Problems,assumptions and solutions in locomotive design,traction and operational studies

Railway Engineering Science - Locomotive design is a highly complex task that requires the use of systems engineering that depends upon knowledge from a range of disciplines and is strongly...     

Characterization of the chemistry, biochemistry and volatile profile of Kuflu cheese, a mould-ripened variety

The chemistry, biochemistry and volatile compounds of Kuflu cheese, a Turkish mould-ripened variety were studied. A total of 29 samples were analysed and the titratable acidity, moisture, salt-in-moisture, fat-in-dry matter and total protein contents (as mean values) were 0.96%, 49.97%, 7.49%, 12.18% and 37.84%, respectively, and the pH of the cheeses was 6.29. Indices of proteolysis (i.e., the levels of pH 4.6- and trichloroacetic acid-soluble nitrogen) were high; however, these values were lower than those of other Blue cheeses probably due to proportionally higher levels of total nitrogen and salt-in-moisture in Kuflu cheese samples. Urea-polyacrylamide gel electrophoresis of the pH 4.6-insoluble fractions of the cheeses showed that both α_s1- and β-caseins were extensively degraded, but β-casein was less degraded than α_s1-casein. RP-HPLC peptide profiles of the pH 4.6-soluble fractions from Kuflu cheeses showed that some minor quantitative differences were found between the samples, while peptide profiles of the samples were qualitatively similar. One hundred and thirty-eight compounds were identified in the volatile fractions of Kuflu cheese by gas chromatography-mass spectrometry (GC-MS) using a solid-phase microextraction technique. Ketones and alcohols were the principal class of volatile components in Kuflu cheeses, and terpenes and sulphur compounds were found at substantial levels in the majority of the samples, but aldehydes and lactones were present at low levels. The RP-HPLC and GC-MS data were analysed by principal component analysis based on their peptide and volatile profiles, respectively. Kuflu cheeses obtained from different markets had some differences in terms of chemical composition, proteolysis and patterns of aroma compounds.     

Molecular Baskets in Supercritical CO(2)

Calixarenes are synthetic macrocyclic compounds, described as "molecular baskets" as they possess high ionophoric selectivity and form inclusion complexes with many important ionic guests. In our initial work, hexameric and tetrameric tert-butylcalixarenes, unfunctionalized at the lower rim, are shown to be separable on a diol column using supercritical fluid chromatography with methanol/chloroform-modified CO(2) as mobile phase. The variation in capacity factors for these calixarenes was studied as a function of modifier composition. However, the solubility of these molecular baskets in unmodified supercritical CO(2) is enhanced by fluorination at the upper rim. For example, when p-allylcalix[4]arene is derivatized by a thiol-ene addition reaction with heptadecafluorodecanethiol, CF(3)(CF(2))(7)(CH(2))(2)SH, a solubility of >0.12 mol L(-)(1) in supercritical CO(2) is measured for the p-heptadecafluorodecylthio-n-propylcalix[4]arene at 60 °C and 200 atm. However, subsequent lower rim functionalization to form the tetrahydroxamate derivative, while reducing the solubility, allows supercritical fluid extraction of Fe(III) by the fluorinated calix[4]arene ligands to be studied as a function of temperature and pressure and monitored using UV/visible and atomic absorption spectrometry. In particular, the visible absorption spectra obtained for the extracted Fe(III)-calix[4]arene tetrahydroxamate complex, collected in dimethyl sulfoxide, are indicative of octahedral Fe(III) complexation in a manner similar to that displayed by water-soluble siderophores. Studies on the efficiency and selectivity of Fe(III) extraction are also reported.     

Influence of emulsifying salts on the textural properties of nonfat process cheese made from direct acid cheese bases

