Comparison of six methylation methods for analysis of the fatty acid composition of albacore lipid

Six methods widely used to produce methyl esters for the gas chromatographic determination of the fatty acid composition of a marine lipid were compared. Four acid-catalyzed methods (1% H₂SO₄: CH₃OH; 5% HCl: CH₃OH; 7% and 14% BF₃: CH₃OH) and two base-catalyzed methods [0.5M NaOCH₃: CH₃OH; (1:4) tetramethylguanidine: CH₃OH] were used.
The use of BF₃: CH₃OH (7% and 14%) gave a lower content of 18:1 n9 than the other methods and produced an artefact (2.7–3.2% of total fatty acid content) eluting between the 20:5 and 24:1 fatty acid methyl esters. No significant differences were obtained between the other four methods.
Accordingly the use of BF₃: CH₃OH for transmethylation of marine lipids is not recommended. Results obtained in the other four methods showed that all are comparable.     

Amino acid profiles and liposomes: Their role as chemosensory information carriers in the marine environment

Yellowfin tuna enhance their hunting success in the vast pelagic environment by using their sense of smell to detect intact (uninjured) prey that are beyond visual range. However, the olfactory cues that tuna use would normally face huge and rapid dilution in the open ocean. We demonstrate that these prey odors are complexed within biologically derived lipid structures that probably delay the dilution of the amino acids to subthreshold concentrations and provide persistent arousal and search cues for the tuna. This may be the first demonstration of an extracorporeal biological function for liposomes. Tuna may also form chemical search images to maximize feeding efficiency. We demonstrate that the amino acid profiles of various prey species are consistent over time and between schools, which makes the formation of search images feasible.     

Proton nuclear magnetic resonance rapid and structure-specific determination ofω-3 polyunsaturated fatty acids in fish lipids

Based on proton nuclear magnetic resonance (¹H-NMR) spectroscopy, a rapid and structure-specific method for the determination of ω-3 polyunsaturated fatty acids (PUFAs) in fish lipids is presented. The different chemical shift observed for the methyl resonance of ω-3 PUFAs (δ=0.95 ppm) with respect to the methyl resonance of all other fatty acids (δ=0.86 ppm) has provided the possibility of proposing a new and rapid method for the determination of ω-3 PUFA content. Twenty-four fish lipid samples (raw, cooked and canned albacore tuna) produced results that showed good agreement between¹H-NMR analysis and gas chromatographic determination. Raw and cooked samples showed significantly higher levels of ω-3 PUFA than canned tuna.     

冷藏处理方式对大目金枪鱼贮藏品质及内源酶活性的影响

为研究不同冷藏处理方式对大目金枪鱼贮藏品质与内源酶活性的影响,分别研究4℃冷藏、碎冰与流化冰贮藏的大目金枪鱼的理化指标(质构特性、电导率与总挥发性盐基氮)、微生物指标(菌落总数)、ATP关联产物与酶活(腺苷脱氨酶、酸性磷酸酶),并结合低场核磁共振技术共同表征不同冷藏条件对大目金枪鱼综合品质的影响。结果表明:随着贮藏时间的延长,流化冰处理可显著抑制大目金枪鱼肉电导率值、TVB-N值、菌落总数、次黄嘌呤(Hx)含量的升高,其质构值(硬度、弹性、咀嚼性)、三磷酸腺苷及肌苷酸含量降幅较其余两组缓慢。此外,流化冰处理金枪鱼样品的K值、H值、Ki值明显低于另外两组,Fr值呈为平缓地降低趋势。3组样品贮藏后期的酸性磷酸酶和腺苷脱氨酶活性显著增长,其中酸性磷酸酶活性与菌落总数显著相关,流化冰对其有一定抑制作用。通过低场核磁共振分析得出,大目金枪鱼鱼肉中的不可流动水(T22)逐渐向自由水(T23)转化,肌原纤维内水分含量降低,肌肉品质劣化。由此得出,与4℃冷藏组、碎冰处理组样品相比,流化冰处理可通过控制内源酶活性和微生物生长,减缓ATP关联产物的降解与品质劣变,从而达到延缓大目金枪鱼食用品质劣变的目的。     

Optimization of adhesive strength to plywood of gelatin processed from dorsal skin of yellowfin tuna (<Emphasis Type="Italic">Thunnus albacares</Emphasis>)

Gelatin from yellowfin tuna (Thunnus albacares) dorsal skin was optimized for adhesive strength to plywood using surface response methodology of a central composite design with a dependent variable of adhesive strength (Y, kg _f /cm²) and two independent variables of gelatin concentration (X₁, %) and hardening time (X₂, hrs). From the above design, a maximum adhesive strength of 49.84 kg _f /cm² was obtained under the optimal treatment condition of 15.85% gelatin concentration and 25.68 hr hardening time. The adhesive strength under optimum conditions was 50.93 kg _f /cm². The adhesive strength of the tuna gelatin was shown to be superior to that of bovine and porcine gelatins which had adhesive strengths of 34.75 and 34.9 kg _f /cm², respectively.     

