D-氨基酸氧化酶性质研究

D-氨基酸氧化酶（DAAO）是一种以黄素腺嘌呤二核苷酸（FAD）为辅基的典型黄素酶。它催化D-氨基酸生成相应的α-酮酸和氨。该文介绍了D-氨基酸氧化酶的研究现状及其特性，包括它的生理功能、基本特性、结构特性、光学动力学特性。     

Properties of Rhodotorula gracilis D-amino acid oxidase immobilized on magnetic beads through his-tag

D-amino acid oxidase catalyzes one of the key steps in the production of semisynthetic cephalosporins. We expressed and purified recombinant Rhodotorula gracilis D-amino acid oxidase with C-terminal his-tags. This engineered enzyme was immobilized onto Ni(2+)-chelated nitrilotriacetic acid magnetic beads through the interaction between his-tag and Ni(2+). The kinetic constants, storage properties, and the reusability of the immobilized d-amino acid oxidase were determined. The effects of temperature, pH, and hydrogen peroxide on the activity of immobilized d-amino acid oxidase were also studied. The highest activity recovery was 75%. Thermal stability was improved after immobilization; the relative activity of the immobilized enzyme was 56% whereas the free enzyme was completely inactivated after incubation at 50 degrees C for 1 h. In the presence of 10 mM hydrogen peroxide, the immobilized enzyme did not show a rapid loss of activity during the first 2 h of incubation, which was observed in the case of the free enzyme; the residual activity of the immobilized enzyme after 9 h was 72% compared with 22% of the free form. The long-term storage stability was improved; the residual activity of the immobilized enzyme was 74% compared with 20% of the free enzyme when stored at room temperature for 10 d. The immobilized form retained 37% of its initial activity after 20 consecutive reaction cycles.     

三角酵母D-氨基酸氧化酶基因在毕赤酵母中的转化

利用跨越内含子的PCR技术,从三角酵母(Trigonopsisvariabilis)中扩增得到D-氨基酸氧化酶基因(DAAO),通过TA克隆的方法将其克隆至pBS-T载体,并转化大肠杆菌TOP10。序列测定结果表明,所得DAAO基因的5’端内含子已被删除,基因总长度为1071bp。之后将该基因与酵母表达载体pPIC3.5K连接,转化巴斯德毕赤酵母(Pichiapastoris)。     

蚕茧丝素肽保健饮料生产工艺研究

以废蚕茧为原料，采用Alcalase酶和Flavourzyme酶双酶水解工艺，得到丝素肽的低分子量降解物，经过对降解物进行脱色、脱异味处理，用超滤膜分离出分子量1000以内的丝素肽，制成含丝素肽3％、含糖量13％、pH值4．4的不同水果香型的功能性丝素肽饮料，4℃贮藏达12个月以上无沉淀产生，解决了丝素蛋白的酶解率低、生物效价低等问题，为蚕茧蛋白食品的开发提供了一条有效途径。     

乳酸菌抗菌肽(细菌素)抗菌机理的研究进展

乳酸菌抗菌肽是乳酸菌代谢过程产生的一类具有活性的多肽或蛋白质物质,可抑制或杀死食品中的病原菌或腐败菌。很多乳酸菌产生的抗菌肽不仅抑制相关菌种,还包括很多种类的革兰氏阳性腐败菌和食源性致病菌。在抗菌肽被广泛使用之前很久科学家们已经发现了某些细菌的抑菌活性,甚至在抗菌肽生产菌没有确定的条件下就已经将抗菌肽应用于发酵食品中。近几年,乳酸菌对其他细菌的拮抗作用的机理研究得最多的是乳酸菌抗菌肽。乳酸菌抗菌肽在食品行业中具有广泛的应用前景,它被认为是一种"天然"的食品添加剂而容易被人们接受。本文首先对所有乳酸菌抗菌肽的作用机制进行简短叙述,总结出乳酸菌抗菌肽抑菌机制的五种模型,分别是:"桶板"模型、"楔"模型、"虫孔"模型、"毯式"模型、"凝聚"模型。以此为基础,对不同种类的乳酸菌抗菌肽抑菌机制分别进行论述,最后对其最新进展进行总结。     

