Influence of formaldehyde in the formation of fluorescence related to fish deterioration

 In previous studies fluorescence detection at different excitation/emission maxima during common fish processing has been used. A bathochromic shift towards higher wavelength maxima was observed and measured as the ratio between absorption at two of the maxima tested. This fluorescence ratio (δF) value correlates positively with fish damage. In the present work, the influence of formaldehyde (FA) on the value δF was studied. A model system was set up in which FA reacted at 30°C for 25 days with propylamine and fish muscle. It was observed that FA was less able to produce fluorescent compounds compared with common fish oxidation products that were also tested, i. e. propanal and hexanal. However, in the presence of both lipid oxidation aldehydes, the FA-containing mixtures led to a higher δF value. Model systems consisting of FA and fatty fish (sardine) muscle produced more fluorescence than FA and lean fish (cod), because of the formation of lipid oxidation compounds under the reaction conditions of the former systems. It is thus concluded that the presence of FA in a reacting medium enhances fluorescence formation, such that δF be can used as an accurate measure of fish damage. It is thought that measurement of δF in processes such as the freezing of gadoid fish, in which both FA and lipid oxidation are produced, could be of benefit. Received: 23 June 1997     

Effect of pH on fluorescence formation related to fish deterioration

 Earlier studies have investigated fluorescence at different excitation/emission maxima during common types of fish processing. A shift towards higher wavelength maxima was observed and measured as the ratio between two of the maxima tested. This fluorescence ratio (δF) correlated with increased fish damage. The present work is focused on the effect that pH can have on the formation of fluorescent compounds in fish muscle systems. Minced hake muscle was homogenised with 0.1 M phosphate buffer of different pH values (5, 6, 7 and 8) and was stored at 30  °C for up to 30 days. Lipid damage, measured as the δF value of the aqueous reaction medium and the fish lipid extract, indicated little difference between the effect of different pH values under the conditions employed in the present experiment. The effetct of formaldehyde (FA) in the same reaction medium was also evaluated. It was observed that FA had a positive effect on the fluorescence shift occurring in the aqueous reaction medium, so that a higher δF value was observed for pH 7 and pH 8, especially for the latter. It is concluded that changes in the δF value during fish storage and/or processing are of special interest as, in addition to FA formation and lipid oxidation, significant pH increases are expected to occur as a result of damage. Received: 2 February 1998 / Revised version: 6 April 1998     

Differential lipid damage in various muscle zones of frozen hake (Merluccius merluccius)

 A comparison of the lipid damage produced in different hake zones was carried out during frozen storage at –11 and –18  °C. Three light muscle zones and the dark muscle were considered. Lipid oxidation [conjugated dienes; thiobarbituric acid index (TBA-i); fluorescence formation] and hydrolysis (free fatty acids, FFA) were determined. The most predominant lipid damage in all zones was hydrolysis, at the end of storage reaching values of about 40% (for the light muscle zones) and 12% (for the dark muscle) of the total lipids at –11  °C. Significant (P<0.05) correlation value (r=0.67–0.85) relationships between the frozen storage time and the FFA content were obtained for the four muscle zones at both temperatures. A comparison of the regression lines slopes in the different zones showed that a lower (P<0.05) lipolitic activity was produced in the dark muscle compared to the three light zones at both temperatures. A low lipid oxidation development was produced in the three light muscle parts, so that no significant differences between them could be assessed. However, the dark muscle showed a higher oxidation development (TBA-i and fluorescence formation) as a result of a higher lipid content and the presence of prooxidant constituents. Received: 16 June 1998     

Differential lipid damage in various muscle zones of frozen hake (Merluccius merluccius)

