Fishy Off-flavor Research Articles

Physicochemical Characteristics and Flavor Properties of Texturized Dual-Proteins Extrudates: Effect of Surimi to Soybean Flour Ratio.

This study investigated the effects of surimi to soybean flour ratio (0:10, 1:9, 2:8, 3:7, 4:6) on the physicochemical characteristics and flavor properties of dual-proteins extrudates. The increasing ratio of surimi improved the color of extrudates and raised the apparent viscosity of the mixed raw materials, which led to the decrease of extrudates' thickness. The excess ratio of surimi and soybean flour (more than 2:8) was bad for extrudates' physicochemical characteristics with sharply decreased tensile strength, macroscopic longitudinal fracture, broken and unevenly distributed microstructure, increased water mobility and decreased free water content. However, the increasing ratio of surimi had no effect on the protein secondary structure of extrudates. Sensory evaluation, E-tongue and E-nose analysis suggested that adding surimi significantly changed the flavor properties of extrudates, with increased sweetness and umami taste, and an appropriate ratio (2:8 or 3:7) could reduce the beany flavor and without an obvious fishy off-flavor.

Effects of tannic acid interfacial absorption on the physicochemical stability of algal oil-loaded emulsions and inhibition of fishy off-flavor

In the present study, the inhibition of fishy off-flavor and destabilization in algae oil-loaded emulsions by tannic acid (TA) adsorption on octenyl succinic anhydride (OSA) starch interfaces were investigated. The changes of typical fishy off-flavor components in the emulsion, physiochemical stability, and interaction between TA and OSA starch were analyzed. The TA fortification significantly prevented the production of fishy smell-related volatile components such as heptanal and (E, E)-3, 5-octadiene-2-one. The proportion of TA on the interface was more than 90 %, forming an interfacial film with the antioxidant function. The emulsions stabilized by OSA starch-TA complexes had better oxidative and physical stability. The isothermal titration calorimetry suggested that the interaction between OSA starch and TA included hydrogen bonding and van der Waals forces (ΔG = -13.272 kJ·mol−1·K−1, ΔH = -1.302 × 103 kJ·mol−1, ΔS = -4.326 kJ·mol−1·K−1). Altogether, these results provided application guidance for developing starch-based oil-in-water emulsion systems with antioxidant properties.

Effects of thermoultrasonic treatment on characteristics of micro-nano particles and flavor in Greenland halibut bone soup

In order to investigate the effects of thermoultrasonic treatment (TUT) on the formation of colloidal micro-nano particles (MNPs) and the quality of halibut bone soup, nutrients, particle characteristics, and flavor characteristics were analyzed. The morphology of MNPs was studied using an optical microscope. Results showed that TUT could increase the nutrient content (total sugars, 22.15 mg/100 mL; water soluble proteins, 173.24 mg/mL; fatty acids, 1779.7 mg/100 mL; solids, 3.16 g/100 mL), reduce the particle size (605.92 nm) and interfacial tension. Meanwhile, TUT make the halibut bone soup has better emulsifying characteristics and stability. The contents of flavor substances, such as esters, 5′-nucleotides, organic acids in the halibut bone soup were more abundant, while the contents of hexanal and 1-octen-3-ol and fishy off-flavor were reduced in TUT group. The overall odor and taste outline were more harmonious. Therefore, TUT can be used in the production of high quality fish bone soup, and TUT could be considered as a good deep processing technology for halibut bone and improve economic efficiency.

Effects of Thermoultrasonic Treatment on Characteristics of Micro-Nano Particles and Flavor in Greenland Halibut Bone Soup

In order to investigate the effects of thermoultrasonic treatment (TUT) on the formation of colloidal micro-nano particles (MNPs) and the quality of halibut bone soup, nutrients, particle characteristics, and flavor characteristics were analyzed. The morphology of MNPs was studied using an optical microscope. Results showed that TUT could increase the nutrient content (total sugar, 22.15 mg/100 mL; water-soluble protein, 173.24 mg/mL; fatty acid, 1779.7 mg/100 mL; solid matter, 3.16 g/100 mL), reduce the particle size (605.92 nm) and interfacial tension, and make the halibut bone soup has better emulsifying characteristics and stability. The contents of flavor substances, such as esters, 5’-nucleotides, organic acids in the halibut bone soup were more abundant, while the contents of hexanal and 1-octen-3-ol and fishy off-flavor were reduced in TUT group. The overall odor and taste outline were more harmonious. Therefore, TUT can be used in the production of high quality fish bone soup, and TUT could be considered as a good deep processing technology for halibut bone and improve economic efficiency.

