Spoilage of refrigerated (4 °C) Litopenaeus vannamei: cooperation between Shewanella species and contribution of cyclo‐(L‐Pro‐L‐Leu)‐dependent quorum sensing

The spoilage potential of Shewanella putrefaciens and S. baltica isolated from spoiled refrigerated Litopenaeus vannamei was evaluated by in vitro assays for trimethylamine oxide reduction, extracellular hydrolytic enzymes and biofilm formation, and in vivo inoculation into surface‐sterilised shrimp followed by microbial, biochemical and sensory analyses during storage for 5 days at 4 °C. S. baltica displayed higher spoilage potential than S. putrefaciens both in vitro and in vivo. Shrimp co‐inoculated with them had one‐day shorter shelf life than those mono‐inoculated, based on the results of bacterial density, volatile base nitrogen, trimethylamine, volatile organic compounds and sensory analysis, which strongly suggests cooperation of Shewanella species in shrimp spoilage. Exogenous cyclo‐(L‐Pro‐L‐Leu) boosted bacterial growth, extracellular protease and collagenase activities, and biofilm formation of S. putrefaciens and S. baltica at least before they entered the stationary phase, indicating that cyclo‐(L‐Pro‐L‐Leu)‐dependent quorum sensing, a recently suggested communication mechanism between them, contributes to the cooperation.     

不同解冻方式对生食鱼片解冻品质的影响

为探究不同解冻方式对生食鱼片品质的影响,以虹鳟鱼为研究对象,对冷藏室解冻、水浴解冻、微波解冻和常温空气解冻4种不同解冻方式下生食鱼片的感官、解冻速率、解冻损失率、色泽、菌落总数、挥发性盐基氮（total volatile basic nitrogen,TVB-N）含量、微观组织结构、质构特性、水分迁移和挥发性气味特征等进行测定。结果表明：冷藏室解冻的生食鱼片感官得分虽显著高于其余3种解冻方式（P<0.05）,但其解冻速率明显低于其余3种解冻方式;水浴解冻组的解冻损失率显著低于其余3种解冻方式（P<0.05）,有利于生食鱼片水分的保留,且其TVB-N含量及菌落总数仅较微波解冻组分别高1.02 mg/100 g、0.46(lg(CFU/g)),其感官得分仅较冷藏室解组冻低3.19分;微波解冻组的白度、菌落总数和TVB-N含量结果虽均优于其他3种解冻方式,能有效抑制解冻过程中色泽的改变、微生物的滋生和缓解生食鱼片中氨及胺类等碱性含氮物质的产生,但微波解冻使生食鱼片受热不均导致其部分熟化的现象明显,其感官和质构指标均较差,不适宜用于解冻生食鱼片;相较于其他3种解冻方式,常温空气解冻...     

长鳍金枪鱼多肽制备及其对H2O2诱导的张氏肝细胞的保护作用

目的:以长鳍金枪鱼废弃物为原料提取多肽,探究其对H2O2诱导的张氏肝细胞的保护作用。方法:以H2O2诱导张氏肝细胞损伤建立细胞模型组,以相对增殖率为指标筛选长鳍金枪鱼废弃物最适酶种,通过正交试验确定最佳酶解条件。酶解产物经超滤、阴离子交换色谱、凝胶过滤色谱和反相高效液相色谱方法纯化分离得到多肽,用噻唑蓝(MTT)比色法对其每步分离效果进行评价。多肽活性的评价是利用试剂盒方法测定张氏肝细胞上清液中AST、ALT、MDA、ADH和SOD的含量,倒置显微镜观察细胞形态及流式细胞仪检测多肽对H2O2诱导后的张氏肝细胞凋亡的影响。结果:最适酶种为胰蛋白酶,最佳酶解条件为料液比1∶3(g/mL),pH 9,加酶量900 U/g,温度45℃,时间5 h。经一系列纯化后制成多肽,命名为长鳍金枪鱼多肽。其氨基酸序列为Gly-Ala-Pro-Gly-Glu-Arg-Gly-Ser-Lys-Cys-Phe-Lys。经长鳍金枪鱼多肽作用于H2O2诱导的张氏肝细胞后,ALT、AST、ADH和MDA含量下降,SOD含量上升。通过流式细胞仪检测发现晚期凋亡细胞相比于模型组减少明显。结论:利用酶解方法提取的长鳍金枪鱼多肽对H2O2损伤的张氏肝细胞具有一定的保护作用。     