 A comparison of the lipid damage produced in different hake zones was carried out during frozen storage at –11 and –18  °C. Three light muscle zones and the dark muscle were considered. Lipid oxidation [conjugated dienes; thiobarbituric acid index (TBA-i); fluorescence formation] and hydrolysis (free fatty acids, FFA) were determined. The most predominant lipid damage in all zones was hydrolysis, at the end of storage reaching values of about 40% (for the light muscle zones) and 12% (for the dark muscle) of the total lipids at –11  °C. Significant (P<0.05) correlation value (r=0.67–0.85) relationships between the frozen storage time and the FFA content were obtained for the four muscle zones at both temperatures. A comparison of the regression lines slopes in the different zones showed that a lower (P<0.05) lipolitic activity was produced in the dark muscle compared to the three light zones at both temperatures. A low lipid oxidation development was produced in the three light muscle parts, so that no significant differences between them could be assessed. However, the dark muscle showed a higher oxidation development (TBA-i and fluorescence formation) as a result of a higher lipid content and the presence of prooxidant constituents.     

Influence of the in vivo addition of alpha-tocopheryl acetate with three lipid sources on the lipid oxidation and fatty acid composition of Beluga sturgeon, Huso huso, during frozen storage

This study was conducted to investigate the effect of dietary alpha-tocopheryl acetate (vitamin E) and oil sources on fish flesh quality characteristics of Huso huso during frozen storage. Practical-type diets containing 0 or 250 mg vitamin E kg⁻¹ with three lipid sources, fish oil (FO), soybean oil (SO) and canola oil (CO), were fed to H. huso for 120 days. Fillet samples were analysed fresh or after storage at −18 ± 1 °C for 12 months. Replacement of FO by SO and CO in diets for H. huso significantly altered the fatty acid (FA) profile, which also influenced the FA composition during frozen storage. Dietary vitamin E had a significant effect on muscle vitamin E content and lipid oxidation during storage (P > 0.05). Oxidation was reduced for fish fed vitamin E and results showed that dietary vitamin E supplementation can slow down the level of lipid oxidation in H. huso muscles during frozen storage.     

Food authenticity using natural carbon isotopes (12C, 13C, 14C) in grass-fed and grain-fed beef

Natural carbon isotopes, ¹²C, ¹³C, and ¹⁴C, help to authenticate/trace foods and beverages. Levels of total carbon (TC), ¹³C (δ¹³C), and ¹⁴C in muscle and lipid tissues from grass-fed versus grain-fed steers are reported. The δ¹³C in muscle versus lipid of steaks were around 5‰ higher in grain over grass-fed (p<0.05). The δ¹³C and ¹⁴C levels were higher in muscle over lipid tissues while the opposite was true for TC (p<0.05). TC content was around 20% higher in lipid over muscle due to different elemental compositions, lipid versus muscle, not carbon isotopes discrimination.     

Inhibition of lipid damage in refrigerated salmon (Oncorhynchus kisutch) by a combined treatment of CO2 packaging and high-pressure processing

The effect of a previous combined treatment (CO₂-enriched modified atmosphere packaging, MAP and high-pressure processing, HPP, 150 MPa/5 min) on lipid stability of refrigerated (10 days/4 °C) salmon (Oncorhynchus kisutch) was studied. The following processing conditions were compared: B-0 (fish without MAP or HPP), B-1 (fish packaged under MAP and without HPP), B-2 (fish subjected to HPP without MAP) and B-3 (fish subjected to MAP and HPP). An inhibitory effect (P < 0.05) on lipid hydrolysis and oxidation was obtained by the presence of CO₂ in the packaging medium; values detected at day 10 for B-0 and B-1 fish were 80.72 and 49.61 (g free fatty acids, FFA, kg⁻¹ lipids), 6.14 and 2.81 (meq active oxygen kg⁻¹ lipids; peroxide value), 5.05 and 3.10 (mg malondialdehyde kg⁻¹ muscle), and 5.56 and 2.70 (fluorescence ratio), respectively. Furthermore, inhibition of lipid damage was observed for HPP alone; values detected at day 10 for B-2 fish were 76.24 (g FFA kg⁻¹ lipids) and 5.28 (meq active oxygen kg⁻¹ lipids). The lowest average values for lipid hydrolysis and oxidation were obtained in samples corresponding to the combined treatment (B-3 batch), differences being significant (P < 0.05) at day 10 for FFA (41.43 g kg⁻¹ lipids), peroxide (1.84 meq kg⁻¹ lipids) and fluorescence (2.50) values.     

