Freezing point osmometry of milk to determine the additional water content – an issue in general quality control and German food regulation

Background  

The determination of the osmolality of aqueous samples using a freezing point osmometer is a well-established, routine laboratory method. In addition to their use in clinical and pharmaceutical laboratories, freezing point osmometers are also employed in food testing laboratories. One application is the determination of the osmolality of milk. Although cow's milk is a natural product whose water content is approximately 87%, the osmolality of milk is a significant value when the milk is collected from a larger population of animals. This value is used in milk processing to control the water content, based on the German Food Control Regulations for Milk.     

Rapid freeze-quench 57Fe Mössbauer spectroscopy: monitoring changes of an iron-containing active site during a biochemical reaction

Nuclear gamma resonance spectroscopy, also known as M?ssbauer spectroscopy, is a technique that probes transitions between the nuclear ground state and a low-lying nuclear excited state. The nucleus most amenable to M?ssbauer spectroscopy is 57Fe, and 57Fe M?ssbauer spectroscopy provides detailed information about the chemical environment and electronic structure of iron. Iron is by far the most structurally and functionally diverse metal ion in biology, and 57Fe M?ssbauer spectroscopy has played an important role in the elucidation of its biochemistry. In this article, we give a brief introduction to the technique and then focus on two recent exciting developments pertaining to the application of 57Fe M?ssbauer spectroscopy in biochemistry. The first is the use of the rapid freeze-quench method in conjunction with M?ssbauer spectroscopy to monitor changes at the Fe site during a biochemical reaction. This method has allowed for trapping and subsequent detailed spectroscopic characterization of reactive intermediates and thus has provided unique insight into the reaction mechanisms of Fe-containing enzymes. We outline the methodology using two examples: (1) oxygen activation by the non-heme diiron enzymes and (2) oxygen activation by taurine:alpha-ketoglutarate dioxygenase (TauD). The second development concerns the calculation of M?ssbauer parameters using density functional theory (DFT) methods. By using the example of TauD, we show that comparison of experimental M?ssbauer parameters with those obtained from calculations on model systems can be used to provide insight into the structure of a reaction intermediate.     

On nonorientation drawing of polyethyleneterephthalate (PET)

Summary The drawing behaviour of amorphous PET-films in the temperature interval between room temperature and 160 °C has been investigated in the present paper. Measurements of stress-strain behaviour, of birefringence, of density, of heat of fusion, of melting point, of glass temperature, of crystal structure and of superstructure prove that drawing temperature and drawing velocity posses a determining influence on forming morphology and technological properties. Within the temperature interval from 85 to 105 °C using low drawing velocities a drawing process of films without any molecular orientation is observed.

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Zusammenfassung Das Verstreckverhalten von amorphen PET-Folien im Temperaturbereich von Raumtemperatur bis 160 °C wird in der vorliegenden Arbeit untersucht. Messungen des Spannungs-Dehnungs-Verhaltens, der Doppelbrechung, der Dichte, der Schmelzenthalpie, des Schmelzpunktes, der Einfriertemperatur und der Kristall- und Überstruktur zeigen, daß Verstrecktemperatur und Verstreckgeschwindigkeit einen entscheidenden Einfluß auf die entstehende Morphologie und die technologischen Eigenschaften besitzen. Im Temperaturbereich zwischen 85 und 105 °C beobachtet man bei kleinen Verstreckgeschwindigkeiten eine Verstreckung der Folien ohne molekulare Orientierung. nt]mis|With 13 figures and 1 table