The high-resolution time-of-flight spectrometer TOFTOF

The TOFTOF spectrometer is a multi-disc chopper time-of-flight spectrometer for cold neutrons at the research neutron source Heinz Maier-Leibnitz (FRM II). After five reactor cycles of routine operation the characteristics of the instrument are reported in this article. The spectrometer features an excellent signal to background ratio due to its remote position in the neutron guide hall, an elaborated shielding concept and an s-shaped curved primary neutron guide which acts i.a. as a neutron velocity filter. The spectrometer is fed with neutrons from the undermoderated cold neutron source of the FRM II leading to a total neutron flux of 10¹⁰n/cm²/s in the continuous white beam at the sample position distributed over a continuous and particularly broad wavelength spectrum. A high energy resolution is achieved by the use of high speed chopper discs made of carbon-fiber-reinforced plastic. In the combination of intensity, resolution and signal to background ratio the spectrometer offers new scientific prospects in the fields of inelastic and quasielastic neutron scattering.     

Effects of low-voltage electrical stimulation during exsanguination on meat quality and display colour stability

Five steers from each of four slaughter groups were randomly assigned to a low-voltage electrical stimulation (LVES) treatment during exsanguination (within 5 min after stunning) and five served as controls (C). LVES consisted of 50V of 60 Hz alternating current (1 s on and 1 s off for 2 min).

At 28 h, LVES longissimus (LM) was lighter in colour, softer, coarser in texture and tended to have lower marbling estimates than C. LVES LM steaks were lighter red at 0 and 1 days, but more discoloured at 5 days, of display than C steaks. Both the deep (DSM) and superficial (SSM) portions of LVES semimembranosus (SM) steaks were lighter red at 0 and 1 days of display than C steaks. Water-holding capacity for LVES LM and DSM steaks was lower than for C steaks. A trained sensory panel found LVES LM steaks to be less juicy and less tender than C steaks. Also, LVES LM steaks had greater cooking losses than C steaks in two of the four slaughter groups. We conclude that LVES during exsanguination, coupled with relatively slow initial chilling, may be detrimental to muscle quality.     

Secondary structure of bovine alphaS2-casein: theoretical and experimental approaches

Circular dichroism and Fourier transform infrared spectroscopy of bovine alphaS2-casein both report a 24 to 32% content of alpha-helix. A consensus of sequence based predictions for alpha-helix suggests a Lys77-Gln91 helix within the sequence (Ser61-Arg125). This motif is repeated at (Ser143-Leu207), and this region contains a longer Thr145-Leu177 predicted alpha-helix. A short, seven-member alpha-helix may also organize the N-terminal peptide that precedes the first phosphoserine [-Srp-]3 cluster. As was found for other caseins studied by these spectroscopic methods, a high degree of extended beta-sheet (approximately 30%) and turns (25 to 30%) are predicted for alphaS2-casein.     

Cholesterol oxides I. Isolation and determination of some cholesterol oxidation products

Cholesterol in purified triolein was subjected to saponification by two procedures employing hot alkali and was found to give rise to oxidation products despite precautions. The isomeric 5,6-epoxycholestanols and 7-hydroxycholesterols were stable under saponification conditions, but 7-ketocholesterol and 6-ketocholestanol were destroyed by hot alkali. The oxidation of cholesterol during saponification was not inhibited by the addition of BHT. The determination of a number of standard cholesterol oxides by direct on-column GC was demonstrated with good resolution. Their order of elution was different from that of the TMS-derivatized products.     

Secondary structural studies of bovine caseins: temperature dependence of β-casein structure as analyzed by circular dichroism and FTIR spectroscopy and correlation with micellization

To obtain a molecular basis for the similarities and dissimilarities in the functional, chemical, and biochemical properties between β-casein and the other caseins, three-dimensional models have been presented. Secondary structural prediction algorithms and molecular modeling techniques were used to predict β-casein structure. The secondary structure of bovine β-casein was re-examined using Fourier transform infrared and circular dichroism spectroscopies to test these predictions. Both methods predict a range of secondary structures for β-casein (28–32% turns, 32–34% extended) at 25°C. These elements were highly stable from 5 to 70°C as viewed by circular dichroism. More flexible conformational elements, tentatively identified as loops, helix and short segments of polyproline II, were influenced by temperature, increasing with elevated temperatures. Another view is that as temperature decreases, these elements are lost (cold denaturation). Several distinct transitions were observed by circular dichroism at 10, 33 and 41°C, and another transition, extrapolated to occur at 78°C. Calculations from analytical ultracentrifugation indicate that the 10, 33 and 41°C transitions occur primarily in the monomeric form of the protein. As β-casein polymers are formed, and increase in size, the transitions at higher temperature may reflect changes in the more flexible conformational elements as they adjust to changes in surface charge during polymer formation. The transition at 10°C may represent an actual general conformational change or cold denaturation. Over the range of temperatures studied, the sheet and turn areas remain relatively constant, perhaps forming a supporting hydrophobic core for the monomers within the micelle-like polymer. This interpretation is in accord with the known properties of β-casein, and those predicted from molecular modeling.     

Effects of anaphylaxis mediators on partitioned pulmonary vascular resistance during ragweed shock in dogs

We examined the effect of anaphylactic shock on the longitudinal distribution of pulmonary vascular resistance (PVR) in ragweed-sensitized dogs in which PVR was partitioned into an upstream arterial component (Rus) and a downstream venous and capillary component (Rds). We also assessed whether Rus and Rds would be reduced by pretreatment with histamine H1- and H2-receptor blocking agents and with cyclooxygenase and lipoxygenase pathway inhibitors. Anesthetized animals were examined on separate occasions 3 wk apart in which one of the treatments was randomly given. The pulmonary arterial occlusion technique was used to determine segmental pressure drops. During ragweed challenge, PVR increased approximately 4 times compared with the preshock value (3.04 vs. 12. 07 mmHg . l-1 . min; P < 0.05). Although both Rus and Rds increased postshock, the greatest relative increase occurred in Rds. None of the treatments reduced partitioned resistances compared with no treatment. Our results show that, under conditions of anaphylactic shock, increases in Rus and Rds could not be ascribed to release of histamine or products of the cyclooxygenase and lipoxygenase pathways.