HISTAMINE PRODUCTION BY FOOD-BORNE BACTERIAL SPECIES12

A total of 112 bacterial strains representing 38 species were tested for their potential to elicit food poisoning outbreaks via histamine formation in foods. Proteus morganii and Enterobacter aerogenes displayed a quantitative superiority in terms of histamine production on a trypticase-soy broth-histidine (TSBH) medium and a tuna fish infusion broth (TFIB). When bacteria were incubated under standardized conditions in TSBH medium, histamine accumulated to levels exceeding 50 nmoles/ml of media with a total of 23 strains, including 13 of 15 P. morganii strains, 3 of 3 E. aerogenes strains, 3 of 12 Hafnia alvei strains, 1 of 4 Providencia alcalifaciens strains, 1 of 5 Enterobacter cloacae strains, 1 of 1 Proteus rettgeri strains, and 1 of 1 Citrobacter diversus strains. However, only 8 of the 15 P. morganii strains and the 3 E. aerogenes strains were capable of generating histamine in excess of 200 nmoles/ml in the TSBH medium. Of the 23 strains capable of appreciable histamine production in TSBH medium, P. morganii and E. aerogenes were, by far, the most prolific histamine producers in TFIB. Of the organisms tested, only P. morganii and E. aerogenes would appear to have the capability of forming sufficient histamine in scombroid fish products to elicit food poisoning outbreaks.     

Relative Role of Phospholipids, Triacylglycerols, and Cholesterol Esters on Malonaldehyde Formation in Fat Extracted from Chicken Meat

Fresh breast and leg meat was collected from 11-wk-old pullets fed a high protein-low fat starter ration. Lipid oxidation measured in malonaldehyde (MA) equivalents in total fat extracted from meat, and in phospholipids (PL), triacylglycerol (TG), and cholesterol ester (CE) fractions of total fat was determined by an improved TBA assay with antioxidant protection. It was found that breast meat had two-fold less fat than leg. Breast fat contained 70.1% PL, 22.2% TG, and 1.2% CE; leg fat contained 42.9% PL, 51.4% TG, and 0.8% CE. After separation by thin layer chromatography, the individual lipid classes were tested for TBA reactivity. The PL fraction was found to contribute approximately 90% of the MA measured in total fat from chicken meat.     

Coordination Chemistry in Mineral Processing

Abstract

In mineral processing industry, achieving an optimal extraction of valuable mineral components is an extremely important goal. The processes of leaching, solvent extraction and flotation are major methods of processing minerals under aqueous conditions in which coordination chemistry may play an important role, and in facilitating the realization of this goal. The success of some of these processes is ascribed to the ability of the chemical reagents to form stable coordination complexes with metal ions in the aqueous solution or on the surfaces of the mineral lattice. Leaching processes which involve complex formation usually result in increased dissolution of mineral values in aqueous solution, and may include cyanide, basic and chloride leaching. In solvent extraction, the extractant and masking reagents react with metal ions to form principally coordination complexes, which are either selectively extracted into the organic phase or retained in the aqueous raffinate. This is the basis underlying the concentration and purification of metal values by this process. Flotation processes, which employ collectors and depressants whose interactions with metal ions in aqueous solution lead to complex formation through coordinate bonding are believed to be more efficient than other analogous processes. In an effort to contribute to the understanding of the chemistry of these processes, the authors have attempted to review the role of coordination chemistry in mineral processing by flotation, leaching and solvent extraction.     

NEW DEVELOPMENTS IN STRUCTURAL OPTIMIZATION USING ADAPTIVE MESH REFINEMENT AND MULTIPOINT APPROXIMATIONS

Combining Shape Optimization (SO) with Adaptive Mesh Refinement (AMR) potentially offers a higher accuracy and higher computational efficiency, especially if the applied target error for AMR is reduced in the course of the optimization process. The disadvantage of that approach is that the rate of convergence of the corresponding optimization processes can be significantly lower as compared to processes which apply a fixed target error for AMR. In the present paper the so-called Multipoint Approximation Method (MAM) is used as a basis for SO in conjunction with AMR. Several techniques for improvement of the rates of convergence are presented and investigated. Firstly, alternative algorithms for determining the approximation functions using a weighted least squares method are investigated. The focus is on weights which depend on the discretization errors. Secondly, different strategies for moving and resizing the search sub-regions in the space of design variables are presented. The proposed methods are illustrated by means of several optimization problems in which the effect of AMR with changing discretization errors is modelled by artificially introduced numerical noise.     

