Role of lingonberry press cake in producing stable herring protein isolates via pH-shift processing: A dose response study

The effects of cross-processing lingonberry press cake (LPC) (2.5-30 %, dw/dw) with herring co-products on protein yield, oxidative stability and color of pH-shift-produced protein isolates were investigated. Even at 2.5 % LPC, the formation of volatile oxidation-derived aldehydes, including hexanal, (E)-2-hexenal, heptanal, octanal, and 2,4-heptadienal, were prevented during the actual protein isolate production. Adding 10 % LPC successfully prevented formation of all these aldehydes also during eight days ice storage which was explained by the partitioning of phenolics, especially ideain (1.09 mg/g dw) and procyanidin A1 (65.5 mg/g dw), into isolates. Although higher amounts of LPC (20-30 %) further prolonged the oxidation lag phase, it reduced total protein yield, increased the consumption of acid and base, and darkened protein isolates. Therefore, it is recommended to use 10 % LPC when pH-shift-processing sensitive fish raw materials as a route to mitigate lipid oxidation and at the same time promote industrial symbiosis and more circular food production.

Oxidative stability differences of aqueous model systems of photoautotrophic n-3 LC-PUFA rich microalgae: The antioxidative role of endogenous carotenoids

Microalgae rich in omega-3 long-chain polyunsaturated fatty acids (n-3LC-PUFA) have already shown their potential for developing functional food rich in these healthy fatty acids. Not only could they offer a more sustainable alternative for the fish stock that is currently relied upon but is unable to keep up with the demand, enrichment with certain microalgae also leads to oxidatively stable products. Although the reason for this stability has been attributed to the presence of endogenous carotenoids, further insight into their antioxidative role is missing and would be clarifying for selecting the proper microalgae for food enrichment. In trying to further accomplish this, a storage experiment (4 weeks, 37 °C) was set up with the parallel analysis of both oxidation products (primary and secondary) and carotenoids of two aqueous model systems of different (promising) microalgae (Nannochloropsis and Phaeodactylum). The results showed a clear difference in oxidative stability despite both microalgae containing endogenous carotenoids: Nannochloropsis led to oxidatively unstable and Phaeodactylum to oxidatively stable products. This was clearly confirmed by the analysis of n-3LC-PUFA throughout storage which showed a breakdown of half of the n-3LC-PUFA for Nannochloropsis. All carotenoids (violaxanthin, zeaxanthin and β-carotene for Nannochloropsis, and fucoxanthin and β-carotene for Phaeodactylum) acted as an antioxidant as shown by their degradation throughout storage, but the difference in oxidative stability pointed out an impact of carotenoid content and (possibly) type. The presence of a sufficient amount of carotenoids seems to be an important factor for perceiving oxidative stability. Phaeodactylum has shown to be more potent for food enrichment.

Formation of Lipid-Derived Flavors in Dry-Cured Mackerel (Scomberomorus niphonius) via Simulation of Autoxidation and Lipoxygenase-Induced Fatty Acid Oxidation

In this study, lipoxygenase (LOX) extracted from dry-cured mackerel was purified, resulting in a 4.1-fold purification factor with a specific activity of 493.60 U/min·g. LOX enzymatic properties were assessed, referring to its optimal storage time (1-2 days), temperature (30 °C), and pH value (7.0). The autoxidation and LOX-induced oxidation of palmitic acid (C16:0), stearic acid (C18:0), oleic acid (C18:2n9c), linoleic acid (C18:2n6c), arachidonic acid (C20:4), EPA (C20:5), and DHA (C22:6n3) were simulated to explore the main metabolic pathways of key flavors in dry-cured mackerel. The results showed that the highest LOX activity was observed when arachidonic acid was used as a substrate. Aldehydes obtained from LOX-treated C18:1n9c and C18:2n6c oxidation, which are important precursors of flavors, were the most abundant. The key flavors in dry-cured mackerel were found in the oxidative products of C16:0, C18:0, C18:1n9c, C18:2n6c, and C20:4. Heptanaldehyde could be produced from autoxidation or LOX-induced oxidation of C18:0 and C18:1n9c, while nonal could be produced from C18:1n9c and C18:2n6c oxidation. Metabolic pathway analysis revealed that C18:1n9c, C18:2n6c, EPA, and DHA made great contributions to the overall flavor of dry-cured mackerel. This study may provide a relevant theoretical basis for the scientific control of the overall taste and flavor of dry-cured mackerel and further standardize its production.

