Effect of pH on survival, thermotolerance, and verotoxin production of Escherichia coli O157:H7 during simulated fermentation and storage

Heat treatment is increasingly being introduced to fermented meat processing, since the acid tolerance properties of Escherichia coli O157:H7 can permit this organism to survive traditional processing procedures. This study investigated the effect of growth pH and fermentation on the thermotolerance at 55 degrees C of E. coli O157:H7 in a model fermented meat system. E. coli O157:H7 (strain 380-94) was grown at pH 5.6 or 7.4 (18 h at 37 degrees C), fermented to pH 4.8 or 4.4 in brain heart infusion broth, and stored for 96 h. Cells grown at pH 5.6 had higher D values at 55 degrees C (D55 degrees C) than cells grown at pH 7.4 (P < 0.001). Cells fermented to pH 4.8 had higher D55 degrees C than those fermented to pH 4.4 (P < 0.001). Cells fermented to pH 4.8 demonstrated an increase in D55 degrees C during storage (P < 0.001), whereas cells fermented to pH 4.4 showed a decrease in D55 degrees C during the same period (P < 0.001). The effect of growth pH on verotoxin production by E. coli O157:H7 was assessed using the verotoxin assay. Cells grown at pH 5.6 had lower verotoxin production then cells grown at pH 7.4. This effect was not sustained over storage. These results indicate that a lower growth pH can confer cross-protection against heat. This has implications for the production of acidic foods, such as fermented meat, during which a heating step may be used to improve product safety.     

A micro mechanical model for isotropic cyclic loading of isotropically clastically compressed soil

This paper presents a simple micro mechanical model for the behaviour of overconsolidated soils. The simplest case of isotropic unloading and reloading is considered for a soil which has been subjected to isotropic plastic (clastic) or "normal" compression. Such a material has a wide disparity in particle sizes, such that small particles are kinematically unstable, and large particles are stable. A simple unit cell is defined with one of the largest grains at the centre, surrounded by a fractal matrix of finer particles. On unloading, the unit cell exhibits elastic behaviour followed by "kinematic yielding", which is the onset of sliding of grains. On reloading, kinematic yielding may not occur, but the inhomogeneous stresses in the cell may induce "clastic yielding" before re-joining the normal compression line. The unit cell is shown to reproduce micro mechanical features of a real aggregate having particle size disparity, and leads to realistic hysteresis loops which permit possible ratchetting on cyclic loading. A simple dilatancy rule is shown to offer micro mechanical insight into the form of the unloading curves evident in much of the soil mechanics literature.     

Effects of biotin supplementation on peripartum performance and metabolites of Holstein cows

Fifty-two multiparous Holstein cows were randomly assigned to receive 0 or 20 mg of biotin/d starting at an average of 16 d prepartum and then switched to 0 or 30 mg of biotin/d from calving through 70 d postpartum to determine whether supplemental biotin would affect cow performance, hepatic lipidosis, and plasma metabolites. Mean concentration of biotin in plasma sampled weekly was greater in cows fed biotin (4.3 vs. 9.4 nmol/L). Postpartum dry matter intake as a percentage of body weight (3.9% vs. 4.0%), milk production (35.8 vs. 34.8 kg/d), and milk fat concentrations (3.59% vs. 3.69%) were similar between treatment groups. Milk from biotin-supplemented cows tended to have a greater concentration of protein (2.73% vs. 2.83%). Concentrations of plasma nonesterified fatty acids were lower at wk 2 (652 vs. 413 microEq/mL) and 4 (381 vs. 196 microEq/mL) postpartum in cows fed supplemental biotin. However, mean plasma concentrations of beta-hydroxybutyric acid were not affected by biotin supplementation. Mean concentration of plasma glucose was greater for lactating cows fed supplemental biotin (63.4 vs. 66.6 mg/dL). Biopsies of liver were taken at 2, 16, and 30 d postpartum. The triacylglycerol concentration in liver (wet basis) tended to decrease at a faster rate after d 2 postpartum with biotin supplementation compared with control cows. The potential mechanisms that link improved glucose status and decreased lipid mobilization in cows supplemented with biotin warrant further investigation.     

