Bo Jørgensen

Quality Index Method (QIM) scheme developed for farmed Atlantic salmon (Salmo salar)

Abstract The aim of the study was to develop a Quality Index Method (QIM) scheme for raw, farmed Atlantic salmon ( Salmo salar ) and to evaluate the scheme in a shelf life study. QIM is based on the evaluation of key parameters in the deterioration of seafoods. Demerit points are assigned to selected parameters according to their importance and a Quality Index (QI) is established by cumulating the resulting scores. The maximum storage time in ice was determined with Quantitative Descriptive Analysis (QDA) of the salmon after cooking and found to be 20–21 days. This was used as a reference to enable prediction of the remaining storage time of raw salmon in ice with QIM. The calculated QI evolved linearly with storage time in ice (QI=0.82x (days in ice)+0.18, R 2 =0.97). Individual salmon varied in QI within each storage day. However, the multivariate analysis (PLS1) demonstrated that storage time could be predicted with an accuracy of±1. 5 days, assuming that five salmon from each batch were included in the QIM assessment.

Multivariate data analysis as a tool in advanced quality monitoring in the food production chain

Abstract This paper summarizes some recent advances in mathematical modeling of relevance in advanced quality monitoring in the food production chain. Using chemometrics – multivariate data analysis – it is illustrated how to tackle problems in food science more efficiently and, moreover, solve problems that could not otherwise be handled before. The different mathematical models are all exemplified by food related subjects to underline the generic use of the models within the food chain. Applications will be given from meat storage, vegetable characterization, fish quality monitoring and industrial food processing, and will cover areas such as analysis of variance, monitoring and handling of sampling variation, calibration, exploration/data mining and hard modeling.

Simultaneous determination of ammonia, dimethylamine, trimethylamine and trimethylamine-n-oxide in fish extracts by capillary electrophoresis with indirect UV-detection

Abstract A capillary electrophoretic method with indirect UV detection is described for simultaneous determination of ammonia, dimethylamine (DMA), trimethylamine (TMA) and trimethylamine- n -oxide (TMAO) in aqueous extracts of fish. A buffer consisting of 4 mM formic acid, 5 mM copper(II)sulfate and 3 mM crown ether 18-crown-6 enabled separation of the analytes in 5–10 min. The use of an extended light path capillary technique resulted in a good sensitivity and repeatability. The linear dynamic range, based on a hydrostatic injection at 50 mbar for 2 s, was from the detection limit to at least 2.5 mM. The detection limit for ammonia, DMA, TMA, and TMAO was less than 0.04 mM, corresponding to 2 mg nitrogen per 100 g fish. As an extra benefit, the method also provided a quantitative determination of potassium, sodium, calcium and magnesium ions.

Combination of statistical approaches for analysis of 2-DE data gives complementary results

Five methods for finding significant changes in proteome data have been used to analyze a two-dimensional gel electrophoresis data set. We used both univariate (ANOVA) and multivariate (Partial Least Squares with jackknife, Cross Model Validation, Power-PLS and CovProc) methods. The gels were taken from a time-series experiment exploring the changes in metabolic enzymes in bovine muscle at five time-points after slaughter. The data set consisted of 1377 protein spots, and for each analysis, the data set were preprocessed to fit the requirements of the chosen method. The generated results were one list from each analysis method of proteins found to be significantly changed according to the experimental design. Although the number of selected variables varied between the methods, we found that this was dependent on the specific aim of each method. CovProc and P-PLS focused more on getting the minimum necessary subset of proteins to explain properties of the samples. These methods ended up with less selected proteins. There was also a correlation between level of significance and frequency of selection for the selected proteins.

Extractin information from two-dimensional electrophoresis gels by partial least squares regression

Two‐dimensional gel electrophoresis (2‐DE) produces large amounts of data and extraction of relevant information from these data demands a cautious and time consuming process of spot pattern matching between gels. The classical approach of data analysis is to detect protein markers that appear or disappear depending on the experimental conditions. Such biomarkers are found by comparing the relative volumes of individual spots in the individual gels. Multivariate statistical analysis and modelling of 2‐DE data for comparison and classification is an alternative approach utilising the combination of all proteins/spots in the gels. In the present study it is demonstrated how information can be extracted by multivariate data analysis. The strategy is based on partial least squares regression followed by variable selection to find proteins that individually or in combination with other proteins vary informatively in relation to the experimental conditions. Finding of such coherent protein patterns leads to identification of potential relations between the involved proteins, and will be useful for focusing further investigation of proteins that relate to the chosen experimental conditions.

