6种金枪鱼脂肪酸组成与含量差异性研究

目的比较捕捞于不同海域不同品种的6种金枪鱼的脂肪酸种类与含量。方法收集来源于大西洋、太平洋、印度洋的蓝鳍金枪鱼(Thunnus thynnus)、黄鳍金枪鱼(Thunnus albacores)、大目金枪鱼(Thunnus obesus)、马苏金枪鱼(Thunnus maccoyii)、长鳍金枪鱼(Thunnus alalunga)、鲣鱼(Katsuwonus pelamis)6种金枪鱼,采用三氟化硼甲醇甲酯化金枪鱼肌肉组织的脂肪酸,利用气相色谱法测定脂肪酸甲酯含量;再通过SPSS 24对各脂肪酸组成结果进行相关性分析。结果 6种金枪鱼肌肉脂肪酸种类与含量丰富,蓝鳍金枪鱼、大目金枪鱼等5种金枪鱼不饱和脂肪酸的含量明显高于鲣鱼,蓝鳍金枪鱼的不饱和脂肪酸种类最多且含量最高,捕捞于太平洋海域的大目金枪鱼、黄鳍金枪鱼的不饱和脂肪酸种类明显多于其他海域,人工饲养的马苏金枪鱼(太平洋)比野生马苏金枪鱼(印度洋)的不饱和脂肪酸种类丰富;6种金枪鱼主要组分间的相关性分析结果显示,C20:0与所测的9种脂肪酸呈负相关,C18:1与C18:2呈极显著正相关(r=0.900～1.000),C14:0与C17:1呈负相关,与其他8种脂肪酸呈正相关。结论 6种金枪鱼存在脂肪酸种类与含量的差异,不同海域与不同养殖方式下的金枪鱼脂肪酸的种类也存在差异。     

Purification of docosahexaenoic acid from tuna oil by a two-step enzymatic method: Hydrolysis and selective esterification

Purification of docosahexaenoic acid (DHA) was attempted by a two-step enzymatic method that consisted of hydrolysis of tuna oil and selective esterification of the resulting free fatty acids (FFA). When more than 60% of tuna oil was hydrolyzed with Pseudomonas sp. lipase (Lipase-AK), the DHA content in the FFA fraction coincided with its content in the original tuna oil. This lipase showed stronger activity on the DHA ester than on the eicosapentaenoic acid ester and was suitable for preparation of FFA rich in DHA. When a mixture of 2.5 g tuna oil, 2.5 g water, and 500 units (U) of Lipase-AK per 1 g of the reaction mixture was stirred at 40°C for 48 h, 83% of DHA in tuna oil was recovered in the FFA fraction at 79% hydrolysis. These fatty acids were named tuna-FFA-Ps. Selective esterification was then conducted at 30°C for 20 h by stirring a mixture of 4.0 g of tuna-FFA-Ps/lauryl alcohol (1:2, mol/mol), 1.0 g water, and 1,000 U of Rhizopus delemar lipase. As a result, the DHA content in the unesterified FFA fraction could be raised from 24 to 72 wt% in an 83% yield. To elevate the DHA content further, the FFA were extracted from the reaction mixture with n-hexane and esterified again under the same conditions. The DHA content was raised to 91 wt% in 88% yield by the repeated esterification. Because selective esterification of fatty acids with lauryl alcohol proceeded most efficiently in a mixture that contained 20% water, simultaneous reactions during the esterification were analyzed qualitatively. The fatty acid lauryl esters (L-FA) generated by the esterification were not hydrolyzed. In addition, L-FA were acidolyzed with linoleic acid, but not with DHA. These results suggest that lauryl DHA was generated only by esterification.     

Determination of water activity of canned fish using gravimetric, hygrometric and psychrometric methods

The water activity ( a _w) of canned mackerel, tuna and sardine was determined using three methods: a gravimetric and two instrumental methods. The a _w values obtained by the gravimetric method, which only requires simple laboratory apparatus, were not significantly different from the values obtained by the other two methods, and can be used to determine high a _w values.     

Differences in Gelation Characteristics of Natural Actomyosin from Two Species of Bigeye Snapper, Priacanthus tayenus and Priacanthus macracanthus

ABSTRACT: Natural actomyosin (NAM) of P. tayenus exhibited higher turbidity and storage modulus (G') upon heating, compared to that of P. macracanthus , suggesting the higher protein aggregation and rigidity. At temperature above 35 °C, P. tayenus NAM had higher surface hydrophobicity and disulfide bond formation than P. macracanthus NAM. The α-helix content of NAM from both fish species decreased as the temperature increased, indicating changes in structural conformation during heating. NAM gel from P. tayenus rendered more three-dimensional network than that from P. macracanthus. These results indicated that P. tayenus NAM possessed superior gelling characteristic to P. macracanthus NAM due to the higher aggregation of protein caused by both hydrophobic interaction and disulfide bond.     

Histamine reduction by Maillard reaction with glucose

Histamine, well known as a toxic biogenic amine, is found in a variety of foods. Reducing its concentration and toxicity is desirable. In this study, the glucose/histamine Maillard reaction was proposed as a novel tool for histamine control. Effects of temperature, heating time, initial pH value, NaCl concentration, initial histamine concentration and initial glucose concentration on percentage removal of histamine in the glucose/histamine Maillard reaction model were investigated. The results showed that histamine reduction was affected by these variables, and could be almost eliminated under appropriate conditions. Fluorescence intensity and ultraviolet–visible spectroscopy analyses were used to characterize the glucose/histamine Maillard reaction. Cytotoxicity assay revealed that the glucose/histamine Maillard reaction significantly reduced the toxicity of histamine (P < 0.05). Furthermore, histamine concentrations in canned tuna samples were significantly reduced by thermal treatment with glucose (P < 0.05). This study demonstrates that the glucose/histamine Maillard reaction is a promising method for histamine control.     

