Protein and lipid oxidation during frozen storage of rainbow trout (Oncorhynchus mykiss)

This study aimed at investigating protein and lipid oxidation during frozen storage of rainbow trout. Rainbow trout fillets were stored for 13 months at -20, -30, or -80 degrees C, and samples were analyzed at regular intervals for lipid and protein oxidation markers. Lipid oxidation was followed by measuring lipid hydroperoxides (PV), as well as secondary oxidation products (volatiles) using dynamic headspace GC-MS. Free fatty acids (FFA) were measured as an estimation of lipolysis. Protein oxidation was followed using the spectrophotometric determination of protein carbonyls and immunoblotting. Significant oxidation was observed in samples stored at -20 degrees C, and at this temperature lipid and protein oxidation seemed to develop simultaneously. FFA, PV, and carbonyls increased significantly for the fish stored at -20 degrees C, whereas the fish stored at -30 and -80 degrees C did not show any increase in oxidation during the entire storage period when these methods were used. In contrast, the more sensitive GC-MS method used for measurement of the volatiles showed that the fish stored at -30 degrees C oxidized more quickly than those stored at -80 degrees C. Detection of protein oxidation using immunoblotting revealed that high molecular weight proteins were oxidized already at t = 0 and that no new protein oxidized during storage irrespective of the storage time and temperature. The results emphasize the need for the development of more sensitive and reliable methods to study protein oxidation in order to gain more explicit knowledge about the significance of protein oxidation for food quality and, especially, to correlate protein oxidation with physical and functional properties of foods.     

Uptake by dietary exposure and elimination of aflatoxins in muscle and liver of rainbow trout (Oncorhynchus mykiss)

Uptake and elimination of aflatoxins (AFs) by rainbow trout ( Oncorhynchus mykiss ) during a long-term (21 days) dietary exposure were studied to assess contamination by AFs in aquaculture fish fed AF-containing feed. The uptake factor (UF) of aflatoxin B(1) (AFB(1)) in muscle ranged from 0.40 × 10(-3) to 1.30 × 10(-3). AFB(1) concentrations in liver were 165-342 times higher than in muscle. AFs from feed were more highly accumulated in liver than in muscle. Aflatoxicol (AFL) and aflatoxin M(1) (AFM(1)) were detected in muscle and liver and also in the rearing water. AFL concentrations were higher than AFM(1) by 2 orders of magnitude in muscle, and AFL was a major metabolite of AFB(1). The elimination rate constants (α) of AFB(1) and AFL in muscle (1.83 and 2.02 day(-1), respectively) and liver (1.38 and 2.41 day(-1), respectively) were very large. The elimination half-life (t(1/2)) of AFB(1) was 0.38 days (9.12 h) in muscle and 0.50 days (12.00 h) in liver. The elimination half-life of AFL in muscle and liver was 0.34 day (8.16 h) and 0.29 day (6.96 h), respectively. These data show that AFs are eliminated rapidly and are not biomagnified in fish. Thus, AFB(1) concentration in muscle of fish fed AFB(1)-containing feed (ca. 500 μg/kg) decreased to below the detection limit (20 ng/kg) of the most sensitive analytical method at 1.54 days (36.96 h) after the change to uncontaminated feed.     

Effect of pH on the bioaccumulation of low level,dissolved methylmercury by rainbow trout (Oncorhynchus mykiss)

An inverse relationship has been observed between pH and McHg concentration in freshwater fish. Many hypotheses exist regarding the mechanisms which lead to elevated levels of organic Hg in fish from low pH lakes. To determine if pH has a direct effect on the rate of McHg bioaccumulation in fish, rainbow trout fingerlings (Oncorhynchus mykiss) were exposed to a low concentration of aqueous methylmercuric chloride (1.38 ± 0.49 ng·L^?1) at four pH-levels (8.2, 7.0, 6.3, 5.8) for eight weeks. McHg and total Hg were specifically determined on whole fish homogenates and water samples. The pH was found to have a significant: inverse effect on the rate of McHg bioaccumulation in the fish only in the lowest exposure level. Fish held at pH 5.8 had an uptake rate of 1.11 ± 0.07 ng·g^?1·d^?1, while those at pH ≥ 6.3 had a MeHg tissue uptake rate of ≤ 0.64 ± 0.07 ng·g^?1·d^?1. Total body burden of MeHg in the fish held at pH 5.8 also showed an elevated level of MeHg when compared with fish held at higher pH-levels, but the difference was less dramatic. These results suggest that a portion of the Hg burden in fish from low pH systems may be due to the direct effects of low pH on bioaccumulation, but that a threshold may exist above which pH does not play a significant role.     