Microalgae as Functional Ingredients in Savory Food Products: Application to Wheat Crackers.

Crackers are widely consumed snack foods and there is an increasing trend in adding functional ingredients to their composition. In the present work, the dried biomasses of four microalgae strains—Arthrospira platensis F&M-C256, Chlorella vulgaris Allma, Tetraselmis suecica F&M-M33, and Phaeodactylum tricornutum F&M-M40—were used as a source of proteins, antioxidants, and other bioactive molecules in artisanal wheat crackers. Two incorporation levels were tested: 2% (w/w) and 6% (w/w). The impact of microalgae addition was evaluated in terms of physical properties, biochemical composition, antioxidant activity, in vitro digestibility, and sensory characteristics. Microalgae crackers presented stable color and texture throughout eight weeks of storage. Microalgae crackers were slightly thinner and lighter than the control but presented a similar density in agreement with scanning electron microscope images, indicating that gas retention was not greatly affected by microalgae addition. Regarding biochemical composition, 6% A. platensis and C. vulgaris crackers presented a significantly higher protein content (13.2–13.5%), for which they could be claimed to be a “source of protein” according to the Regulation (EC) No. 1924/2006. A. platensis crackers showed the highest antioxidant activity and attained better sensory analysis scores. T. suecica and P. tricornutum crackers showed high phenolic content and antioxidant activity but attained low sensory scores mainly because of their unattractive fishy off-flavor.

Physicochemical and sensory characteristics of pasta enriched with fish (Oreochromis niloticus) waste flour

Five pasta formulations containing 0 (PTWF0), 6 (PTWF6), 12 (PTWF12), 17 (PTWF17), and 23 g/100 g (PTWF23) of tilapia-waste flour (TWF), and a commercial pasta were evaluated concerning physicochemical and sensory characteristics. TWF increased (p < 0.05) protein, lipid and ash levels, energy value, cooking loss (CL), redness, yellowness, chroma (C*), total color difference (ΔE), hardness, and chewiness, and decreased (p < 0.05) carbohydrate content, optimal cooking time (OCT), water absorption index (WAI), swelling index (SI), lightness, hue angle (H°), springiness, cohesiveness, and resilience. Considering PTWF0 and PTWF23, the results ranged between 8.44 and 18.38 g/100 g for protein, 1.88 and 4.94 g/100 g for lipid, 1.88 and 4.08 for redness, 19.24 and 28.45 for yellowness, 3.13 and 4.66 N for hardness, 1.75 and 3.01 N × mm for chewiness. PTWF0, PTWF6, PTWF12, PTWF17 and PTWF23 had 9.00, 9.30, 9.30, 7.30, 7.00 and 6.00 min of OCT, 97.30, 97.10, 96.19, 88.82, 85.41 and 83.02 g/100 g of WAI, 2.49, 2.53, 2.49, 2.23, 2.18 and 2.03 g water/g dry pasta of SI, and 2.43, 2.45, 2.51, 3.17, 3.69 and 4.06 g/100 g of CL, respectively. The addition of 12–23 g/100 g TWF resulted in a negative effect on sensory characteristics, such as color (darkening), texture (crumbly/brittle/grainy dough), aroma and flavor (fishy off-flavor), with consequent decrease in overall consumer acceptance. Despite these findings and considering a consumer rejection probability of 50%, a survival analysis revealed that TWF may be added to pasta at up to 11.10 and 11.34 g/100 g without compromising acceptance and purchase intention (p < 0.05), respectively. Thus, the addition of 6 g/100 g TWF improves product nutritional value without jeopardizing pasta quality attributes, representing a potential alternative for the bakery industry.