Enzyme-assisted aqueous extraction of fish oil from Baltic herring (Clupea harengus membras) with special reference to emulsion-formation, extraction efficiency, and composition of crude oil

Enzyme-assisted aqueous extraction (EAAE) is a green, and scalable method to produce oil and protein hydrolysates from fish. This study investigated the role of different parameters on emulsion formation, oil recovery, and the composition of crude oil during EAAE of Baltic herring (Clupea harengus membras). Fatty acid compositions, lipid classes, tocopherols, and oxidation status of the EAAE crude oils were studied. Compared to solvent-extracted oil, EAAE resulted in a lower content of phospholipids accompanied by a 57% decrease in docosahexaenoic acid. Changing fish to water ratio from 1:1 to 2:1 (w/w) with ethanol addition led to the greatest reduction (72%) of emulsion, which resulted in an increase in oil recovery by 11%. The addition of ethanol alone, or reduction of enzyme concentration from 0.4% to 0.1% also reduced emulsion-formation significantly. Overall, emulsion reduction resulted in higher content of triacylglycerols and n - 3 polyunsaturated fatty acids in the crude oil extracted.

Antioxidative properties of fish roe peptides combined with polyphenol on the fish oil oleogel

BACKGROUND

This study aimed to investigate the effects of large yellow croaker (Larimichthys crocea) roe protein hydrolysate (LYCPH)-polyphenol (catechin (CA), gallic acid (GA), and tannic acid (TA)) conjugates on the oxidative stability of fish oil in an oleogel system.

RESULTS

Scanning electron microscopy and Fourier transform infrared spectroscopy suggested that the LYCPH-polyphenol conjugates were nearly spherical and non-covalent and that covalent effects could coexist between LYCPH and polyphenols. LYCPH-TA exhibited the highest ABTS scavenging, reducing capacities, and emulsifying stability. Raman spectra and chemometrics revealed that LYCPH-TA loaded with oleogels had the best oxidative stability. Additionally, 32 volatile compounds were identified in fish oil by headspace gas chromatography-ion mobility spectrometry.

CONCLUSION

Overall, this study demonstrated that fish oil oleogels loaded with LYCPH-polyphenol conjugates could inhibit fish oil oxidation. © 2022 Society of Chemical Industry.

Effect of Feeding Acid Oils on European Seabass Fillet Lipid Composition, Oxidative Stability, Color, and Sensory Acceptance

Acid oils (AO) are fat by-products of edible oil refining with a high energetic value, being an interesting option for a more sustainable aquaculture nutrition. This study was conducted to evaluate the effects of the partial replacement of fish oil (FO) in diets by two AO instead of crude vegetable oils on the lipid composition, lipid oxidation and quality of fresh European seabass fillets, and after their commercial refrigerated storage for 6 days. Fish were fed with five different diets, the added fat being FO (100%) or a blend of FO (25%) and another fat (75%): crude soybean oil (SO), soybean-sunflower acid oil (SAO), crude olive pomace oil (OPO), or olive pomace acid oil (OPAO). Fresh and refrigerated fillets were assessed for fatty acid profile, tocopherol (T) and tocotrienol (T3) composition, lipid oxidative stability, 2-thiobarbituric acid (TBA) value, volatile compound content, color, and sensory acceptance. Refrigerated storage did not affect T + T3 total content but increased secondary oxidation products (TBA values and volatile compound contents) in fillets from all diets. The FO substitution decreased EPA and DHA and increased T and T3 in fish fillets, but the recommended human daily intake of EPA plus DHA could still be covered with 100 g of fish fillets. Both a higher oxidative stability and a lower TBA value were found in SO, SAO, OPO, or OPAO fillets, obtaining the greatest oxidative stability in OPO and OPAO fillets. Sensory acceptance was not affected by the diet or the refrigerated storage, while the differences found in color parameters would not be perceived by the human eye. According to the oxidative stability and acceptability of flesh, SAO and OPAO are adequate replacements of FO as energy source in European seabass diets, which implies that these by-products can be upcycled, improving the environmental and economical sustainability of aquaculture production.

A point of view on human fat olfaction - do fatty derivatives serve as cues for awareness of dietary fats?