Relation of biogenic amines' formation with microbiological and sensory attributes in Lactobacillus-inoculated vacuum-packed rainbow trout (Oncorhynchus mykiss) fillets

The biogenic amine (BA) content of vacuum-packed filleted rainbow trout (Oncorhynchus mykiss) inoculated or not with two different Lactobacillus strains, individually or in combination, was monitored during refrigerated storage for 20 days and related to respective bacteriological and sensory changes occurring during the same period. Eight amines, namely putrescine, cadaverine, tyramine, tryptamine, beta-phenylethylamine, histamine, spermine, and spermidine, were determined, whereas agmatine was not detected in any of the samples. In all cases, BA concentration was higher (P < or = 0.05) in the controls compared to all inoculated treatments, whereas the trend with regard to the bacterial populations (Enterobacteriaceae, pseudomonads, and H2S-producing bacteria) and the off-odor scores was similar. Inoculation with Lactobacillus sakei CECT 4808 showed the best preservative effect among inoculated treatments. Concentrations of putrescine and cadaverine, the main BAs formed, correlated well with both spoilage bacterial counts and off-odor scores and can be useful indicators of shelf life. Spermine and spermidine contents decreased during storage, while levels of the other determined BAs remained below 10 mg/kg even after sensory rejection.     

Modifications of trout (Oncorhynchus mykiss) muscle proteins by preslaughter activity

The effect of two different preslaughter procedures (limited or 15-min intense muscular activity) on muscle trout proteins was investigated. Muscle was sampled 45 min and 24 h post-mortem, proteins were separated using two-dimensional electrophoresis, and spots of interest were tentatively identified by MALDI-TOF spectrometry. Twenty-nine and 4 spots were differentially represented between the two groups of fish at 45 min and 24 h post-mortem, respectively. Spots that could be identified corresponded mainly to proteins involved in energy-producing pathways (triosephosphate isomerase, enolase, pyruvate dehydrogenase) or to structural proteins (desmin, cap-Z, myosin heavy chain fragment). Persistent under-representation of desmin, a key cytoskeletal protein, in fish submitted to intense muscular activity suggests that such a preslaughter treatment can have an effect on post-mortem muscle integrity.     

Effect of soybean phospholipids on canthaxanthin lipoproteins transport, digestibility, and deposition in rainbow trout (Oncorhynchus mykiss) muscle

This study was designed to assess the effect of dietary soybean phospholipids on canthaxanthin transport by serum lipoproteins and canthaxanthin muscle deposition in trout. Three groups of 12 immature trout in triplicate with a mean body weight of 130 g were fed with three experimental diets containing (1) canthaxanthin plus lecithin plus fish oil, (2) canthaxanthin plus lecithin, and (3) canthaxanthin alone, for 12 days. The two major lipoprotein classes in rainbow trout are high-density lipoproteins, which transport principally carotenoids present in the serum, and low-density lipoproteins, which are responsible for the transport of cholesterol, both independently of the administered diet. In addition, very low density lipoproteins are responsible for triglyceride transport in serum. Nevertheless, the amount of canthaxanthin in the serum increased when carotenoid was associated with phospholipids plus fish oil. When canthaxanthin is transported by lecithin plus fish oil, the amount of phospholipids, cantaxanthin, and cholesterol deposited in muscle increased but not significantly. The highest apparent canthaxanthin digestibility coefficient was obtained when canthaxanthin was carried by lecithin plus fish oil. The administration of canthaxanthin carried by phospholipids improved its accumulation in the muscle of rainbow trout. This accumulation could be enhanced if the time of administration of canthaxanthin is increased.     

