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Utilization of fish rest raw material for fish oil extraction has received interest with the increasing demand for sustainable food sources. Enzymatic hydrolysis is an efficient method for the extraction of value-added compounds, but its effectiveness may be enhanced by high-pressure processing (HPP). However, HPP can induce lipid oxidation, affecting the quality of the oil. This study aimed to evaluate the quality of fish oil obtained after enzymatic hydrolysis of a mixture of rainbow trout (Oncorhynchus mykiss) and Atlantic salmon (Salmo salar) rest raw material pretreated by HPP. Six pretreatments were tested prior to enzymatic hydrolysis; 200 MPa × 4 min, 200 MPa × 8 min, 400 MPa × 4 min, 400 MPa × 8 min, 600 MPa × 4 min, and 600 MPa × 8 min. The oil samples were analyzed for lipid oxidation parameters, free fatty acid content, fatty acid composition, and color changes over 8 weeks. The results confirmed that HPP may induce lipid oxidation and revealed significant influence of HPP parameters on lipid oxidation, with higher pressures leading to increased oxidation. Fatty acid composition varied among samples, but it was not substantially affected by HPP. [ABSTRACT FROM AUTHOR]

The aim of the present study was to evaluate the effects of various sous-vide time–temperature regimes and their interactions on quality parameters of Atlantic mackerel (Scomber scombrus) during chilled storage. The mackerel fillets were exposed to sous-vide treatment at 60, 75, and 90°C for 10, 15, and 20 min and further stored for 1, 3, and 7 days at 4 ± 1°C before analysis. Changes in pH, water content and cook loss, amount of water- and salt-soluble proteins, texture, and color parameters, as well as accumulation of lipid oxidation products in sous-vide-cooked mackerel were assessed. Sous-vide cooking time and temperature had the lowest contribution to the formation of primary and secondary products of lipid oxidation, as well as increase in yellowness of the fish flesh due to their accumulation; whereas duration of chilled storage led to a significant increase in oxidation and yellowness (p < 0.05). Duration of chilled storage also affected structural and textural properties of the fish muscle, leading to a decreased cook loss. At the same time, sous-vide cooking decreased the firmness of the fish muscle. Duration of chilled storage was found to have the highest significant effect (p < 0.001) on all physicochemical characteristics of sous-vide-cooked mackerel. [ABSTRACT FROM AUTHOR]

Reactive oxygen species (ROS) are generated in all aerobic organisms. Free radicals are highly reactive ROS that cause damage to biological materials. Fish is rich in polyunsaturated fatty acids, and hence, very prone to lipid peroxidation. Both lipid and protein oxidations are important for quality loss during storage of fish, with high impact on taste and texture. Also, there are interactions between protein and secondary lipid oxidation products (aldehydes) that occur in foods because the oxidation products from one reaction can further react with both lipids and proteins respectively. This review focuses on the mechanisms and pathways of the lipid and protein oxidation and their possible relationship. Additionally, the target amino acids and final impacts of this relationship were considered. We propose that the products of lipid oxidation promote protein oxidation in fish rather than the other way around specially, during frozen storage, while during postmortem changes protein oxidation dominates. Finally, it seems that, secondary products of lipid oxidation might have more impact on the functionality of proteins from both Michael addition and Schiff base reaction rather than lipid hydroperoxides and lipid radical transfer. [ABSTRACT FROM AUTHOR]