Antioxidant activity of bigeye tuna (Thunnus obesus) head protein hydrolysate prepared with Alcalase

The antioxidant activities of tuna head protein hydrolysate (THPH) prepared with Alcalase were evaluated. THPH showed evident radical scavenging activity in a dose‐dependent manner with the IC₅₀ values for 1,1‐diphenyl‐2‐pycrylhydrazyl (DPPH), superoxide and hydroxyl radicals being 1.34, 1.20 and 2.84 mg mL^?1, respectively, and its reducing power was 0.948 at 12.5 mg mL^?1. THPH showed good inhibitory activity in soybean oil peroxidation after accelerated oxidation at 60 °C, and the oils with 0.01%, 0.05% and 0.1% THPH had significantly (P < 0.05) lower peroxide values than the control, after storage at 60 °C. Moreover, the inhibited oxidation effect of 0.1% THPH was similar to that of 0.01% butylated hydroxytoluene (BHT). The molecular weight distribution of THPH revealed that 70.5% of the total amount was peptides with molecular weight lower than 5000 Da, composing mostly of low molecular weight peptides located at 1020–2585 Da (30.78%) and 241–1020 Da (37.15%).     

The effect of different atmospheric conditions on the changes in myoglobin and colour of refrigerated Eastern little tuna (Euthynnus affinis) muscle

BACKGROUND: Oxidation of myoglobin is responsible for the undesirable appearance and loss in acceptability of fish and fish products. The retardation of such a change by a modification of the surrounding atmosphere would be a means to maintain the quality of fish during the refrigerated storage. RESULTS: The changes in oxymyoglobin and metmyoglobin from dark muscle of Eastern little tuna (Euthynnus affinis) as affected by different atmospheric systems (closed system, opened system and flushed oxygen system) were determined. A saturated oxygen atmosphere more likely weakened the haem–globin complex, especially as the exposure time increased. Autoxidation of the oxy form proceeded rapidly in the presence of oxygen with the concomitant formation of the met form. When the oxygen was excluded, oxidation of oxymyoglobin was retarded. With flushed oxygen and increasing exposure time, conformational changes of globin occurred, mainly associated with protein oxidation. Generally, oxymyoglobin was more susceptible to oxidation and conformational change than did metmyoglobin. After keeping the samples at 4 °C for 3 days, dark muscle of tuna fillet kept in vacuum packaging had a slight decrease in redness and it was still acceptable. The fillets stored in exposed air or packed in 100% O₂ atmosphere turned brown, most likely due to myoglobin oxidation. CONCLUSION: The oxygen level of the packaging atmosphere had a profound impact on myoglobin alteration, which was governed by the forms of myoglobin. Copyright © 2011 Society of Chemical Industry     

溴麝香草酚蓝/玉米醇溶蛋白指示标签对金枪鱼新鲜度的监测

近年来,智能检测食品新鲜度的比色膜受到越来越多的关注。本实验利用静电纺丝技术研制出一种溴麝香草酚蓝（bromothymol blue,BTB）/玉米醇溶蛋白（zein,ZN）新型智能比色标签,用于金枪鱼鱼片的新鲜度监测。BTB在pH值为5～12时的明显颜色变化赋予了指示标签灵敏的pH值传感效果。通过场发射扫描电子显微镜、傅里叶变换红外光谱、X射线衍射、差示扫描量热仪对不同BTB添加量的BTB/ZN指示标签的形貌和结构进行表征。再将BTB/ZN指示标签应用于金枪鱼鱼片新鲜度的指示验证实验,对指示标签的指示效果进行验证。结果表明,BTB/ZN指示标签的微观结构良好,BTB可以很好地与ZN结合在一起,并且不破坏二者的结构;质量分数4% BTB的BTB/ZN指示标签的指示效果最佳,能灵敏地反映金枪鱼的新鲜度变化。指示标签的色度和金枪鱼鱼肉的总挥发性盐基氮含量之间存在显著相关性,这证明BTB/ZN指示标签能有效监测金枪鱼鱼片的新鲜度。     

Effects of Docosahexaenoic Acid Content in Triacylglycerol on Human Taste Perception

ABSTRACT: To elucidate the contribution of docosahexaenoic acid (DHA) in triacylglycerol to tuna oil specific taste effects, suppression of bitterness and enhancement of umami, we conducted sensory analysis employing an oil-in-water emulsion prepared with taste substances and the oils differed in the DHA content. The tuna oil specific taste effects were linearly dependent on DHA content. The increase of DHA in oil also linearly enhanced umami and flavor (continuity and richness) of synthetic tuna extract. These results indicate that DHA, a major fatty acid of tuna oil, greatly contributes to tuna oil specific effects on basic tastes and flavor.     

Computer Simulation on Onboard Chilling and Freezing of Albacore Tuna

We extended the application of a commercial finite-element computer program package, PDEase, to the simulation of chilling and freezing of albacore tuna. Tuna was described as an infinite elliptical cylinder, where nonuniform boundary conditions present complications in computer simulation. Equations were developed to define the elliptical boundary. Temperature-dependent thermal properties and time-dependent ambient temperature conditions were used. Onboard experiments were conducted to measure the core temperature of individual tuna in slush ice tanks and in air-blast and brine-spray freezing systems. Measured time-temperature profiles were compared with those of the simulation. Predicted chilling and freezing curves agreed with experiments ±3 to 6%. This program enables testing of important fish industry operation strategies.