Unraveling of the Fishy Off-Flavor in Steam-Treated Rapeseed Oil Using the Sensomics Concept.

The sensomics concept was applied to two steam-treated rapeseed oils, one eliciting a fishy off-flavor (OF) and the other the desired aroma attributes (PC = positive control). After screening the most important odorants via comparative aroma extract dilution analysis, identification experiments and quantitation via stable isotope dilution analysis (SIDA) using gas chromatography-mass spectrometry (GC-MS) were performed. Only five compounds differed in their concentrations by a factor ≥5. In addition, trimethylamine with an intense fishy odor quality and first overlooked by gas chromatography-olfactometry, was only present in OF and finally characterized via ion exchange chromatography and solid phase microextraction GC-MS. For data validation, recombination experiments were performed using all odorants with OAVs ≥ 1, and excellent accordance between GS and OF and their corresponding recombinates was achieved, confirming a correct characterization of all key odorants with trimethylamine as the only odorant responsible for the fishy off-flavor.

Palatability of Beef from Cattle Fed Extruded Flaxseed before Hay or Mixed with Hay

This study was undertaken to evaluate the eating quality of longissimus thoracis steaks and hamburgers (80/20 gluteus medius to perirenal fat) with enhanced profiles of potentially healthy fatty acids. The profile of health favorable fatty acids (n-3, vaccenic and rumenic) was improved in beef by feeding co-extruded flaxseed (flaxseed, peas, and alfalfa) and alfalfa-grass hay as a total mixed ration (TMR), and further enhanced by feeding co-extruded flaxseed before alfalfa-grass hay (Non-TMR). Compared to TMR, feeding steers the Non-TMR resulted in tougher steaks (P &lt; 0.05) with lower beef flavor (P &lt; 0.01) and greater off-flavor (P &lt; 0.01) intensity to an extent that might be detectable by consumers. High levels of trans-monounsaturated fatty acids, mainly of vaccenic acid, were associated with a fishy off-flavor, although actual changes in flavor may relate to correlated combined effects of conjugated fatty acids, atypical dienoic acids and ɑ-linolenic acid. Diet had no significant effect on sensory attributes of hamburgers, but when panelists described off-flavors, they noted more ‘other’ off-flavors (P &lt; 0.05) with fishy and stale/cardboard notes being more prominant in Non-TMR hamburgers. Overall, beef samples with threshold levels of vaccenic acid over 6.12% of total fatty acids resulting from feeding flaxseed products, while of potentially greater health benefit, may pose challenges in terms of eating quality. Areas worthy of further investigation to ensure acceptable eating quality might be the influence of ageing on antioxidant capacity in beef with enhanced fatty acid profiles, and the potential use of protective packaging to limit deterioration.

Odorant synergy effects as the cause of fishy malodors in algal marine oils.

As unsaturated lipids oxidize, they form hydroperoxides, which are susceptible to further oxidation or decomposition to secondary reaction products including aldehydes, ketones, acids, and alcohols. While oxidation reactions of docosahexaenoic acid (DHA) and eicosapentaenoic acid (EPA) are responsible for fishy off-flavors in marine oils, gas chromatography-olfactometry (GC-O) and other types of analytical studies have failed to reveal which specific oxidation products are involved. Previous research (Marsili, R.T.; Laskonis, C. The importance of odourant synergy effects in understanding malodour problems in DHA and EPA products. Lipid Technol. 2014, 26 (2), 31-34) has indicated that fishy malodor may be caused by the presence of two lipid oxidation products, heptanal and (E,Z)-3,5-octadien-2-one. The aims of the present study are to provide experimental method details and offer further evidence that these two oxidation products are indeed the cause of fishy malodors. Initial GC-MS-O studies of marine oils with fishy malodors revealed numerous oxidation products, but none were characterized as fishy. However, when all sample volatiles were captured together and then desorbed simultaneously in GC-O experiments, the fishy malodor was evident, indicating odorant synergy effects were responsible. A simple, novel method was developed using an olfactometry detector as a fraction collector to trap various peaks in marine oil chromatograms. The nose cone of the olfactometry detector was replaced with a PDMS foam absorption tube at various times during GC analysis. Combinations of GC peaks were trapped on PDMS tubes, desorbed in a Gerstel thermal extractor (off-line), and sniffed. The combination of two analytes was found to cause fishy malodors: heptanal and (E,Z)-3,5-octadien-2-one. Purge-and-trap, solid phase microextraction (SPME), and headspace stir bar sorptive extraction (HSSE) sample preparation methods prior to GC-MS were investigated. All methods confirmed the combination of heptanal and (E,Z)-3,5-octadien-2-one as the cause of fishy odor.

