John G. Phillips

Model for the survival of Staphylococcus aureus in nongrowth environments

A model was developed to estimate the survival times of Staphylococcus aureus in nongrowth environments. A four strain mixture of S. aureus was inoculated into BHI broth that had a lactate buffer with various combinations of pH (3-7) and lactate (0-1%), NaCl (0.5-20%) and NaNO2 (0-200 ppm) and stored at different temperatures (4-42 degrees C). At appropriate times the survivors were enumerated by sampling and spreading on TSA plates. The survival curves were modeled with two forms of a logistic equation and the D values were determined. Polynomial regression equations were then calculated to predict the effect of the environmental factors on the D values. Survival times were increased with higher pH values, lower temperatures, and lower nitrite and lactate concentrations. Added salt increased survival times until the salt concentrations exceeded that of most foods.

Influence of agitation, inoculum density, pH, and strain on the growth parameters of Escherichia coli O157:H7—relevance to risk assessment

Foods may differ in at least two key variables from broth culture systems typically used to measure growth kinetics of enteropathogens: initial population density of the pathogen and agitation of the culture. The present study used nine Escherichia coli O157:H7 strains isolated from beef and associated with human illness. Initial kinetic experiments with one E. coli O157:H7 strain in brain-heart infusion (BHI) broth at pH 5.5 were performed in a 2 x 2 x 3 factorial design, testing the effects of a low (ca. 1-10 colony-forming units [CFU]/ml) or high (ca. 1000 CFU/ml) initial population density, culture agitation or no culture agitation, and incubation temperatures of 10, 19, and 37 degrees C. Kinetic data were modeled using simple linear regression and the Baranyi model. Both model forms provided good statistical fit to the data (adjusted r(2)>0.95). Significant effects of agitation and initial population density were identified at 10 degrees C but not at 19 or 37 degrees C. Similar growth patterns were observed for two additional strains tested under the same experimental design. The lag, slope, and maximum population density (MPD) parameters were significantly different by treatment. Further tests were conducted in a 96-well microtiter plate system to determine the effect of initial population density and low pH (4.6-5.5) on the growth of E. coli O157:H7 strains in BHI at 10, 19, and 37 degrees C. Strain variability was more apparent at the boundary conditions of growth of low pH and low temperature. This study demonstrates the need for growth models that are specific to food products and environments for plausible extrapolation to risk assessment models.

Effect of Gamma Irradiation on the B Vitamins of Pork Chops and Chicken Breasts

A study was made of the effect of low-dose gamma irradiation on the content of thiamine (B1), riboflavin (B2), niacin, pyridoxine (B6) and cobalamin (B12) in pork chops, and thiamine, riboflavin and niacin in chicken breasts. Gamma irradiation from a caesium-137 source was used to irradiate the samples in a range of 0.49 to 6.65 kGy from -20 to +20 degrees C. Over the range of dose and temperature studied it was possible to derive a mathematical expression for predicting the losses. A calculation was made of the effect of the loss of thiamine, riboflavin and niacin due to irradiation on the overall loss of these vitamins in the American diet. The losses of riboflavin and niacin were of the order of a fraction of a per cent. Pork is an important source of thiamine, but the calculated loss at 1.0 kGy of this vitamin in cooked pork was only 1.5 per cent. There were initial increases with radiation doses up to 2-4 kGy in the measured concentrations of riboflavin and niacin in both pork and chicken. The increases were highly significant, and are of concern both to the study of radiation effects and the chemical method of the determination of these two vitamins.

Model for Aerobic Growth of Shigella flexneri Under Various Conditions of Temperature, pH, Sodium Chloride and Sodium Nitrite Concentrations

A modified factorial design was used to measure the effects and interactions of temperature (10 to 37°C), pH (5.5 to 7.5), sodium chloride (0.5 to 5.0%), and sodium nitrite (0 to 1000 ppm) on the aerobic growth kinetics of Shigella flexneri in brain heart infusion broth. A total of 592 cultures were analyzed, with growth curves being generated using the Gompertz equation. A quadratic model for growth of S. flexneri in terms of temperature, pH, sodium chloride, and sodium nitrite concentrations was obtained by response surface analysis. This model provides an estimate of bacterial growth in response to any combination of the variables studied within the specified ranges. Estimates obtained with the model compared favorably with growth of S. flexneri in milk.

Thermal Resistance of Aeromonas hydrophila

Thermal resistance of five strains of Aeromonas hydrophila (three clinical and two food isolates) was studied at 45 to 51°C in saline solution and raw milk. In addition, effects of growth temperature and growth phase on thermal resistance of the cells were also studied. Survivors after various heat treatments were plated on starch phenol red agar; colonies were counted after 24 h at 28°C. Cells heated at 48°C and 51°C exhibited a diphasic response and the data presented are from the initial and final linear phases. Data were expressed as D- and z-values. Most variables caused small but statistically significant changes in D-value of the initial linear phase. At 48°C, D-values for stationary phase cells heated in saline solution ranged from 3.49 to 6.64 min; for cells heated in raw milk, the D-values ranged from 3.20 to 6.23 min. At 48°C, D-values for log-phase cells heated in saline solution ranged from 2.23 to 3.73 min, and z-values ranged from 5.22 to 7.69°C. These results indicate that A. hydrophila should be killed by many of the heat treatments given foods during processing. The thermal resistance of A. hydrophila appears similar to that of other gram-negative bacteria associated with food.