Fluorescence changes in amine model systems related to fish deterioration

Earlier studies have investigated fluorescence at different excitation/emission maxima during common fish processing. A shift towards higher wavelength maxima was observed and measured as the ratio between absorption at two of the maxima tested. This fluorescence ratio (δF) value correlated with increased fish damage. In the present work, different kinds of amines were tested to compare the fluorescence produced with that measured during fish processing. Amines with different substitution degree, and primary amines with different steric hindrance and chain length were reacted with cod liver oil and glutaraldehyde at 30°C in model systems. All the amine classes produced changes in the fluorescent properties of the systems, higher δF values being associated with lower degree of substitution and steric hindrance of the −NH₂ group, and also as a result of a longer chain length and higher concentration of the amine compound.     

Effect of brine freezing on the rancidity development during the frozen storage of small pelagic fish species

Brine freezing was applied to two small pelagic underutilised fish species (mackerel, Scomber scombrus; horse mackerel Trachurus trachurus). Rancidity development was studied during their frozen (–18 °C) storage up to 9 months, and quality change results were compared to common freezing conditions (control treatment). Fish samples treated under brine freezing conditions showed a higher lipid oxidation development (peroxide value and thiobarbituric acid index) and worse marks on some sensory attributes (general aspect, odour and colour) than control fish. However, samples treated under brine freezing conditions provided a lower lipid hydrolysis development (free fatty acid formation) and better scores for consistency. Comparison between both fish species led to a higher secondary lipid oxidation formation (thiobarbituric acid index) for mackerel, while horse mackerel showed to be more prone to interaction compound formation (fluorescence detection); however, both fish species showed the same shelf-life times (3 and 5 months for brine and control freezing conditions, respectively). As a result of the brine freezing conditions, an increase in NaCl content in white muscle of both species was observed. According to the results obtained in the present work, the brine freezing treatment is not recommended for these two small pelagic fish species.     

Influences of potassium ferrocyanide on lipid oxidation of salted cod (Gadus morhua) during processing, storage and rehydration

The effects of added potassium ferrocyanide (CN) in different concentrations (2.5 ppm, 7.5 ppm and 100 ppm), in salt, on lipid oxidation in cod during salting, storage and rehydration were examined in this study. An increase in CN concentration accelerated lipid oxidation of the salted cod, as observed by increases in lipid hydroperoxides (PV) and thiobarbituric acid-reactive substances (TBARS), as well as in the development of fluorescence compounds (δF_or and δF_aq). A yellow discolouration (higher b^∗ value) of salted cod was associated with higher levels of oxidation derivatives. High correlation between PV, TBARS and free fatty acid (FFA), as well as between FFA and δF_or, was found. The results of principal component analysis showed that TBARS, b^∗ value and δF_or were the strongest indicators of lipid oxidation during salting and storage.     

Effect of dietary levels of fat, α-tocopherol and astaxanthin on colour and lipid oxidation during storage of frozen rainbow trout (Oncorhynchus mykiss) and during chill storage of smoked trout