Determination of niclosamide residues in rainbow trout (Oncorhynchus mykiss) and channel catfish (Ictalurus punctatus) fillet tissue by high-performance liquid chromatography

Bayluscide [the ethanolamine salt of niclosamide (NIC)] is a registered piscicide used in combination with 3-(trifluoromethyl)-4-nitrophenol (TFM) to control sea lamprey populations in streams tributary to the Great Lakes. A high-performance liquid chromatography (HPLC) method was developed for the determination of NIC residues in muscle fillet tissues of fish exposed to NIC and TFM during sea lamprey control treatments. NIC was extracted from fortified channel catfish and rainbow trout fillet tissue with a series of acetone extractions and cleaned up on C(18) solid-phase extraction cartridges. NIC concentrations were determined by HPLC with detection at 360 and 335 nm for rainbow trout and catfish, respectively. Recovery of NIC from rainbow trout (n = 7) fortified at 0.04 microg/g was 77 +/- 6.5% and from channel catfish (n = 7) fortified at 0.02 microg/g was 113 +/- 11%. NIC detection limit was 0.0107 microg/g for rainbow trout and 0.0063 microg/g for catfish. Percent recovery of incurred radioactive residues by this method from catfish exposed to [(14)C]NIC was 89.3 +/- 4.1%. Percent recoveries of NIC from fortified storage stability tissue samples for rainbow trout (n = 3) analyzed at 5 and 7.5 month periods were 78 +/- 5.1 and 68 +/- 2.4%, respectively. Percent recoveries of NIC from fortified storage stability tissue samples for channel catfish (n = 3) analyzed at 5 and 7.5 month periods were 88 +/- 13 and 76 +/- 21%, respectively.     

Chemical and sensory quantification of geosmin and 2-methylisoborneol in rainbow trout (Oncorhynchus mykiss) from recirculated aquacultures in relation to concentrations in basin water

Globally, aquaculture systems with water recirculation experience increasing problems with microbial taste and odor compounds (TOCs) such as geosmin and 2-methylisoborneol (MIB). This study investigated the content of geosmin and MIB in water and the flesh of 200 rainbow trouts from eight recirculated aquaculture systems in Denmark. TOC content in the fish flesh was measured by a dynamic headspace extraction method and was evaluated by a sensory panel. The results showed significant correlations between TOC content in water and fish and between chemical analysis and sensory perception. When geosmin exceeded 20 ng/L in the water, 96% of the fish had an intense muddy flavor, but below 10 ng geosmin/L, 18% of the fish (only 3% in special depuration ponds) had an intense muddy flavor. The results indicate that TOC levels <10 ng/L will ensure that a negligible portion of the fish obtains an unpalatable taste and flavor due to TOCs.     

Protein recovery from rainbow trout (Oncorhynchus mykiss) processing byproducts via isoelectric solubilization/precipitation and its gelation properties as affected by functional additives

Solubility of rainbow trout proteins was determined between pH 1.5 and 13.0 and various ionic strengths (IS). Minimum solubility occurred at pH 5.5; however, when IS = 0.2, the minimum solubility shifted toward more acidic pH. Isoelectric solubilization/precipitation was applied to trout processing byproducts (fish meat left over on bones, head, skin, etc.), resulting in protein recovery yields (Kjeldahl, dry basis) between 77.7% and 89.0%, depending of the pH used for solubilization and precipitation. The recovered protein contained 1.4-2.1% ash (dry basis), while the trout processing byproducts (i.e., starting material) 13.9%. Typical boneless and skinless trout fillets contain 5.5% ash, and therefore, the isoelectric solubilization/precipitation effectively removed impurities such as bones, scales, skin, etc., from the trout processing byproducts. The recovered proteins retained gel-forming ability as assessed with dynamic rheology, torsion test, and texture profile analysis (TPA). However, the recovered proteins failed to gel unless beef plasma protein (BPP) was added. Even with BPP, the recovered protein showed some proteolysis between 40 and 55 degrees C. Addition of potato starch, transglutaminase, and phosphate to the recovered proteins resulted in good texture of trout gels as confirmed by torsion test and TPA. Higher ( P < 0.05) shear stress and strain were measured for gels developed from basic pH treatments than the acidic counterparts. However, proteins recovered from acidic treatments had higher ( P < 0.05) lipid content than the basic treatments. This is probably why the gels from acidic treatments were whiter ( L* - 3 b*) ( P < 0.05) than those from the basic ones. Our study demonstrates that functional proteins can be efficiently recovered from low-value fish processing byproducts using isoelectric solubilization/precipitation and subsequently be used in value-added human foods.     

