Soil amidase activity in polyacrylamide-treated soils and potential activity toward common amide-containing pesticides

 Polyacrylamide (PAM) is currently used as an irrigation water additive to significantly reduce the amount of soil erosion that occurs during furrow irrigation of crops. Elevated soil amidase activity specific toward the large PAM polymer has been reported in PAM-treated field soils; the substrate specificity of the induced amidase is uncertain. PAM-treated and untreated soils were assayed for their capacity to hydrolyze the amide bond in carbaryl (Sevin), diphenamid (Dymid), and naphthalene acetamide. Based on results obtained with a soil amidase assay, there was no difference between PAM-treated and untreated soils with respect to the rate of amide bond hydrolysis of any of the agrochemicals tested. It appears that under these assay conditions the PAM-induced soil amidase is not active toward the amide bonds within these molecules. However, carbaryl was hydrolyzed by a different soil amidase. To our knowledge, this is the first soil enzyme assay-based demonstration of the hydrolysis of carbaryl by a soil amidase. Received: 23 June 1999     

Analysis of free and esterified ergosterol in tomato products

A new extraction and chromatographic procedure to quantify free and esterified ergosterol in tomato products was devised. The extraction solution was composed of a dichloromethane/methanol mixture in a 2:1 (v/v) ratio. This extraction solvent allowed for higher ergosterol recovery from tomato products (an average of 25% more) compared to hexane, which is frequently employed for ergosterol extraction. Both free and esterified ergosterol were determined by HPLC reverse-phase chromatography employing a Nova-Pak C-18 column (300 x 3.9 mm), filled with 4 mm average particle size and a guard column of the same material. The elution was performed at a flow rate of 1 mL. min(-1) with a linear gradient of solvent A (methanol/water, 80:20, v/v) and solvent B (dichloromethane). The gradient, starting at sample injection, was from 0 to 50% B for 20 min for the free ergosterol analysis and additional 15 min at 50% B to analyze the ergosterol esters. This technique has proven to be more sensitive for ergosterol determination than other reported chromatographic procedures. Moreover, ergosterol esters, extracted from various fungal sources, separated well and were easily quantified.     

Antioxidant activity of dietary polyphenols as determined by a modified ferric reducing/antioxidant power assay

Most nonenzymatic antioxidant activity (scavenging of free radicals, inhibition of lipid peroxidation, etc.) is mediated by redox reactions. The antioxidant (AO) activity of polyphenols (PPs), as ferric-reducing power, was determined for the first time using a modified FRAP (ferric reducing/antioxidant power) assay. Reaction was followed for 30 min, and both Fe(II) standards and samples were dissolved in the same solvent to allow comparison. Selected representative PPs included flavonoids (quercetin, rutin, and catechin), resveratrol, tannic acid, and phenolic acids (gallic, caffeic, and ferulic). Carotenoids (beta-carotene and zeaxanthine), ascorbic acid, Trolox, and BHA were included for comparison. Equivalent concentration 1 (EC(1)), as the concentration of AO with a reducing effect equivalent to 1 mmol/L Fe(II), was used to compare AO efficiency. PPs had lower EC(1) values, and therefore higher reducing power, than ascorbic acid and Trolox. Tannic acid and quercetin had the highest AO capacity followed by gallic and caffeic acids. Resveratrol showed the lowest reducing effect. Carotenoids had no ferric reducing ability. Polyphenol's AO efficiency seemed to depend on the extent of hydroxylation and conjugation.     

Mechanism and characteristics of protein release from lactitol-based cross-linked hydrogel

Lactitol-based cross-linked hydrogel was synthesized, and model proteins (alpha-chymotrypsin, beta-lactoglobulin, bovine serum albumin (BSA), and gamma-globulin) were incorporated into the cross-linked hydrogel. The larger-molecular-weight proteins have lower diffusivity (D(e)) in the hydrogel. Increasing temperature accelerated the diffusion rate of proteins; however, the diffusion did not follow the Arrhenius equation at temperatures above 37 degrees C. The swelling ratio of the hydrogel was slightly decreased after heating for 2 h at 37 and 45 degrees C, and significantly reduced after 1 h at 60 degrees C. Therefore, diffusion of beta-lactoglobulin and BSA may be decreased by hydrogel shrinking at temperature over 37 degrees C. The model proteins have high affinities to buffer solution compared to the hydrogel network structure, resulting in high partition coefficients (K > 1) which do not affect the calculation of D(e) values. Incorporated protein release follows the theory of hindered diffusion.     

Estimation of soil strength properties for critical rooting conditions

Methods to aid in the large-scale testing and characterization of Coastal Plain soils based on their susceptibility to root-limiting strength problems were developed and analyzed. They were basically regression equations modeled after a Taylor series expansion. The equations relate changes of soil strength, bulk density and soil water content between field and “critical rooting conditions”. Once equations wered eveloped from a data set of 426 laboratory samples, critical rooting bulk density was predicted for a separate set of laboratory and field samples. All laboratory samples and appropriate field samples were equilibrated at — 100 kPa soil-water potential. Soils used were sandy Ultisols, which may limit the scope of equations.