Fat (triglycerides) consumption is critical for the survival of animals, including humans. Being able to smell fat can be advantageous in judging food value. However, fat has poor volatility; thus, olfaction of fat seems impossible. What about fatty acids that comprise fat? Humans smell and discriminate medium-chain fatty acids. However, no conclusive evidence has been provided for the olfactory sense of long-chain fatty acids, including essential acids such as linoleic acid (LA). Instead, humans likely perceive the presence of essential fatty acids through the olfaction of volatile compounds generated by their oxidative breakdown (e.g., hexanal and γ-decalactone). For some people, such scents are pleasing, especially when they come from fruit. Nonetheless, it remains unclear whether the olfaction of these volatiles leads to the recognition of fat per se. Nowadays, people often smell LA-borne aldehydes such as E,E-2,4-decadienal that occur appreciably, for example, from edible oils during deep frying, and are pronely captivated by their characteristic "fatty" note, which can be considered a "pseudo-perception" of fat. However, our preference for such LA-borne aldehyde odors may be a potential cause behind the modern overdose of n-6 fatty acids. This review aims to provide a view of whether and, if any, how we olfactorily perceive dietary fats and raises future purposes related to human fat olfaction, such as investigating sub-olfactory systems for detecting long-chain fatty acids.

The Potential of Phaeodactylum as a Natural Source of Antioxidants for Fish Oil Stabilization

Worldwide, fish oil is an important and rich source of the health-beneficial omega-3 long-chain polyunsaturated fatty acids (n-3 LC-PUFA). It is, however, troubled by its high susceptibility towards lipid oxidation. This can be prevented by the addition of (preferably natural) antioxidants. The current research investigates the potential of Phaeodactylum carotenoids in this regard. The oxidative stability of fish oil and fish oil with Phaeodactylum addition is evaluated by analyzing both primary (PV) and secondary (volatiles) oxidation products in an accelerated storage experiment (37 °C). A first experimental set-up shows that the addition of 2.5% (w/w) Phaeodactylum biomass is not capable of inhibiting oxidation. Although carotenoids from the Phaeodactylum biomass are measured in the fish oil phase, their presence does not suffice. In a second, more elucidating experimental set-up, fish oil is mixed in different proportions with a Phaeodactylum total lipid extract, and oxidative stability is again evaluated. It was shown that the amount of carotenoids relative to the n-3 LC-PUFA content determined oxidative stability. Systems with a fucoxanthin/n-3 LC-PUFA ratio ≥ 0.101 shows extreme oxidative stability, while systems with a fucoxanthin/n-3 LC-PUFA ratio ≤ 0.0078 are extremely oxidatively unstable. This explains why the Phaeodactylum biomass addition did not induce oxidative stability.

Photo-Oxidative Stability of Aqueous Model Systems Enriched with Omega-3 Long-Chain Polyunsaturated Fatty Acid-Rich Microalgae as Compared to Autoxidative Stability

Several species of microalgae are promising as an alternative source of omega-3 long-chain polyunsaturated fatty acids (n-3 LC-PUFA). Photoautotrophic species show the greatest potential, since incorporating them into food products leads to oxidatively stable products; however, the presence of photosensitizers could reduce the shelf-life due to the appearance of photo-oxidation on exposure to light. This study investigated the oxidative impact of illumination for aqueous model suspensions enriched with Phaeodactylum (phototrophic microalgae─containing potential photosensitizers) and Schizochytrium (heterotrophic microalgae─lacking photosensitizers) during storage for 28 days at 37 °C. Primary (peroxide value) and secondary (volatiles with gas chromatography (GC)-mass spectrometry) oxidation products, n-3 LC-PUFA content (GC), and pigments (high-pressure liquid chromatography) were assessed. The results showed that photo-oxidation did not cause oxidative instability for Phaeodactylum samples compared with strong autoxidation in Schizochytrium samples. For the Phaeodactylum-enriched suspensions, only minimal photo-oxidation could be detected and the n-3 LC-PUFA content remained stable throughout storage regardless of illumination.