Characterization of aroma-active compounds in raw and cooked pine-mushrooms (Tricholoma matsutake Sing.)

The characteristic aroma-active compounds in raw and cooked pine-mushrooms (Tricholoma matsutake Sing.) were investigated by gas chromatography-olfactometry using aroma extract dilution analysis. 1-Octen-3-one (mushroom-like) was the major aroma-active compound in raw pine-mushrooms; this compound had the highest flavor dilution factor, followed by ethyl 2-methylbutyrate (floral and sweet), linalool (citrus-like), methional (boiled potato-like), 3-octanol (mushroom-like and buttery), 1-octen-3-ol (mushroom-like), (E)-2-octen-1-ol (mushroom-like), and 3-octanone (mushroom-like and buttery). By contrast, methional, 2-acetylthiazole (roasted), an unknown compound (chocolate-like), 3-hydroxy-2-butanone (buttery), and phenylacetaldehyde (floral and sweet), which could be formed by diverse thermal reactions during the cooking process, together with C8 compounds, were identified as the major aroma-active compounds in cooked pine-mushrooms.     

Characterization of volatiles and aroma-active compounds in honeybush (Cyclopia subternata) by GC-MS and GC-O analysis

Volatile organic compounds (VOCs) in fermented honeybush, Cyclopia subternata, were sampled by means of a high-capacity headspace sample enrichment probe (SEP) and analyzed by gas chromatography-mass spectrometry (GC-MS). Stereochemistry was determined by means of enantioselective GC-MS with derivatized β-cyclodextrin columns as chiral selectors. A total of 183 compounds, the majority of which are terpenoids (103; 56%), were identified by comparing their mass spectra and retention indices with those of reference compounds or tentatively identified by comparison with spectral library or literature data. Of these compounds, 37 were determined by gas chromatography-olfactometry (GC-O), using detection frequency (DF) and aroma extract dilution analysis (AEDA), to be odor-active (FD ≥ 2). (E)-β-Damascenone, (R/S)-linalool, (E)-β-damascone, geraniol, (E)-β-ionone, and (7E)-megastigma-5,7,9-trien-4-one were identified with the highest FD factors (≥512). The odors of certain compounds, that is, (6E,8Z)-megastigma-4,6,8-trien-3-one, (6E,8E)-megastigma-4,6,8-trien-3-one, (7E)-megastigma-5,7,9-trien-4-one, 10-epi-γ-eudesmol, epi-α-muurolol, and epi-α-cadinol, were perceived by GC-O assessors as typically honeybush-like.     

Influence of dietary genistein levels on tissue genistein deposition and on the physical, chemical, and sensory quality of rainbow trout, Oncorhynchus mykiss

