Höfundur: admin

The aerobic respiratory chain of the thermohalophilic bacterium Rhodothermus marinus has been extensively studied. In this study the isolation and characterization of a third oxygen reductase expressed in this organism are described. This newly isolated enzyme is a typical member of the type B family of haem-copper oxygen reductases, showing 43% amino acid sequence identity and 63% similarity with the ba₃ oxygen reductase from Thermus thermophilus. It constitutes two subunits with apparent molecular masses of 42 and 38 kDa. It contains a low-spin B-type haem and a high-spin A-type haem. A stoichiometry of 1B: 1A haem per protein was obtained by spectral integration of UV-visible spectra. Metal analysis showed the presence of two iron and three copper ions, which is in agreement with the existence of a Cu_A centre.

Taking advantage of having two spectroscopically distinct haems, the redox behaviour of the ba₃ oxygen reductase was analysed and discussed in the framework of a model with interacting centres. Both haems, B and A, present two transitions, have unusually low reduction potentials of −65 mV and an interaction potential of −52.5 mV.

Hlekkur að grein

An α-l-rhamnosidase (E.C. 3.2.1.40) from a newly discovered thermophilic bacterium was expressed in Escherichia coli BL21 DE3 pRIL cells. The cells were immobilized in Ca²⁺-alginate beads. The temperature of 50 °C used in reactions, appeared to be sufficient for making the mesophilic strain porous enough for the substrate to access the cloned thermostable enzyme. Pretreatment of cells with heat or lysozyme prior to bead formation did not improve the results. The best cell concentration (w/w) for bead preparation was found to be 0.0192 g ml⁻¹ and stability of beads increased if CaCl₂ concentration in buffers and substrate was kept at 50 mM. In a 60 min assay, the optimal pH of the entrapped cells was found to be 7.8 and the optimal temperature 60 °C. By packing the beads in a column, a bioreactor for production of l-rhamnose from naringin was created. Full degradation of 7.9 mM naringin could be reached by running the reactor at 1 ml min⁻¹ at 50 °C. The optimal running temperature of the reactor was found to be 50 °C and the reactor was fully stable over 3 days at that temperature. On the fourth day, substrate degradation capacity had decreased by 10–15%.

Hlekkur að grein

Organotin compounds have been widely used as stabilizers and anti-fouling agents with the result that they are ubiquitously distributed in the environment. Organotins accumulate in the food chain and potential effects on human health are disquieting. It is not known as yet whether cell surface adsorption or accumulation within the cell, or indeed both is a prerequisite for the toxicity of organotin compounds. In this study, the alkylated tin derivatives monomethyltin trichloride (MMT), dimethyltin dichloride (DMT), trimethyltin chloride (TMT) and tetramethyltin (TetraMT) were investigated for cyto- and genotoxic effects in CHO-9 cells in relation to the cellular uptake. To identify genotoxic effects, induction of micronuclei (MN), chromosome aberrations (CA) and sister chromatid exchanges (SCE) were analyzed and the nuclear division index (NDI) was calculated. The cellular uptake was assessed using ICP-MS analysis. The toxicity of the tin compounds was also evaluated after forced uptake by electroporation. Our results show that uptake of the organotin compounds was generally low but dose-dependent. Only weak genotoxic effects were observed after exposure of cells to DMT and TMT. MMT and TetraMT were negative in the test systems. After forced uptake by electroporation MMT, DMT and TMT induced significant DNA damage at non-cytotoxic concentrations. The results presented here indicate a considerable toxicological potential of some organotin species but demonstrate clearly that the toxicity is modulated by the cellular uptake capability.

Hlekkur að grein

The influence of factors in catching and processing of cod on fillet yield, gaping, number of nematodes and prevalence of bruises was studied in close cooperation with an Icelandic fisheries company. Data was collected onboard fishing vessels and in a fish processing plant in N-Iceland, for 29 months. Conditions during trawling and storing were recorded. Fishing ground had significant effect (95% significance limit) on fillet yield, gaping and number of parasites. Time of year had significant effect on all variables. The time-lag from catch to processing (age of the raw material) affected both gaping and bruises significantly. Fillet yield was closely correlated to both condition factor and head proportion. The results can be used for decision-making on where to direct the fishing boats and what to do with the catch after unloading it.

Hlekkur að grein

This paper describes the responses of consumers in six European countries (Greece, Italy, Spain, France, Iceland and United Kingdom) tasting meat from twelve different local types of lambs produced in those same six countries. Animals represented 10 breeds and crossbreeds, three sexes, several diets composed of either milk, concentrates and various forages as main ingredients and different slaughter ages, from 1 and 12 months, and carcass weights, from 5.5 to 30.4 kg. Tests were conducted by 36 volunteer families in each of the six countries involved in the study. Families were asked to roast the joints using their own cooking criteria, evaluating (from “dislike extremely” to “like extremely”) flavour, tenderness, juiciness and overall liking. Also the cook was asked to rate the odour during cooking. Country and lamb type and their interaction were statistically significant for all the variables analysed. Results suggest a link between the assessments of a given lamb type and the consumers’ culinary background, showing clear associations between country and lamb type preferences. It was possible to separate, independently of the country, different groups of families with similar preferences. Five family groups, which included 88 families (40.74%), had a clear Mediterranean origin and preferred types of lamb fed either milk or mainly concentrate diets. Seven family groups, which included 93 families (43.06%) with a clear northern origin, preferred types reared on grass or with grass included in the diet. The rest of the groups (four) that included 35 families (16.20%) had no clear composition (northern or Mediterranean), and they had a wider taste preference. It can clearly be seen that there are two categories of consumers of lamb in the analysed European market: those who prefer “milk or concentrate taste” and those who prefer “grass taste”.

