EVALUATION OF BIOGENIC AMINES FORMATION BY PROTEOLYTIC ENTEROCOCCI STRAINS ISOLATED FROM RAW DROMEDARY MILKS FROM SOUTHERN ALGERIA

Twenty-three strains of lactic acid enterococci isolated from dromedary raw milks in Southern Algeria were investigated for their proteolytic activity and ability to produce biogenic amines by decarboxylating amino acids: histidine, tyrosine and ornithine. All strains tested displayed proteolytic activities, but none of them were able to produce detectable biogenic amines in the usual adequate laboratory media, namely, Joosten and Northolt medium and Leuschner medium. Polymerase chain reaction experiments indicate a positive correlation between the absence of the hdc and odc genes and the lack of histamine and putrescine production for all tested strains. By contrast, all strains appeared to possess tdc gene, but no correlation was found with a negative expression of tyrosine decarboxylase.

PRACTICAL APPLICATIONS

In foods, biogenic amines are mainly generated by decarboxylation of the corresponding amino acids through substrate-specific enzymes of the microorganisms present in this environment, particularly histidine, tyrosine, lysine, ornithine and arginine, and the capability of enterococci and some other lactic acid bacteria to produce biogenic amines has been described. For this purpose, several qualitative and quantitative methods to determine biogenic amines production by these microorganisms have been developed. There is great interest to identify and to characterize the bacteria strains intended for an industrial use and to verify if they are potentially able to produce biogenic amines in order to prevent it's synthesis and limit the poisoning risk.     

循环荷载下非饱和结构性黄土的损伤模型

在边界面弹塑性模型基础上,借助胶结体损伤理论与非饱和土力学,提出一个可以描述循环荷载作用下非饱和黄土力学特性的弹塑性本构模型.在损伤模型中,定义胶结体弹性衰减规律,将结构损伤与应变增量的绝对累计值联系起来;并利用土的持水曲线建立常含水量下吸力与土体应力之间的耦合作用关系.通过与循环三轴试验结果的比较,表明该模型能够较好地模拟非饱和黄土在循环荷载作用下的力学特性.     

Angular Position Controller and Its Design Model Verification for the Electro-Hydraulic Servo Control System

The angular position controller is system （EHSAS） to control the output of the rotary applied to electro-hydraulic servo actuator actuator. It works as a compensator based on the frequency response of the EHSAS. Its design model is verified on the state-space model of EHSAS by using simulation program SIMULINK. Real data used to test the system. Simulation results give a good agreement for the controller and also for the state-space model.