Effect of Surface Tungstate W<Superscript>5+</Superscript> Species on the Metathesis Activity of W-Doped Spherical Silica Catalysts

The high surface area W-doped spherical silica (SSP) catalysts were prepared with different sequences of W and Si addition (W–Si_(Alt), Si₁–W_2, and W₁–Si₂) by the sol–gel method with CTAB as a structure directing agent and compared with the impregnated one (W/SSP). All the catalysts exhibited high specific surface area (～?1100 m² g^?1) with a closely perfect spherical shape. The presence of surface/sub-surface tungstate W⁵⁺ species, crystalline bulk WO₃, and tetrahedral tungsten oxide species on the prepared catalysts was investigated by means of X-ray photoelectron spectroscopy depth profile analysis, X-ray diffraction, and Raman spectroscopy. Without in situ reduction by the reactants/products, tungstate W⁵⁺ species was found on the top surface of the as-prepared W–Si_(Alt) whereas for the Si₁–W₂, W/SSP, and W₁–Si₂, the W⁵⁺ appeared only on the sub-surface of the catalysts after 5 and 15 s Ar⁺ etching. The abundance of surface W⁵⁺ species is suggested to facilitate the establishment of the active tungsten carbenes and was correlated well to the catalytic activity in propene metathesis. The surface W⁵⁺-activity relationship of the WO₃-based metathesis catalysts is useful especially when the catalyst activity did not depend solely on the amount of active tetrahedral coordinated tungsten oxides.     

Lipid oxidation and fishy odour development in protein hydrolysate from Nile tilapia (Oreochromis niloticus) muscle as affected by freshness and antioxidants

Lipid oxidation and fishy odour development in protein hydrolysate from fresh and ice-stored Nile tilapia (Oreochromis niloticus) were investigated. During iced storage of 18 days, heme iron content decreased with a concomitant increase in non-heme iron content (P < 0.05). Peroxide value (PV) and thiobarbituric acid reactive substances (TBARS) values increased. Phospholipid content decreased with a corresponding increase in free fatty acid content. The results suggested that lipid hydrolysis and oxidation took place during storage. When protein hydrolysates were produced from fresh and 18 days ice-stored Nile tilapia muscle, higher lipid oxidation and fishy odour/flavour along with higher amount volatile compounds were obtained in hydrolysate for unfresh sample (P < 0.05). However, the addition of mixed antioxidants during hydrolysis process markedly lowered lipid oxidation, b^∗, ΔC^∗, ΔE^∗ values, fishy odour/flavour as well as the formation of volatile compounds in the resulting hydrolysates prepared from both fresh and unfresh samples. Therefore, hydrolysate from Nile tilapia muscle with reduced fishy odour and lighter colour could be prepared by using fresh fish and incorporation of mixed antioxidants during hydrolysis.     

Optimization of enzymatic hydrolysis of fish soluble concentrate by commercial proteases

Fish protein hydrolysate (FPH) was produced from fish soluble concentrate (FSC), a by-product from canned fish industry, by using Flavourzyme™ and Kojizyme™. Hydrolysis conditions were optimized by using a response surface methodology (RSM). The model equations were proposed with regard to the effects of temperature (T), time (t), and enzyme concentration (E) on the degree of hydrolysis (DH). The optimum values for Flavourzyme™ concentration, substrate concentration, temperature, and hydrolysis time were found to be 50 LAPU/g protein, 20% (w/w), 45 °C, and 6 h, respectively (LAPU; Leucine Aminopeptidase Unit). While those values for Kojizyme™ were 40 LAPU/g protein, 20% (w/w), 50 °C, and 6 h, respectively. Kojizyme™ enhanced the formation of some bitter-taste amino acids such as tryptophan during hydrolysis process whereas Flavourzyme™ did not. The spray-dried FPH produced with Flavourzyme™ contained high protein content (66%). The bitterness of FPH was less than that of 1 ppm caffeine solution.     

Autolysis of goatfish (Mulloidichthysmartinicus) mince: Characterisation and effect of washing and skin inclusion

Autolysis of goatfish mince and washed mince incubated at different temperatures (30–70 °C) was investigated. The highest autolytic activity was generally observed in mince and washed mince at 60 °C as evidenced by the highest trichloroacetic acid (TCA) soluble peptide content and the greatest disappearance of myosin heavy chains (MHCs). Autolysis of both mince and washed mince was maximised at pH 4, and lower autolytic activity was observed at pH 7. trans-epoxysuccinyl-l-leucyl-amido (4-guanidino) butane (E-64) showed the greatest inhibition of autolysis at pH 4, showing that at least one cysteine protease was active in goatfish muscle. Nevertheless, soybean trypsin inhibitor effectively inhibited the autolysis at neutral pH (pH 7), suggesting that goatfish muscle also contained at least one serine protease. Generally, autolysis of mince was more pronounced than that of washed mince, indicating that washing could lower the autolytic activity of mince. In the presence of skin, a higher autolysis was obtained with the goatfish mince. Therefore, both sarcoplasmic and myofibril-associated proteases in muscle as well as the contamination of skin likely contributed to the degradation of muscle proteins of goatfish.     