Measurement of trimethylamine concentration and evaluation of pig meat natural quality by a spectrophotometric method

Pig meat off-flavor is attributed to trimethyla- mine (TMA) concentration, and it is considered as the precursor of the fishy off-flavor problems. In this study, TMA concentrations in pig meat were determined, and the interactions with breed and gender effects were discussed. In addition, the TMA threshold for meat off-flavor and pig meat natural quality was measured in relation to meat storage and movement, and the influential factors includ- ing the pig breed and storage time were discussed. The results indicated positive effects on the precursor of the fishy off-flavor and the TMA threshold. Native breeds were found to have lower TMA concentrations than European breeds (P<0.01), and females and castrated males had significantly lower TMA concentration than males (P<0.01), The threshold concentration of TMA when meat was classed as off-flavored was 25 μg$g -1 , and this occurred after 35-38 h of storage. The natural qualities, such as appearance, flavor, color and overall acceptable scores declined significantly after 4 days in storage (P<0.01). It is concluded that pig meat off-flavor, breed and gender were essential factors affecting flavor for meat breeding programs, and storage time is important for pig meat natural quality.

Comparative Evaluation of Diagnostic Tools for Oxidative Deterioration of Polyunsaturated Fatty Acid-Enriched Infant Formulas during Storage.

The challenge in the development of infant formulas enriched with polyunsaturated fatty acids (PUFAs) is to meet the consumers’ expectations with regard to high nutritional and sensory value. In particular, PUFAs may be prone to fatty acid oxidation that can generate potential rancid, metallic and/or fishy off-flavors. Although such off-flavors pose no health risk, they can nevertheless lead to rejection of products by consumers. Thus, monitoring autoxidation at its early stages is of great importance and finding a suitable analytical tool to perform these evaluations is therefore of high interest in quality monitoring. Two formulations of infant formulas were varied systematically in their mineral composition and their presence of antioxidants to produce 18 model formulas. All models were aged under controlled conditions and their oxidative deterioration was monitored. A quantitative study was performed on seven characteristic odor-active secondary oxidation products in the formulations via two-dimensional high resolution gas chromatography-mass spectrometry/olfactometry (2D-HRGC-MS/O). The sensitivity of the multi-dimensional GC-MS/O analysis was supported by two additional analytical tools for monitoring autoxidation, namely the analysis of lipid hydroperoxides and conjugated dienes. Furthermore, an aroma profile analysis (APA) was performed to reveal the presence and intensities of typical odor qualities generated in the course of fatty acid oxidation. The photometrical analyses of lipid hydroperoxides and conjugated dienes were found to be too insensitive for early indication of the development of sensory defects. By comparison, the 2D-HRGC-MS/O was capable of monitoring peroxidation of PUFAs at low ppb-level in its early stages. Thereby, it was possible to screen oxidative variances on the basis of such volatile markers already within eight weeks after production of the products, which is an earlier indication of oxidative deterioration than achievable via conventional methods. In detail, oxidative variances between the formulations revealed that lipid oxidation was low when copper was administered in an encapsulated form and when antioxidants (vitamin E, ascorbyl palmitate) were present.

