Hydrolysis and oxidation of European eel oil during frozen storage for 48 weeks

The quality assessment of the wild European eel (Anguilla anguilla) stored at −20 °C was assessed by sensory, chemical (total volatile basic nitrogen (TVB-N), peroxide value (PV), free fatty acid (FFA), thiobarbituric values (TBA) and pH) methods. The sensory analysis of showed that European eels were acceptable by panellists and can be stored for more than 48 weeks at −20 °C. No effects of frozen storage were observed on the proximate composition of eel. The level of TVB-N showed fluctuations (7.09–14.72 mg TVB-N/100 g) during frozen storage period, thus TVB-N could not be used as an indicator of frozen eel quality. FFA, PV and TBA values showed fluctuations during frozen storage period but remained low at the end of storage period, PV reached to the maximum level of 13.20±1.73 meq/kg, which did not exceed the maximum recommended value for human consumption (20 meq/kg). The release of FFA slightly increased (P>0.05) from the initial value of 0.88 to 2.14 (expressed as % of oleic acid) until 32 weeks of frozen storage while TBA increased from the initial value of 0.085 mg MA/kg to maximum level of 0.7696 mg MA/kg after week 40. After that, their values decreased to 1.82 and 0.5577 at week 48, respectively. This study showed that off-flavour and off-odour was not detected and frozen European eels were still acceptable by panellists and can be stored for more than 48 weeks at −20 °C.     

Effects of cooking and reheating methods on the fatty acid profile of sea bream treated with rosemary extract

BACKGROUND: The effects of rosemary extract on the fatty acid profile of sea bream fillets cooked by different methods (oven baking, grilling and pan frying) as well as the effects of different reheating methods (microwave and conventional oven) on the fatty acid composition of fish after frozen storage for 4 months were investigated. RESULTS: The proportion of saturated fatty acids increased only slightly in fried samples but significantly in oven‐baked and grilled samples, while the proportion of polyunsaturated fatty acids (PUFAs) increased significantly in fried samples but only slightly in oven‐baked and grilled samples. The proportion of monounsaturated fatty acids remained relatively constant after cooking. Of the fatty acids analysed, the most significant increases (P < 0.05) were observed in C18:1n‐9 and C18:2n‐6 and the most significant decreases (P < 0.05) in C14:0, C16:1, C20:5n‐3 and C22:6n‐3. Although sea bream fillets fried in sunflower oil showed an increase in PUFAs, the lowest eicosapentaenoic and docosahexaenoic acid contents were found in fried samples. CONCLUSION: Sea bream fillets treated with rosemary extract showed slower oxidation than untreated fish. Neither conventional nor microwave reheating after frozen storage for 4 months had a detrimental effect on the fatty acid profile and its stability. Copyright © 2009 Society of Chemical Industry     

Block copolymer synthesis and chain extension from TEMPO‐terminated chains formed by ultrasonic chain scission

Long poly(ethyl methacrylate) (M_n = 2,300,000) and polystyrene (M_n = 1,200,000) chains were subjected to ultrasonic scission in the presence of a radical scavenger, 2,2,6,6‐tetramethyl‐1‐piperidinyloxy (TEMPO). This procedure yielded polymers with lower molecular weights and TEMPO terminal units. Application of these polymers in stable radical mediated polymerization of styrene resulted in chain extension and block copolymers, depending on the precursor polymer. Block copolymer formation was evidenced by NMR measurement, and chain extension was shown by GPC analysis. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 77: 1950–1953, 2000     

The effects of ice storage on inosine monophosphate, inosine, hypoxanthine, and biogenic amine formation in European catfish (Silurus glanis) fillets

European catfish fillets in ice were evaluated by measuring nucleotide components and biogenic amine contents and these then compared with sensory and microbiological assessment during the 21 days of iced storage. Analyses were carried out using two different rapid HPLC methods for nucleotid degradation products and biogenic amine contents in European catfish fillets. Sensory evaluation showed that storage life of European catfish found to be 14–18 days. Initial inosine monophosphate (IMP) level was 12.6 μmol g^­1 and then decreased during the rest of storage period. Inosine (INO) level increased rapidly until 7 days of storage. Hypoxanthine (Hx) level increased almost linearly with storage time. The most accumulated biogenic amines were putrescine, cadaverine, spermidine, spermine, and serotonin in all the European catfish fillets during the storage, although the formation of biogenic amines levels was fluctuated. Histamine was only detectable at 4 and 7 days of storage as low as 1 mg 100 g^­1 fish. Total viable count in European catfish increased rapidly with storage time and reached ≤10⁹ cfu g^­1 when the fillets were not acceptable for consumption.     