 Female rainbow trout (Oncorhynchus mykiss) with an initial weight of 0.8–0.9 kg were raised in two experiments including a total of 2550 fish divided into 17 groups. The fish were raised for 6 months on 13 different feeds (four fish groups were replicates) varying in dietary levels of fat (27% or 32%), astaxanthin (40, 70 or 100 mg astaxanthin/kg feed) and vitamin E (α-tocopherol; 100, 300 or 600 mg all-rac-α-tocopheryl acetate/kg feed). The levels of fat, astaxanthin and α-tocopherol in the fillets all increased with increasing dietary levels of each feed component. Furthermore, astaxanthin deposition was found to be significantly improved by increasing the dietary fat level from 27% to 32%, but was not affected by dietary levels of α-tocopherol. The highest deposition of α-tocopherol was found in fish fed the lowest level of astaxanthin (40 mg/kg), whereas α-tocopherol deposition was unaffected by the dietary fat level. Frozen storage (–28  °C) of gutted, cleaned and glazed raw fish for 18 months significantly reduced astaxanthin and α-tocopherol levels, while lipid oxidation, measured as thiobarbituric acid reactive substances (TBARS) was limited. In the first experiment, the highest TBARS levels were found during frozen storage in fish fed the lowest level of astaxanthin (40 mg/kg versus 70 mg/kg or 100 mg/kg); unaffected by dietary levels of α-tocopherol (100 mg/kg versus 600 mg/kg), whereas the dietary astaxanthin level (70 mg/kg versus 100 mg/kg) did not influence lipid oxidation in frozen fish in the second experiment. After brine injection, fillets of fish were smoked and a vacuum-packed (95%), sliced product in a transparent laminate was produced. The quality (pigmentation and lipid oxidation) during 3 weeks of illuminated, chill storage (3  °C) was compared for smoked products produced from fresh fish and from fish stored at –28  °C for 12 months and 18 months. Smoked fillets from fish fed 32% fat were found to be less red than those from fish fed 27% fat, and the astaxanthin content and surface redness of the smoked product decreased during chill storage. Lipid oxidation was pronounced in smoked trout, but a high level of α-tocopherol in the fillet significantly reduced lipid oxidation during chill storage of the smoked product. Lipid oxidation in smoked fillets from fish fed 32% fat was more pronounced than in fish fed 27% fat, but increasing the dietary α-tocopherol level from 300 mg/kg feed to 600 mg/kg feed effectively counteracted the negative effect of the high-fat diet on lipid oxidation in the smoked product. Astaxanthin did not affect lipid oxidation in the chill-stored smoked product, in contrast to the frozen, raw fish. Astaxanthin seems to protect against the very early stages of lipid oxidation, while α-tocopherol is more important as an antioxidant at more advanced stages of lipid oxidation. Received: 8 January 1998 / Revised version: 23 March 1998     

Lipid changes during long-term storage of canned tuna (Thunnus alalunga)

 Lipid damage during prolonged storage of canned fish was studied. Albacore tuna was processed under two sterilization conditions (115°C, 74 min; 120°C, 40 min) and then stored for up to 6 years. Analyses (lipid oxidation and hydrolysis, browning and formation of fluorescent compounds) of the lipids extracted from the white muscle of the fish and the packing oils were carried out. Muscle lipids were partially extracted by the packing oil, so that an increase in the storage time produced higher levels of free fatty acids, browning and fluorescence development in the packing oils. As regards the types of muscle, little difference between them throughout the canned storage was detected. Received: 17 February 1997 / Revised version: 12 May 1997     

Effect of a Polyphenol–Vacuum Packaging on Lipid Deterioration During an 18-Month Frozen Storage of Coho Salmon (<Emphasis Type="Italic">Oncorhynchus kisutch</Emphasis>)

A packaging system combining a polyphenol-rich film and vacuum (PPRF–VP) was applied to farmed coho salmon (Oncorhynchus kisutch) muscle for an 18-month storage (−18 °C). For it, two different concentrations of polyphenol compounds (namely, p-coumaric and ferulic acids) obtained from a barley husk extract were applied (PPRF–VP conditions) and compared to vacuum packaging without polyphenol presence (vacuum control; VP condition) and to packaging in the absence of vacuum and polyphenols (control; CP condition). The study was addressed to lipid hydrolysis and oxidation development and to lipid changes related to nutritional value. Both PPRF–VP conditions provided an inhibitory effect (p < 0.05) on conjugated diene and fluorescent compound formation in frozen salmon. Compared to CP condition, vacuum packaging (PPRF–VP and VP conditions) led to lower (p < 0.05) peroxide and anisidine values and to an inhibitory effect (p < 0.05) on α- and γ-tocopherol losses. No effect (p > 0.05) of polyphenol presence and vacuum packaging could be inferred on free fatty acid formation (hydrolysis development) and on polyunsaturated fatty acid retention (polyene index assessment). A low rancid odour development was observed in all kinds of fish samples, this being lower (p < 0.05) in fish kept under vacuum (PPRF–VP and VP) conditions.     