Digital Image Analysis for Fabric Assessment

Conventional methods of fabric inspection are tedious and require close association. In this work, digital image analysis for fabric assessment (DIAFA) is applied to modem and historic fabrics. Fabric images are divided into arrays of pixels with peak intensities distributed over gray scale ranges (histograms) and along constructed lines (line profiles). Fabric cover is measured by segmenting a histograms B/w pixels, yarn spacing, and yarn thickness from moving point averages by calculating the breadth of a peak corresponding to an individual yarn at half the maximum peak height for a given line profile. The results show very good agreement with known values (r = 0.919, n = 30, p < 0.01). Fourier power spectra provide facile measurements of yarn parameters in close agreement with the results from line profiling. With DIAFA, a small tool kit is developed to assist in the objective analysis of the structural integrity of fabrics in the museum environment, and it could be very useful in advancing automated fabric inspection.

Evaluation of root-mean-square radius of gyration as a parameter for universal calibration of polysaccharides

Abstract High-performance, size-exclusion chromatography columns were calibrated in average root-mean-square radii of gyration (μ R gz ) by a combination of commercial “narrow” pullulan and “broad” dextran standards. The nonlinear calibration-curves were fitted by a computer-aided, iterative, least-squares procedure. Values of (μ R gz ), obtained from a point-by-point transformation of the respective pullulan and dextran chromatograms by utilizing universal calibration, were compared with inputted μ R gz calibration values. For standards ranging in μ R gz value from 20.1 to 389 A, the accuracy ranged from 1 to 15.3%. Furthermore, from relationships in the literature, μ R gz values were transformed to μ M w . These values of μ M w were comparable to, but generally less accurate than, μ M w values from direct, molecular-weight calibration.

Transfer Coefficient Models for Escherichia coli O157:H7 on Contacts between Beef Tissue and High-Density Polyethylene Surfaces†

Risk studies have identified cross-contamination during beef fabrication as a knowledge gap, particularly as to how and at what levels Escherichia coli O157:H7 transfers among meat and cutting board (or equipment) surfaces. The objectives of this study were to determine and model transfer coefficients (TCs) between E. coli O157:H7 on beef tissue and high-density polyethylene (HDPE) cutting board surfaces. Four different transfer scenarios were evaluated: (i) HDPE board to agar, (ii) beef tissue to agar, (iii) HDPE board to beef tissue to agar, and (iv) beef tissue to HDPE board to agar. Also, the following factors were studied for each transfer scenario: two HDPE surface roughness levels (rough and smooth), two beef tissues (fat and fascia), and two conditions of the initial beef tissue inoculation with E. coli O157:H7 (wet and dry surfaces), for a total of 24 treatments. The TCs were calculated as a function of the plated inoculum and of the cells recovered from the first contact. When the treatments were compared, all of the variables evaluated interacted significantly in determining the TC. An overall TC-per-treatment model did not adequately represent the reduction of the cells on the original surface after each contact and the interaction of the factors studied. However, an exponential model was developed that explained the experimental data for all treatments and represented the recontamination of the surfaces with E. coli O157:H7. The parameters for the exponential model for cross-contamination with E. coli O157:H7 between beef tissue and HDPE surfaces were determined, allowing for the use of the resulting model in quantitative microbial risk assessment.

Combined bleaching, shrinkage prevention, and biopolishing of wool fabrics

In earlier work, we established that alkaline hydrogen peroxide systems that include dicyandiamide, gluconic acid, and Triton X surfactant, used alone or followed by enzyme treatments, control shrinkage in wool fabrics to 3.0% and 1.2%, respectively. We have perfected this system for complete shrinkage control with no loss in mechanical properties by using the same pretreatment and enzyme applied from a buffered triethanolamine solution that incorporates sodium sulfite. Fabrics treated by this method are bright white and exhibit a soft handle with a smoothed surface. Digital image analysis is used to quantify fiber projections above the fabric surface for a measurement of smoothness. A statistical analysis with a central composite design reveals the optimum concentrations of enzyme, sodium sulfite, and exposure time that maximize shrinkage control while maintaining adequate levels of tensile strength and weight loss.

CRITICAL EVALUATION OF CRISPY AND CRUNCHY TEXTURES: A REVIEW

Crispness and crunchiness are important factors in the enjoyment of many foods, but they are defined differently among dictionaries, consumers, and researchers. Sensory, mechanical, and acoustic methods have been used to provide data on crispness and crunchiness. Sensory measurements include biting force and sound intensity. Mechanical techniques resemble mastication and include flex, shear, and compression. Acoustical techniques measure frequency, intensity, and number of sound events. Water and oil content contribute to crispness and crunchiness, which also have temporal aspects. Information in the literature is compared in this article to develop definitions of crispness and crunchiness.