Storage life of frozen salmonoids Effect of light and packaging conditions on carotenoid oxidation and lipid oxidation

Summary The combined effect of oxygen transmission of packaging material and of exposure to light with different spectral distribution on the oxidative degradation of carotenoids and lipids in frozen salmonoids has been characterized in a storage experiment with steaks of rainbow trout. The degradation of the carotenoid astaxanthin, as followed by HPLC analysis and tristimulus colorimetric measurement, was sensitive to the radiant flux density of UV light and less sensitive to the oxygen transmission rate of the packaging material, in agreement with previous findings for photooxidation of carotenoids in food model systems. This is in contrast to the lipid oxidation, which was found to be dependent on the accessability of oxygen rather than on exposure to UV light. Formation of peroxides in the product culminated after 3 months of storage (up to 8.4 mEq kg^–1 oil), and preceded the formation of thiobarbituric-acid-reactive substances. The product in packaging material with a high oxygen transmission rate (60 cm³ m^–2 bar^–1 per 24 h) reached a level of approximately 5 mol malonaldhyde/kg^–1 product, when stored exposed to standard fluorescent light or fluorescent light with a high UV component. Rancid taste was not detected by sensory evaluation for any of the products after 6 months of storage, whereas a bitter taste was noted for the product exposed to UV light.

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Die Haltbarkeit von Lachsforellen Einfluß von Licht und Verpackung auf die Carotenoid- und Fettoxydation

Zusammenfassung Der kombinierte Effekt von Sauerstoffdurchgang durch Verpackungsmaterial und der Lichteinwirkung verschiedener spektraler Verteilung auf den oxidativen Abbau der Carotinoide und Fette in gefrorenen Lachsforellen wurde in einem Lagerungsversuch untersucht. Der Abbau des Carotenoids Astaxanthin wurde mit HPLC undTristimulus-Calorimetrie beobachtet, und war empfindlich gegenüber UV-Licht und weniger empfindlich gegenüber der Sauerstoffdurchlässigkeit der Verpackung, was mit früheren Ergebnissen für Photooxidation der Carotinoide in Modellsystemen übereinstimmt. Dies widerspricht der Fettoxidation, die mehr von Sauerstoffzugang abhängig ist als von der Entwicklung des UV-Lichtes. Die Bildung von Peroxiden des Produktes kuliminierte nach 3monatiger Lagerung (bis 8,4 meq/kg Öl) und ging der Bildung von Thiobarbitursäure-aktiven Substanzen voraus. Das Produkt im Material mit hohem Sauerstoffdurchgang (60 cm³ m^–2 bar^–1 pro 24 h), das bei normalen fluorescierendem Licht oder bei fluorescierendem Licht mit hohem UV-Anteil aufbewahrt wurde, erreichte einen TBS-Wert von ungefähr 5 mol Malonaldehyd/kg Fleisch. Ein ranziger Geschmack wurde durch sensorische Bewertung nach 6monatiger Lagerung nicht erkannt, wohl aber ein bitterer Geschmack bei dem UV-Licht ausgesetzten Proben.

     

New method for rapid and sensitive quantification of sulphide-producing bacteria in fish from arctic and temperate waters

The offensive, fishy, rotten H2S-off-odours in spoiled, aerobically and cold stored fish from arctic and temperate waters are generally caused by sulphide-producing bacteria (SPB), mainly Shewanella putrefaciens. In the present work, a new, rapid, simple and accurate method for estimation of the SPB content in fish from these areas is described. The quantification is based on the formation rate of iron sulphide during growth of SPBs incubated at 30 degrees C in a liquid growth medium containing cysteine, sodium thiosulphate and iron(III)citrate as specific substrates for iron sulphide formation. The iron sulphide turns the medium grey and masks the background fluorescence in the medium when the SPB content in the assay is approximately 10(9) cfu/ml. The fluorescence change could be detected instrumentally and the colour change visually. The method was developed and evaluated in tests with S. putrefaciens CCUG 13452 DT as well as naturally occurring SPBs in cod, salmon, wolf fish and coal fish. A linear correlation between the SPB count and detection time was obtained over the entire range from 1 to 10(9) cfu SPB/g, corresponding to detection times 17 and 1 h, respectively. The correlation is described by the equation: log cfu/g fish= -0.59(+/- 0.17) x DT+ 9.65(+/- 0.09), where DT is the detection time in hours. The model was valid for all the tested fish species and all tested naturally occurring SPBs in these species. The regression coefficients (R2) for cod, coal fish, wolf fish and salmon were 0.99, 0.92, 0.97 and 0.97, respectively. The detection level of the method is 1 SPB per sample tube, corresponding to 16 cfu/g fish. The method could be used to predict the remaining shelf life of the fish for different markets, even when the time-temperature history during storage of the fish is unknown.     

