Performance of a compact, hybrid optical evanescent-wave sensor for chemical and biological applications

We describe a hybrid evanescent-wave sensor component that we fabricated by using an integrated optical interferometer with a specially adapted photodetector array. The design of the interferometer is based on the use of tapered waveguides to obtain two intersecting collimated beams. Phase shifts can be measured with an angular precision of better than 10(-3) rad, which corresponds to a superstrate index change inferior of 10(-6) with our structure. The interest in the device as a chemical sensor is experimentally demonstrated. The same optical component could be used in a variety of other sensor applications, e.g., biological and immunological sensors.     

Shrimp processing assessed by low field nuclear magnetic resonance, near infrared spectroscopy, and physicochemical measurements--the effect of polyphosphate content and length of prebrining on shrimp muscle

The effect of using polyphosphates during prebrining and the effect of prebrining time of cold water shrimp (Pandalus borealis) was studied with low field nuclear magnetic resonance (LF-NMR) transverse relaxation time measurements (benchtop and unilateral) and near infrared (NIR) spectroscopy with the aim of improving shrimp processing. Strong calibrations were obtained for moisture content and water-holding capacity (WHC) using the NIR technique. Multivariate analysis indicated significant correlations between benchtop NMR parameters and moisture content and WHC, as measured with physicochemical methods and NIR spectroscopy. Significant correlations were also observed between NMR parameters and muscle pH, protein content, and phosphate content. The study showed that LF-NMR contribute to improved understanding of the shrimp brining process and to improved process control on-line or at-line, especially in combination with NIR measurements. However, optimization of the unilateral device is necessary.     

Process control of lightly salted wild and farmed Atlantic cod (Gadus morhua) by brine injection, brining, and freezing--a low field NMR study

The aim of this study was to use low-field nuclear magnetic resonance (NMR) and traditional chemical methods to investigate the physical and chemical differences in wild and farmed cod processed pre- and postrigor, and how these properties were affected by brine injection, brining, and freezing. In prerigor processed farmed or wild cod, brine injections followed by brining for 2 d, with brine concentrations up to 5.5% and 4%, respectively, were not sufficient to reach a muscle salt concentration of 2% as aimed for, while wild cod processed postrigor had sufficient salt uptake after the same processing. Low-field NMR gave valuable information about the differences in the muscle structure between wild and farmed cod as well as the state of the water in the muscle during brine injection, brining, and during rigor tension. Low-field NMR is, therefore, a valuable tool that can be used to optimize the salting and storing processes of lightly salted cod products from both wild and farmed cod. For farmed cod to be used in the production of lightly salted products further research is needed. Practical Application: Optimal processing of lightly salted cod products is important to the fish industry, due to an increasing market for this product in southern Europe. Farmed cod, which is seen as a potential steady raw material source for this production, differs considerably from its wild counterparts by having other chemical and physical muscle properties, such as lower water content and lower pH. With the processing procedures used today the farmed cod can, therefore, only be used in some of the products, where wild cod is currently used as raw material. It is, therefore, important that the processing of these products is optimized with regard to these differences in the raw material. This study gives a valuable contribution to further studies about optimal combinations of brine injections, brining, and freezing of pre- and postrigor processed farmed compared to wild cod.     

Superchilled,chilled and frozen storage of Atlantic mackerel (Scomber scombrus) – effect on lipids and low molecular weight metabolites

Quality changes in Atlantic mackerel fillets during superchilled, chilled and frozen storage focusing on lipid quality, colour and changes in low molecular weight metabolites relevant for quality and safety were studied. Low formation of oxidation products was observed in chilled (up to 7 days), superchilled (up to 14 days) and frozen storage (up to one year). Only slight formation of TBARS was measured in the samples which correlated with the increasing fillet yellowness. The profile of low molecular weight compounds, analysed by high-resolution NMR, showed clear grouping of the different samples according to both treatment and storage time. The increase in K-value was highest in the chilled samples, reaching a K-value of 93 ± 3% on day 5, exceeding the proposed limit of human consumption (80%) while superchilling reached a K-value of ca 90 % after 14 days. Frozen samples showed acceptable quality in the whole storage period.     

Metastable structures and isotope exchange reactions in polyoxometalate ions provide a molecular view of oxide dissolution

Reactions involving minerals and glasses in water are slow and difficult to probe spectroscopically but are fundamental to the performance of oxide materials in green technologies such as automotive thermoelectric power generation, CO2 capture and storage and water-oxidation catalysis; these must be made from geochemically common elements and operate in hydrous environments. Polyoxometalate ions (POMs) have structures similar to condensed oxide phases and can be used as molecular models of the oxide/water interface. Oxygen atoms in POM exchange isotopes at different rates, but, at present, there is no basis for predicting how the coordination environment and metal substitution influences rates and mechanisms. Here we identify low-energy metastable configurations that form from the breaking of weak bonds between metals and underlying highly coordinated oxygen atoms, followed by facile hydroxide, hydronium or water addition. The mediation of oxygen exchange by these stuffed structures suggests a new view of the relationship between structure and reactivity at the oxide/solution interface.     

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.     

Superchilled,chilled and frozen storage of Atlantic mackerel (Scomber scombrus) fillets – changes in texture,drip loss,protein solubility and oxidation

Changes in quality characteristics in relation to protease activity and protein oxidation in chilled, superchilled and frozen mackerel fillets during storage were studied. The solubility of sarcoplasmic proteins was quite stable in mackerel samples for all storage experiments, whereas the solubility of myofibrillar proteins decreased in both superchilled and frozen samples. A significant correlation (r = 0.983, P < 0.05) between the increased activity of cathepsin B+L in chilled fillets and softening of the fish flesh during storage was revealed. Contrary with chilled samples, the texture of superchilled mackerel fillets became tougher along the storage period, which can be explained by a higher rate of myofibrillar oxidation (r = 0.940, P < 0.05). The hardness and drip loss decreased slightly at the end of frozen storage. Superchilling preserved the quality of mackerel fillets with the least side effects in relation to protein solubility, drip loss and softening of the fish tissue as compared to chilled and frozen storage.