Chemical Compositional Changes in Over-Oxidized Fish Oils

A recent study has reported that the administration during gestation of a highly rancid hoki liver oil, obtained by oxidation through sustained exposure to oxygen gas and incident light for 30 days, causes newborn mortality in rats. This effect was attributed to lipid hydroperoxides formed in the omega-3 long-chain polyunsaturated fatty acid-rich oil, while other chemical changes in the damaged oil were overlooked. In the present study, the oxidation condition employed to damage the hoki liver oil was replicated, and the extreme rancidity was confirmed. A detailed analysis of temporal chemical changes resulting from the sustained oxidative challenge involved measures of eicosapentaenoic acid/docosahexaenoic acid (EPA/DHA) omega-3 oil oxidative quality (peroxide value, para-anisidine value, total oxidation number, acid value, oligomers, antioxidant content, and induction time) as well as changes in fatty acid content, volatiles, isoprostanoids, and oxysterols. The chemical description was extended to refined anchovy oil, which is a more representative ingredient oil used in omega-3 finished products. The present study also analyzed the effects of a different oxidation method involving thermal exposure in the dark in contact with air, which is an oxidation condition that is more relevant to retail products. The two oils had different susceptibility to the oxidation conditions, resulting in distinct chemical oxidation signatures that were determined primarily by antioxidant protection as well as specific methodological aspects of the applied oxidative conditions. Unique isoprostanoids and oxysterols were formed in the over-oxidized fish oils, which are discussed in light of their potential biological activities.

Effect of Phospholipase A1 and High-Pressure Homogenization on the Stability, Toxicity, and Permeability of Egg Yolk/Fish Oil Emulsions

Enzymatic treatment of egg yolk with phospholipases can enhance its emulsifying properties and thermal stability. Additionally, a two-step process (primary and secondary homogenization) could form emulsions with better stability. Thus, in this study we used a split-split-plot in time design to assess the effect of enzymatic treatment, processing, and storage conditions on the encapsulation efficiency, stability, toxicity, and permeability of egg yolk/fish oil emulsions stored up to 10 days at 45 °C. Egg yolk solutions before and after treatment with phospholipase A₁ were used as carriers of fish oil containing ≥82% eicosapentaenoic and docosahexaenoic acids. Emulsions were formed by primary (24,000 rpm, 4 min) and secondary (200 MPa) homogenization. The combined effect of treatment with phospholipase A₁ and secondary homogenization resulted in emulsions with improved stability, increased the encapsulation efficiency of the carriers, and reduced the release of oil to the particle surface, resulting in lower formation of oxidation products. At the end of storage time, none of the emulsions were toxic to Caco-2 cells at a concentration of 75 μg/mL medium, while nonencapsulated fish oil reduced cell viability to 81%. Only eicosapentaenoic acid was detected in the basolateral side of Caco-2:HT29 monolayers, and its apparent permeability from nonencapsulated fish oil was significantly lower than that from emulsions.

Evaluations of the Peroxidative Susceptibilities of Cod Liver Oils by a 1H NMR Analysis Strategy: Peroxidative Resistivity of a Natural Collagenous and Biogenic Amine-Rich Fermented Product

High-resolution 1H nuclear magnetic resonance (NMR) analysis was employed to molecularly screen the lipid, lipid oxidation product (LOP), and antioxidant compositions of four natural (unrefined) cod liver oil (CLO) products. Products 1-3 were non-fermented CLOs, whilst Product 4 was isolated from pre-fermented cod livers. Supporting analytical data that were acquired included biogenic amine, flavanone, tannin, phenolic antioxidant, α-tocopherol, and oxygen radical absorbance capacity (ORAC) determinations by recommended HPLC, LC/MS/MS, or spectrophotometric methods. SDS-PAGE, HPLC, and 1H NMR analyses investigated and determined collagenous antioxidants and their molecular mass ranges. 1H NMR analysis of aldehydic LOPs was employed to explore the susceptibilities/resistivities of each CLO product to peroxidation that is induced by thermal stressing episodes (TSEs) at 180°C, or following prolonged (42 day) storage episodes at 4 and 23 °C. Product 4 displayed extremely high ORAC values, which were much greater than those of Products 1-3, and that were predominantly ascribable to significant levels of peroxidation-blocking and/or aldehyde-consuming collagenous polypeptides/peptides and ammoniacal agents therein. Significantly lower levels of toxic aldehydes were generated in the pre-fermented Product 4 during exposure to TSEs, or the above long-term storage episodes. These results confirmed the enhanced peroxidative resistivity of a fermented, antioxidant-fortified natural CLO product over those of non-fermented unrefined products. Product 4: Green Pasture Blue Ice™ Fermented Cod Liver Oil.