超高压杨梅复合果蔬汁的研制及贮藏品质

本文以杨梅、西瓜和茭白为混合原材料,研究了不同比例的杨梅汁、西瓜汁及茭白汁对复合果蔬汁感官指标的影响,同时以菌落总数、糖、酸和V_C含量为指标,研究4 ℃环境下超高压复合果蔬汁的贮藏品质变化。在单因素实验基础上,应用Box-Behnken响应面优化配方参数。结果表明,复合果蔬汁最优配方为杨梅汁为52.1%、西瓜汁为29.4%、茭白汁为18.5%。优化条件下模型预测感官得分为92.28分,验证试验结果(91.42±0.50,n=7)与模型预测结果接近。超高压处理能有效杀灭微生物,对糖、酸、V_C含量无显著影响。在4 ℃下贮藏12 d,超高压复合果蔬汁菌落总数上升了0.43 lg CFU/mL,V_C含量下降了2.09%,糖酸度均无显著性变化,很好地保持了复合果蔬汁的贮藏品质。     

Biphasic calcium phosphate scaffolds fabricated by direct write assembly: Mechanical,anti-microbial and osteoblastic properties

The present work reports on the fabrication of 3-D porous calcium phosphate scaffolds by robocasting from biphasic (HA/β-TCP ≈ 1.5) powders, undoped and co-doped with Sr and Ag. Scaffolds with different pore sizes and rod diameter of 410 μm were fabricated and sintered at 1100 °C. The size and morphology of the powder particles, and the concentrations of the processing additives, were shown to play major roles in the robocasting process. For all pore sizes tested, the compressive strength of scaffolds was comparable to or even higher than that of cancellous bone, and mechanical data could be systematically correlated with the porosity fraction. Co-doping the starting powders with Sr and Ag enhanced the mechanical strength of scaffolds, conferred good antimicrobial activity against Staphylococcus aureus and Escherichia coli, and did not induce any cytotoxic effects on human MG-63 cells. Furthermore, the co-doped powder was more effective in inducing pre-osteoblastic proliferation.     

类蛋白反应在蛋白水解物风味改善中的研究进展

蛋白质在酶解过程中,大量疏水性氨基酸残基暴露出来,产生浓重的苦味影响到蛋白质的风味.在酶的作用下,疏水性氨基酸残基经过类蛋白反应后数量降低,达到风味改善的效果.类蛋白反应与物化法改善蛋白水解液相比,具有无添加、无毒副作用等优点,应用前景广阔.     

Air pollution modelling at a regional scale

A mesoscale simulation system Meso-NH-C allowing for on line coupling between dynamics and chemistry is presented. Further advantages of this system lie in high vertical resolution, nesting capabilities and a full set of parametrization schemes. This system is applied from 9 to 11 August 1997 for a pollution episode over Western Europe. In this episode, both a European and a regional scale analysis have been performed (Greater Paris area). The possibilities of such a modelling system have been emphasized, particularly regarding the evaluation of transboundary fluxes.     

青蛤酶解多肽对RAW264.7巨噬细胞的免疫调节作用

研究酶解法制备的青蛤多肽（Cyclina sinensis peptides,CSP）对RAW264.7巨噬细胞的免疫调节作用。以RAW264.7巨噬细胞相对增殖率为指标,选用胃蛋白酶对青蛤肉进行酶解,酶解液经超滤、冷冻干燥后,采用噻唑蓝（methyl thiazolyltetrazolium,MTT）法筛选出增殖活性最高的组分进行免疫调节作用研究。采用MTT细胞增殖实验、倒置显微镜观察、中性红吞噬实验、硝酸根还原酶法及酶联免疫吸附检测法（enzyme-linked immunosorbent assay,ELISA）测定CSP-5对RAW264.7巨噬细胞的生长与增殖、细胞形态、吞噬能力、一氧化氮（nitric oxide,NO）分泌能力及细胞因子白介素（interleukin,IL）-1β、IL-6和肿瘤坏死因子-α（tumor necrosis factor-α,TNF-α）分泌能力的影响;同时还研究了CSP-5对巨噬细胞各周期分布的影响。结果表明,分子质量小于3 kDa的CSP-5对RAW264.7细胞的生长与增殖具有明显的促进作用,且主要作用于G0/G1期,对细胞吞噬能力、NO分泌能力和细胞因子分泌能力的提高具有显著的促进效果;形态学观察结果显示经CSP-5作用后巨噬细胞体积变大且长出较多伪足。由此可知,CSP-5具有激活巨噬细胞增强机体免疫力的潜在作用。