IN FOOD RHEOLOGY

Shear stress development at inception of a constant shear rate was studied for marshmallow cream, peanut butter, squeeze margarine, tub margarine, whipped butter, whipped cream cheese and whipped dessert topping using the cone and plate geometry of the Rheometrics Mechanical Spectrometer. For most foods studied transient shear stresses showed increasing shear stress oversoots with increasing shear rate. At the highest shear rate of 100 s^?1, transient stresses were as large as 425% of the steady state shear stresses, with the actual magnitude of overshoot depending on the particular food investigated. The Bird-Leider equation was chosen to model this time dependent flow behavior by incorporating both steady viscous and elastic properties of the foods. By assuming that the viscosity function and primary normal stress coefficient followed power-law behavior, and constructing a time constant from the calculated parameters, the Bird-Leider model provided a good prediction of maximum and steady state stresses as well as the time at which they occur, but only a crude prediction of shear stress decay. The model supplied two more empirical constants “a” and “b” where “a” can be regarded as a pseudo-elastic modulus. Variation in “a” with shear rate shows that all materials studied are nonlinear viscoelastic.     

Agar-Gel Immunodiffusion Test for Rapid Identification of Pollock Surimi in Raw Meat Products

A test for the rapid identification of raw pollock surimi (TRIPS) was developed. This was an adaptation of previously developed field screening agar-gel immunodiffusion tests for speciation of meat products. It was specific for Alaska pollock surimi at 2% concentration and other surimis at higher concentrations, showed detectable sensitivity to surimi in meat at 2–4%, and was 100% accurate in detection in laboratory trials.     

Simulation of the Vacuum Infusion Process using Idealized Components: Effects of Pore Size and Suspension Concentration

Vacuum infusion of porous food matrices (i.e., extruded starch crackers) with calorically dense suspensions of food powders in fat was investigated in an ideal system. Experiments involved infusion of model matrices with lipid suspensions consisting of milled, size-characterized sucrose in corn oil. The influences of pore size/particle size ratio and suspension concentration on the penetration of liquid and particles were determined. A mathematical model that allows prediction of future behavior was fitted to the test results. The model indicates that dry-weight particle penetration is strongly correlated with pore size and independent of initial particle concentration. Infusion of liquid plus particles was increased by raising porosity and lowering particle concentration.     

Iron-Enriched Bread: Interaction Effect of Protein Quality and Copper on Iron Bioavailability

These studies examined the bioavailability of iron in iron-enriched breads. The test breads also contained added protein in the form of gluten, soy or nonfat dry milk. Bioavailability was assessed based on net hemoglobin synthesis in rats initially made iron deficient and then fed bread-based diets containing 38.5 ppm iron (NRC requirement for rat, 35 ppm) and 3.75, 5.00, or 6.25 ppm copper (NRC requirement for rat, 5 ppm). More hemoglobin was synthesized on milk-supplemented (83 mg/mg iron) and on soy-supplemented (85 mg/mg iron) bread diets than on gluten-supplemented (59 mg/mg iron) bread diets. Copper appeared to have no influence on hemoglobin regeneration or on hepatic iron accumulation under the conditions of this experiment.