Quail FMO3 Gene Cloning, Tissue Expression Profiling, Polymorphism Detection and Association Analysis with Fishy Taint in Eggs

Quail eggs comprise a significant and favourable part of table eggs in certain countries. Some quail eggs, however, present fishy off-flavor which directly influences their quality. It is reported that flavin-containing monooxygenase 3 (FMO3) is associated with fish-odour trait in human and animal products. FMO3 is responsible for the degradation of trimethylamine (TMA) in vivo. Loss-of-function mutations in FMO3 gene can result in defective TMA N-oxygenation, giving rise to disorder known as “fish-odour syndrome” in human, as well as the fishy off-flavor in cow milk and chicken eggs. In order to reveal the genetic factor of fishy taint in quail eggs, we cloned the cDNA sequence of quail FMO3 gene, investigated FMO3 mRNA expression level in various tissues, detected SNPs in the coding region of the gene and conducted association analysis between a mutation and the TMA content in quail egg yolks. The 1888 bp cDNA sequence of quail FMO3 gene encoding 532 amino acids was obtained and characterized. The phylogenetic analysis revealed quail FMO3 had a closer relationship with chicken FMO3. The FMO3 mRNA was highly expressed in liver and kidney of quail. Nine SNPs were detected in the coding sequence of quail FMO3 gene, including a nonsense mutation (Q319X) which was significantly associated with the elevated TMA content in quail egg yolks. Genotype TT at Q319X mutation loci was sensitive to choline. With addition of choline in the feed, the quails with homozygote TT at the Q319X mutation loci laid fish-odour eggs, indicating an interaction between genotype and diet. The results indicated that Q319X mutation was associated with the fishy off-flavor in quail eggs. Identification of the unfavorable allele T of quail FMO3 gene can be applied in future quail breeding to eliminate fishy off-flavor trait in quail eggs.

Model Studies on the Key Aroma Compounds Formed by an Oxidative Degradation of ω-3 Fatty Acids Initiated by either Copper(II) Ions or Lipoxygenase

Due to the high number of double bonds, ω-3-polyunsaturated fatty acids such as eicosapentaenoic aid (EPA) or docosahexaenoic acid (DHA) are prone to rapid oxidation, leading to the formation of intense taints often described as "fishy". To clarify the compounds responsible for such off-flavors, EPA, DHA, and α-linolenic acid (ALA) were oxidized singly either in the presence of copper ions or in the presence of lipoxygenase. The autoxidation of EPA and DHA led to a mixture of odorants eliciting an overall fishy odor quality, whereas neither the oxidation of ALA by copper ions nor that by lipoxygenase led to an unpleasant odor. Application of aroma extract dilution analysis (AEDA) on the volatiles generated by autoxidation of EPA revealed trans-4,5-epoxy-(E,Z)-2,7-decadienal, identified for the first time as fatty acid degradation product, (Z)-1,5-octadien-3-one, (Z)-3-hexenal, (Z,Z)-2,5-octadienal, (Z,Z)-3,6-nonadienal, and (E,E,Z)-2,4,6-nonatrienal with the highest flavor dilution (FD) factors. The autoxidation as well as the enzymatic oxidation of all three acids led to the same odorants, but with different FD factors depending on the acid and/or the type of oxidation applied. Thus, the results suggested that a defined ratio of a few odorants is needed to generate a fishy off-flavor.

Molecular cloning, sequence characterization, SNP detection, and tissue expression analysis of duck FMO3 gene

Flavin-containing monooxygenase 3 (FMO3) is an important monooxygenase for catalytic oxygenation of many harmful xenobiotics. Mutations in the FMO3 gene have been identified as causing trimethylaminuria in human and fishy off-flavor in cow milk and chicken eggs. In this study, the full-length cDNA sequence of Pekin duck FMO3 gene was cloned, sequenced, and characterized. The full-length cDNA sequence consisted of 1,846 bp and contained a 1,599 bp open-reading frame encoding 532 amino acids. Duck FMO3 gene shared a similar nine exon-eight intron structure with chicken and human. The duck FMO3 putative protein sequence showed high identity with that of chicken (82 %), and relative low identity with those of mammals (61-66 %). We also found that the duck FMO3 gene was dramatically expressed in liver, lung, and kidney compared to that in other tissues in the ducks, indicating the possible roles the FMO3 gene could play in the three tissues. By bidirectional sequencing, we also found one nonsense mutation, 5 nonsynonymous, and 21 synonymous mutations in the coding region of the FMO3 gene in 11 duck breeds and some of them were predicted to be potentially associated with the activities of FMO3 protein.