Influence of storage time and temperature on lipid deterioration during cod (Gadus morhua) and haddock (Melanogrammus aeglefinus) frozen storage

Lean fish deterioration during frozen storage (−30 and −10 °C) for up to 1 year was studied by the assessment of lipid changes. Comparison between a formaldehyde (FA)-forming species (cod) and a non-FA-forming one (haddock) was carried out. Lipid damages were measured on the basis of free fatty acids (FFA), peroxide value (PV), thiobarbituric acid index (TBA-i) and fluorescent compounds. In both species at −30 °C, most lipid damage indices showed significant correlations with the storage time. However, at −10 °C, only the FFA and fluorescence detections provided significant correlations with the storage time. Comparison between the fish species showed higher lipid oxidation (PV and TBA-i) and hydrolysis (FFA content) in haddock than in cod at −10 °C; however, a higher fluorescence development was observed in cod at the same temperature. At −30 °C, little differences in lipid damage indices were detected between the two species. © 1999 Society of Chemical Industry     

LIPID CHANGES IN FROZEN STORED FILLETS FROM PRE- AND POSTSPAWNED HAKE (MERLUCCIUS HUBBSI MARINI)

The lipid composition of frozen stored fillets from pre‐ and postspawned hake was studied. The total lipid (TL) content in the chloroform/methanol extract from unfrozen postspawned hake was four times higher than that of prespawned fish. After freezing, the TL content of postspawning hake muscle remained unchanged whereas the TL extracted from prespawning fish muscle increased about 90%. The TL extractability of muscle from fish in both different gonadal conditions was not affected by frozen storage. Lipolysis in frozen stored fillets from prespawned hake occurs principally by hydrolytic action on phospholipids (PL), and phosphatidylcholine was the main PL hydrolyzed. Triacylglycerols were the main substrates hydrolyzed in frozen stored fillets from postspawned hake. Freezing and frozen storage affected polyenoics and n‐3 fatty acids (FA). The decrease in the contents of n‐3 FA in fillets from postspawned hake was lower than that observed in fillets from prespawned fish.     

Variations in lipid and fatty acid contents in different body parts of Black Sea whiting,Merlangius merlangus euxinus (Nordmann, 1840)

Whiting is a commercially important fish species of the world. This study demonstrates monthly variations in lipid and fatty acid (FA) contents of muscle, liver and roes of Black Sea whiting, Merlangius merlangus euxinus. Significant changes occurred in lipid contents between months (P < 0.05) with the highest values representing in liver 33.8–64.5%. Total polyunsaturated fatty acids (PUFA) in all groups were higher than total saturated and monounsaturated FAs with significant variations between months (P < 0.05). The highest PUFA of muscles, livers and roes were 60.0, 45.9 and 50.9%, respectively. The main FA was docosahexaenoic acid (DHA) of muscle tissue and roes, while oleic acid was the major FA in livers. Although about 164–357 g in muscle tissue or 224–392 g of whiting roe are necessary to consume to cover 1 g day^?1 of eicosapentaenoic acid (EPA)+DHA for a healthy diet, only as low as 5.5–10.0 g of liver would be enough to cover the same amount of daily EPA+DHA requirement. The results indicated that whiting livers constitute a rich and underexploited source of polyunsatured FAs. Furthermore, the results may aid further research on the nutritional studies, the physiology and stock management of whiting species.     

The use of stable isotopes for authentication of gadoid fish species

The rise of processed seafood in international trade has increased the feasibility of fish species substitution. Gadidae fish species are sold commercially as salted fish, and differences in price between fish of different species may lead to falsification. The present study addresses this falsification issue by attempting to discriminate among salted Atlantic cod and salted saithe using isotope ratio mass spectrometry (IRMS) as well as the stable isotope ratios of carbon (δ¹³C) and nitrogen (δ¹⁵N). δ¹⁵N in tissues with lower turnover rates (bone and skin) and in tissues with greater turnover rates (muscle) can be used to authenticate the species of salted fish samples when distinguishing between Atlantic cod and saithe.     