In many cases, changes in the water contents were not a significant factor in the prediction of soil strength. This may be a reflection of the limited capabilities of the equations, the uniform equilibration of soil-water potential of the soils, or the fact that the slope of the strength vs. bulk density curve is independent of water content over the range of samples considered. Nevertheless, it does simplify the equations and may suggest that a series of several equations for different soil types would be better than a single equation that requires soil-water content.     

In-situ soil organic matter studies using scanning electron microscopy and low temperature ashing

The in-situ distribution and morphology of organic materials located on, or near, structural surfaces within some soils is examined on a submicroscopic scale by comparing scanning electron microscope images of the same areas of soil samples before and after low temperature ashing. Electron-translucent organic matter coatings up to 1/2 μm thick, and thinner, electron-opaque organic matter coatings were found on structural surfaces within these soils. Oribatid faecal pellets in one of the soils were found to contain aluminosilicate clay minerals. Fine-clay sized spheres of biogenic opaline silica were found to be contained within the epidermis of a decaying root. These studies show that the combined use of low temperature ashing and scanning electron microscopy will be a valuable technique for in-situ investigations of submicroscopic organic matter within soils.     

Analysis of virgin olive oil volatiles by a novel electronic nose based on a miniaturized SAW sensor array coupled with SPME enhanced headspace enrichment

A novel electronic nose based on solid-phase microextraction (SPME) coupled with a surface acoustic wave (SAW) sensor array has been used to analyze different quality virgin olive oils. A mathematical model was designed with 37 samples to distinguish lampante from the other virgin olive oils categories (extra-virgin and virgin), because lampante-virgin olive oils cannot be consumed without a previous refining process. The model, successfully validated with a test set of 16 samples, was able to classify 90% of the samples correctly. Misclassifications were explained by SPME-HRGC analyses and a second sensory evaluation.     

Foraging behaviour and habitat use by Antechinus flavipes and Sminthopsis murina (Marsupialia: Dasyuridae) in response to predation risk in eucalypt woodland

We examined the foraging behaviour and habitat use of two species of small Australian mammal (Antechinus flavipes and Sminthopsis murina) in response to predation risk in remnant eucalypt woodland. Predation risk was manipulated by providing refuge in the form of ground level wire netting to reduce risks from avian and mammalian predators. Giving-up-densities (GUD) using artificial food trays (20 mealworms in 1.5 l vermiculite) quantified the foraging behaviour in response to predation risk, by measuring the quitting harvest rate. Both A. flavipes and S. murina had lower GUDs (number of mealworms remaining) under the netting than in the open, most likely because these areas have lower predation risk. Animals also made greater visits to tracking tunnels under the netting compared to in the open. Tracking animal movements using fluorescent pigments also revealed preference for natural microhabitats that were structurally complex with animals moving most where logs and rock crevices were present. These results suggest that small mammals may use habitat structure to reduce their risks of predation. If future studies are able to demonstrate commensurate population-level responses, manipulation of habitat may be a useful management option to complement the direct control of exotic predators such as foxes and feral cats.     

Determination of ractopamine in cattle and sheep urine samples using an optical biosensor analysis: comparative study with HPLC and ELISA

A biosensor method, using the surface plasmon resonance (SPR) principle, was developed for the determination of ractopamine in cattle and sheep urine. A monoclonal antibody was used to compete with ractopamine in the sample and ractopamine immobilized on the sensor chip. Addition of bovine serum albumin (BSA, 1 mg/mL) as an antibody stabilizer to the incubation buffer was required to achieve a stable biosensor response throughout each sample set. The calibration curve gave a mean IC(50) of 4.7 +/- 0.21 ng/mL (n = 7). Over sample concentrations from 2.5 to 10 ng/mL recoveries were typically approximately 100-110%, whereas inter- and intra-assay reproducibilities (% CV) were usually less than 10 and 6%, respectively. Comparison of biosensor results with results obtained from high-performance liquid chromatography (HPLC) and enzyme-linked immunosorbent assays (ELISA) using enzyme-hydrolyzed urine (to convert ractopamine conjugates to free ractopamine) gave correlation coefficients of 0.94 for sheep and 0.86 for cattle. Slopes of the lines, with zero intercepts, equaled 0.80 for sheep and 0.74 for cattle. For untreated (nonhydrolyzed) urine samples, the correlations between biosensor and HPLC results were 0.95 for sheep and 0.72 for cattle with slopes of 1.18 (sheep) and 1.69 (cattle). The slopes greater than unity indicate that the biosensor responded to ractopamine metabolites in addition to free ractopamine. The biosensor assay is an excellent analytical tool to screen ractopamine residues in sheep or cattle urine, and the results should be extendible to other species with suitable validation.