Genistein, the primary isoflavone in soybean, is one of the chemical components responsible for some of the off-flavors associated with soy-based foods. The potential effects of genistein on the sensory and chemical quality of fish muscle may affect the full utilization of soybean meal as an alternative protein in aquaculture diets. Fingerling trout fed commercial diets containing 0, 500, 1000, or 3000 ppm pure genistein were analyzed after 6 and 12 months of feeding. Genistein was extracted by enzymatic digestions in Tris buffer and quantified by high-performance liquid chromatography. Moisture, fat, protein, ash, and tristimulus color of the fillets were determined. The extent of lipid oxidation occurring in fillets harvested after 12 months of feeding was studied by measurements of thiobarbituric acid reactive substances (TBARS) after 4 and 8 days of refrigerated storage at 4 degrees C. Triangle tests were performed to determine if there were any detectable sensory differences. A dietary genistein content of 3000 ppm led to the deposition of approximately 5.4 pmol of genistein/mg of fillet. Triangle test panelists were unable to detect any significant (p < or = 0.05) differences between the fillets from trout fed the 0 and 3000 ppm genistein concentrations. Moisture, ash, and protein content were influenced by time of harvest, while color was unaffected. TBARS levels on days 4 and 8 were significantly (p < 0.05) higher in the fillets from the 0 ppm genistein level than in fillets from fish fed dietary genistein.     

Identification of characteristic aroma-active compounds from water dropwort (Oenanthe javanica DC.)

Characteristic aroma components of water dropwort (Oenanthe javanica DC.) were evaluated by aroma extract dilution analysis and solid-phase microextraction-gas chromatography-olfactometry. Alpha-Terpinolene (plastic/cucumber-like) was the most intense aroma-active compound in water dropwort. Other potent aroma-active compounds included p-cymene (kerosene-like), alpha-terpinene (lemon), (E)-caryophyllene (woody), (Z,E)-alpha-farnesene (woody), hexanal (green), (Z)-3-hexenol (green), phenylacetaldehyde (honey), (E)-2-nonenal (cucumber), bornyl acetate (cooked vegetable), and gamma-terpinene (lemon). Of these, p-cymene was believed to be primarily responsible for the distinct kerosene-like aroma note of water dropwort. The aroma property of p-cymene was dependent on its concentration and was described as kerosene-like at relatively high concentrations but changed to citrus and green aroma notes at low concentrations.     

Characterization of the aroma-active compounds in pink guava (Psidium guajava, L.) by application of the aroma extract dilution analysis

The volatiles present in fresh, pink-fleshed Colombian guavas ( Psidium guajava, L.), variety regional rojo, were carefully isolated by solvent extraction followed by solvent-assisted flavor evaporation, and the aroma-active areas in the gas chromatogram were screened by application of the aroma extract dilution analysis. The results of the identification experiments in combination with the FD factors revealed 4-methoxy-2,5-dimethyl-3(2 H)-furanone, 4-hydroxy-2,5-dimethyl-3(2 H)-furanone, 3-sulfanylhexyl acetate, and 3-sulfanyl-1-hexanol followed by 3-hydroxy-4,5-dimethyl-2(5 H)-furanone, ( Z)-3-hexenal, trans-4,5-epoxy-( E)-2-decenal, cinnamyl alcohol, ethyl butanoate, hexanal, methional, and cinnamyl acetate as important aroma contributors. Enantioselective gas chromatography revealed an enantiomeric distribution close to the racemate in 3-sulfanylhexyl acetate as well as in 3-sulfanyl-1-hexanol. In addition, two fruity smelling diastereomeric methyl 2-hydroxy-3-methylpentanoates were identified as the ( R,S)- and the ( S,S)-isomers, whereas the ( S,R)- and ( R,R)-isomers were absent. Seven odorants were identified for the first time in guavas, among them 3-sulfanylhexyl acetate, 3-sulfanyl-1-hexanol, 3-hydroxy-4,5-dimethyl-2(5 H)-furanone, trans-4,5-epoxy-( E)-2-decenal, and methional were the most odor-active.     