Hlekkur að grein

Lipid oxidation and functional properties were monitored in spray dried fish powder made from saithe (Pollachius virens) by-products. The fresh powder exhibited slight antioxidant activity in a model system of linoleic acid emulsion. The freshly made powder had low lipid extract-ability in polar solvents and over 30% free fatty acids (FFA). Further lipid oxidation took place during storage, independent of storage temperatures. Functional properties measured by color changes, water-binding capacity, apparent viscosity and protein solubilty changed more during storage at 30°C than 0°C.

Hlekkur að grein

The influence of different cooling techniques (dry ice/ice packs) and storage temperature (-2°C/3°C) to prolong the shelf life of Arctic charr (Salvelinus alpinus) fillets were evaluated by sensory analysis, physical methods, chemical and microbial analysis. The effects of storage temperature were stronger than of different cooling agents. Superchilling (-2°C) of fillets packed with dry ice resulted in 6 days extension of shelf life compared to chilling (3°C). The use of dry ice parallel to superchilling prolonged shelf life for 1 day compared to fillets stored with ice packs. No negative effects on quality of the fillets where detected that could be linked to cell destruction caused by partial freezing or to sour taste, caused by absorption of CO2 gas in fish flesh.

Hlekkur að grein

Since the early 1990’s, HACCP-based programs are being implemented as a means of preventing food hazards in fish and seafood products. From an engineering perspective, a system designed to control a manufacturing process is expected to result in final product that consistently meet requirements. Although audits are used to verify program implementation, there is a need for some product monitoring to measure the effectiveness and performance of the control systems. This paper discusses the need to monitor final product in seafood HACCP-based programs to measure effectiveness from a systems approach. Information time series of audits and inspections conducted are shown to be more indicative of program performance than snapshot inspections of the final product.

Hlekkur að grein

This study aims to evaluate the performances of the membrane processes during the treatment of blue whiting peptide hydrolysates.

Ultrafiltration with high molecular weight cut-off (MWCO) can be used for the separation between peptides and non-hydrolyzed proteins. A membrane of MWCO 20 kDa was tested on hydrolysates containing 11.4 g of peptides per liter of solution. Steady fluxes were satisfactory (100 l/h/m² at 12 bars and 15 °C) but the nitrogenized matter retention is approximately 30%, which leads to a considerable peptide loss in the permeate.

In addition, ultrafiltration with intermediate MWCO is considered for the enrichment of fractions of peptides of a definite molecular weight range. Two membranes of MWCO 4 and 8 kDa were selected; allowing easy separation between peptides of high and low molecular weight. Moreover, they show variable rejection rates according to classes of molecular weight, which gives hope for a possible fractionation in the range of 1000–7000 Da.

Lastly, the nanofiltration enables the concentration of peptides of low molecular weight by avoiding an excessive concentration of salts. The results with a membrane of MWCO 300 Da are very encouraging because the retention of peptides bigger than 1000 Da is total so that the concentration of the retentate up to about 300 g/l can be reached.

Hlekkur að grein

The aim of this work was to evaluate the effects of freezing and frozen storage at –24 °C on the quality of Icelandic herring fillets, focusing on protein solubility and viscosity at pH 2.7 and 11 used for pH-aided protein isolation. The evaluation of quality was based on chemical analyses, protein degradation measurements, and changes in protein solubility and viscosity at pH 2.7 and 11 after up to 6-mo frozen storage of the herring fillets. Lipid oxidation measured as TBARS values increased significantly during the frozen storage (P < 0.05). Protein solubility at pH 2.7 decreased during frozen storage for 6 mo, where the solubility was about 10% lower after 6-mo frozen storage compared to the beginning (P < 0.05). At pH 11, the solubility became approximately 15% lower after 6-mo frozen storage compared to initial solubility (P < 0.05). Viscosity, measured at pH 2.7, increased after 3 mo of frozen storage (P < 0.05). At pH 11, the viscosity increased significantly after 1-wk frozen storage, compared to fresh herring fillets, but did not increase significantly with further storage (P < 0.05). Changes found in solubility and viscosity indicated protein degradation due to freezing and frozen storage. SDS-PAGE analysis did not reveal any protein cross-linking or aggregation formation, either with frozen storage or due to exposure to low pH.

Hlekkur að grein