The aim of this work was to understand the effect of pH and chelators on free iron (Fe2+/Fe3+)-mediated oxidation in liposome dispersions made of marine phospholipids. Consumption of dissolved oxygen was used to follow lipid oxidation. The highest oxygen uptake rates were found at pH 4-5. The increase in pH (>5.7) enhanced autoxidation rate of Fe2+ to Fe3+ and lowered solubility of Fe3+ causing decrease in oxygen uptake rates. Simultaneously, the negative charge on the liposome vesicles increased with increasing pH improving the attraction between iron and liposomes. The retention of Fe3+ ions by phospholipids is suggested to prevent complete precipitation of Fe3+ at pH > 5, which facilitates a pro-oxidative activity of iron even at higher pH. The tested chelators reduced Fe2+ (10 μM) mediated oxidation at pH 5.5 and at 2:1 chelator-to-iron ratio in the following order: EDTA ∼ casein > citric acid > oxalic acid. However, when pH was reduced below the pKa of the EDTA carboxylic groups, EDTA lost its chelating abilities. The stability constants for complexes between the chelators and iron followed the same sequence as efficacy of the chelators at pH 5.5, making it an additional factor determining the efficacy of chelators. This study shows that the final oxidation rate is dependent on the overall dissolved iron in the system and the degree of attraction between iron and the surface of liposome vesicles at a given pH. Practical applications For successful addition of marine polyunsaturated lipids into emulsified food, it is important to understand how physicochemical conditions affect the pro-oxidative activity of iron and the antioxidant activity of metal chelators. This work addresses the role of pH in oxidation of marine liposomes, and the knowledge may help to characterise effective hurdles for lipid oxidation. This study shows that pH has an impact on iron solubility and attraction between iron and the liposome surface and also affects the efficacy of EDTA. This study also shows that by quantification of the dissolved oxygen consumption, it is possible to screen and evaluate the impact of surrounding conditions (pH, chelators) on iron-mediated oxidation in a water-based system. The study shows that oxidation rate is dependent on the overall dissolved iron in the system and the degree of attraction between iron and the surface of liposome vesicles at a given pH. [ABSTRACT FROM AUTHOR]

Low molecular weight (LMW) iron is present in most food in traces or significant amounts. Upon contact with unsaturated lipids LMW iron acts as a prooxidant. This creates oxidative stability problems for products containing marine polyunsaturated lipids. In this work, LMW iron-mediated oxidation in fish oil emulsions stabilized with phospholipids and Tween and in liposomes made from phospholipids was studied. Marine and non-marine sources of phospholipids were used. The aim was to evaluate how physicochemical factors and lipid properties affect the prooxidant activity of LMW iron. The oxidation was followed by measuring the rate of the dissolved oxygen consumption by fatty acids. Red-ox cycling of iron (Fe3+/Fe2+) aided by decomposition of the pre-formed lipid hydroperoxides was the major prooxidation mechanism in both emulsions and liposomes. The elimination of the pre-formed lipid hydroperoxides prevented LMW iron-mediated oxidation. The oxygen uptake rates were highest for various liposomes/emulsions at pH 4-5 making this an optimum pH for iron activity. The pro-oxidant effect of iron was reduced by using less unsaturated phospholipids, specific amounts of emulsifiers, a presence of chloride anions, or xanthan gum. This work suggests that the iron ions are tightly associated with the phosphate groups within the phospholipids heads. The measurement of oxygen consumption is a good tool for systematic oxidation studies in emulsions and liposomes, and may be useful for assessment of optimal conditions for reduction of LMW iron-mediated oxidation in emulsion-like systems. Practical applications: For a successful addition of marine polyunsaturated lipids into processed food, it is important to understand the pro-oxidation mechanisms of ubiquitous LMW iron, as well as how physicochemical conditions affect the pro-oxidative activity or LMW iron. This work addresses these issues in emulsions and liposomes and the knowledge may help to characterize effective hurdles for pro-oxidant activity of LMW iron. There is a need for quick and inexpensive oxidation assays in order to be able to screen and model the effects of different factors on the oxidative stability of lipids. The measurement of dissolved oxygen in emulsions and liposomes has been used in this study for evaluating the effect of the different psychochemical and chemical factors on iron-mediated oxidation. This method has a potential as a tool for assessment of optimal conditions for prevention of LMW iron-mediated lipid oxidation in emulsion type systems and understanding the possible mechanisms. [ABSTRACT FROM AUTHOR]

