Hemoglobin-mediated lipid oxidation and compositional characteristics of washed fish mince model systems made from cod (Gadus morhua), herring (Clupea harengus), and salmon (Salmo salar) muscle

Relationship between hemolysis and lipid oxidation in red blood cell-spiked fish muscle; dependance on pH and blood plasma

The relationship between hemolysis and lipid oxidation was explored in red blood cell (RBCs)-spiked washed cod mince (WCM). At pH 6.8 and 3 ± 1 °C, intact RBCs (71 µM Hb) delayed lipid oxidation by 1 day compared to WCM with partly or fully lysed RBCs which oxidized immediately. Intact RBCs also lowered peak peroxide value (PV) and thiobarbituric acid reactive substances (TBARS) with up to 59.5% and 48.1%, respectively. Adding 3% (v/w) blood plasma to RBC-spiked WCM delayed the lipid oxidation onset from 1 to 3-4 days without delaying hemolysis. At pH 6.4 the oxidation onset in RBC-WCM was the same as for pH 6.8 while at pH 7.2-7.6 lipid oxidation was suppressed for 7 days. Micrographs revealed RBC-lysis from day 2 at pH 6.4 but at pH 7.6, RBC stayed intact for ≥ 7 days. Thus, assuring presence of plasma-derived antioxidants and/or elevating muscle pH to avoid hemolysis can aid valorization of blood rich underutilized fish raw materials.

Effects of whole seaweed consumption on humans: current evidence from randomized-controlled intervention trials, knowledge gaps, and limitations

Seaweed is often recognized for its potential health benefits, attributed to its abundance of dietary fibers, protein, and polyphenols. While human observational studies have shown promise, the collective evidence from human intervention trials remains limited. This narrative review aims to comprehensively analyze the effects of seaweed intake on humans, while critically assessing the methodology, including Cochrane risk-of-bias assessment. A search was conducted in online databases, including PubMed, Scopus, and Google Scholar, covering the period from 2000 to May 2023. The focus was on randomized controlled clinical trials (RCTs) evaluating the impact of whole seaweed, either consumed as capsules, integrated into food products or as part of meals. Various health outcomes were examined, including appetite, anthropometric measures, cardiometabolic risk factors, thyroid function, markers of oxidative stress, and blood mineral concentrations. Out of the 25 RCTs reviewed, the findings revealed limited yet encouraging evidence for effects of seaweed on blood glucose metabolism, blood pressure, anthropometric measures, and, to a lesser extent, blood lipids. Notably, these favorable effects were predominantly observed in populations with type-2 diabetes and hypertension. Despite most trials selecting a seaweed dose aligning with estimated consumption levels in Japan, considerable variability was observed in the pretreatment and delivery methods of seaweed across studies. Moreover, most studies exhibited a moderate-to-high risk of bias, posing challenges in drawing definitive conclusions. Overall, this review highlights the necessity for well-designed RCTs with transparent reporting of methods and results. Furthermore, there is a need for RCTs to explore seaweed species cultivated outside of Asia, with a specific emphasis on green and red species. Such studies will provide robust evidence-based support for the growing utilization of seaweed as a dietary component in regions with negligible seaweed consumption, e.g., Europe.

Pilot-Scale Antioxidant Dipping of Herring (Clupea harengus) Co-products to Allow Their Upgrading to a High-Quality Mince for Food Production

To enable production of high-quality mince from herring backbones, a scalable antioxidant strategy is needed due to the high susceptibility of herring muscle to lipid oxidation. We here measured the stabilizing effect of lab-/pilot-scale predipping of herring backbones (30-500 kg) in antioxidant solutions prior to production of mechanically separated mince (MSM). The antioxidants were (i) Duralox MANC, a mixture of rosemary extract, ascorbic acid, α-tocopherol, and citric acid, and (ii) rosemary extract with or without isoascorbic acid. Delivery of the key rosemary-derived antioxidant components carnosol and carnosic acid was monitored during the dipping process and ice/frozen storage. Predipping in 2% Duralox MANC gave MSM with 26.7-31.7 mg/kg carnosol + carnosic acid and extended the oxidation lag phase from <1 to 12 days during ice storage and from <1 to 6 months during frozen storage compared to control. Dipping in 0.2% rosemary extract with or without 0.5% isoascorbic acid solution gave MSM with 20.6-28.2 mg/kg carnosol + carnosic acid and extended the lag phase to 6 days and 9 months during ice and frozen storage, respectively. Our results confirmed, in pilot scale, that predipping herring coproducts in antioxidant solutions is a promising strategy to utilize these raw materials for, e.g., mince and burger production rather than for low value products as fish meal.

