State transitions and freeze concentration in trehalose-protein-cornstarch mixtures

State transitions of solutions of mixtures of trehalose, albumen, gelatin, and cornstarch were studied and state diagrams were established. Maximum freeze concentration was achieved by annealing of solutions at a temperature −1 °C. The onset temperatures of glass transitions of maximally freeze-concentrated solutes, , were lower and onset temperatures of ice melting, , were higher for mixtures of trehalose, proteins and cornstarch when compared with those of pure trehalose. Solute concentration in the maximally freeze-concentrated phase, , was 79% for trehalose, trehalose/albumin (1:1), and trehalose/cornstarch (1:1). The of trehalose/gelatin (1:1), and trehalose/cornstarch/gelatin (1:1:1) was 74% and 75%, respectively. The state diagrams established with experimental and predicted T_g values are useful for characterization of thermal phenomena and physical state of carbohydrate-protein-polysaccharide mixtures at various water contents.     

Effectiveness of commercial household steam cleaning systems in reducing the populations of Listeria monocytogenes and spoilage bacteria on inoculated pork skin surfaces

In a previous study conducted in our laboratory, a commercial household steam cleaner was found to be effective in reducing the naturally occurring bacterial populations on 72 beef and 72 hog carcasses processed by four small and very small meat processing plants. The goals of this study were to determine the maximum levels of bacterial reduction caused by treatments using the steam cleaner, and to compare the efficacy of this cleaner with the efficacies of two other commercial household steam cleaning systems in reducing bacterial populations on the surface of pork skin artificially inoculated with ca. 7.61 or of Listeria monocytogenes. The contaminated pork skin samples were treated with the three stream cleaners for 30-180 s in 30 s intervals, and assayed for the populations of L. monocytogenes as well as total aerobic and thermoduric bacteria. The application of steam significantly reduced the population of L. monocytogenes (7.61-), as well as total aerobic (5.68-) and thermoduric (6.12-) bacteria on the surface of pork skin (P?0.05). Significant differences in microbial reductions were observed between different inoculation levels, treatment times, and types of cleaning systems used in the study (P?0.05).     

Efficacy of mixing vegetable oils with pirimiphos-methyl against the maize weevil, Sitophilus zeamais Motschulsky in stored maize

Sitophilus zeamais is a major insect pest of stored maize and grain products in the tropics. The toxicity of coconut, groundnut and soybean oils applied at 1, 2, 5 and 10 ml/kg and pirimiphos-methyl at 2.5, 5 and 10 μl active ingredient in 2 ml of water/kg of grain (, and of the recommended dose), alone or in combination, to adults and immature stages of S. zeamais, the persistence of the treatments in maize grains and their effects on seed viability were evaluated in the laboratory. All the treatments caused significant mortality compared to untreated controls. Low dosages of the oils and pirimiphos-methyl when combined were highly toxic to adult S. zeamais. The mixtures completely inhibited the development of immature stages of the weevil. Only pirimiphos-methyl and the mixtures retained some activity 60 days after application. Pirimiphos-methyl can be used at reduced rates if combined with vegetable oils to control infestations of S. zeamais in stored maize.     

Influence of water activity and molecular mobility on peroxidase activity in salt and sorbitol-maltodextrin systems

Solvent composition, system mobility and viscosity play a central role in the regulation of enzymatic activity.The aim of this study was to investigate the individual and combined effect of water activity (a_w), bulk viscosity and glass transition temperature () on the activity of horseradish peroxidase (HRP) in buffered solutions. For this purpose, the water activity of the solutions was modulated using both a ionic (sodium chloride) and a non-ionic (sorbitol) ligand and viscosity changed upon the addition of maltodextrin.In viscous solutions characterized by different compositions, the effectiveness of a solute in the inhibition of the HRP activity was dependent both on the chemical properties of the solution, as described by a_w, and on the mobility of the system, as described by the inverse of viscosity and T − . Viscosity was the most important factor in the inhibition of HRP activity in solutions characterized by the same value, but when was changed, due to changes in the solutes composition, the latter became a key factor in the regulation of the enzyme activity.In salt-maltodextrin systems the water activity reduction limited HRP activity with higher efficiency at low viscosities whilst in sorbitol-maltodextrin systems, characterised by different values, the a_w lowering by sorbitol addition resulted in the increase of HRP activity depending on its effect on .