High-pressure-induced changes in bovine milk: a review

High-pressure (HP) treatment of food products is a novel processing technique during which the product is treated in a vessel of suitable strength at a high pressure, generally in the range 100–1000 MPa. As a result, several constituents and properties of the treated product are altered. HP-induced changes in the constituents and properties of milk are arguably among the most extensive of the range of food products studied to date. HP treatment of milk induces solubilization of minerals associated with the casein micelles, denatures whey proteins and, depending on pressure, can either induce aggregation or disruption of the casein micelles. These HP-induced changes in milk constituents affect the properties of the milk; cheesemaking properties of milk can be enhanced considerably, indicating potential application of HP treatment in this area; furthermore, encouraging results have also been reported for HP treatment of milk prior to yogurt manufacture. HP treatment of milk also affects its microflora; however, considerable variation in baroresistance between bacterial species and strains exists. Further applied research appears warranted to establish the full commercial potential of HP treatment of milk.     

Fermentation of specially formulated milk with single strains of bifidobacteria

A number of strains of bifidobacteria have been used to ferment milk to a yoghurt-like product. The milk used for fermentation was fortified with whey protein and threonine. It was prepared by mixing skimmed milk and cheddar cheese whey which had been concentrated using ultrafiltration membranes which allowed lactose to permeate. A 2 percent inoculum was used, and fermentation was carried out at 37° C overnight. The resulting products resembled voghurt, having good consistency. 'walnutty' aroma (acetaldehyde). and pleasant acidity.     

Variation in the Levels of Sodium and Other Minerals of Nutritional Importance in Louisiana Oysters (Crassostrea Virginica)

The concentrations of nine individual minerals were determined in oysters harvested over a 10-month period. Significant (p > 0.01) monthly variations were observed in the levels of all the minerals determined. Salinity of the growing waters was significantly (p > 0.01) correlated to levels of sodium, magnesium, iron, chromium, and nickel in the oysters. Levels of potassium, copper and chromium were related to pH. Zinc and iron levels were correlated (p > 0.05) to water temperature. In this study, variations in the mineral content of oysters were often directly influenced by the growing water. This variation must be taken into consideration, should sodium labeling be required for fresh oysters.     

Adsorption of Gas-Phase Phenanthrene on Atmospheric Water and Ice Films

The adsorption of gas-phase phenanthrene on atmospheric water and ice films was investigated in a flow-tube reactor with a view to understanding the processing of semi-volatile organic compounds by fog and snow. Air-water (ice) interface partition constants were obtained by measuring the mass uptake of phenanthrene vapor on thin water and ice films with varying thickness. Adsorption enthalpies and entropies were obtained from the temperature dependence of the interfacial partition constants. The surface adsorption is the predominant mechanism for the uptake of phenanthrene in water and ice films with small film thickness or at low temperature. The adsorption of phenanthrene to ice resembles that to sub-cooled water and there's no significant difference between the adsorption of phenanthrene to water and that to quasi liquid layer (QLL) if we take into account the uncertainties on the thermodynamic quantities measured. Molecular dynamics simulations of phenanthrene at air/water and air/ice interfaces support these experimental observations. The interfacial air-water and air-ice partition constants of phenanthrene increased greatly in the presence of surface-active substances, indicating that surface active materials effectively enhanced the uptake of organic compounds by atmospheric water and ice films.     

挤压态AZ81镁合金的热压缩变形行为

在温度为320～440℃、应变率为0.001～1s-1的变形条件下,采用Gleeble-1500热模拟机对挤压态AZ81镁合金的热压缩变形行为进行研究.结果表明挤压态AZ81镁合金的流变应力随变形温度的升高而降低,随应变率的升高而升高,且随应变的增加,流动应力很快达到峰值,然后逐渐降低并趋于稳定.为评价挤压态AZ81镁合金在热模压成形过程中流动应力,结合Arrhenius方程并引入Zener-Hollomon参数,对流动应力做出相应的修正,根据修正后的流动应力构建挤压态AZ81镁合金流变应力高温变形本构模型.模拟结果表明该模型的应力预测值与试验值吻合较好,计算精度较高,为后续的模压近／净终成形工艺参数的制定提供一定的理论参考.