The objective of this study was to investigate the influence of several types of emulsifying salts (ES) on the texture of nonfat process cheese (NFPC). Improperly produced nonfat cheese tends to exhibit several problems upon baking including stickiness, insufficient or excessive melt, pale color upon cooling, formation of a dry skin (skinning) often leading to dark blistering, and chewy texture. These attributes are due to the strength and number of interactions between and among casein molecules. We propose to disrupt these interactions by using suitable emulsifying salts (ES). These ES chelate Ca and disperse caseins. Stirred curd cheese bases were made from skim milk using direct acidification with lactic acid to pH values 5.0, 5.2, and 5.4, and ripened for 1 d. Various levels of trisodium citrate (TSC; 0.5, 1, 1.5, 2, 2.5, 3, and 5%), disodium phosphate (DSP; 1, 2, 3, and 4%), or trisodium phosphate (TSP; 1, 2, 3, and 4%) were blended with the nonfat cheese base. Cheese, ES, and water were weighed into a steel container, which was placed in a waterbath at 98°C and then stirred using an overhead stirrer for 9 min. Molten cheese was poured into plastic containers, sealed, and stored at 4°C for 7 d before analysis. Texture and melting properties were determined using texture profile analysis and the UW-Melt-profiler. The pH 5.2 and 5.4 cheese bases were sticky during manufacture and had a pale straw-like color, whereas the pH 5.0 curd was white. Total calcium contents were approximately 400, 185, and 139 mg/100 g for pH 5.4, 5.2, and 5.0 cheeses, respectively. Addition of DSP resulted in NFPC with the lowest extent of flow, and crystal formation was apparent at DSP levels above 2%. The NFPC manufactured from the pH 5.0 base and using TSP had reduced melt and increased stickiness, whereas melt was significantly increased and stickiness was reduced in NFPC made with pH 5.4 base and TSP. However, for NFPC made from the pH 5.4 cheese and with 1% TSP, the pH value was >6.20 and crystals were observed within a few days. Use of TSC increased extent of flow up to a maximum with the addition of 2% ES for all 3 types of cheese bases. Addition of high levels of TSC to the pH 5.2 and 5.4 cheese bases resulted in increased stickiness. Similar pH trends for attributes such as extent of flow, hardness, and adhesiveness were observed for both phosphate ES but no consistent pH trends were observed for the NFPC made with TSC. These initial trials suggest that the pH 5.0 cheese base was promising for further research and scale-up to pilot-scale process cheese making, because cheeses had a creamy color, reasonable melt, and did not have high adhesiveness when TSC was used as the ES. However, the acid whey produced from the pH 5.0 curd could be a concern.     

Evidence of a relationship between autolysis of starter bacteria and lipolysis in cheddar cheese during ripening

Cell viability, autolysis and lipolysis were studied in Cheddar cheese made using Lactococcus lactis subsp. cremoris AM2 or Lactococcus lactis subsp. cremoris HP. Cheddar cheese was made in triplicate over a 3 month period and ripened for 238 days at 8 degrees C. Cell viability in cheese was lower for AM2 (a non-bitter strain) than for strain HP (a bitter strain). Autolysis, monitored by the level of the intracellular marker enzyme, lactate dehydrogenase (EC 1.1.1.27) in cheese 'juice' extracted by hydraulic pressure, was much greater in the cheese made using AM2 than that made with HP. Lipolysis was determined by the increase during ripening of individual free fatty acids (FFA) from butyric (C4:0) to linolenic acid (C18:3) measured using a high performance liquid chromatographic technique. Levels of individual FFA from butyric (C4:0) to linolenic (C18:3) acids increased significantly (P<0.05) during ripening in cheeses made with either starter culture. Palmitic (C16:0) and oleic (C18:1) acids were the most abundant FFA throughout ripening in all cheeses. Levels of caprylic (C8:0), myristic (C14:0), palmitic (C16:0) and stearic (C18:0) acids were significantly higher (P<0.05) in cheeses manufactured with Lc. lactis subsp. cremoris AM2 than in cheeses manufactured with Lc. lactis subsp. cremoris HP. Differences in levels of lipolysis between strains was not due to differences in the specific lipolytic or esterolytic activities in cell free extracts of the strains as measured by activity on triolein (lipase) and p-nitrophenylbutyrate (esterase) substrates. Therefore, evidence is provided for a relationship between the extent of starter cell autolysis and the level of lipolysis during Cheddar cheese ripening.     

