Angiotensin I‐converting enzyme inhibitory and Ca‐binding activities of peptides prepared from tuna cooking juice and spleen proteases

Tuna cooking juice is a by‐product from the tuna canning industry. In this study, tuna cooking juice was hydrolysed by proteases extracted from the spleen. Tuna cooking juice showed the highest ACE inhibitory and Ca‐binding activities after hydrolysis for 270 and 180 min, respectively. The hydrolysate was further fractionated by ultrafiltration. The permeate exhibited highest ACE inhibitory and Ca‐binding activities when passed through 1 and 5 kDa cut‐off membranes, respectively. Gel filtration chromatography was used to determine the MW of bioactive peptides that exhibited highest ACE inhibitory and Ca‐binding activities. Those peptides that exhibited highest ACE inhibitory and Ca‐binding activities were the MW range of 238–829 Da and 1355–1880 Da, respectively. These results suggest that the tuna cooking juice and the spleen protease extract are a potential source of bioactive peptides that can be utilised as bioactive ingredients in functional food and nutraceuticals.     

Concentration of docosahexaenoic acid in glyceride by hydrolysis of fish oil withcandida cylindracea lipase

In an attempt to concentrate the content of DHA (docosahexaenoic acid) in a glyceride mixture containing triglyceride, diglyceride and monoglyceride, fish oil was hydrolyzed with six kinds of microbial lipase. After the hydrolysis, free fatty acid was removed and fatty acid components of the glyceride mixtures were analyzed. When the hydrolysis withCandida cylindracea lipase was 70% complete, the DHA content in the glyceride mixture was three times more than that in the original fish oil. The EPA (eicosapentaenoic acid) content became almost 70% of the original fish oil. Hydrolysis with other lipases did not result in an increase in the DHA content in the glyceride mixtures. Hydrolysis of DHA-rich tuna oil (DHA content is about 25%) withCandida cylindracea lipase resulted in 53% DHA in the glyceride mixture. The EPA content, however, remained close to that of the original tuna oil. In this report, the acyl chain specificity of lipases is evaluated in terms of hydrolysis resistant value (HRV). HRV is the ratio between the DHA contents in the glyceride mixture of hydrolyzed oil and original oil. HRV clearly indicates differences in hydrolysis between DHA and other fatty acids (e.g., saturated and monoenoic acids).     

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.     

Synthesis of 2‐monoglycerides by alcoholysis of palm oil and tuna oil using immobilized lipases

Commercial immobilized lipases were used for the synthesis of 2‐monoglycerides (2‐MG) by alcoholysis of palm and tuna oils with ethanol in organic solvents. Several parameters were studied, i.e., the type of immobilized lipases, water activity, type of solvents and temperatures. The optimum conditions for alcoholysis of tuna oil were at a water activity of 0.43 and a temperature of 60 °C in methyl‐tert‐butyl ether for ～12 h. Although immobilized lipase preparations from Pseudomonas sp. and Candida antarctica fraction B are not 1, 3‐regiospecific enzymes, they were considered to be more suitable for the production of 2‐MG by the alcoholysis of tuna oil than the 1, 3‐regiospecific lipases (Lipozyme RM IM from Rhizomucor miehei and lipase D from Rhizopus delemar). With Pseudomonas sp. lipase a yield of up to 81% 2‐MG containing 80% PUFA (poly‐unsaturated fatty acids) from tuna oil was achieved. The optimum conditions for alcoholysis of palm oil were similar as these of tuna oil alcoholysis. However, lipase D immobilized on Accurel EP100 was used as catalyst at 40 °C with shorter reaction times (<12 h). This lead to a yield of ～60% 2‐MG containing 55.0‐55.7% oleic acid and 18.7‐21.0% linoleic acid.     

卫星遥感在中东太平洋大眼金枪鱼渔场与环境关系的应用研究

中东太平洋延绳钓渔业主要以钓获大眼金枪鱼为主,我国远洋延绳钓渔船虽然也在该海域作业,但渔获量比日本少得多,且渔获种类多为黄鳍和长鳍金枪鱼,经济价值不高,归根结底是因为对该海域大眼金枪鱼渔场渔况掌握不够。为了精确预测该海域大眼金枪鱼渔场,本文采用卫星遥感反演全球区域月平均海表温度(SST)、海面高度(SSH)、叶绿素浓度(Chlo)以及由SST计算得到的温度梯度(TGR)等数据,结合太平洋共同体秘书处(SPC)提供的大眼金枪鱼历史捕获数据,辅助预测大眼金枪鱼渔场。通过把渔获数据与环境数据进行地理关联统计分析得到以下结果:在SST(26℃~29℃),Chlo(0.1mg/m3~0.2 mg/m3)、SSH(-2cm~1.5cm)和TGR(0.1℃/60nmi~0.4℃/60nmi)等环境因子分布区间内大眼金枪鱼延绳钓渔场渔获努力量(CPUE)数值较高。目前的海洋遥感监测卫星已能够提供准实时海洋环境因子监测数据,因此,应用遥感手段获取环境因子数据,同时结合历史渔获量与环境因子的统计关系,大眼金枪鱼渔场渔情的预报精度将被大大提升。     

