食品防腐剂:山梨酸钾

<正> 为什么需要食品防腐剂?虽然食品加工的卫生标准已得到确立,但每年在世界各地仍有数以吨计的高质量食品因受到霉菌,酵母菌和细菌污染而被废弃。被微生物污染的食品,不但使生产商蒙受经济和形象上的损失,同时微生物在食品上产生的毒素,亦会损害消费者的健康。不过以上的问题都可通过有效的防腐方法而得到纾解,常用的防腐方法包括高温处理、过泸和添加防腐剂等。 在过去2000多年来,人类采用了不同的物质作为防腐剂,其中包括盐、醋酸和加於酒中的硫化物等。防     

Crosslinking and scission in thermooxidative degradation of PVC

Summary Crosslinking and chain scission in thermooxidative PVC degradation have been studied. Gel formation was found to give linear Charlesby-Pinner plots, consistent with the constant rate of crosslinking and scission. Similarly to thermal degradation, partial reversibility of crosslinking was observed also in oxygen.     

Investigation of the projectile atomic number dependence of the L-subshell ionization

Relative L-subshell ionization cross sections have been measured using a series of ions at a fixed collision velocity in order to study the projectile nuclear charge dependence. Thin Sm, Er, and Au targets were bombarded by ²H⁺, ⁴He⁺, ¹²C⁺, and ¹⁴N⁺ ions $\text{MeV}\text{u}$ impact energy. The cross sections were normalized to the data obtained by deuterons. The experimental results have been compared with calculations in the perturbed stationary state approximations with Coulomb deflection, binding and relativistic corrections included (CPSSR) as well as with the recent second order calculations. Particularly large discrepancies have been found for the L₂ subshell comparing the CPSSR results with the measured values. These discrepancies have been reduced significantly by the inclusion of the second order effects.     

Reversible crosslinking during thermal degradation of PVC

Summary PVC undergoes rapid crosslinking during thermal degradation. Diels-Alder addition of conjugated polyenes was proposed as a possible crosslinking mechanism by earlier authors. By the use of conditions favoring retro Diels-Alder reaction of crosslinks (treatment with maleic anhydride at elevated temperature) it was proved that crosslinks are largely reversible. Evidently Diels-Alder addition of the conjugated polyenes plays an important role in crosslinking during thermal degradation of PVC.     

Lewis acid initiated melt reactions of polystyrene and EPDM rubber

Summary In order to obtain high impact polystyrene (PS), experiments have been performed on coupling of EPDM rubber and PS in the mixing chamber of a HAAKE plastograph. Lewis acids were added to the melt and the torque increase observed by their addition proved that chemical reactions take place in the system. During the reaction, the rubber proved to be more active, it became crosslinked and/or it was coupled with the PS molecules. Only a small fraction of the PS present coupled to the rubber molecules. No significant degradation process could be detected. Mechanical properties (tensile modulus and strength) improved during the reaction. This can be interpreted by the increased solubility of the coupled rubber molecules in the continuous PS phase.     

Genetic polymorphisms and the risk of progressive renal failure in elderly Hungarian patients

The relationship between renal disease progression and genetic polymorphism of enzymes influencing endothelial function remains incompletely understood. We genotyped three cohorts of elderly Hungarian patients: 245 patients with end‐stage renal disease (ESRD) on chronic hemodialysis (HD), 88 patients with mild chronic kidney disease (CKD), and 200 healthy controls. The underlying diagnoses of renal diseases were primary glomerulonephritis, interstitial nephritis, hypertension, diabetic nephropathy, and hereditary diseases. We examined genetic polymorphisms of eight candidate genes associated with endothelial function: endothelial constitutive nitric oxide synthase (ecNOS) T‐786C, endothelin‐1 G5727T, methylenetetrahydrofolate reductase (MTHFR) C677T, paraoxonase‐1 Q192R and M55L, angiotensinogen M235T, angiotensin‐converting enzyme (ACE) I/D and angiotensin II type 1 receptor A1166C gene. Six gene polymorphisms were detected by real‐time polymerase chain reaction with melting‐point analysis, and two via allele‐specific amplification and gel electrophoresis. Control group patients were in Hardy‐Weinberg equilibrium for all tested genotypes. In ESRD patients attributed to hypertension, the endothelin gene G5727T GG genotype occurred significantly less but GT genotype more frequently (P < 0.01 for both). In ESRD patients attributed to primary glomerulonephritis, more ACE DD and less ID genotypes were found (P < 0.02 for both) than in the controls. The underlying diagnosis may modify the association of genetic polymorphism and dialysis‐dependent ESRD.     