Determination of trimethylamine in spinach, cabbage, and lettuce at alkaline pH by headspace solid-phase microextraction.

Trimethylamine (TMA) found in some leafy vegetables, such as spinach, cabbage, and lettuce, at alkaline pH was identified and quantified using headspace solid-phase microextraction and gas chromatography-mass spectrometry (HS-SPME and GC-MS). HS-SPME conditions were optimized at an adsorption temperature of 50 °C, equilibration time of 5 min, and adsorption time of 5 min with 65 μm of polydimethylsiloxane/divinylbenzene fiber. The TMA that was formed from spinach, cabbage, and lettuce was assayed at pH 7 to 11 for 0 to 4 h at 50 °C using HS-SPME. The results showed that the amount of TMA formed was dependent on pH. The amount of TMA formed increased dramatically at a pH greater than 9. TMA was not formed at a pH lower than 7. Spinach produced a higher amount of TMA than cabbage or lettuce. TMA was formed at alkaline pH from choline, betaine, and carnitine, which are TMA precursors. To confirm the SPME results, TMA was quantitated using the AOAC official method. Data obtained from chemical analysis were in good agreement with the SPME data. The formation mechanism of TMA is thought to be the Hofmann elimination reaction, which generates amine compounds at alkaline pH. Fishy off-flavor in foods is associated with trimethylamine (TMA), which is frequently found in fish and seafood. In this study, TMA was identified for the first time in some leafy vegetables, such as spinach, cabbage, and lettuce, at alkaline pH. The presence of TMA in leafy vegetables under certain circumstances such as high pH and temperature may affect the sensory properties of foods containing these vegetables.

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. 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.

Fortification of reduced-fat Cheddar cheese with n-3 fatty acids: Effect on off-flavor generation

The objective of this study was to fortify 50% reduced fat Cheddar cheese with n-3 fatty acids and evaluate whether this fortification generated specific off-flavors in the cheese. Docosahexaenoic (DHA) and eicosapentaenoic (EPA) fatty acids were added to the cheese to obtain 3 final fortification levels [18, 35, and 71mg of DHA/EPA per serving size (28g) of cheese] representing 10, 20, and 40% of the suggested daily intake level for DHA/EPA. The presence of oxidized, rancid, and fishy flavors as a function of fortification level and cheese aging (6 mo) was evaluated using a sensory descriptive panel. No differences were found in the oxidized and rancid flavors as a consequence of DHA/EPA fortification, with only slight intensities of these flavors. The presence of fishy off-flavor was dependent on the fortification level. Cheeses with low fortification levels (18 and 35mg of DHA/EPA per serving size) did not develop significant fishy off-flavor compared with the control, whereas at the highest fortification level (71mg of DHA/EPA per serving size) the fishy off-flavor was significantly stronger in young cheeses. The fishy flavor decreased as a function of age and became nonsignificant compared with the control at 3 mo of storage. Even though fishy flavors were detected in the fortified cheeses, the DHA/EPA content during storage remained constant and complied with the suggested values for food fortification. Results obtained from this research indicate that 50% reduced-fat Cheddar cheese aged for 3 mo can be used as a vehicle for delivery of n-3 fatty acids without generation of off-flavors.

Lipid Oxidation in Milk, Yoghurt, and Salad Dressing Enriched with Neat Fish Oil or Pre-Emulsified Fish Oil

