The objective of this study was to investigate the performance of a photochromic time–temperature indicator (TTI) under dynamic temperature conditions simulating real fresh fish distribution chain scenarios. The work aimed at testing the possibility of extending the application of the TTI kinetic model, developed for specific temperature range of isothermal conditions, at low temperatures. The results showed that the TTI presented reproducible responses after being charged and during the discolouration process under different conditions, which revealed the reliability of the indicator. The TTI reflected well the temperature conditions of the studied scenarios, which indicates its potential application to continuously monitor the temperature history of the fresh fish supply chain. The kinetic model gave good fits in non-abused scenarios at temperatures below 2 °C, presenting the potential for application of the model in determining the right charging level to suit a product’s shelf life at low temperatures.
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Experiments were carried out to compare the thermal performance of wholesale fresh fish boxes made of corrugated plastic (CP) and expanded polystyrene (EPS). Free standing boxes containing whole, fresh fillets were exposed to dynamic thermal loads. The chilling effect of frozen ice packs was studied by including them in some of the boxes. The frozen ice packs proved efficient for protecting fresh fish fillets against temperature abuse. Furthermore, the results show that the insulating performance of EPS is significantly better than the insulating capacity of CP. Maximum fish temperature of 16.1 °C (CP) and 11.0 °C (EPS) were recorded inside the thermally abused boxes without ice packs, initially at 1.9 to 2.1 °C and stored for 6.1 h at a mean ambient temperature of 19.4 °C. The fish temperature distributions during thermal abuse were studied with a numerical model for both packaging types, applying effective thermal properties of the sandwich-structured CP box. The purpose of the model was to cost effectively improve the packaging design. A satisfactory agreement between numerical results and experimental results was obtained.
Functional and biochemical properties of fish protein hydrolysates (FPH) from blue whiting (BW) were studied. FPH (2.5%, 5%, 10%, and 15% degree of hydrolysis [DH]) were made from isolated proteins from headed and gutted BW with Alcalase 2.4 L. The properties of dried BW mince and protein isolate compared to 4 reference proteins (soy and milk protein) were studied: color, solubility, water-holding capacity (WHC), oil-binding capacity (OBC), emulsion capacity (EC), and emulsion stability (ES). The angiotensin I-converting enzyme (ACE) inhibitory activities of the soluble fraction of BW powders were also investigated. Furthermore, the products were characterized by analyzing their chemical composition. Chemical composition, solubility, OBC, and EC of the BW powders was significantly (P < 0.05) different with different DH, while color, ES, and WHC were not significantly (P > 0.05) different. Salt content of the FPH was high (4% to 19%) and increased with increased DH. Protein solubility varied from 10% to 70% and increased with increased DH. WHC of the FPH was around 97% and was higher than that of all the reference proteins tested. OBC decreased with increased DH (from 3.5 to 2.1 g oil/g protein) and was higher than OBC of the soy and milk proteins (1.6 to 1.9 g oil/g protein). EC of FPH was similar or lower than the reference proteins. ES of FPH (60% to 90%) was similar to or lower than soy and whey proteins (60% to 98%) but higher than casein (20%). ACE inhibition activity increased as DH was increased.
Over the years several β-glucan transferases from yeast and fungi have been reported, but enzymes with such an activity from bacteria have not been characterized so far. In this work, we describe the cloning and expression of genes encoding β-glucosyltransferase domains of glycosyl hydrolase family GH17 from three species of proteobacteria: Pseudomonas aeruginosa PAO1, P. putida KT2440 and Azotobacter vinelandii ATCC BAA-1303. The encoded enzymes of these GH17 domains turned out to have a non-Leloir trans-β-glucosylation activity, as they do not use activated nucleotide sugar as donor, but transfer a glycosyl group from a β-glucan donor to a β-glucan acceptor. More particularly, the activity of the three recombinant enzymes on linear (β1 → 3)-linked gluco-oligosaccharides (Lam-Glc4–9) and their corresponding alditols (Lam-Glc4–9-ol) was studied. Detailed structural analysis, based on thin-layer chromatography, matrix-assisted laser desorption ionization time-of-flight mass spectrometry, electrospray ionization mass spectrometry, and 1D/2D 1H and 13C nuclear magnetic resonance data, revealed diverse product spectra. Depending on the enzyme used, besides (β1 → 3)-elongation activity, (β1 → 4)- or (β1 → 6)-elongation, or (β1 → 6)-branching activities were also detected.
1. A previous study has shown that emulsions of monocaprin in citrate lactate buffer at pH 4·1–4·3 are highly active in killing Campylobacter in water, where they reduce viable bacterial counts by more than 6 log10 colony forming units (cfu) in 1 min at a concentration of 1·25 mM (0·03%).
2. The present study was carried out to evaluate whether monocaprin emulsions could be used to kill Campylobacter on raw poultry.
3. It was shown that immersion of naturally contaminated chicken legs in 20 mM (0·5%) monocaprin emulsion at pH 4·1 for 1 min at 20°C reduced the number of Campylobacter by 2·0 to 2·7 log10 cfu. Pre-chill dipping of whole carcases into 20 mM monocaprin emulsion in the slaughterhouse also caused a significant reduction in Campylobacter contamination.
4. Immersion in monocaprin emulsions at pH 4·1 was also assessed as a means to reduce the number of psychrotrophic spoilage bacteria. There were lower psychrotrophic bacteria counts on treated chicken parts than on untreated controls after storage at 3°C for up to 14 d.
5. Immersion in emulsions of monocaprin, which is a natural lipid classified as GRAS, may be a feasible method to reduce the number of Campylobacter and spoilage bacteria on raw poultry. This method could reduce the risk of human exposure to Campylobacter, and at the same time increase the shelf-life of poultry products.