Highlights: [•] Influence of authentic human gastric juice on oxidation of marine lipids is evaluated. [•] Marine lipids in emulsion and liposomes oxidised during a modelled digestion period. [•] No difference was found between oxidation in an authentic gastric juice and a hydrochloric acid solution. [•] Gastric juice inhibited pro-oxidative activity of dietary iron ions, but not met-hemoglobin. [•] Beverages may both positively and negatively affect post-prandial oxidation of marine lipids. [Copyright &y& Elsevier]

The aim of this study was to assess lipid oxidation development in sous-vide cooked Atlantic mackerel during chilled storage by fluorescence microscopy coupled with chemical, physical and data analysis methods. Sous vide-cooking at 70 °C and 80 °C for 10 and 20 min was performed with and without use of antioxidants. Fluorescence micrographs of lipids extracted from the fish samples on 1st, 3rd, 7th, and 9th day of chilled storage at 4 ± 1 °C, were acquired in the wavelength region of λex 475/40 and λem 530/50 (44 FITC filter). The obtained images were numerically processed and the resulting data correlated with 2-thiobarbituric acid reactive substances (TBARS) determined by conventional chemical method of lipid oxidation analyses. Total lipid content and color characteristics of mackerel fillets were analyzed as well. The yellowness of the fish flesh significantly correlated (p < 0.05, R = 0.859) with conjugated trienes generated from thermal polymerization of lipids during chilled storage of sous-vide cooked mackerel. Results showed that higher temperature and cooking times generally accelerated lipid oxidation in mackerel samples prepared both with and without addition of antioxidants in terms of conjugated trienes and tetraenes. However, the addition of antioxidants enhanced the lipid oxidation stability of cooked mackerel fillets. • Fluorescence correlated with 2-thiobarbituric acid reactive substances. • Yellowness of the fish flesh correlated with conjugated tetraenes. • Conjugated structures increased with increased cooking temperature and time. • Antioxidants enhanced lipid oxidation stability of cooked mackerel fillets. [ABSTRACT FROM AUTHOR]

Abstract: The effect of five variables on the rate of lipid oxidation in fish oil was investigated. Two approaches for analysing the data were compared. The first approach was based on detailed chemical knowledge about the system, e.g. kinetics. The second approach was based on experimental design and empirical response surface modelling. The second approach gave slightly better predictions than the first. The measurement error in the experimental area of interest was estimated by repeated measurements, and based on this the signal to noise ratio was calculated. The SNR turned out to be the same in all of the measured levels, indicating that the measurement error of the system is proportional to the signal level. [Copyright &y& Elsevier]

• Mechanically filleted mackerel was susceptible to lipid oxidation during storage. • Dipping fillets into sodium erythorbate prolonged shelf-life from 2.5 to >15 months. • Results of TBARS did not correlate with sensory evaluation results. • TBARS a questionable method for 2. oxidation assessment in complex muscle systems. This study aimed to evaluate the shelf-life of mechanically filleted well-fed Atlantic mackerel during frozen storage at −25 °C and effect of treatment with antioxidants (sodium erythorbate and a polyphosphate mixture) and different antioxidant application methods (dipping, spraying and glazing). Both physicochemical measurements and sensory analysis were applied. Antioxidant treatments prolonged shelf-life of mackerel. Sensory analysis indicated that untreated fillets had a shelf-life of less than 2.5 months, while all antioxidant treated fillets exceeded that. The most effective treatment, dipping fillets into a sodium erythorbate solution, yielding a shelf-life of 15 months. Physicochemical methods used to evaluate degradation of lipids in the fillets were free fatty acids (FFA), lipid hydroperoxides (PV) and thiobarbituric acid reactive substances (TBARS). They did not correlate with sensory results and might therefore be a questionable choice for evaluation of oxidation and development of rancid flavour and odour in complex matrixes such as Atlantic mackerel. [ABSTRACT FROM AUTHOR]