Effect of pre-slaughter physiological conditions on the oxidative stability of colour and lipid during chill storage of pork

The physiological condition of the live animal was found to significantly affect colour, lipid oxidation and water holding capacity of chill stored pork chops (M. Longissimus dorsi) in a study, where various pre-slaughter conditions were achieved by the following four treatments: (A) control; (B) subjected to treadmill exercise immediately prior to stunning; (C) given epinephrine injection 15 h prior to slaughter; and (D) given epinephrine injection 15 h before slaughter and further subjected to treadmill exercise immediately before stunning. The treatments resulted in variations in energy metabolites (glycogen, lactate, creatine phosphate, ATP) and ultimate pH (pH_u), with the lowest pH_u in chops from treatments A and B, and in significantly different tristimulus colour L^*-, a^*- and b^*-parameters, although the effect of treatment on colour was not consistent during the chill storage period of 6 days. Overall, chops from treatments A and B had significantly higher L^*- and b^*-values (were paler and less blue) than chops from C and D during storage under conditions typical for retail trade. The initial a^*-values were higher (redder) in chops from treatments A and B, but the colour, as judged by the a^*-values, was less stable in meat from these treatments compared with treatments C and D. Lipid oxidation, evaluated by thiobarbituric acid reactive substances (TBARS) in the fresh meat, and drip loss, measured after 6 days of storage, were both significantly higher in chops from treatments A and B compared to chops obtained from treatments C and D. Statistical analysis relating the pH and the level of various energy metabolites post-mortem in the individual animals to the measured quality parameters, revealed that pH_u was the most important factor affecting product quality. In conclusion, over all product quality depends on obtaining a pH_u in the narrow range where both meat quality parameters such as colour, lipid oxidation and drip loss as well as microbiological aspects have to be considered.     

By-products from herbs essential oil production as ingredient in marinade for turkey thighs

Herb decoctions—the aqueous extract of rosemary, sage and thyme, left as by-product after steam distillation of essential oils, were investigated as a source of antioxidants in marinades for turkey thigh meat. Lipid oxidation after marinating, cooking and chill storage (warmed over flavour, WOF) was assessed by thiobarbituric acid-reactive substances (TBARS), GC-MS and sensory judgement on marinated and untreated meat. Results showed that marinating with herb decoctions, which exerted antioxidant activity (free radical scavenging), was an effective means of retarding lipid oxidation in raw and cooked meat. Meat from the rosemary marinade had the lowest TBARS values and volatile levels, while the control samples showed the highest values throughout the marinating, cooking and storage period. Oxidative changes in meat marinated with thyme and sage were significantly more advanced than in meat marinated with rosemary decoction. The partial least squares regression (PLS-R) showed that control samples were strongly related to the oxidation variables (volatiles, TBARS, rancidity) while the marinated meat had high scores for spicy and acidic odour and flavour. Results indicated that antioxidants contained in herb decoction, could be exploited in marinades to prevent rancidity in stored, heat-treated turkey meat products.     

The combined effect of rosemary (Rosmarinus officinalis L.) and modified atmosphere packaging as protection against warmed over flavour in cooked minced pork meat

Rosemary (dried leaves ofRosmarinus officinalis L.) added to cooked meat balls (minced pork) was found to retard the formation of warmed over flavour (WOF) during chill storage. The spice was added to pork meat (Longissimus dorsi) balls in an amount acceptable for the product, as evaluated by a sensory panel (0.05% of total weight). After cooking (water bath, internal temperature 80°C), the meat balls were packed using five atmosphere packaging conditions: (i) air; (ii) 5% O₂/95% N₂; (iii) 3% O₂/97% N₂; (iv) 1% O₂/99% N₂; and (v) 100% N₂. During chill storage (5°C), the sensory quality of the reheated meat balls was evaluated by a trained sensory panel, and lipid oxidation was followed by measurement of thiobarbituric acid reactive substances (TBARS). The combination of decreased O₂ atmosphere in the packages and addition of rosemary resulted in a significantly (p<0.05) lower amount of TBARS and a significantly (p<0.05) better sensory score.