Limitations for Dairy Production in Developing Countries

Animal products (fish, eggs, meat, and milk) provide nearly 53 million Mt of edible protein and more than 1 billion Meal of energy per year. This is equivalent to 53% of the protein and 26% of the energy from cereal grains. The 550 million Mt of milk provides 53% of all animal protein. Present production is equivalent to .36 liters per capita, but consumption is high in developed countries, .5 to .8 liters per day but less than .2 liters in developing countries. From 1969 to 1978 world milk supplies increased 1.4% peryr, but human population grew 2.1%. Comparing rates of increase in cattle numbers (1.1%) and in milk (1.4%) indicates milk per animal has changed little. Land for agricultural cropping increased 1.1% per year 1969 to 1978. Expansion of cropping into traditional grazing areas and rise in fossil fuel prices has tended to reduce availability of milk in urban centers of developing countries. Elasticity of demand for milk in developing countries is high, but general market growth is slow because of limits in income growth by the majority of the population.Many developing countries are giving greater emphasis to milk supplies and are seeking bank loans to support development of infrastructure for dairying both on and off farms. Growth in milk must come largely from small farms which will require identification of constraints and development of appropriate technology. On subsistence farms there is a high dependence on animals to provide goods and services of nonfood nature which also will require consideration in developing milk supplies. Potential for growth of milk supplies in developing countries is high and affords an excellent opportunity for dairy scientists in the United States to assist in training and research.     

More on Herrnstein's hyperbola.

Responds to E. Ubell's (see record 1984-05704-001) transformation of Herrnstein's mathematical statement of the law of effect from a hyperbolic to a linear function. This transformation of the relationship between response and reinforcement allows the law to be stated in terms of period rather than frequency. The present author argues that the linear and hyperbolic forms are not statistically interchangeable. (6 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Mechanisms affecting the infiltration and distribution of ethanol-blended gasoline in the vadose zone

One- and two-dimensional experiments were conducted to examine differences in the behavior of gasoline and gasohol (10% ethanol by volume) as they infiltrate through the unsaturated zone and spread at the capillary fringe. Ethanol in the spilled gasohol quickly partitions into the residual water in the vadose zone and is retained there as the gasoline continues to infiltrate. Under the conditions tested, over 99% of the ethanol was initially retained in the vadose zone. Depending on the volume of gasoline spilled and the depth to the water table, this causes an increase in the aqueous-phase saturation and relative permeability, thus allowing the ethanol-laden water to drain into the gasoline pool. Under the conditions tested, the presence of ethanol does not have a significant impact on the overall size or shape of the resulting gasoline pool at the capillary fringe. Residual gasoline saturations in the vadose zone were significantly reduced however because of reduced surface and interfacial tensions associated with high ethanol concentrations. The flux of ethanol in the effluent of the column ranged from 1.4 x 10(-4) to 4.5 x 10(-7) g/(cm2 min) with the LNAPL and from 6 x 10(-3) to 3.0 x 10(-4) g/(cm2 min) after water was introduced to simulate rain infiltration. The experimental results presented here illustrate that the dynamic effects of ethanol partitioning into the aqueous phase in the vadose zone create an initial condition that is significantly different than previously understood.     

Dissemination of central nervous system tissue from the brain and spinal cord of cattle after captive bolt stunning and carcass splitting

In the absence of reliable live animal tests for the presence of BSE in cattle, a number of measures have been applied to exclude specified risk materials (SRM) from the human food chain. However, concerns remain that current practices in the stunning and slaughter of cattle may disseminate central nervous system (CNS) tissue to meat and meat contact surfaces. The objective of this study was to establish the particular risks of CNS tissue dissemination associated with captive bolt stunning and carcass splitting. The study applied enzyme linked immunosorbent assays (ELISAs) in the detection and quantification of two CNS proteins, syntaxin 1b and GFAP. The study observed extensive dispersal of both CNS proteins onto equipment, beef hide and personnel. These results demonstrate that despite the rigorous application of current SRM control policies, normal slaughter practices continue to present significant opportunities for CNS material including BSE prion present in the CNS of any sub-clinically infected cattle to contaminate meat entering the human food chain.