MICROBIAL STABILIZATION OF INTERMEDIATE MOISTURE FOOD SURFACES I. CONTROL OF SURFACE PRESERVATIVE CONCENTRATION

Changing environmental conditions to which intermediate moisture foods (IMF's) are exposed during production, storage, distribution and use, are important microbial stability factors. Temperature changes result in local surface condensations leading to microbial outgrowth on the surface. An approach to improved surface stability using a high preservative surface concentration maintained by an impermeable edible food coating was developed. Permeability tests predicted that zein was an acceptable coating. Sorbic acid distribution experiments confirmed its barrier properties. Apparent diffusion coefficient was estimated between 3 and 7 × 10⁻⁹ cm²/s. These values were 150–300 times smaller than the value measured in the bulk of the IMF model food system used in this study, 10⁻⁶ cm²/s.     

ISOLATION OF INTACT TYPE V COLLAGEN FROM FISH INTRAMUSCULAR CONNECTIVE TISSUE

A purification method for intact type V collagen from fish intramuscular connective tissue was developed. Collagens were extracted with 0.5 M acetic acid from fish intramuscular connective tissue. Intact type V collagen could not be isolated by conventional salt fractionation which has been used for isolation of pepsinized collagens. Isolation was achieved by ion-exchange chromatography in the presence of 5 M urea. This is the first report on isolation of intact type V collagen from muscle tissue.     

Corrosion of Silicon Nitride Ceramics in Aqueous Hydrogen Chloride Solutions

The leaching behavior of pressureless sintered and hotpressed Si₃N₄ containing Y₂O₃, Al₂O₃, and AlN and hot isostatically pressed Si₃N₄ without additives was studied in 0.1 M to 10 M HCl aqueous solutions at 50° to 100°C. Y and Al ions contained in the grain-boundary phase dissolved in HCl solutions, but dissolution of the Si ion from the matrix was negligible. The dissolution of Y and Al ions in HCl solutions was adequately described by a surface-chemical-reaction-controlled, shrinking-core model in <1 M HCl solutions and by a diffusion-controlled, shrinking-core model in >5 M HCl solutions. The rates of dissolution of both Y and Al ions decreased as the degree of crystallinity of the grain-boundary phase increased. The fracture strength of the corroded samples linearly decreased with increasing degree of dissolution of soluble Y and Al ions.     

Dual-colour microscopy of single fluorophores bound to myosin interacting with fluorescently labelled actin using anti-Stokes fluorescence

We have refined prismless total internal reflection fluorescence microscopy with extremely low background to visualize single fluorophores attached to protein molecules interacting with a filamentous biopolymer labelled with different colour fluorophores. By using Stokes and anti-Stokes fluorescence, two different colour fluorescences from two different colour fluorophores excited with a single wavelength laser can be observed simultaneously. This microscopy was applied to visualize motor proteins, actin and myosin molecules. Single myosin molecules labelled with a tetramethylrhodamine-5-iodoacetamide interacting with a BODIPY FL-labelled actin filament, a filamentous polymer of actin molecules, were observed clearly and simultaneously in aqueous solution. Individual hydrolysis reactions of Cy3-labelled ATP by single myosin molecules and sliding of a BODIPY FL-labelled actin filament along the myosin molecules could also be observed simultaneously. Thus, this technique is useful for observing single molecular processes of proteins interacting with a biological macromolecule such as an actin filament and a DNA.     

贴近墙面移动圆柱体周围的不可压缩流体的数值仿真(英)

采用边界压力单向条件的流函数旋度方程,对在不可压缩流体中贴近墙面平行移动的圆柱体周围的流场进行了二维数值仿真．计算结果与实验结果有较高的一致性,证明了在边界压力单向条件下流函数旋度方程的有效性．     

Secretion of Mouse α-Amylase from Kluyveromyces lactis

We constructed two mouse α-amylase secretion vectors for Kluyveromyces lactis using the well-characterized signal sequence of the pGKL 128 kDa killer precursor protein. Both PHO5 and PGK expression cassettes from Saccharomyces cerevisiae directed the expression of mouse α-amylase in YPD medium at a similar level of efficiency. K. lactis transformants secreted glycosylated and non-glycosylated α-amylase into the culture medium and both species were enzymatically active. The K. lactis/S. cerevisiae shuttle secretion vector pMI6 was constructed, and K. lactis MD2/1(pMI6) secreted about four-fold more α-amylase than S. cerevisiae YNN27 harboring the same plasmid, indicating that K. lactis is an efficient host cell for the secretion and production of recombinant proteins. © 1997 John Wiley & Sons, Ltd.     

贴近墙面移动圆柱体周围的不可压缩流体的数值仿真

采用边界压力单向条件的流函数-旋度方程,对在不可压缩流体中贴近墙面平行移动的圆柱体周围的流场进行了二维数值仿真.计算结果与实验结果有较高的一致性,证明了在边界压力单向条件下流函数-旋度方程的有效性.     

Strength of Protein Gels Prepared with Microbial Transglutaminase as Related to Reaction Conditions

Influence of gelling reaction conditions on the strength of several protein gels prepared with microbial transglutaminase (TGase) was investigated. A method was developed to gel proteins and measure gel breaking strength in a micro well plate. Enzyme concentration range for maximum gel breaking strength varied from 10 to 40 units/g protein. Maxima gel breaking strengths were achieved at 50°C for SPI, caseinate and gelatin and 65°C for egg yolk and egg white proteins. Optimum pH resulting in strong gels was pH 9 for SPI, caseinate, and egg yolk, and pH 6 for gelatin and egg white. Adjusting pH was promoted in egg white the formation of ?-(γ-glutamyl)lysine crosslinks and increased its gel breaking strength.