Effect of storage conditions on differential scanning calorimetry profiles from thawed cod muscle

Differential scanning calorimetry (DSC) was used for measuring thermal denaturation (30–80°C) in cod fillets stored at −20°C and −30°C for up to 12 months and subsequently from 0 to 21 days in modified atmosphere at +2°C. The denaturation profiles were subjected to multivariate data analysis in order to extract the effects of the various storage conditions. The main effect of the storage conditions was the difference in the denaturation profiles between short time chill storage for all samples and long time chill storage for samples stored at −30°C. There was also a smaller effect due to the difference between short time frozen storage and long time frozen storage for samples stored at −20°C. The variation in the thermograms was primarily due to changes in size and position of the myosin, sarcoplasmatic protein and actin denaturation peaks, where variation in position could be related to changes in pH. Frozen storage at both temperatures and chill storage for samples previously stored at −30°C caused a decrease in the myosin denaturation peak. The relationship between the denaturation profiles and the water distribution (determined by low-field NMR relaxation) was found to involve mainly the two fastest relaxing populations (named III and IV), where IV is expected to contain the water most tightly bound to protein. The amount of water in pool III and IV appeared to be directly correlated to the changes in the denaturation profile during storage: the amount of MIV increased and MIII decreased when myosin and sarcoplasmatic proteins denatured and the actin denaturation peak shifted to a lower temperature.

Low-temperature transitions in cod and tuna determined by differential scanning calorimetry

Differential scanning calorimetry measurements have revealed different thermal transitions in cod and tuna samples. Transition temperatures detected at −11°C, −15°C and −21°C were highly dependent on the annealing temperature. In tuna muscle an additional transition was observed at −72°C. This transition appeared differently than the thermal events observed at higher temperatures, as it spanned a broad temperature interval of 25°C. The transition was comparable to low-temperature glass transitions reported in protein-rich systems. No transition at this low temperature was detected in cod samples. The transitions observed at higher temperatures (−11°C to −21°C) may possibly stem from a glassy matrix containing muscle proteins. However, the presence of a glass transition at −11°C was in disagreement with the low storage stability at −18°C during practical time scales. It was proposed that freezing of cod could be associated with more than one glass transition, with a glass transition at a temperature lower than −11°C being too small to be detectable with instrument, yet governing important deterioration processes. In order to optimize frozen storage conditions, the relationship between deterioration processes important for preservation of quality and glass transition temperatures still needs to be established.

Aqueous solutions of proline and NaCl studied by differential scanning calorimetry at subzero temperatures

Abstract The hydration properties of proline are studied by differential scanning calorimetry (DSC) in aqueous solutions during freezing to −60°C and subsequent heating to +20°C. The concentration of proline in the freeze concentrated solution was estimated to approximately 50 wt% (w/w) indicating a high water solubility of proline at subzero temperatures. No glass transition was observed within the concentration range 0.9–40.1 wt% (w/w), neither at a low scanning rate of 2.5°C/min nor at a higher scanning rate of 10°C/min. Eutectic crystallization of proline was not observed during freezing or melting which shows that proline has the ability to stay in solution at subzero temperatures. Samples containing proline-NaCl-water were also investigated by DSC and it was shown that the solubility of proline is maintained in aqueous salt solutions at temperatures as low as −60°C. From DSC measurements it was found that the eutectic crystallization of NaCl is prevented by the presence of proline, even when NaCl (initially) is present in molar excess ( [ NaCl ] [ proline ] = 2.6 ). The possible association of these findings with the occurrence of proline accumulation in some plants and insects living under water stress conditions is discussed.

Effect of Frozen Storage Temperature on Quality-Related Changes in Rainbow Trout (Oncorhynchus mykiss)

The effect of frozen storage temperature on quality-related parameters of rainbow trout (Oncorhynchus mykiss) muscle was studied in the interval from −10 to −80°C on samples stored for 1 to 18 months. The following quantities were measured: drip loss, water holding capacity and water distribution, color, lipid oxidation (thiobarbituric acid-reactive substances, TBARS), and membrane stability (enzyme activity). No effect of temperature on drip loss, water holding capacity, water distribution, or membrane stability was observed for samples stored below −20°C, whereas storage at −40°C or lower compared to −30°C or higher resulted in a reduced level of secondary lipid oxidation (TBARS). No advantage was gained by using temperatures below −40°C for frozen storage of trout regarding any of the properties investigated.

Effect of temperature on quality-related changes in cod (Gadus morhua) during short- and long-term frozen storage.

Cod (Gadus morhua) was stored at eight temperatures (−10 to −80°C) for 1 to 18 months, after which quality indicators were measured—including drip loss, water holding capacity, low field NMR spin-spin relaxation, color, amount of thiobarbituric acid reactive substances, and sarcoplasmic reticulum Ca2+-ATPase and lysosomal Cathepsin D activities. Results from samples stored up to 12 months showed no significant differences between −30°C and lower temperatures. The NMR measurements, however, indicated some changes in the water distribution of samples stored at −30°C for 12 or more months compared to storage at −40°C or lower.