不同冻结方式对黄鳍金枪鱼品质变化的比较研究

为了研究不同冻结保鲜方式对金枪鱼肉的保鲜效果,本文通过测定冻藏期间金枪鱼背肌的K值、TBA值、TVB-N值、高铁肌红蛋白含量与色差,并结合感官评定,分析了液氮冻结、自制冷冻液冻结、-80℃超低温冻结和-18℃低温冻结等四种不同冻结方式对黄鳍金枪鱼背肌品质的影响。结果显示:液氮冻结的金枪鱼背肌的K值、TBA值、TVB-N值、高铁肌红蛋白含量较其他三组低,可以较长时间保持金枪鱼肉的新鲜度,从这一角度来说,液氮冻结为最佳冻结方式。但由于冻结速度极快,样品表面出现轻微裂缝,色差和感官评分指标比冷冻液浸渍冻结方式差。      

生食金枪鱼肉冷藏过程鲜度的变化

对解冻生食黄鳍金枪鱼肉0、2、4、6、8℃冷藏过程中鲜度变化展开系统研究,以K值小于20%确定各冷藏温度下生食终点,冷藏过程中采用K值、p H等指标评价品质,获得生食金枪鱼肉冷藏品质变化规律。生食黄鳍金枪鱼肉冷藏过程ATP关联物中ATP快速下降,ADP、AMP缓慢下降,IMP有累积趋势,Hx R蓄积量较大,为Hx R生成型鱼种。p H在生食期间没有显著差异,对鲜度高的生食生鱼片品质不适合采用p H判断鲜度间的小差异。建立生食金枪鱼肉冷藏K值随时间变化规律的动力学模型,模型符合一级动力学反应方程。冷藏温度对反应速率常数的影响用Arrhenius方程描述,有较高的拟合精度。      

基于NAD的分解对金枪鱼块流水解冻工艺的优化

为对高品质金枪鱼流水解冻工艺进行优化,本实验将鱼肉从-60℃超低温冰箱中取出后在-12⁰℃的低温冰箱中贮藏相应的时间后再流水解冻。结果表明:-6℃15 h和-9℃3 d冷藏贮藏后流水解冻可有效缓解鱼肉收缩现象,减少汁液流失,比直接流水解冻具有更好的咀嚼特性,与冷藏室解冻相比无显著性差异。对优化解冻过程中金枪鱼三磷酸腺苷（ATP）、烟酰胺腺嘌呤二核苷酸（NAD）含量变化进行检测分析,结果表明当NAD分解至0.20μmol/g,ATP降解到2.0μmol/g时,既能缓解鱼肉收缩、降低汁液流失,又能保证K值在一级鲜度20%范围内。本研究采用的优化工艺可有效提高冻结金枪鱼流水解冻的品质。      

金枪鱼肌原纤维蛋白热凝及流变特性的研究

鱼肉的组织学特性和肌原纤维蛋白的凝胶学特性有很大的相关性。深入探讨金枪鱼肉肌原纤维凝胶体系的凝胶机理,有利于开发保证质量的金枪鱼肉制品。本研究通过小振幅及大振幅振荡剪切流变学方法,探讨NaCl浓度(0.3~0.6mol/L)对金枪鱼肌原纤维蛋白热凝胶特性及流变特性的影响。结果表明,热诱导凝胶过程中,在47℃之前,弹性模量(G’)随NaCl浓度的增加而增大,在47℃之后总体趋势发生改变,G’在NaCl浓度为0.4mol/L达到最大值。NaCl浓度在肌原纤维蛋白凝胶形成过程中对流变的影响最大。对数模型能很好地关联线性粘弹性区间的应变同G’的数量关系。大振幅振荡测试(LAOS)表明,随着浓度的增加,网络结构更紧密,剪切一周期所消耗能量越大,在较大的应变下能够更稳定地保持线性粘弹性。      

金枪鱼油加热后脂肪酸的动态变化

为探讨不同加热时间和加热温度对金枪鱼油脂肪酸组成的影响。本文将金枪鱼油分别在100、130、160、180、210、240、270℃温度下短时间加热1² min,在160℃、180℃持续加热10、20、30 min。将这些鱼油进行甲酯化后,使用气相色谱-质谱法（GC-MS）对其进行定量分析,研究其脂肪酸的组成。结果显示:金枪鱼油经不同温度短时间加热后,其脂肪酸组成成分及含量保持稳定,不同温度间脂肪酸的组成无显著差异;在160℃及以上高温长时间加热会逐步破坏甘油三酯的稳定性,导致不饱和脂肪酸含量急剧降低,饱和脂肪酸含量显著升高,营养成分受到影响,DHA含量显著变化。所以,金枪鱼油不适宜长时间加热。