Five cuts from herring (Clupea harengus): Comparison of nutritional and chemical composition between co-product fractions and fillets

Weight distribution, proximate composition, fatty acids, amino acids, minerals and vitamins were investigated in five sorted cuts (head, backbone, viscera + belly flap, tail, fillet) emerging during filleting of spring and fall herring (Clupea harengus). The herring co-product cuts constituted ∼ 60 % of the whole herring weight, with backbone and head dominating. Substantial amounts of lipids (5.8-17.6 % wet weight, ww) and proteins (12.8-19.2 % ww) were identified in the co-products, the former being higher in fall than in spring samples. Co-product cuts contained up to 43.1 % long-chain n-3 polyunsaturated fatty acids (LC n-3 PUFA) of total FA, absolute levels peaking in viscera + belly flap. All cuts contained high levels of essential amino acids (up to 43.3 %), nutritional minerals (e.g., iodine, selenium, calcium, and iron/heme-iron), and vitamins E, D, and B12. Co-products were, in many cases, more nutrient-rich than the fillet and could be excellent sources for both (functional) food and nutraceuticals.

Effects of Weak Acids on the Microbiological, Nutritional and Sensory Quality of Baltic Herring (Clupea harengus membras)

Baltic herring (Clupea harengus membras) pickled in vinegar is a common product in the Nordic countries. Other weak acids are used to cook and preserve fish in other food cultures. The aim of this study was to evaluate the potential of weak acids to produce safe and nutritious pickled fish products with varying sensory properties. The influence of acetic, citric, lactic, malic, and tartaric acids on the preservability and quality of pickled and marinated Baltic herring was studied by measuring microbiological quality, pH, chemical composition, and lipid oxidation and by sensory profiling. Pickling with these acids with pH levels of 3.7-4.2 resulted in pickled Baltic herring products with high microbiological quality. The results of the chemical analysis of the samples indicated that pickling and storage on marinade influenced the chemical composition of fish. The most significant changes in chemical composition were the increase in moisture and decrease in protein content of the samples during storage. Fat content decreased during the storage period in acetic acid and malic acid samples. All tested acids inhibited lipid oxidation for one month, but at three and four month time points, the content of oxidation products increased except in the samples pickled with tartaric acid. The highest oxidation level was observed in the case of citric acid and the lowest with tartaric acid. The results indicate that replacing acetic acid with other weak acids frequently used in the food industry results in pickled and marinated fish products with novel and milder sensory profiles.

Lipid oxidation in sorted herring (Clupea harengus) filleting co-products from two seasons and its relationship to composition

Lipid oxidation in ice-stored sorted herring fractions (head, backbone, viscera + belly flap, tail, fillet) from spring and fall, and its association with endogenous prooxidants, antioxidants and lipid substrates were investigated. Peroxide value (PV) and thiobarbituric acid reactive substances (TBARS) had increased significantly in all fractions after 1 day, but for both seasons, the most rapid PV and TBARS development occurred in head, which also had highest hemoglobin (Hb) levels and lipoxygenases (LOX) activity. Viscera + belly flap was overall the most stable part, and also had the highest α-tocopherol content. Pearson correlation analyses across all five fractions confirmed a significant impact of Hb, LOX and α-tocopherol on the lipid oxidation susceptibility, while content of total iron, copper, lipids or polyunsaturated fatty acids provided no significant correlation. Overall, the study showed which pro-oxidants that should be inhibited or removed to succeed with value adding of herring filleting co-products and the fillet itself.