Citric acid and the browning of solutions containing ascorbic acid

Model systems were used to simulate lemon juice so that the findings may be applicable to the non-enzymic browning phenomenon which occurs on storage of citrus juices. The addition of citric acid to systems containing ascorbic acid resulted in augmented chromophore development. Evidence is given to show that citric acid neither acts as a catalyst nor yields reactive carbonyl compounds under aerobic incubation conditions. Thin-layer chromatographic separation of the brown pigments in different systems demonstrated a specific chromophore which occurred only when citric acid and ascorbic acid were both present. The presence of amino acids in ascorbic systems is the major contributor to the development of browning but it is suggested that citric acid, or a derivative, is incorporated into some of the brown pigments.     

小米汽奶的研究与开发

以小米与奶粉为原料研制一款新型的碳酸饮料,解决小米汽奶在加工过程中由淀粉、蛋白质引起的沉淀问题,通过正交试验设计,确定了最佳工艺条件:小米浆汁与奶质量比1∶1,复合稳定剂(海藻酸钠∶卡拉胶1.5∶1)添加量0.04%,乳化剂(单甘酯)添加量0.15%。此工艺条件下生产的小米汽奶色泽和组织状态良好,风味独特,营养丰富。     

植物源性食物中活性肽氨基酸组成的研究进展

植物源性食物中含有丰富的活性肽,其中抗氧化肽,降压肽,免疫调节肽,抗肥胖肽,抗胆固醇肽,抗肿瘤肽,阿片肽,抗血栓肽等均已被广泛研究报道。该文从肽序列的氨基酸组成入手,综述了目前已鉴定出氨基酸序列的植物源性食物中的各种生物活性肽,以为此类活性肽的进一步研究应用提供参考。     

Thermostable ATP regeneration system using polyphosphate kinase from Thermosynechococcus elongatus BP-1 for D-amino acid dipeptide synthesis

D-alanine-D-alanine ligase from Thermotoga maritima ATCC 43589 (TmDdl) was a useful biocatalyst for synthesizing D-amino acid dipeptides. TmDdl showed a broad substrate specificity at a high temperature; however, ATP was required for its reaction. One of the methods for an effective ATP supply was the coupling reaction with an ATP regeneration system. However, ATP regeneration systems consisted of enzymes from mesophiles and were difficult to operate at high temperatures. Therefore, an ATP regeneration system that could be used at high temperatures was desired to utilize TmDdl for the effective production of D-amino acid dipeptides. To establish a thermostable ATP regeneration system, polyphosphate kinase from a thermophile, Thermosynechococcus elongatus BP-1 (TePpk), was characterized. TePpk showed thermostability up to 70 degrees C; therefore, it was considered that a thermostable ATP regeneration system could be established using TePpk. In the coupling reaction with purified TmDdl and TePpk at 60 degrees C, the amount of ATP required for D-alanyl-D-alanine synthesis could be reduced to 1% of the theoretical amount required when there was no ATP regeneration. When the coupling reaction was applied to a resting cell reaction, ATP was regenerated from an adenosine scaffold in the cell, and D-alanyl-D-alanine was successfully synthesized in the maximum yield of 80% (mol/mol) without the addition of ATP. Thus, an effective synthesis of D-amino acid dipepitides was achieved using the thermostable ATP regeneration system.     