BACKGROUND: Cereal-based snacks are usually low in protein and other nutrients. Increased health awareness of consumers has led the food industry to develop fortified snacks with functional ingredients. Three types of extruded corn-fish snacks, containing 150 g kg−1 carp mince and 150 g kg−1 trout mince, 30 g kg−1 freeze-dried saithe protein and a regular corn snack (control). were produced to study quality changes and storage stability of the products during 6-month storage at 27 ± 2 °C.
RESULTS: All products had the same level of water activity and proximate composition except for protein. Fortified snacks had a protein content of 93–98 g kg−1, compared with 65 g kg−1 in the control. A significant increase was observed for peroxide value during storage (0.0 to 2.8 meq kg−1). Scores for attributes describing oxidation and off odors and flavors increased after 5–6 months’ storage but attributes describing puffed corn snack odor and flavor did not change during storage of any of the products.
CONCLUSION: Extrusion of corn grits with fish flesh/fish protein can be used to produce high-protein products that would be an option to provide nutrient snacks for consumers and to increase fish consumption.
The aim of this study was to compare the effects of different storage temperatures (+2°C, -4°C, -12°C, -18°C and -24°C) and time (0, 1, 3 and 6 weeks) on the quality of heavily salted cod. The color, water content, water holding capacity (WHC), cooking yield, total volatile basic nitrogen (TVB-N) and trimethylamine (TMA) of the samples were determined. Results showed that the whiteness of the salted cod decreased slightly, whereas the yellow/orange color increased during the storage period. The WHC and cooking yield increased and were inversely related to water content. The TVB-N value increased slightly, whilst a lightly decrease in TMA value was observed. Storage at -4°C and lower temperatures had a detrimental influence on the color of the product which is the main quality criterion for salted cod. Therefore, it is not suitable to store the product at -4°C or lower temperatures.
Background
Approximately half of the mitochondrial genome inherent within 546 individual Atlantic salmon (Salmo salar) derived from across the species’ North Atlantic range, was selectively amplified with a novel combination of standard PCR and pyro-sequencing in a single run using 454 Titanium FLX technology (Roche, 454 Life Sciences). A unique combination of barcoded primers and a partitioned sequencing plate was employed to designate each sequence read to its original sample. The sequence reads were aligned according to the S. salar mitochondrial reference sequence (NC_001960.1), with the objective of identifying single nucleotide polymorphisms (SNPs). They were validated if they met with the following three stringent criteria: (i) sequence reads were produced from both DNA strands; (ii) SNPs were confirmed in a minimum of 90% of replicate sequence reads; and (iii) SNPs occurred in more than one individual.
Results
Pyrosequencing generated a total of 179,826,884 bp of data, and 10,765 of the total 10,920 S. salar sequences (98.6%) were assigned back to their original samples. The approach taken resulted in a total of 216 SNPs and 2 indels, which were validated and mapped onto the S. salar mitochondrial genome, including 107 SNPs and one indel not previously reported. An average of 27.3 sequence reads with a standard deviation of 11.7 supported each SNP per individual.
Conclusion
The study generated a mitochondrial SNP panel from a large sample group across a broad geographical area, reducing the potential for ascertainment bias, which has hampered previous studies. The SNPs identified here validate those identified in previous studies, and also contribute additional potentially informative loci for the future study of phylogeography and evolution in the Atlantic salmon. The overall success experienced with this novel application of HT sequencing of targeted regions suggests that the same approach could be successfully applied for SNP mining in other species.
Microsatellite genotyping is a common DNA characterization technique in population, ecological and evolutionary genetics research. Since different alleles are sized relative to internal size-standards, different laboratories must calibrate and standardize allelic designations when exchanging data. This interchange of microsatellite data can often prove problematic. Here, 16 microsatellite loci were calibrated and standardized for the Atlantic salmon, Salmo salar, across 12 laboratories. Although inconsistencies were observed, particularly due to differences between migration of DNA fragments and actual allelic size (‘size shifts’), inter-laboratory calibration was successful. Standardization also allowed an assessment of the degree and partitioning of genotyping error. Notably, the global allelic error rate was reduced from 0.05 ± 0.01 prior to calibration to 0.01 ± 0.002 post-calibration. Most errors were found to occur during analysis (i.e. when size-calling alleles; the mean proportion of all errors that were analytical errors across loci was 0.58 after calibration). No evidence was found of an association between the degree of error and allelic size range of a locus, number of alleles, nor repeat type, nor was there evidence that genotyping errors were more prevalent when a laboratory analyzed samples outside of the usual geographic area they encounter. The microsatellite calibration between laboratories presented here will be especially important for genetic assignment of marine-caught Atlantic salmon, enabling analysis of marine mortality, a major factor in the observed declines of this highly valued species.
Aqualysin I, is a subtilisin-like serine proteinase, from the thermophilic bacterium Thermus aquaticus. It is predicted that the enzyme contains a salt bridge, D17-R259, connecting the N- and C-terminal regions of the enzyme. Previously we reported on the stabilizing effect of the incorporation of a salt bridge at a corresponding site in VPR, a related cold adapted enzyme from a marine Vibrio sp. Here we describe the effect of the reverse change, i.e. the elimination of the salt bridge on the thermal stability and kinetic properties of aqualysin I. Deletion of the putative salt bridge in the D17N mutant of the enzyme destabilized the enzyme by 8-9 °C in terms of T50%, determined by thermal inactivation and over 4°C in Tm, as measured from melting curves of the inhibited enzyme. The mutation, however, had no significant effect on the kinetic parameters of the enzyme under standard assay conditions.