Polymer assisted isolation of hydroxyapatite from Thunnus obesus bone

The combination of micro and nanostructured hydroxyapatite (HAp) was isolated from Thunnus obesus bone via thermal calcination method in the presence of polymers such as poly ethylene glycol (PEG), poly (ethylene glycol)-block-poly (propylene glycol)-block-poly (ethylene glycol) (PEG-PPG-PEG) and poly vinyl alcohol (PVA). The thermal stability, crystalline phase, chemical composition and morphology of the derived HAp were characterized by thermal gravimetric analysis, X-ray diffraction analysis, Fourier transform infrared spectroscopy and field emission scanning electron microscopy analysis. The physicochemical characteristic examination revealed that derived HAp was coherent with standard HAp data. Moreover, FE-SEM depicted significant difference in the crystal size of HAp derived with thermal calcination, with and without added polymers. The crystallinity of HAp isolated in the presence of polymer was lower than that obtained in the absence of polymers. The biocompatibility of the derived HAp crystals was checked with MC3T3-E1 osteoblastic cells by MTT assay and Hoechst-33342 staining. The biocompatibility of HAp derived by polymer assisted thermal calcination method revealed that it is less toxic as compared to HAp derived in the absence of polymer. As an inference, polymer assisted thermal calcination derived HAp is good in terms of the presence of combined micro and nanostructured HAp and its low toxicity will bring about new orthopaedic applications.     

金枪鱼油的精炼及其脂肪酸组成特征

粗鱼油中通常含有一定量的非甘油三酯杂质成分,这些杂质会影响鱼油的稳定性和进一步的深加工,通过精炼可以除去这部分杂质.研究表明,黄鳍金枪鱼鱼油精炼的工艺参数为:80%的H3PO4脱胶,添加量为油量的1%;30%的NaOH脱酸,添加量为油量的2%;活性白土脱色,添加量为油量的10%;85℃减压蒸馏脱臭15 min.经过精炼,鱼油呈淡黄色,澄清透明,具有较淡的鱼腥味,理化指标均达到鱼油的SC/T 3502-2000标准的精制鱼油一级要求,精制鱼油中PUFA的总含量达37.06%,DHA和EPA含量分别为25.10%和4.45%.     

大目金枪鱼外部与内部解冻法的品质变化

研究外部解冻法与内部解冻法对冻结大目金枪鱼块解冻后的品质变化的影响,包括空气解冻、真空解冻、微波解冻和超声波解冻,筛选出适合冻结金枪鱼块的解冻方法.测定解冻时间、菌落总数及解冻过程中金枪鱼肉的持水率、pH、盐溶蛋白含量和总巯基含量变化.综合以上6个指标得出,真空解冻能更好地保持金枪鱼的品质,解冻至终点后的鱼块持水率为63.33％,pH为6.11,盐溶蛋白含量为37.49mg/g,总巯基含量为5.69x 10-4mol·g-1,菌落总数为2.971g CFU/g,符合金枪鱼生食标准.真空解冻是最适合冻结大目金枪鱼块的解冻工艺.     

冰鲜法对黄鳍金枪鱼片品质的影响

取斐济岛黄鳍金枪鱼背部肌肉,模拟寿司店保存生鱼片的方法,定时观察鱼片物理(色泽、失重率)、生化(pH 值、TVB-N 值、鲜度指标K 值)、感官及微生物等各项指标的变化。结果表明,冰鲜法能在0～4h 内较好地保持黄鳍金枪鱼片的品质。0～1h 内色泽鲜红、气味芳香、滋味鲜美,处于理想的食用状态,1～4h 内色泽由亮变暗,鱼香味和鲜味随汁液流失,品质逐步下降。超过4h 金枪鱼不再新鲜,失去固有的口感、色泽,不具备商业价值。