Thermal properties and heat-induced aggregation of natural actomyosin extracted from goatfish (Mulloidichthys martinicus) muscle as influenced by iced storage

Thermal properties and aggregation of natural actomyosin (NAM) extracted from fresh and 9 days ice-stored goatfish were comparatively studied. Myosin of fresh goatfish had the higher thermal stability than that of ice-stored counterpart as indicated by the higher maximum transition temperature (T_max). Additionally, the thermal inactivation rate constant (K_D) of Ca²⁺-ATPase in NAM from fresh goatfish was lower than that of ice-stored counterpart when incubated at the temperature range of 20–40 °C, indicating the lower thermal stability of the latter NAM. NAM from fresh goatfish exhibited the higher turbidity, surface hydrophobicity and disulfide bond formation than did NAM of iced-stored sample when heated at temperature from 35 to 75 °C, suggesting the higher extent of aggregation of the former. However, goatfish NAM showed the lower extent of heat-induced aggregation than did bigeye snapper NAM. As visualized by transmission electron microscopy, network strands of aggregates from bigeye snapper NAM were finer and more uniform than those from goatfish. NAM from goatfish stored in ice showed the lower extent of heat-induced aggregation than did NAM from fresh counterpart. Therefore, heat-induced aggregation of goatfish muscle proteins was governed by freshness.     

The molecular mechanism of the termination of insect diapause, part 1: A timer protein, TIME-EA4, in the diapause eggs of the silkworm Bombyx mori is a metallo-glycoprotein

TIME-EA4 is an ATPase that measures time intervals, functioning as a diapause duration clock in diapause eggs of the silkworm, Bombyx mori. Characterization of the primary and higher structures of the TIME-EA4 would be desirable to clarify the mechanism by which the protein measures the time intervals. In our current studies, the whole sequence of TIME-EA4 has been established as that of a metallo-glycoprotein by combinational means involving peptide sequence analysis, nano-HPLC-ESI-Q-TOF-MS and MS/MS, and cDNA dictation. The amino acid sequence of TIME-EA4 showed 46-55 % homology with the reported proteins of the Cu,Zn-SOD (superoxide dismutase) family; in particular, the SOD active site (core domain) includes metal-binding amino acid ligands and a disulfide bond, and these structures are completely identical in Bombyx SOD, bovine SOD, and TIME-EA4 proteins. We found, however, that TIME-EA4 contains one more copper ion than other SODs, as was proven under neutral nondenaturing conditions. ESI mass spectrometry revealed that the timer function was not in the SOD core domain. In addition, TIME-EA4 has an attached sugar chain, which is indispensable to its functioning as a timer protein.     

Effect of pretreatment on lipid oxidation and fishy odour development in protein hydrolysates from the muscle of Indian mackerel

Impact of different pretreatments on chemical compositions of Indian mackerel mince was studied. Mince prepared using washing/membrane removal/alkaline solubilisation process (W–MR–Al) contained the lowest remaining myoglobin and haem iron content and also showed the lowest total lipid and phospholipid contents. When mince and W–MR–Al were hydrolysed using Alcalase for up to 120 min, a higher degree of hydrolysis (DH) was found in W–MR–Al after 30 min of hydrolysis. Furthermore, hydrolysate from W–MR–Al had lower peroxide value (PV), thiobarbituric acid reactive substances (TBARS) and non-haem iron content throughout hydrolysis period (P < 0.05). When hydrolysate powder produced from mince and W–MR–Al (0–0.3% w/v) were fortified in milk, the former resulted in the lower likeness score (P < 0.05) at all levels used. The addition of the latter, for up to 0.2%, had no effect on likeness of all attributes, compared with milk without fortification (P > 0.05). Therefore, the appropriate pretreatment of mince yielded hydrolysate with lower fishy odour.     

A highly selective electrochemical sensor for l‐tryptophan based on a screen‐printed carbon electrode modified with poly‐p‐phenylenediamine and CdS quantum dots

A new highly selective electrochemical sensor for the determination of l ‐tryptophan was proposed by modifying the surface of screen‐printed carbon electrodes (SPCEs). The surface of SPCE was firstly modified by electropolymerization of p‐phenylenediamine (PPD). The polymer film was then covalently linked with cysteamine capped cadmium sulfide quantum dots (Cys‐CdS QDs) by using glutaraldehyde (GA) as a cross‐linker resulted in an organic–inorganic hybrid composite film (QDs/GA/PPD/SPCE). The modified electrode was applied as a working electrode for detecting various amino acids. It was found that the modified electrode gave an electrochemical response selectively to l ‐tryptophan over other amino acids. The experimental parameters, including pH of solution, buffer types, electropolymerization cycles, scan rate, and accumulation time, were studied and optimized. The proposed sensor can be used to detect l ‐tryptophan with a low detection limit of 14.74 µmol L^?1 with good precision and the relative standard deviation less than 3.7%. The modified electrode was used to detect l ‐tryptophan in beverage samples and gave satisfactory recoveries from 91.9 to 104.9%. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40356.