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Gemeinsamer Effekt von Rosmarin (Rosmarinus officinalis L.) und Verpackung in modifizierter Atmosphäre auf den Aufwärmegeschmack (WOF) von wärmebehandeltem, gehacktem Schweinefleisch

Zusammenfassung Rosmarin (getrocknete Blätter vonRosmarinus officinalis L.), erwärmten Fleischklößen (gehacktes Schweinefleisch) zugesetzt, hinderte die Entwicklung des Aufwärmgeschmacks (warmed over flavour) während der Kühllagerung. Das Gewürz wurde den aus Schweinefleisch (Longissimus dorsi) hergestellten Fleischklößen in einer für das Produkt akzeptablen Menge zugegeben, beurteilt von einem sensorischen Panel (0.05% des Totalgewichtes). Nach der Wärmebehandlung (Wasserbad, Zentrum-Temperatur 80°C) wurden die Fleischklöße in fünf unterschiedlichen und kontrollierten Atmosphären wie folgt verpackt: (i) Luft; (ii) 5% O₂/95% N₂; (iii) 3% O₂/97% N₂; (iv) 1% O₂/99% N₂ und (v) 100% N₂. Während der Kühllagerung (5°C) wurde die sensorische Qualität der wiedererwärmten Fleischklöße von einem geschulten Panel beurteilt und die Lipid-Oxidation durch Messung der Thiobarbitursäure-reaktiven Substanzen (TBARS) beobachtet. Die Kombination von ermäßigtem Sauerstoffgehalt in den Verpackungen mit der Zugabe von Rosmarin ergab eine signifikant (p<0.05) niedrigere Menge TBARS wie auch signifikant (p<0.05) bessere Punkte in der sensorischen Beurteilung.

     

Suitability of four blackcurrant cultivars for industrial syrup production

The four blackcurrant cultivars Øjebyn, Ben Nevis, Ben Lomond and Silvergieter have been evaluated with reference to their suitability for syrup production. The examination was based on sensory and physico-chemical characterisation, and was performed on the berries themselves and the syrup. The results show that Øjebyn is less suitable for syrup production, while Ben Nevis and Ben Lomond differ insignificantly in most qualities from the reference cultivar, Silvergieter. Criteria for the evaluation of cultivars for industrial suitability are discussed.     

Antioxidative activity of summer savory (Satureja hortensis L.) and rosemary (Rosmarinus officinalis L.) in minced, cooked pork meat

The sensory intensity measured as theabsolute threshold value of spice andrecognition of spice was evaluated for summer savory and rosemary in meat balls. The values forabsolute threshold value of spice were found to be significantly lower for rosemary than for summer savory. The antioxidative activity of the spices was analysed in two accelerated model systems and in a storage experiment. In one of the model systems, oxidation was accelerated by heat and by an elevated pressure of oxygen. Both spices significantly improved the oxidative stability of the meat balls in this model system. In the second model system metal catalyst oxidation in a meat slurry was used and a reduction in the oxidative processes in samples containing the spices was again shown. In both model systems a slightly higher antioxidative activity was seen for rosemary compared to summer savory. In the storage experiment, the spices were added at a sensorially acceptable level and the heat-treated meat balls were stored at 5°C. A significant reduction in the development of warmed-over flavour (WOF) caused by the addition of spices was measured by a reduction in 2-thiobarbituricacid-reactivesubstances (TBARS) and in hexanal. A reduction in TBARS of approximately 30% in meat balls containing added spices was seen independently of packaging in 1% oxygen or in atmospheric air and the reduction (30%) was constant throughout the storage period.     

Energy demand in the Norwegian building stock: Scenarios on potential reduction

A model has been developed for studying the effect of three hypothetical approaches in reducing electricity and energy demand in the Norwegian building stock: wide diffusion of thermal carriers, heat pumps and conservation measures, respectively. Combinations of these are also considered. The model has a demand side perspective, considers both residential and service sectors, and calculates energy flows from net to delivered energy. Energy demand is given by the product of activity and intensity matrices. The activity levels are defined for the stock and the new construction, renovation and demolition flows. The intensity properties are defined in archetypes, and are the result of different energy class and heating carriers share options. The scenarios are shaped by combining the activity flows with different archetypes. The results show that adopting conservation measures on a large scale does allow reducing both electricity and total energy demand from present day levels while the building stock keeps growing. The results also highlight the importance of making a clear distinction between the assumptions on intensity and activity levels.