Analysis of the effects of thermal protein denaturation on the quality attributes of sous‐vide cooked tuna

Traditional (low temperature, long time) and novel (low temperature, short time) sous‐vide cooking of lean tuna were characterized by analyzing the effects of thermal protein denaturation (TPD) on quality attributes, such as color, appearance, shrinkage, drip loss, and texture. TPD was analyzed by differential scanning calorimetry and estimated for several thermal schedules by kinetic analysis, following the dynamic method. When heated at a rate of 10 °C/min, myosin began to denature at around 35 °C. Actin did not denature, even when the temperature rose to approximately 51 °C, until the denaturation of myosin was complete. However, actin began to denature at approximately 58 °C and was completely denatured at 76 °C. Actin denaturation had a stronger effect than myosin denaturation on texture changes, whereas myosin denaturation was responsible for changes in color and appearance. A better preservation of tuna quality was obtained by novel sous‐vide cooking over the traditional sous‐vide method.

Practical applications

The results of this study are useful to both the research community and industry because they provide quantitative characterization of the consequences of sous‐vide cooking method on food quality explained by estimating TPD. Moreover, the kinetic parameters of the denaturation rate collected for kinetic modeling of the TPD of tuna, not only have application to simulate denaturation of actin and myosin under different thermal schedules of sous‐vide cooking, but also they can be used for the analysis of additional thermal treatments.     

Dielectric Liquid-in-Liquid Dispersion by Applying Pulsed Voltage

Liquid-in-liquid dispersion, such as organic liquid in water or water in organic liquid, has been performed using dc or ac voltage applied between nozzle and ground electrode. In the present study, pulsed high voltage was applied to produce droplets with controlled diameter in wide range. The high voltage pulse source was capacitor discharge type with 20 - 50 Hz and ranged from 0 to several kV. Water glass was atomized in alcohol solution into diameters ranging from several mum to sub-mm, depending on applied voltage. The atomized water glass droplets were solidified by removing water molecules from the water glass. Synchronized droplet formation with pulse frequency was possible by controlling pulse voltage, width and frequency, which produced uniform sized droplets successively. When the pulse voltage was raised, the droplet formation mode changed from the synchronized formation to dispersion mode through transient mode. In the dispersion mode, droplets of several mum diameter having high uniformity were produced. Utilization of high voltage and high-speed pulse to liquid-liquid dispersion could make it possible to atomize in a conductive liquid without electrolysis.     

Analysis of heat-treated graphite oxide by X-ray photoelectron spectroscopy

X-ray photoelectron spectroscopy (XPS) is among the most powerful methods to determine the surface chemical properties of carbon materials. Because heat-treated graphite oxide includes various defects, analyses of the structure by XPS help us understand the structures of various carbon materials. Thus, XPS spectra of graphene-related materials containing various functional groups and other defects on edges and in the basal plane were simulated and full width at half maximums (FWHMs) and peak shifts were obtained by density functional theory calculation. Shifts of whole C1s spectra were influenced by the electron-withdrawing functional groups such as C=O-containing functional groups. FWHMs of the main peak of C1s spectra were influenced by mainly electron-withdrawing functional groups in addition to defects such as vacancy, pentagons, and heptagons. Analyses using only XPS provide us limited information, even though the peak tops and FHWMs of simulated XPS spectra are used for assignment. Combination use of peak shifts and FWHMs of XPS spectra, infrared spectroscopy, and density functional theory calculation provided more reliable assignments of defects including oxygen-containing functional groups of carbon materials than commonly used methods using only peak shifts of XPS spectra.     

Stabilized zirconia-based sensor utilizing SnO2-based sensing electrode with an integrated Cr2O3 catalyst layer for sensitive and selective detection of hydrogen

A highly selective hydrogen (H₂) sensor has been successfully developed by using an yttria-stabilized zirconia (YSZ)-based mixed-potential-type sensor utilizing SnO₂ (+30 wt.% YSZ) sensing electrode (SE) with an intermediate Al₂O₃ barrier layer which was coated with a catalyst layer of Cr₂O₃. The sensor utilizing SnO₂ (+30 wt.% YSZ)-SE was found to be capable of detecting H₂ and propene (C₃H₆) sensitively at 550 °C. In order to enhance the selectivity towards H₂, a selective C₃H₆ oxidation catalyst was employed to minimize unwanted responses caused by interfering gases. Among the examined metal oxides, Cr₂O₃ facilitated the selective oxidation of C₃H₆. However, the addition or lamination of Cr₂O₃ to SnO₂ (+30 wt.% YSZ)-SE was found to diminish the sensing responses to all examined gases. Therefore, an intermediate layer of Al₂O₃ was sandwiched between the SE layer and the catalyst layer to prevent the penetration of Cr₂O₃ particles into the SE layer. The sensor using SnO₂ (+30 wt.% YSZ)-SE coated with a catalyst layer of Cr₂O₃ as well as an intermediate layer of Al₂O₃ exhibited a sensitive response toward H₂, with only minor responses toward other examined gases at 550 °C under humid conditions (21 vol.% O₂ and 1.35 vol.% H₂O in N₂ balance). A linear relationship was observed between sensitivity and H₂ concentration in the range of 20–800 ppm on a logarithmic scale. The results of sensing performance evaluation and polarization curve measurements indicate that the sensing mechanism is based on the mixed-potential model.     

Overview of hydrogen production technologies from biogas and the applications in fuel cells

Traditionally, H₂ is a large-scale production by the reforming process of light hydrocarbons, mainly natural gas, used by the chemical industry. However, the reforming technologies currently used encounter numerous technical/scientific challenges, which depend on the quality of raw materials, the conversion efficiency and security needs for the integration of H₂ production, purification and use, among others. Biogas is a high-potential versatile raw material for reforming processes, which can be used as an alternative CH₄ source. The production of H₂ from renewable sources, such as biogas, helps to largely reduce greenhouse gas emissions. Within this context, the integration of biogas reforming processes and the activation of fuel cell using H₂ represent an important route for generating clean energy, with added high-energy efficiency. This work expounds a literature review of the biogas reforming technologies, emphasizing the types of fuel cells available, the advantages offered by each route and the main problems faced.     

Anisotropy of structural response of single crystal austenitic stainless steel to friction stir welding

The structural response of an austenitic stainless steel single crystal to friction stir welding (FSW) was examined. The microstructural changes induced by FSW were found to essentially vary around the rotating tool. This effect was attributed to variable orientation of the shear plane and shear direction inherent to the FSW process, which significantly influenced slip activity of the single crystal.