A Recyclable Dipping Strategy to Stabilize Herring (Clupea harengus) Co-products During Ice Storage

Applying value-adding techniques to fish filleting co-products is rendered difficult due to their high susceptibility to lipid oxidation, microbial spoilage, and amine formation. In this study, a recyclable dipping strategy was developed and investigated for its ability to stabilize herring (Clupea harengus) co-products (head, backbone, caudal fin, intestines, belly flap, skin, and in some cases roe) against oxidation and microbial spoilage. From initial screening of seven antioxidative components/formulas in minced herring co-products during ice storage, an oil-soluble rosemary extract (RE-B) and isoascorbic acid (IAA) were identified as most promising candidates. These compounds were then formulated to a recyclable solution to be used for dipping of the herring co-products. The commercial Duralox MANC antioxidant mixture was used as a positive control. Dipping in 0.2% RE-B solution ± 0.5% IAA or in 2% Duralox MANC solutions remarkably increased the oxidation lag phase from < 1 day to > 12 days during subsequent storage on ice (0–1 °C) of minced or intact co-products, respectively, even when the antioxidant solutions were re-used up to 10 times. The dipping also reduced microbiological growth and total volatile basic nitrogen, but the effect became weaker with an increased number of re-using cycles. The presented dipping strategies could hereby facilitate more diversified end use of herring co-products from current fish meal to high-quality minces, protein isolates, or oils for the food industry.

From stale bread and brewers spent grain to a new food source using edible filamentous fungi

By-products from the food sector with a high load of organic matter present both a waste-handling problem related to expenses and to the environment, yet also an opportunity. This study aims to increase the value of stale bread and brewers spent grain (BSG) by re-introducing these residues to the food production chain by converting them to new protein-enriched products using the edible filamentous fungi Neurospora intermedia and Rhizopusoryzae. After 6 days of solid state fermentation (at 35°C, with a95% relative humidity and moisture content of 40% in the substrate) on stale bread, a nutrient-rich fungal-fermented product was produced. The total protein content, as analyzed by total amino acids, increased from 16.5% in stale sourdough bread to 21.1% (on dry weight basis) in the final product with an improved relative ratio of essential amino acids. An increase in dietary fiber, minerals (Cu, Fe, Zn) and vitamin E, as well as an addition of vitamin D2 (0.89 µg/g dry weight sample) was obtained compared with untreated stale bread. Furthermore, addition of BSG to the sourdough bread with the aim to improve textural changes after fermentation showed promising outcomes. Cultivation of N. intermedia or R. oryzae on stale sourdough bread mixed with 6.5% or 11.8% BSG, respectively, resulted in fungal-fermented products with similar textural properties to a commercial soybean burger. Bioconversion of stale bread and BSG by fungal solid state fermentation to produce a nutrient-enriched food product was confirmed to be a successful way to minimize food waste and protein shortage.

Effect of recovery technique, antioxidant addition and compositional features on lipid oxidation in protein enriched products from cod- salmon and herring backbones

The influence of recovery technique (pH-shift processing vs mechanical separation), antioxidant addition and endogenous factors on lipid oxidation in protein-enriched products from herring, salmon and cod backbones was investigated. Salmon-derived products were very stable during both ice and -20 °C storage. Contrary, peroxide value and TBA-reactive substances in herring- and cod-derived products increased rapidly during ice storage, with the pH-shift-produced protein isolates (PI) being most susceptible to oxidation in case of cod. Duralox MANC (0.5%) however largely increased the oxidation lag phase in both PI and mechanically separated meat (MSM); from <1 day to >15 days. At -20 °C, mainly the herring products oxidized, and particularly the MSM. Pearson correlation tests showed that endogenous levels of Hb, total Fe, ascorbic acid and α-tocopherol correlated significantly (p < 0.05) with lipid oxidation development. Evaluating the role of pre-processing storage indicated that fish co-products should be processed immediately after the filleting process unless antioxidants are added.