COMPARISON OF CATHEPSIN B, D, H AND L ACTIVITY IN FOUR SPECIES OF PACIFIC FISH

The activities of cathepsins B, D, H and L were compared in crude muscle extracts from four species of fish: Pacific whiting (PW), (Merluccius productus); arrowtooth flounder (ATF), (Atheresthes stomias); Alaska pollock (AP), (Theragra chalcogramma); and Pacific cod (PC), (Gadus macrocephalus). Both PW and ATF are known to undergo softening during post-mortem handling and cooking while AP and PC do not. Cathepsin B and L activities were both higher in extracts of PW and ATF than in AP and PC. Cathepsins B and L activities were both much higher in PW than in ATF. Cathepsin H activity was highest in AP followed by ATF with PC and PW having the lowest activities. Cathepsin D activity was extremely low in all four species. The heat stability of the various cathepsin activities showed cathepsin B to be the most heat labile and was inactivated by 50C heating for 15 min. Cathepsin H activity was inactivated at 60C, while cathepsin L required 70C for inactivation. Cathepsins B and L are the most likely responsible for softening in PW and ATF during holding and subsequent processing. However, during cooking, cathepsin L likely causes the most damage since it requires 70C for inactivation. The difference in heat stability of cathepsins B and L can be used to differentiate between their activities.     

Effects of Frozen Storage and Cooking on Lipid Oxidation in Chicken Meat

Fresh chicken breast and leg meat samples, which were frozen for 3 months or 6 months at −18°C, were cooked in microwave and convection ovens and then tested for levels of lipid oxidation. After 6 months storage, malonaldehyde in fat from meat samples, as measured by a TBA assay, modified to avoid sample autoxidation, increased 2.5 fold, while the fluorescence excitation (360 nm) and emission (440 nm) spectra increased an average of 34%. Fat from meat cooked in a convection oven averaged 83% higher malonaldehyde concentration and 21% higher fluorescence compared to levels before cooking. Levels of lipid oxidation products in fat from chicken breast and leg meat were not significantly different in microwave compared to convection oven cooking; but certain secondary fluorescent products were higher in meats cooked by convection oven.     

C-Axis Oriented MOCVD YMnO3 Thin Film and Its Electrical Characteristics in MFIS FeTRAM

Yttrium manganate (YMO) thin films were prepared on SiO₂ buffered silicon as a candidate for ferroelectric transistor random access memory (FeTRAM). The films were deposited by flash evaporated MOCVD at low temperature and post annealed to crystallize the c-axis oriented hexagonal YMO phase. It is found that oxygen content and substrate temperature are major parameters determining c-axis orientation. For the electrical characteristics, P_r (remnant polarization) ～2 μ C/cm² and ? (dielectric constant) ～ 20 are obtained in Pt/YMO/Pt structures. It is also found that a top buffer layer of 30 nm ZrO₂ helps to reduce the leakage current of Pt/top buffer/YMO/SiO₂/Si stack to 10^{? 7} A/cm² and improves the C-V memory window from 0.2 V to 2 V.     

Experiments on Pore Closure During Hot Isostatic Pressing and Forging

The effect of stress on pore closure was studied by hot isostatic pressing and hot forging of sintered Al₂O₃, cubic ZrO₂, and finer-grained Al₂O₃/ZrO₂ (cubic) composite materials containing pores remnant of monosized plastic spheres. For the temperature-time conditions explored, plastic deformation was the dominant mechanism for pore shape change and closure. Namely, only pores in the highly deformable two-phase material were observed to either change shape (under uniaxial forging) or shrink (during hot isostatic pressing). Large plastic strains (0.3 to 0.6, dependent on location) were required to produce pore closure under forging conditions. At temperatures where the two-phase materials were sufficiently deformable to affect pore closure, pores close to the surface would puncture as the thin web of material separating the pore from the surface was deformed into the pore. These results are discussed in terms of the common practice of finishing by hot isostatic pressing of sintered materials.