Pyruvate Metabolism in Saccharomyces cerevisiae

In yeasts, pyruvate is located at a major junction of assimilatory and dissimilatory reactions as well as at the branch-point between respiratory dissimilation of sugars and alcoholic fermentation. This review deals with the enzymology, physiological function and regulation of three key reactions occurring at the pyruvate branch-point in the yeast Saccharomyces cerevisiae: (i) the direct oxidative decarboxylation of pyruvate to acetyl-CoA, catalysed by the pyruvate dehydrogenase complex, (ii) decarboxylation of pyruvate to acetaldehyde, catalysed by pyruvate decarboxylase, and (iii) the anaplerotic carboxylation of pyruvate to oxaloacetate, catalysed by pyruvate carboxylase. Special attention is devoted to physiological studies on S. cerevisiae strains in which structural genes encoding these key enzymes have been inactivated by gene disruption.     

Methods to Determine Partition Coefficient of Organic Compounds in Water/Polystyrene Systems

Three experimental techniques were employed to determine the partition coefficient (K) of toluene, d-limonene, and ethyl acetate between water and polystyrene. These techniques were gas chromatography, (GC) gel permeation chromatography (a novel approach), and a dynamic thermal stripping-thermal desorption procedure. Comparative results of K values, range of applicability and the limitations of each technique were determined. GC was very suitable for systems showing high K values, while gel permeation chromatography was excellent for direct measurement of sorbed compounds. Statistical analysis of results and kinetics of the sorption process were included. Values of K were 800 for toluene, 5100 for d-limonene and 1.9 for ethyl acetate.     

EVALUATION OF PLASTICS PACKAGING MATERIALS FOR FOOD PACKAGING APPLICATIONS: FOOD SAFETY CONSIDERATIONS

In evaluating a packaging system for food packaging applications, consideration must be given to the physical properties, chemical composition and extractivity of the packaging material. The last point, extractivity, or migration from the packaging material to a food contact phase, is of major concern in the selection and use of plastics packaging materials for food packaging.
The present article deals specifically with migration of indirect food additives from plastics packaging materials and the scientific principles related to migrant transport or diffusion, as they apply to food safety. These principles and their experimental basis are discussed.     

The effect of changing environmental conditions on microwave signatures of forest ecosystems: preliminary results of the March 1988 Alaskan aircraft SAR experiment

Abstract

In preparation for the first European Space Agency (ESA) Remote Sensing(ERS-I) mission,a series of multitemporal, multifrequency, multipolarization aircraft synthetic aperture radar (SAR) data sets were acquired over the Bonanza Creek Experimental Forest near Fairbanks, Alaska in March, 1988. P-, L- and C-band data were acquired with the NASA/JPL Airborne SAR on five differentdays over a period of two weeks. The airborne data were augmented with intensiveground calibration data as well as detailed, simultaneous in situ measurements of the geometric, dielectric and moisture properties of the snow and forest canopy. During the time period over which the SAR data were collected, the environmental conditions changed significantly; temperatures ranged from unseasonably warm (I to 9°C) to well below freezing (-8 to - 15°C), and the moisture content of the snow and trees changed from a liquid to a frozenstate. The SAR data clearly indicate the radar return is sensitive to these changing environmental factors and preliminary analysis of the L-band SAR data shows a 0·4 to 5·8dB increase (depending on polarization and canopy type) in the radar cross section of the forest stands under the warm conditions relative to the cold. These SAR observations are consistent with predictions from a theoretical scattering model. These preliminary results are presented to illustrate the opportunity afforded by the ERS-l SAR to monitor temporal changes in forest ecosystems.     

SURVEY OF FOOD INGREDIENT-DDT REACTIONS UNDER THERMAL PROCESSING CONDITIONS

Aqueous solutions or suspensions of single or multiple food ingredients were heated at 100°C for 2 hr with carbon–14 labeled DDT. Thin-layer chromatography on alumina plates resolved the resulting mixtures into regions corresponding to R_f values for five known transformation products or analogs of DDT. The radioactivity of each plate region was related to the quantity of each product formed. DDT is relatively stable in heated water or buffer solutions of pH 3 to 8 as shown by recoveries of DDT (98–100%); at pH 8.1, approximately 4% of DDE was formed. The compositional changes in radioactive DDT due to heating with water-soluble vitamins, disphosphopyridine nucleotide, yeast nucleic acid, amino acids, peptides and casein were determined. The maximum reduction in DDT content of a suspension heated with a single component (cysteine hydrochloride) was 10%. A mixture of DDT with nine components heated for 2 hr produced a 20% reduction in DDT content.     

Northern Ireland milk production — opportunities and constraints in the European Community context*

The paper indicates how the Northern Ireland dairy industry compared with the United Kingdom and the European Community of 10 over the last 15 years in production and the use of certain major intervention support measures. It considers changes in the manufacturing sector and the factors which affect production and highlights hidden constraints which should be capable of being overcome. It ends with a summary of areas where potential opportunities are being examined in an attempt to help the dairy industry meet the problems of the future.