Metabolism of 13C-Labeled Fatty Acids in Term Human Placental Explants by Liquid Chromatography-Mass Spectrometry

Placental lipid transport and metabolism are poorly understood despite the importance for fetal development and lifelong health. We aimed to explore fatty acid (FA) processing in human villous placental explants from seven uncomplicated term singleton pregnancies delivered by elective cesarean section. Explants were treated with stable isotope-labeled palmitic acid (13C-PA), oleic acid (13C-OA), or docosahexaenoic acid (13C-DHA) for 3, 24, or 48 hours. Stable isotope-labeled lipids synthesized by placental explants from labeled FA were quantified, alongside endogenous unlabeled placental lipids, by liquid chromatography-mass spectrometry. Labeled phosphatidylcholines (PCs), triacylglycerols (TAGs), and phosphatidylethanolamines were detected in explants, whereas labeled lysophosphatidylcholines were found in both explants and conditioned media. 13C-PA was primarily directed into PC synthesis (74% of 13C-PA-labeled lipids), whereas 13C-OA was directed almost equally into PC and TAG synthesis (45% and 53%, respectively, of 13C-OA-labeled lipids). 13C-DHA was only detectable in TAGs. TAGs demonstrated the highest isotopic enrichment for all 13C-FAs with 13C-OA-TAGs comprising >50% of total OA-TAGs (unlabeled and labeled), consistent with TAGs being a labile and accessible reservoir for FA storage. Variations in lipid incorporation were correlated to maternal glycemia and body mass index, suggesting that this experimental model could be used to investigate the effect of maternal factors on placental lipid metabolism. We conclude that lipid metabolic partitioning of freshly imported FAs into labile and less labile lipid reservoirs in placenta is FA dependent. This process may partly mediate the physiological preferential transplacental transfer of particular FAs to the fetus, but may also be implicated in the fetoplacental pathophysiology of maternal metabolic dysfunction.

Effective Prevention of Oxidative Deterioration of Fish Oil: Focus on Flavor Deterioration

Docosahexaenoic acid (DHA) and eicosapentaenoic acid (EPA), both abundant in fish oil, are known to have significant biochemical and physiological effects primarily linked to the improvement of human health, especially cardiovascular and brain health. However, the incorporation of fish oil into foods and beverages is often challenging, as fish oil is very easily oxidized and can cause undesirable flavors. This review discusses this rapid formation of the fishy and metallic off-flavors, focusing especially on an early stage of fish oil oxidation. Although oxidative stability and quality of commercialized fish oil have improved over the past few years, there is a still a problem with its application: Flavor deterioration can be found even at very low oxidation levels. This review also notes the effective way to inhibit the formation of the volatile compounds responsible for the flavor deterioration.

Volatiles formation in gelled emulsions enriched in polyunsaturated fatty acids during storage: type of oil and antioxidant

Gelled emulsions with carrageenan are a novel type of emulsion that could be used as a carrier of unsaturated fatty acids in functional foods formulations. Lipid degradation through volatile compounds was studied in gelled emulsions which were high in polyunsaturated oils (sunflower or algae oil) after 49 days of storage. Aqueous Lavandula latifolia extract was tested as a natural antioxidant. Analysis of the complete volatile profile of the samples resulted in a total of 40 compounds, classified in alkanes, alkenes, aldehydes, ketones, acids, alcohols, furans, terpenes and aromatic hydrocarbons. During storage, the formation of the volatile compounds was mostly related to the oxidation of the main fatty acids of the sunflower oil (linolenic acid) and the algae oil (docosahexaenoic acid). Despite the antioxidant capacity shown by the L. latifolia extract, its influence in the oxidative stability in terms of total volatiles was only noticed in sunflower oil gels (p < 0.05), where a significant decrease in the aldehydes fraction was found.

The effects of different extraction methods on composition and storage stability of sturgeon oil

The objective of this study was to assess the effect of different extraction methods on oil yield, colour attributes, oxidative stability, fatty acids composition and production of volatile compounds in sturgeon oil during storage. The supercritical fluid extraction (SFE) method with carbon dioxide resulted in higher oil yields, better colour attributes, and higher oxidative stability compared to other traditional extraction methods such as enzymatic extraction, amino, and wet reduction. After storage at 4 °C for 33 days, the aldehyde content in oil extracted by the enzymatic extraction and wet reduction methods was twice as high as that obtained by the other methods. There was a significant reduction in the content of total acids in oils extracted by the enzymatic extraction and wet reduction methods (p<0.05), whereas amine compounds were mainly detected in oil extracted by the amino method. The oil extracted by SFE exhibited higher UFA and lower SFA. Significant diffidence among PUFA with C above 20 was observed in oil extracted with SFE.