Impact of Processing Technology on Macro- and Micronutrient Profile of Protein-Enriched Products from Fish Backbones

Impacts of processing technology (mechanical separation and pH-shift processing) on protein recovery from salmon, herring and cod backbones and the content of macro- and micronutrients in the recovered protein enriched products were investigated. Mechanical separation led to higher protein recovery compared with the pH-shift process and using both techniques, recovery ranked the species as herring > salmon > cod. However, the pH-shift process up-concentrated protein from herring and salmon backbones more efficiently than mechanical separation by removing more fat and ash. This consequently reduced n-3 PUFA and vitamin D content in their protein isolates compared with the backbones and mechanically separated meat (MSM). Cod protein isolate, however, contained higher levels of these nutrients compared with MSM. Mechanical separation concentrated vitamins E and C in salmon MSM but not for cod and herring. Opposite, pH-shift processing reduced levels of these two vitamins for cod and herring backbones, while vitamins D and C were reduced for salmon. For minerals, selenium, calcium, magnesium, and potassium were lower in protein isolates than MSM, while copper, zinc, iron and manganese were similar or higher. Overall, there is a major potential for upcycling of fish backbones to food ingredients, but processing technology should be carefully balanced against the desired nutrient profile and final application area.

Improving the Stability of Red Blood Cells in Rainbow Trout (Oncorhynchus mykiss) and Herring (Clupea harengus): Potential Solutions for Post-mortem Fish Handling to Minimize Lipid Oxidation

This study aimed at limiting hemolysis of fish red blood cells (RBCs) as a strategy to limit hemoglobin (Hb)-induced lipid oxidation during post-mortem handling and processing. Effects of varying temperature, salinity, and mechanical impact were studied using washed resuspended RBCs (wr-RBCs) and whole blood (WB) from rainbow trout (Oncorhynchus mykiss) and herring (Clupea harengus). The wr-RBCs were most stable avoiding mechanical stress, keeping isotonic conditions (0.9–1.3% NaCl) and low temperature 0–6 °C, with predicted minimum at 2.5 °C. When compared at the same salinity, it was found that hemolysis was more pronounced in herring than trout wr-RBCs. Furthermore, WB was more stable than wr-RBCs, showing protecting the effects of blood plasma. Studying individual plasma components, stabilizing effects were found from glucose, proteins, and ascorbic acid. This study indicates that small adjustments in the early handling and processing of fish such as changing salinity of storage and rinsing solutions could minimize Hb contamination of the fish muscle and thereby improve quality.

Effect of antioxidants on the sensory quality and physicochemical stability of Atlantic mackerel (Scomber scombrus) fillets during frozen storage

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.

Size Matters: Ingestion of Relatively Large Microplastics Contaminated with Environmental Pollutants Posed Little Risk for Fish Health and Fillet Quality

In this study, we investigated biological effects associated with ingestion of polystyrene (PS) microplastic (MPs) in fish. We examined whether ingestion of contaminated PS MPs (100-400 μm) results in chemical stress in rainbow trout (Oncorhynchus mykiss) liver and we explored whether this exposure can affect the oxidative stability of the fillet during ice storage. Juvenile rainbow trout were fed for 4 weeks with four different experimental diets: control (1) and feeds containing virgin PS MPs (2) or PS MPs exposed to sewage (3) or harbor (4) effluent. A suite of ecotoxicological biomarkers for oxidative stress and xenobiotic-related pathways was investigated in the hepatic tissue, and included gene expression analyses and enzymatic measurements. The potential impact of MPs exposure on fillet quality was investigated in a storage trial where lipid hydroperoxides, loss of redness and development of rancid odor were assessed as indications of lipid peroxidation. Although, chemical analysis of PS MPs revealed that particles sorb environmental contaminants (e.g., PAHs, nonylphenol and alcohol ethoxylates and others), the ingestion of relatively high doses of these PS MPs did not induce adverse hepatic stress in fish liver. Apart from small effect on redness loss in fillets of fish exposed to PS MPs, the ingestion of these particles did not affect lipid peroxidation or rancid odor development, thus did not affect fillet's quality.

