Effect of season and fishing ground on the activity of cathepsin B and collagenase in by-products from cod species

Cathepsin B and collagenase are important enzymes in the quality-deteriorating processes of fish products. Fish by-products are the left-overs after preparation of the main product and are highly perishable fractions of the fish. They do, however, contain high-quality protein with a potential for utilization. This study characterizes the activity of cathepsins B and collagenase in by-products from five species of cod caught in different fishing grounds and in different seasons. Mean maximum cathepsin B activity was measured at 35 °C in the viscera and the liver, and 50 °C in cut off, while collagenase showed mean maximum activity at 20 °C in cut off, 35 °C in liver and 50 °C in viscera. Species, season and fishing ground significantly affected activity of cathepsin B and collagenase in cut off samples, while viscera samples were not significantly affected. Cathepsin B was more heat stable than collagenase in all three fractions. Both cathepsin B and collagenase from cut off were less heat stable than the corresponding enzymes from the other two fractions.     

Modeling of laser-pumped Tm and Ho lasers accounting forupconversion and ground-state depletion

Models for numerical simulations of laser-pumped thulium- and thulium-holmium-doped lasers have been developed. In the models, upconversion losses and ground-state depletion in both thulium and holmium are accounted for, as well as spatial dependencies of the pump and resonator modes. The models apply to CW operation and to the build-up of population inversion prior to lasing in pulsed modes of operation. It is shown that upconversion losses in Tm:Ho:YAG significantly reduce the output from the laser in both CW and Q-switched mode. Simulations of CW lasers show good agreement with experimental results     

Mathematical modelling of mixing of salt in minced meat by bowl-cutter

Salting is one of the basic procedures in food processing. The NaCl concentration influences water holding properties, viscosity, texture, emulsification, etc. It is important to study and model mixing processes by mathematical methods to predict properties of the matrix and the food quality. The objective of this study was to develop a mathematical model of mixing of salt and meat in a bowl cutter and verify this with experimental data. The bowl cutter is described as a continuous stirred tank reactor, combined with a plug flow reactor in a repetitive series-model. The theoretical model shows that 30 rounds are sufficient to get a salt concentration in the whole bulk of meat with a deviation between maximum and minimum values of about 5%. The comparison of the theoretically predicted salt gradient and the experimental results showed that the mathematical equation developed is appropriate to describe the process.     

Quality changes during superchilled storage of cod (Gadus morhua) fillets

Superchilling is a method with potential for extending the shelf life of food products by partial freezing. For centuries, Atlantic cod (Gadus morhua) has been the most important commercial species in the North Atlantic fisheries and is now regarded as a very promising species in cold water fish farming. In the present work, superchilled storage at −2.2 °C of fillet portions of farmed cod was investigated. Superchilled cod showed increased shelf life with respect to reduced growth of sulphide producing bacteria compared to ice chilled. Drip loss was lower in superchilled cod. However, liquid loss by low-speed centrifugation was higher in superchilled cod fillets compared to ice chilled. This can be explained by freeze denaturation of muscle proteins, which is supported by the lower extractability of salt soluble proteins. There is a need for process optimization to minimize protein denaturation.     

Changes in myofibrillar structure of silver carp (Hypophthalmichthys molitrix) as affected by endogenous proteolysis under acidic condition

Effect of endogenous proteolysis on myofibrillar conformational changes under acidic condition was investigated by spectroscopic techniques. The result of intrinsic tryptophan fluorescence showed that tryptophan residues were exposed to polar environment by acid denaturation of protein and participation of endogenous proteolysis. Extrinsic fluorescence indicated that average surface hydrophobicity (S_hANS) decreased by reduction of pH but increased by endogenous proteolysis. Second‐derivative UV‐spectroscopy implied that the decrease of S_hANS under acidic condition may be due to burying of some aromatic amino acid residues into hydrophobic cores induced by acid‐induced aggregation, such as tyrosine, while S_hANS increased by exposure of some hydrophobic amino acids due to the effect of endogenous proteases. Raman spectra verified the changes in microenvironment of tryptophan and tyrosine residues, and showed that aliphatic amino acids were mainly exposed to polar solvent by both acid denaturation and endogenous proteolysis. In addition, new disulphide bonds were less likely to form by acid‐induced aggregation and proteolytic cleavage, while random coils increased and smaller water domains were found.     

Acoustic Field of a Medical Ultrasound Probe Operated in Continuous-Wave Mode Investigated by TV Holography

Time-averaged TV holography has been shown to be a useful technique for investigating acoustic fields in transparent media. The theory of time-averaged TV-holography measurements of ultrasonic fields in water is described. Projections of the phase and the amplitude of a 3.25-MHz ultrasonic field from an annular ultrasound probe operated in cw mode are presented. Quantitative measurements with a spatial resolution of better than 100 mum have been obtained. A set of such projections may be processed into a three-dimensional mapping of the phase and the amplitude of the acoustic field by tomographic techniques. This process is described, and an example of a tomographic reconstruction of the same ultrasonic field is presented.     

Phasor-Difference Method for Measuring the Amplitude and the Phase of Small-Amplitude Vibrations with TV Holography

A new, to the author's knowledge, method for time-averaged TV holography measurements of small-amplitude vibrations is presented. In time-averaged TV holography with sinusoidal phase modulation of the reference arm of the interferometer, two phasors describe the object vibration and the modulation of the reference arm. By inversion of the squared zero-order Bessel function of the first kind, it is possible to measure the distance between these two phasors. The distances from an object-vibration phasor to a number of known reference phasors are measured to determine the amplitude and the phase of the object vibration. The method is demonstrated by the measurement of a vibration mode of a circular metal disk. The results are compared with theoretical data and with data obtained by a commonly used method in phase-modulated TV holography.