This study compared the oxidative stabilities of fish-oil-enriched milk, yoghurt, and salad dressing and investigated the effects on oxidation of adding either neat fish oil or a fish-oil-in-water emulsion to these products. Milk emulsions had higher levels of a fishy off-flavor and oxidized faster, as determined by the peroxide value and volatile oxidation products, than fish-oil-enriched yoghurt and dressing, despite the fact that dressings had a higher fish oil content and were stored at room temperature. Additionally, fish-oil-enriched yoghurt generally had higher oxidative stability than fish-oil-enriched dressings, irrespective of the mode of fish oil addition. Yoghurt thus seemed to be a good delivery system of lipids containing n-3 polyunsaturated fatty acids. Different effects of adding fish oil either as neat fish oil or as a fish-oil-in-water emulsion were observed for milk, yoghurt, and dressing. Yoghurt and dressing enriched with neat fish oil were more stable than those enriched with a fish-oil-in-water emulsion, whereas milk enriched with neat fish oil was less stable than milk enriched with the fish-oil-in-water emulsion. Overall, it seemed that application of neat fish oil was a good option for preserving the final quality in yoghurt and dressings, but a pre-emulsion may still be considered for the fish oil enrichment of certain food products, for example, milk.

Enrichment of channel catfish ( Ictalurus punctatus) fillets with conjugated linoleic acid and omega-3 fatty acids by dietary manipulation

An experiment was conducted in aquaria with channel catfish ( Ictalurus punctatus) to determine the efficacy of augmenting fillets with conjugated linoleic acid (CLA) and omega-3 highly unsaturated fatty acids ( n − 3 HUFA) by feeding diets amended with products containing high levels of these nutrients. Refined menhaden fish oil at 1.5% of diet supplied the n − 3 HUFA. CLA was used at dietary levels of 0.5% and 1% with a preparation that contained approximately 65% isomers of CLA. Corn oil was added to the basal diet at maximum inclusion level for added lipids of 3% for the control diet and to adjust total added lipid content of the other diets to 3%. Average initial body weight was 57.39 ± 0.25 g/fish. Six experimental diets were fed twice daily to four replicate aquaria for six weeks. At that time, fish were group weighed for determination of weight gain and feed conversion. Fillets of six fish per aquarium were recovered and stored at − 80 °C for moisture and total lipid analyses, fatty acid analysis, and sensory evaluation. Results showed feed consumption and feed conversion did not differ ( P > 0.05). Significantly ( P < 0.05) greater body weight gains were observed only for fish fed the diets with two combinations of CLA and 1.5% fish oil compared to fish fed the diet containing 0.5% CLA and corn oil. Fillet n − 3 HUFA levels were significantly ( P < 0.05) elevated for fish fed diets containing fish oil when compared to n − 3 HUFA of fillets of fish fed diets containing either corn oil or CLA and corn oil. Similarly, fillets from fish fed diets amended with CLA contained substantial amounts of CLA of up to 6.4% of total lipids. Fillets from fish fed corn oil or fish oil diets had no CLA. Taste panel evaluation indicated that fillets containing n − 3 HUFA and CLA were essentially without fishy off-flavor and had excellent sensory qualities. Catfish fillets produced by amending diets with sources of n − 3 HUFA and CLA at the levels used in this study would contain elevated levels of these nutraceuticals and could be an important human food source for these healthful fatty acids.

Fishy taint in chicken eggs is associated with a substitution within a conserved motif of the FMO3 gene

Fishy odor of urine and other secretions is a characteristic of trimethylaminuria in humans, resulting from loss-of-function mutations in the flavin-containing mono-oxygenase isoform FMO3. A similar phenotype exists in cattle, in which a nonsense mutation in the bovine orthologue causes fishy off-flavor in cow's milk. The fishy odor is caused by an elevated level of excreted odorous trimethylamine (TMA), due to deficient oxidation of TMA. We report the mapping of a similar disorder (fishy taint of eggs) and the chicken FMO3 gene to chicken chromosome 8. The only nonsynonymous mutation identified in the chicken FMO3 gene (T329S) changes an evolutionarily highly conserved amino acid and is associated with elevated levels of TMA and fishy taint in the egg yolk in several chicken lines. No differences in the expression of FMO3 were found among individuals with different associated genotypes, indicating that the trait is not caused by a linked polymorphism causing altered expression of the gene. The results support the importance and function of the evolutionarily conserved motif FATGY, which has been speculated to be a substrate recognition pocket of N-hydroxylating siderophore enzymes and flavin-containing mono-oxygenases.