Oxidation of marine oils during in vitro gastrointestinal digestion with human digestive fluids - Role of oil origin, added tocopherols and lipolytic activity

The formation of malondialdehyde (MDA), 4-hydroxy-2-hexenal (HHE), 4-hydroxy-2-nonenal (HNE), and 4-oxo-2-nonenal (ONE) in cod liver-, anchovy-, krill-, and algae oil during in vitro digestion with human gastrointestinal fluids was investigated. Adding rabbit gastric lipase, lipase inhibitor (orlistat) and tocopherols to cod liver oil, lipolysis and oxidation was also studied. Among the marine oils, the highest aldehyde levels (18 µM MDA, 3 µM HHE and 0.2 µM HNE) were detected after digestion of cod liver oil, while the lowest levels were detected in krill and algae oils. Addition of rabbit gastric lipase significantly increased the release of HNE during the digestion. Orlistat significantly reduced lipolysis and MDA formation. Formation of MDA and HHE was delayed by tocopherols, the tocopherol mix Covi-ox® T 70 EU being more effective than pure α-tocopherol.

Sensory properties of frozen herring (Clupea harengus) from different catch seasons and locations

Freezing of herring (Clupea harengus) for human consumption is increasing in the Nordic herring industry, either onboard the fishing vessels or right after landing. The quality of frozen herring as a raw material does not only depend on the frozen storage conditions applied, but also on compositional features, something which in turn can vary with season and catching ground. To unravel the link between biological variations, basic muscle composition, and sensory properties of frozen herring, a unique herring raw material was caught by commercial fishing vessels at three locations: around Iceland, outside the Norwegian coast, and in Kattegat/Skagerrak. The samplings were done according to a specific scheme and conducted over several seasons and 2 years. The herring was converted into butterfly fillets, packed in cardboard boxes, frozen, and then stored at -20 °C or -80 °C for up to 18 mo. The sensory quality was characterized by objective sensory profiling. It was shown that two generalized sensory variables could be defined from a principal component analysis of the sensory data. Except for the expected pronounced effect from storage time, the most distinct variation followed the lipid content, which in turn varied with season. An unexpected conclusion was that catching location only had a minor affect on the changes in sensory quality of herring during frozen storage. Knowledge about how season and catching location affect herring during frozen storage will be useful for optimizing the utilization of herring for frozen storage for human consumption.

PRACTICAL APPLICATION

The results of this study constitute important information for the herring processing industry when handling raw materials with different geographical and seasonal history. The reported information on a highly equal sensory quality of geographically diverse raw materials will give consumers and retailers valuable knowledge on the changes in eating quality to expect after long-term frozen storage under conditions similar to household freezers or refrigerated counters in supermarkets.

Oxidation of cod liver oil during gastrointestinal in vitro digestion

Oxidation of cod liver oil rich in long-chain n-3 polyunsaturated fatty acids (LC n-3 PUFA) was investigated during a gastrointestinal (GI) in vitro digestion. The digestion stimulated TBA-reactive substances (TBARS) formation in both the gastric and intestinal steps, whereas levels of lipid hydroperoxides remained nearly constant. The presence of digestive compounds was decisive for the TBARS development because TBARS did not change when the cod liver oil was subjected only to the temperature and pH gradient of the GI model. Preformed oxidation products in the cod liver oil resulted in further elevated TBARS levels during the digestion. Addition of hemoglobin (11.5 μM) to emulsified cod liver oil dramatically increased TBARS and lipid hydroperoxide levels during GI digestion, whereas 1 mg α-tocopherol/g oil did not show any protection against oxidation. Specific concern thus needs to be taken in the design of foods containing LC n-3 PUFA to preserve these lipids and avoid harmful oxidation, both before and after consumption.

Effects of storage atmosphere and heme state on the color and visible reflectance spectra of salmon ( Salmo salar ) fillets

It has previously been observed that the color of mackerel muscle is dependent on the status of heme as myoglobin and hemoglobin and hence the storage atmosphere. This study gives strong indications of this being the case also in salmon. Three different storage conditions were used to promote the oxidized, reduced, and carbon monoxide (CO) bound forms of heme in salmon and mackerel fillets. Color determination (instrumental color analysis, imaging, and sensory evaluation) and spectroscopic measurements were performed to study how spectral changes corresponded to color variations. Storage in CO significantly increased the redness in mackerel. This was also seen in salmon to such a degree that it was visible over normal levels of salmon carotenoids. Air storage increased the yellowness and reduced the redness in mackerel, but this effect was partly concealed in salmon by the astaxanthin absorption. The spectral differences due to storage condition could be ascribed to the spectral features characterizing heme of different oxidation states and bound to different ligands. The status of heme should therefore always be considered when experiments related to salmon color are performed. The findings could help in the understanding, control, and prediction of color loss in salmon during processing, storage, and transport.