Stability of omega-3 LC-PUFA-rich photoautotrophic microalgal oils compared to commercially available omega-3 LC-PUFA oils

Microalgae are the primary producers of omega-3 LC-PUFA, which are known for their health benefits. Their oil may thus be a potential alternative for fish oil. However, oxidative and hydrolytic stability of omega-3 LC-PUFA oils are important parameters. The purpose of this work was therefore to evaluate these parameters in oils from photoautotrophic microalgae (Isochrysis, Phaeodactylum, Nannochloropsis gaditana, and Nannochloropsis sp.) obtained with hexane/isopropanol (HI) and hexane (H) and compare them with commercial omega-3 LC-PUFA oils. When the results of both the primary and secondary oxidation parameters were put together, it was clear that fish, tuna, and heterotrophic microalgae oil are the least oxidatively stable oils, whereas krill oil and the microalgae oils performed better. The microalgal HI oils were shown to be more oxidatively stable than the microalgal H oils. The hydrolytic stability was shown not to be a problem during the storage of any of the oils.

Oxidative Stability of Polyunsaturated Edible Oils Mixed With Microcrystalline Cellulose

The oxidative stability of mixtures of edible oils containing polyunsaturated fatty acids (PUFA) and microcrystalline cellulose (MCC) was investigated. The mixtures studied consisted of oils of either camelina (CAM), cod liver (CLO), or salmon (SO) mixed with either colloidal or powdered MCC. A 50:50 (w/w) ratio of oil:MCC resulted in an applicable mixture containing high levels of PUFA edible oil and dietary fiber. The oxidative stability of the formulated mixtures and the pure oils was investigated over a period of 28 days. The peroxide value (PV) was assessed as a parameter for primary oxidation products and dynamic headspace gas chromatography mass spectrometry (GC/MS) was used to analyze secondary volatile organic compounds (VOC). CAM and the respective mixtures were oxidatively stable at both 4 and 22 °C during the storage period. The marine oils and the respective mixtures were stable at 4 °C. At 22 °C, an increase in hydroperoxides was found, but no increase in VOC was detected during the time-frame investigated. At 42 °C, prominent increases in PV and VOC were found for all oils and mixtures. Hexanal, a common marker for the degradation of n-6 fatty acids, propanal and 2,4-heptadienal (E,E), common indicators for the degradation of n-3 fatty acids, were among the volatiles detected in the headspace of oils and mixtures. This study showed that a mixture containing a 50:50 ratio of oil:MCC can be obtained by a low-tech procedure that does not induce oxidation when stored at low temperatures during a period of 1 month.

Change of volatile compounds in fresh fish meat during ice storage

The change of volatile compounds in fresh fish meat during 3- to 4-d ice storage was investigated for several fishes using an electronic nose system and a gas chromatography-mass spectrometer (GC/MS) with headspace solid-phase micro-extraction (SPME). Principal component analyses for samples using the electronic nose system revealed that the increase of some volatile compounds during storage was rapid in sardine (Sardinops melanostictus), jack mackerel (Trachurus japonicus), and chub mackerel (Scomber japonicus); moderate in yellowtail (Seriola quinqueradiata), skipjack (Katsuwonus pelamis), and young oriental bluefin tuna (Thunnus thynnus). In contrast to these fishes, the change was little in "white meat" fishes such as red seabream (Chrysophrys major), Japanese seabass (Lateolabrax japonicus), flatfish (Paralichthys olivaceus), puffer (Lagocephalus wheeleri), and bartail flathead (Platycephalus indicus). SPME-GC/MS analysis showed that some aldehydes and alcohols such as 1-heptanol, (E)-2-octenal, (E)-2-hexenal, 1-pentanol, (E,E)-2,4-heptadienal,2,4-hexadienal, 1-hexanol, 4-heptenal, and so forth increased rapidly in jack mackerel and chub mackerel, slowly in skipjack, and a little in red seabream and puffer during the storage. The increase of these compounds was considered to have an effect on the change of electronic nose response. Hexanal was a dominant compound increased from the beginning of the storage in jack mackerel. The increase of volatile compounds was little in red seabream and puffer. The increase of these aldehydes and alcohols was thought to be an appropriate marker for monitoring the freshness of "fresh" fish except for white meat fish.

PRACTICAL APPLICATION

The results of this study are ready to apply for preventing fishy off-flavor of fisheries products. Lipid oxidative derivatives other than trimethylamine contributed to fresh fish flavor; therefore, to prevent lipid oxidation seemed important.