Impact of icing systems with aqueous,ethanolic and ethanolic‐aqueous extracts of alga Fucus spiralis on microbial and biochemical quality of chilled hake (Merluccius merluccius)

The study focuses on the impact of icing systems with aqueous (AQ batch), ethanolic (ET batch) and ethanolic‐aqueous (ET‐AQ batch) extracts of alga Fucus spiralis on the microbial and biochemical quality of chilled hake (Merluccius merluccius). After a 13‐day storage, comparison with fish kept under traditional ice proved a significant (P < 0.05) antimicrobial effect against aerobes, psychrotrophs, proteolytic and lipolytic bacteria, derived of the presence of F. spiralis ethanolic extracts in the icing medium (ET and ET‐AQ batches). Additionally, an inhibitory effect of both ethanol extracts was also obtained concerning lipid oxidation development (i.e. secondary and tertiary lipid oxidation compounds). Additionally, lipid damage assessment showed lower mean values in tertiary oxidation compound formation in hake belonging to the ET‐AQ batch throughout the whole storage period. Present research indicates that ET‐AQ ice condition can lead to a marked quality and safety enhancement as well as to profitable commercial value increases.     

Effect of brine pre-treatment on lipid stability of frozen horse mackerel (<Emphasis Type="Italic">Trachurus trachurus</Emphasis>)

The rancidity development during the frozen storage (-20 °C) of an under-utilised medium-fat fish species (horse mackerel; Trachurus trachurus) was investigated. Special attention was given to a pre-freezing treatment consisting of an immersion in NaCl solution (5%, 10%, and 20%) and its effect on lipid damage during the fish frozen storage. Lipid hydrolysis (free fatty acid content) and oxidation (conjugated dienes formation; peroxide value, PV; thiobarbituric acid index, TBA-i; fluorescence formation, FR) were studied up to 270 days of frozen storage. Oxidative rancidity measured by the PV, TBA-i, and FR showed an increase with the frozen storage time and also as a result of an increasing salt content in fish muscle. A high peroxide formation was observed at day 210 of frozen storage, especially in the case of 20% NaCl treated samples. Lipid hydrolysis also increased with the frozen storage time; at the end of the experiment (270 days), a decreasing effect of muscle salt content on lipid hydrolysis was observed. Employment of appropriate antioxidant additions is recommended if salting pre-treatment is to be needed to avoid a large lipid oxidation development and ensure a longer shelf-life time.     

Fatty acid composition and oxidative stability of oils recovered from acid silage and bacterial fermentation of fish (Sea bass – Dicentrarchus labrax) by‐products

Lipid quality and fatty acid compositions of fish oils recovered from fish (Sea bass – Dicentrarchus labrax) waste silages produced with formic acid (FA) and five different LAB strains (Lactobacillus plantarum (LP), Pediococcus acidilactici (PA), Enterococcus gallinarum (EG), Lactobacillus brevis (LB) and Streptococcus spp. (ST)) were assessed to ensure for the usage for human consumption. Generally, it was observed that there were no significant differences between PUFA contents (23.27–23.64%). Peroxide (PV) (2.12 meq active O₂/per kg of oil) and TBA values (1.07 mg malonaldehyde (MA) g^?1 oil) of fish oils from acid silage were significantly higher than those of the fermented ones (1.14–1.91 meq active O₂ kg^?1, 0.67–0.81 mgMA g^?1 oil, respectively). Anisidine values (AV) were determined in range of 8.04–11.14 for fermented silages and 13.08 from acid silage. The highest totox value (17.33 ± 0.88) was also detected in acid silage oil whereas fermented groups gave totox value in the range of 10.40–13.88. It can be concluded that the initial lipid quality of fermented fish waste silages was better than the initial lipid quality of acid fish waste silage. Therefore, fish oils recovered from fermented silages can be used as food additives or supplements for animal and human diets.