Role of the raw composition of pelagic fish muscle on the development of lipid oxidation and rancidity during storage

The muscle composition of a pelagic fish species, Atlantic mackerel (Scomber scombrus), has been studied to determine the relationship with its susceptibility to develop lipid oxidation during chilled storage. For such an aim, the initial concentrations of the major components (water, total lipids, protein, and PUFAs) and minor pro-oxidant and antioxidant components (ascorbic acid, α-tocopherol, hemoglobin, total iron, LMW-iron, copper, and zinc) of different batches of mackerel were characterized. For the study, several batches of mackerel were caught during the spring and summer periods. The different batches were subjected to chilled storage, and the onset of lipid oxidation was statistically related with the initial muscle composition. Results showed significant compositional differences among the mackerel lots, especially for the muscle lipid content (2.83-9.50%). In a first step, a Pearson correlation test was used to check the influence of each component on the progress of lipid oxidation. Results showed a significant relationship between shelf life and water and total lipid contents. Multiple regression was performed to reveal the contribution of each component to the susceptibility to lipid oxidation. The model obtained combines the content of PUFAs, total iron, hemoglobin, and ascorbic acid. An accurate prediction of shelf life in terms of rancidity was achieved by the model created (R(2) = 0.9975). These results establish that the levels of endogenous pro-oxidants and antioxidants present in fish muscle together with the polyunsaturated lipids are relevant factors affecting the shelf life of mackerel muscle.

Galloylated polyphenols as inhibitors of hemoglobin-catalyzed lipid oxidation in fish muscle

The influence of galloyl residues on the antioxidant mechanism of polyphenols to prevent hemoglobin-promoted lipid oxidation was investigated by using polyphenolic fractions with different degrees of galloylation: nongalloylated structures from pine bark (IVP), medium-galloylated from grape pomace (IVG), and high-galloylated from witch hazel bark (IVH). Hemoglobin (Hb) from the pelagic fish horse mackerel (Trachurus trachurus) was employed as a Hb standard. In vitro experiments showed an important increase in the deoxygenation and autoxidation of horse mackerel Hb at acidic pH values. All polyphenolic fractions significantly reduced the redox stability of Hb in buffer solutions, showing a greater deoxygenation and methemoglobin (metHb) formation in the presence of IVH, followed in decreasing order by IVG and IVP. However, galloylated polyphenols (IVH and IVG) were efficient to inhibit the oxidation of the oxygenated Hb (OxyHb) and the formation of lipid oxidation products in chilled washed fish muscle. This antioxidant activity of galloylated proanthocyanidins showed a positive relationship with the phenolic concentration. Polyphenols devoid of galloyl groups (IVP) were less active to prevent either Hb oxidation or lipid oxidation in fish muscle. The results draw attention to the potential role of galloyl residues to lessen Hb-catalyzed lipid oxidation in muscle and to maintain Hb in reduced and oxygenated states, which exhibit lower pro-oxidant activity as compared to the metHb and deoxyHb species.

pH-induced shift in hemoglobin spectra: a spectrophotometeric comparison of atlantic cod ( Gadus morhua ) and mammalian hemoglobin