New insight into the kinetics of diisocyanate‐alcohol reactions by high‐performance liquid chromatography and mass spectrometry

The uncatalyzed reactions of 2,4‐TDI (2,4‐ toluenediisocyanate ) and MDI (4,4 ′ ‐ diphenylmethane‐diisocyanate ) with alcohols including butan‐1‐ol, butan‐2‐ol, diethylene glycol monomethylether (DEGME) were studied by high ‐ performance liquid chromatography (HPLC) and electrospray ionization mass spectrometry (ESI‐MS). The reactions were carried out at different temperatures from 22°C to 75°C using high molar ratios of alcohols to diisocyanates. It was found that the first isocyanate group of the MDI reacts about 1.5 times faster with the alcohols than the second one. The relative reactivities of the isocyanate groups (para and ortho) of 2,4‐TDI as a function of the temperature was also deduced. From the temperature dependence of the rate constants the apparent activation energies were determined. Furthermore, the dependence of the apparent rate constant on the concentration of alcohols was also investigated and a mechanism was proposed for the reaction of diisocyanates with alcohols. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42127.     

Polymodal Transient Receptor Potential Vanilloid (TRPV) Ion Channels in Chondrogenic Cells

Mature and developing chondrocytes exist in a microenvironment where mechanical load, changes of temperature, osmolarity and acidic pH may influence cellular metabolism. Polymodal Transient Receptor Potential Vanilloid (TRPV) receptors are environmental sensors mediating responses through activation of linked intracellular signalling pathways. In chondrogenic high density cultures established from limb buds of chicken and mouse embryos, we identified TRPV1, TRPV2, TRPV3, TRPV4 and TRPV6 mRNA expression with RT-PCR. In both cultures, a switch in the expression pattern of TRPVs was observed during cartilage formation. The inhibition of TRPVs with the non-selective calcium channel blocker ruthenium red diminished chondrogenesis and caused significant inhibition of proliferation. Incubating cell cultures at 41 °C elevated the expression of TRPV1, and increased cartilage matrix production. When chondrogenic cells were exposed to mechanical load at the time of their differentiation into matrix producing chondrocytes, we detected increased mRNA levels of TRPV3. Our results demonstrate that developing chondrocytes express a full palette of TRPV channels and the switch in the expression pattern suggests differentiation stage-dependent roles of TRPVs during cartilage formation. As TRPV1 and TRPV3 expression was altered by thermal and mechanical stimuli, respectively, these are candidate channels that contribute to the transduction of environmental stimuli in chondrogenic cells.     

Genetic parameters of milk yield and composition and their relationships with alternative breeding goals

Milk records on 32,077 Holstein cows in first lactation from 1116 herds on the Quebec Dairy Herd Analysis Service between 1973 and 1983 were used to estimate heritabilities of and genetic correlations between milk, fat, protein, and carrier (water, lactose, ash) yields; fat, protein, and carrier percentages; and ratios of protein to fat and protein plus fat to carrier. The cows were daughters of 451 sires; each sire was represented by five or more daughters. Heritabilities were from .20 to .31 for yields, .59 to .61 for percentages, and .58 to .61 for ratio measures. The heritability of protein yield was considerably lower than other yield traits (.20 vs. .28 to .31). The expected effects of multiple trait selection under 10 alternative breeding goals, using different sets of relative economic values, were considered using the genetic parameter estimates. Selection under the existing pricing system (milk yield plus fat percentage differential) had similar expected genetic gains for fat and protein yields as would be achieved under goals that either gave weight to milk yield and fat yield or to milk yield and the ratio of protein plus fat to carrier. Inclusion of information on protein percentage in an index gave relative little additional genetic progress in most traits, except some increases in protein yield and protein percentage were expected to be greater.