Research on some factors influencing acid and exopolysaccharide produced by dairy propionibacterium strains isolated from traditional homemade Turkish cheeses

In this study, a total of 32 isolated strains and 5 reference strains of dairy propionibacteria were analyzed for acid and exopolysaccharide (EPS) production in skim milk and yeast extract-lactate broth (YEL) media in order to investigate the physiological background and preservative role of acid and EPS. The effects of final culture pH and optical density on acid and EPS production were also determined. On average, all strains produced more acid and reached lower final pH values in skim milk than in YEL medium. While the correlations obtained between the acid produced by propionibacterium strains and their final culture pH in skim milk medium were significant (P < 0.01), no correlations were found between optical density, final pH, and produced acid in YEL medium. Sixteen isolated and five reference strains of propionibacteria were tested further for the ability to produce propionic and acetic acids. On average, Propionibacterium freudenreichii subsp. shermanii and P. freudenreichii subsp. freudenreichii strains produced higher amounts of propionic and acetic acids than did Propionibacterium jensenii in YEL medium. The acid produced by these strains may be used as a preservative in the food industry for replacement or reduction of the increasing use of chemical additives. The EPS production by propionibacterium strains during growth in YEL medium was 72 to 168 mg/liter, while in skim milk it was 94 to 359 mg/liter. The monomer compositions of the EPSs formed by the six selected dairy propionibacteria strains were analyzed. The EPSs may have applications as food grade additives and viscosity-stabilizing agents.     

L‐Carnitine Contents in Seafoods Commonly Eaten in Middle Eastern Countries

Beta‐hydroxy‐gamma‐trimethyl amino butyric acid (L‐carnitine) content of raw and cooked seafood was determined using high‐performance liquid chromatography method. Thirty‐one different fish species and nine different crustaceans were used to compare L‐carnitine content of raw and cooked seafood. Significant differences in L‐carnitine content were found in some species, regardless of the raw or cooked seafood (P < 0.05). There were also significant differences between some of the raw and cooked species (P < 0.05). The levels of L‐carnitine in raw fish samples ranged from 17.98 mg/kg for big‐scale sand smelt to 73.07 mg/kg for European conger (Conger conger). Squid (Loligo vulgaris) and green tiger prawn (Penaeus semisulcatus) were found as the best sources of L‐carnitine among the tested seafood. Microwave cooking also significantly reduced the L‐carnitine content of some seafoods (P < 0.05). The study showed that seafoods are an important origin of L‐carnitine for covering the daily requirements of humans.     

Sterol Content of Fish,Crustacea and Mollusc: Effects of Cooking Methods

Sterol contents (desmosterol, cholesterol, stigmasterol, and sitosterol) of 36 fresh and cooked seafood and four freshwater fish species were investigated by high performance liquid chromatography (HPLC) method. Cholesterol and sitosterol were main sterols in seafood and freshwater fish species. Raw shellfish and molluscs contained cholesterol above 18.92 mg/100 g fish muscle, while the cholesterol content of marine fish ranged from 6.5 to 78.40 mg/100 g fish muscle. The cooking process resulted in significant effects on the sterol contents of seafood and freshwater species (p < 0.05). A remarkable increase in sitosterol (more than 3–4 fold compared to raw fish) was recorded for some fish species cooked in the oven. The highest desmosterol content was observed for fried fish, whereas the frying process resulted in a significant loss in cholesterol and sitosterol contents of marine fish (p < 0.05). The impacts of cooking methods on sterol content of seafood and their form varied depending on fish species and the cooking method used.     

Effects of aluminium foil and cling film on biogenic amines and nucleotide degradation products in gutted sea bream stored at 2±1 °C

Biogenic amines and nucleotide degradation products of sea bream stored in ice, wrapped in aluminium foil (WAF) and in cling film (WCF) at 2±1 °C were investigated by using a rapid HPLC method. Results obtained from this study showed that for household purposes packing fish in different materials has a little effect on the biogenic amines formation and nucleotide degradation products. The highest decrease of IMP content was observed for sea bream in WAF, followed by WCF. INO values showed a fluctuation and remained below the levels of 5.5 μmol/g for all storage conditions. Hx value constantly increased with the storage time during chilled storage. For all of the storage condition, K and Ki value increased linearly with storage time. At the end of the storage period, K, Ki, H and G value reached 60–76%, 65–81%, 30–54% and 89–173%, respectively. Among biogenic amines, (trimetylamine) TMA, putrescine, cadaverine, spermidine, spermine, tryptamine, tyramine, β-phenylalanine and histamine were detected during storage period. TMA and putrescine were observed to increase linearly during storage period. Histamine production was only found at the end of storage period. The highest histamine values for fish wrapped in aluminium foil were 6.4 mg/100 g and fish wrapped in cling film was 4.6 mg/100 g.