Due to a pH-sensitive effect in many fish hemoglobins (Hb), analytical errors may occur when mammalian Hb is used as a standard in quantitative spectrophotometric multicomponent analysis of fish blood. The aim of this work was to examine differences in the optical spectra of mammalian (human) and fish (farmed Atlantic cod) Hb subjected to pH 7.4 and 6.5. The absorption spectra of the common derivatives, deoxy- (HHb), oxy- (OHb), carboxy- (COHb), and methemoglobin (metHb), were determined in the spectral range of 450-700 nm. The metHb spectra of fish differed considerably from the corresponding human Hb spectra, whereas only minor differences in OHb, HHb, and COHb were found. Cod Hb was significantly (P < 0.05) influenced by a drop in pH compared to mammalian Hb. This resulted in deoxygenation of the Hb and increased autoxidation. For human Hb, a pH-independent isosbestic point in the spectra of OHb, HHb, and metHb at 523 nm was found. This isosbestic point was not found in the absorption spectra of cod Hb. In conclusion, spectra of cod metHb and human metHb behave differently. This must thus be taken into account in spectrophotometric multicomponent analysis. Ideally, Hb in muscle or blood should be determined by comparison to a standard made from the same species.

Effect of caffeic acid on haemoglobin-mediated lipid and protein oxidation in washed cod mince during ice and frozen storage

BACKGROUND

Little is known about the relation between haemoglobin (Hb)-mediated lipid and protein oxidation in muscle foods and how these two reactions can be inhibited by naturally occurring antioxidants. This study was aimed at evaluating (1) lipid oxidation and protein oxidation induced by 20 µmol L(-1) Hb during chilled and frozen storage of washed cod mince and (2) the efficiency of 10-1000 ppm (0.063-6.3 mmol L(-1)) caffeic acid in preventing these reactions.

RESULTS

Addition of 20 µmol L(-1) Hb increased peroxide value (PV), rancid odour, protein carbonylation, protein insolubilisation, redness loss and α-tocopherol loss in ice-stored washed cod mince. Since both lipid and protein oxidation developed at the same time, it was not possible to conclude which reaction initiated the other. All studied reactions were efficiently inhibited by ≥ 50 ppm caffeic acid, which could be a result of α-tocopherol regeneration, general radical scavenging, reduced formation of oxidised Hb forms and/or conformational changes in Hb structure. During frozen storage the only clear effect of Hb was increased PV, and here caffeic acid was less efficient as an antioxidant.

CONCLUSION

Hb-induced lipid and protein oxidation occurred quickly in ice-stored washed cod mince, and the two reactions could not be separated in time. During frozen storage, Hb caused only limited lipid oxidation. Caffeic acid (≥50 ppm) was an efficient antioxidant during ice storage.

Involvement of methemoglobin (MetHb) formation and hemin loss in the pro-oxidant activity of fish hemoglobins

The capacity of Atlantic pollock ( Pollachius pollachius ), seabass ( Dicentrarchus labrax ), and horse mackerel ( Trachurus trachurus ) hemoglobin (Hb) to promote lipid oxidation has been evaluated in liposomes and washed minced horse mackerel muscle. The pro-oxidant ability of fish Hbs was related with their vulnerability to suffer oxidation to metHb and release hemin either in spontaneous situation or in the presence of two representative lipid oxidation products, linolein hydroperoxides and trans-2-pentenal. The results indicated similar effectiveness to promote lipid oxidation in liposomes and washed fish muscle: pollock Hb > horse mackerel Hb > seabass Hb. Pollock Hb showed a more elevated autoxidation rate and spontaneous hemin loss and also faster oxidation to metHb in the presence of hydroperoxides and trans-2-pentenal. The autoxidation and spontaneous hemin loss rates were intermediate for horse mackerel Hb, whereas seabass Hb exhibited the highest stability. The isoelectrofocusing (IEF) pattern of pollock Hb revealed the presence of isoforms with elevated anionic character, which are known to have poor oxygen affinity at the pH values found in fish muscle (pH 7.0-5.5). In agreement with the IEF patterns, pollock Hb was less oxygenated at pH 6.8, and seabass Hb exhibited more oxygenation than did horse mackerel. MetHb forms were significantly more effective in catalyzing lipid oxidation than the corresponding reduced fish Hbs and free hemin. The present investigation highlights a direct correlation between the pro-oxidant capacity of fish Hbs and their susceptibility to undergo metHb formation and hemin loss and also suggests a potential role of lipid oxidation byproducts in activating the pro-oxidative action of hemoglobin.