Effect of Electrical Charge on Attachment of Salmonella typhimurium to Meat Surfaces

Treating tissue with electrical current was found to affect both the initial attachment and total numbers of attached Salmonella typhimurium to meat tissues. When lean tissue was attached to the positive terminal of the power supply operating at 50 volts/125 mA DC, the total number of attached cells increased. There was no effect when the samples were attached to the negative terminal. There was a significant (P<0.05) effect on the percentage of strongly attached bacteria with an increase in treating time. Electrical current was found to increase the percentage of strongly attached cells immediately after the current was applied.     

IMPROVED ESTIMATIONS OF TOTAL AND PSYCHROTROPHIC MICROFLORA IN RAW MILK USING REFLECTANCE COLORIMETRY AT 32°C1

A reflectance colorimeter with 32°C incubation/detection temperature successfully quantitated total and psychrotrophic microflora in raw milk. Correlations between reflectance colorimetry and the Standard Plate Count improved with preliminary incubation time: .50 (no preliminary incubation), .74 (24 h at 7°C), to .84 (48 h at 7°C). Correlations between reflectance colorimetry and the Psychrotrophic Bacterial Count were better than those achieved with the Standard Plate Count and improved: .53 (no preliminary incubation). 80 (24 h at 7°C), to .91 (48 h at 7°C). The 48 h preliminary incubation method would cost less and data would be available in 48 to 72 h compared to the 98 to 240 h for psychrotrophic plating methods. A second sample set (no preliminary incubation) could be analyzed to identify high-count samples in less than 24 h. Color detection times following sample refrigeration for 24 h at 0, 4. and 7°C were significantly different from samples tested before refrigeration. Identical sample time/temperature storage conditions are suggested     

MODELING RHEOLOGICAL BEHAVIOR OF GELATINIZING STARCH SOLUTIONS USING MIXER VISCOMETRY DATA

A Brookfield RVTD mixer viscometer was used to gelatinize 5.5, 6.4, and 7.3% (d.b.) native corn starch solutions, and a 6% bean starch solution. Torque, the dependent variable, was used to estimate parameters in a generalized viscosity model. The independent variables were impeller speed, temperature (50–95°C), concentration, temperature-time history, and strain history. The starch dispersions thickened with decreasing temperature and had an Arrhenius activation energy between 6.4 and 12.7 kJ/mol. There was no evidence that retrogradation caused this effect. First-order reaction kinetics was accurate (9.8% standard deviation) in describing viscosity increase during gelatinization. After initial gelatinization, torque decayed exponentially with time. Predicted curves followed experimental pasting curves when interactions among the independent variables were accounted for in the model. The major variables controlling the pasting process were temperature-time history before peak torque, strain history between peak torque and cooling, and temperature during cooling.     

Equilibrium Cation Distribution in NiAl2O4, CuAl2O4, and ZnAl2O4 Spinels

Stoichiometric NiAl₂O₄, CuAl₂O₄, and ZnAl₂O₄ spinels were prepared and equilibrated at temperatures from 600° to 1400°C. The parameters u and x , denoting the oxygen position and fraction of divalent cations on tetrahedral sites, respectively, were determined from a detailed X-ray diffraction analysis. In NiAl₂O₄, x increased from 0.07 at 595° to 0.26 at 1391°C; in CuAl₂O₄, x decreased from 0.68 at 613° to 0.64 at 1195°C; and in ZnAl₂O₄, x decreased from 0.96 at 905° to 0.94 at 1197°C. The form of the temperature dependence of x could not be described using theoretically based equations advanced in the literature. A more general equation which allows for a non-distributional contribution to the configurational entropy was derived and observed to properly describe the temperature dependence; the results indicate that short-range order is of definite significance in these intermediate aluminate spinels.     

Reversible Stress-Induced Martensitic Transformation in ZrO2

Optical observations and X-ray measurements were used to detect the martensitic transformation of tetragonal ZrO₂ to the monocline structure during room-temperature stressing of Mg-PSZ. The transformation occurs at stresses as low as ∼200 MPa and is reversible. Additional observations of transformation around Vickers indentations and cracks suggest that application of much higher stresses prevents the reverse transformation on unloading.     

CONTROL OF BACILLUS CEREUS IN HIGH-pH CRUMPETS

Studies were performed to determine the effects of sorbic hydroxamic acid (SHA) and mastic oil–ethanol (ME) or water‐ethanol (WE) emitters on the growth of Bacillus cereus in high‐moisture, high‐pH (～8.9) English‐style crumpets stored at ambient temperature (25C). While SHA (3000 p.p.m.), alone or in combination with ME emitters, was effective in inhibiting the growth of B. cereus for 14 days in high‐pH crumpets, only SHA formulated crumpets packaged in air had acceptable sensory scores at the end of storage. However, ME emitters alone were ineffective in controlling the growth of this pathogen. This lack of inhibition in crumpets was attributed to the poor absorption of mastic volatiles from the package headspace into the food matrix. Whatever the reason, these preliminary studies showed that SHA has the potential to control the growth of B. cereus in high‐moisture, high‐pH crumpets without compromising product quality.     

LINAMARASE: IMMOBILIZATION OF A CRUDE ENZYME

ABSTRACT Linamarase from cassava cortex was immobilized on polyacrylamide gel. A crude extract of the enzyme containing most of the intracellular proteins was used for the technique to simulate the enzyme in cassava. Immobilization of the enzyme increased the Michaelis constants for all substrates when compared with the native enzyme. Both free and immobilized linamarase hydrolyzed p-nitrophenylβ D-glucoside, linamarin and p-nitrophenylβ-D-galactoside. The immobilized enzyme was more stable than the free enzyme at room temperature (25C) and 41C. Both forms gave a bell-shaped curve with maximal activity at pH 6.0; these data indicated two catalytic ionizable residues with pK_a 5.7 and pK_a 6.5.