Bioaccumulation potential of dietary arsenic, cadmium, lead, mercury, and selenium in organs and tissues of rainbow trout (Oncorhyncus mykiss) as a function of fish growth

The distribution and potential bioaccumulation of dietary arsenic, cadmium, lead, mercury, and selenium in organs and tissues of rainbow trout (Oncorhyncus mykiss Walbaum, 1792), a major aquaculture species, was studied in relation to fish growth over a period of >3 years. Fish were reared under normal farming conditions, that is, fed a standard fish food and exposed to negligible levels of waterborne trace elements. The age-related variations in the content of each trace element in gills, kidney, liver, muscle, and skin were studied through nonparametric regression analysis. A buildup of all elements in all tissues and organs was observed, but due to dilution with growth, the concentrations did not increase, except in a few cases such as cadmium and mercury in liver and kidney. In muscle tissue, the concentrations of mercury, lead, and selenium did not alter significantly with growth, whereas cadmium increased but remained at exceedingly low levels. The concentration of arsenic in muscle tissue peaked at 14 months and then decreased in adult specimens. Arsenic speciation by high-performance liquid chromatography--inductively coupled plasma mass spectrometry revealed that arsenic in muscle was almost exclusively present in the form of nontoxic arsenobetaine. Application of a mercury mass balance model gave predicted concentrations in agreement with measured ones and showed that in farmed rainbow trout the ratio of mercury concentrations in feed and in fish is about 1:1. Therefore, rainbow trout does not approach the limits established for human consumption even when reared with feed at the maximum permitted levels. These findings highlight the low bioaccumulation potential of toxic trace elements such as cadmium, lead, and mercury in rainbow trout following dietary exposure. On the other hand, selenium concentrations in muscle (about 0.2 microg g (-1) of fresh weight) show that rainbow trout may be a good source of this essential element.     

The compositions of volatiles and aroma-active compounds in dried omija fruits (Schisandra chinensis Baillon) according to the cultivation areas

Differences in the compositions of volatiles from dried omija fruits (Schisandra chinensis Baillon) cultivated in different areas (Mungyeong, Jangsu, Jechon, and Hoengseong) in South Korea were determined by applying principal component analysis to gas chromatography-mass spectrometry data sets. Quantitative assessments revealed that terpene hydrocarbons, such as germacrene D, β-selinene, α-ylangene, β-elemene, α-selinene, and (E)-β-farnesene, were the main volatiles in all omija fruit samples. On the other hand, (E)-β-ocimene, calarene, (E)-β-farnesene, β-selinene, nonanal, 2-methylbutanoic acid, benzoic acid, 2,3-butanediol, and phenethyl alcohol were the major volatile components that contributed to the discrimination between omija fruit samples from the four cultivation areas. In addition, aroma-active compounds in four dried omija fruits were investigated and compared by gas chromatography-olfactometry using aroma extract dilution analysis. (E)-β-Ocimene (floral and herbaceous), α-pinene (pine-like and woody), hexanal (cut grass-like), 5-methylfurfural (burnt sugar-like and sweet), and α-terpinene (minty, green, and fresh) were important aroma-active compounds in all omija samples. Interestingly, the flavor dilution factors of most aroma-active compounds were lower for omija sample cultivated in Hoengseong than for those cultivated in Mungyeong, Jangsu, and Jechon.     

Quantification of selected aroma-active compounds in Pinot noir wines from different grape maturities

Effect of grape maturity on aroma-active compounds in Pinot noir wine was investigated using stir bar sorptive extraction-gas chromatograph-mass spectrometry (SBSE-GC-MS). High correlation coefficient (> 0.95) and low standard deviation (< 10%) were obtained for all aroma-active compounds of interest. Two vintages of Pinot noir wines with three different grape maturities each were analyzed. Statistical analysis showed that both grape maturity and growing year significantly affected the aroma composition of the final wine. Analysis of wine samples from the same vintage indicated that grape maturity could affect aroma compounds in different ways, based on their biochemical formation in the wines. For most short-chain fatty acid esters, there were no obvious trends with grape maturity, however, the concentrations of ethyl 2-methylpropanoate and ethyl 3-methylbutanoate consistently decreased with grape maturity. The decreasing trend was also observed for other esters including ethyl cinnamate, ethyl dihydroxycinnamate, and ethyl anthranilate, with the exception of ethyl vanillate, while C13 norisoprenoids, monoterpenes, and guaiacols had increasing trends with grape maturation.