Phytase activity in sourdough lactic acid bacteria: purification and characterization of a phytase from Lactobacillus sanfranciscensis CB1

The phytase activity of 12 species of sourdough lactic acid bacteria was screened. It was intracellular only, largely distributed among the species and strains of Lactobacillus sanfranciscensis possessed the highest levels of activity. A monomeric ca. 50-kDa phytase was purified to homogeneity from L. sanfranciscensis CB1 by three chromatographic steps. L. sanfranciscensis CB1 exhibited the highest hydrolysing activity on Na-phytate after reaching the stationary phase of growth (ca. 12 h). Cells cultivated in the presence of maltose and fructose showed an increase of the phytase activity of ca. 35% with respect to the other carbon sources used. The phytase was optimally active at pH 4.0 and 45 degrees C. The enzyme was strongly inhibited by 2 mM of phenylmethylsulfonyl fluoride (PMSF), and 2 mM Hg(2+) and Fe(2+). It had a pI of ca. 5.0. The substrate specificity was dependent on the type of phosphate ester; a very low activity was detected on alpha-D-glucose-1-phosphate and D-fructose-6- and 1,6-phosphate, while the highest hydrolysis was found towards adenosine-5'-tri-, di- and mono-phosphate. Compared to these substrates, the activity on Na-phytate was also relevant. The enzyme was thermo-stable after exposure to 70 degrees C for 30 min; the D value calculated at 80 degrees C was ca. 10 min. As shown by the Central Composite Design (CCD) applied to study the individual and interactive effects of pH, temperature and NaCl, acidic conditions and elevated temperatures were indispensable for the enzyme adaptation to high NaCl concentrations. L. sanfranciscensis CB1 cells or the correspondent cytoplasmic extract were used to ferment a sourdough for 8 h at 37 degrees C; a marked decreased (64-74%) of the Na-phytate concentration was found compared with the unstarted dough. The sourdough started with L. sanfranciscensis CB1 cells was re-used for several times and the phytase activity was maintained to a considerable level.     

False cyanide formation during drinking water sample preservation and storage

Carefully controlled bench-scale and on-site experiments demonstrated that cyanide can form in the treated drinking water sample container during preservation and storage. In the bench-scale experiment, treated tap water samples were collected on 20 days over six months. The tap water samples were split and some of the splits were spiked with formaldehyde, a known ozone disinfection byproduct, held for three hours and tested for cyanide. Then they were preserved and held for 2-10 days. None of the 69 initial samples had cyanide detects, but 22 of 49 formaldehyde-spiked samples and three of the 20 unspiked samples developed detectable cyanide concentrations during storage. In the on-site experiment, six samples were collected at a finished water tap at an ozone/chloramination treatment plant over three days. Each sample was split, and a portion was spiked with formaldehyde. Each portion was analyzed in triplicate after three different procedures: (1) immediately distilled on-site, (2) stabilized on-site in a distillation tube and distilled back at the laboratory several days later, or (3) following the conventional procedure of preserving the sample to pH > 12 in a container and distilling the sample back at the laboratory. Only the samples handled in the conventional way had detectable amounts of cyanide. Both experiments demonstrated that cyanide can form during conventional preservation and storage, and it is likely that the cyanide detected for this treated drinking water was formed in the sample container as a consequence of the preservation and storage conditions.     

Peptidolytic,esterolytic and amino acid catabolic activities of selected bacterial strains from the surface of smear cheese

Enzymes produced by bacteria present on the surface of smear cheeses play essential roles in flavour development during cheese ripening. In this study, strains including brevibacteria, corynebacteria, staphylococci and brachybacteria, from the surface of two smear cheese (Tilsit and Gubeen) were screened for a range of enzyme activities including aminopeptidase (substrates: Leu-pNA and His-pNA), dipeptidase (Met-Ala, Ala-Met, Pro-Ala, His-Leu and Pro-Leu), tripeptidase (Phe-Gly-Gly, Gly-Gly-Gly and Leu-Ala- Pro), esterase (beta-naphthyl butyrate, beta-naphthyl caprate and beta-naphthyl palmitate). L-methionine aminotransferase and cystathionine lyase activities. There were marked differences in the activities observed between different bacteria studied. Brachybacteria showed low activity on all substrates assayed. There was no consistency in activities within groups of related bacteria. For example, Staphylococcus equorum 14 showed higher activity than S. equorum 6 on all the substrates tested. Among the corynebacteria, Coryebacterium ammoniagenes CA8 had greatest aminopeptidase, esterase and cystathionine lyase activity while C. casei B showed more di- and tri-peptidase activity. It was noted that individual bacteria displayed similar activities on all three esterase substrates, i.e., the chain length of the fatty acid did not appear to affect activity. L-Methionine aminotransferase activity was observed in only one strain (S. equorm 14) whereas all strains had cystathionine lyase activity.