Inhibition of dipeptidyl peptidase IV (DPP-IV) by proline containing casein-derived peptides

Dipeptides with a C terminal Pro inhibit dipeptidyl peptidase IV (DPP-IV), a key enzyme in incretin hormone processing. It was hypothesised that tri- and tetrapeptides with a proline at the C-terminus may also be DPP-IV inhibitors. Therefore, an in silico hydrolysis approach was used to release short (4 ? amino acids) C terminal Pro peptides from the individual caseins which constitute Pro rich substrates. This was achieved using theoretical digestion of caseins with a prolyl oligopeptidase activity. Fifteen peptides were subsequently selected for in vitro DPP-IV inhibitory analysis. Stability of these peptides to gastrointestinal enzymes was also evaluated in silico and the predicted breakdown peptides were assessed for their DPP-IV inhibitory and antioxidant potential. New DPP-IV inhibitors were identified, the most potent being Phe-Leu-Gln-Pro (IC₅₀ 65.3 ± 3.5 μM). A low in vitro antioxidant (2,2-diphenyl-1-picrylhydrazyl (DPPH) scavenging) activity was also associated with the peptides studied. The strategy presented highlights the utility of employing an in silico approach for the prediction of food-derived peptides with a potential role in glycaemic management for subsequent development of functional foods.     

Identification and characterization of a novel yeast omega3-fatty acid desaturase acting on long-chain n-6 fatty acid substrates from Pichia pastoris

A cDNA sequence putatively encoding a omega(3)-fatty acid desaturase gene was isolated from methylotrophic yeast Pichia pastoris GS115. The deduced amino acid sequence of this cloned cDNA showed high identity to known fungal omega(3)-fatty acid desaturases. Functional identification of this gene heterologously in Saccharomyces cerevisiae strain INVScl indicated that the deduced amino acid sequence exhibited omega(3)-fatty acid desaturase activity. The newly identified omega(3)-fatty acid desaturase, named Pp-FAD3, is novel because it showed broad n-6 fatty acid substrate specificity by its ability to convert all the 18-carbon and 20-carbon n-6 substrates examined to the corresponding n-3 fatty acids, with an approximately equivalent high conversion rate. Pp-FAD3 is the first known yeast omega(3)-fatty acid desaturase to act on long-chain n-6 fatty acid substrates. Heterologous expression of the newly identified omega(3) desaturase in different hosts will be an alternative method to increase the flow of n-6 fatty acid intermediates into their n-3 derivatives.     

酸性含乳碳酸饮料稳定性的研究

对酸性含乳碳酸饮料加工过程中易引起沉淀的环节进行了稳定性研究,比较了不同稳定剂的稳定效果,并确定了最佳稳定剂及最优复配稳定剂。结果表明,复配稳定剂(海藻酸钠0.3%+CMC0.4%+卡拉胶0.1%对含乳碳酸饮料的稳定效果最为明显,所得含乳碳酸饮料的形态均匀,产品呈乳白色的稳定体系,并且长时间放置不分层。     

Antihypertensive peptides from whey proteins fermented by lactic acid bacteria

Food Science and Biotechnology - In this study, whey proteins were fermented with 34 lactic acid bacteria for 48 h at 37 °C and their ability to inhibit angiotensin...     

Antibacterial properties of soap containing some fatty acid esters

Chemical microbial inhibitors compatible with formulations of soaps and deodorant perfumes are more effective if they are substantive to the skin. However, highly effective inhibitors are toxic and their substantivity on skin may accentuate the toxicity. Natural compounds such as short to medium chain fatty acids and their derivatives, which are known to be germicidal, offer a viable alternative to chemical inhibitors. We report here the synthesis of sodium 2-lauroyloxy propionate and an in vivo method to test its substantivity on skin following its incorporation in soaps. Among several compounds tested, sodium 2-lauroyloxy propionate was found to be highly substantive in soap formulation.
Propriétés antibactériennes d'un savon contenant des esters d'acides gras     

含磺酸基的阴离子淀粉的制备及吸附性能研究

以对氨基苯磺酸与三聚氯氰进行亲核取代反应,合成6-氯-2,4-二(4-磺酸苯氨基)-1,3,5-三嗪。然后以其为醚化剂,玉米淀粉为原料,制备含磺酸基的阴离子淀粉。对产物结构进行表征;对产物的吸附性能进行探讨分析。结果表明,随着醚化剂用量的增加,产物取代度增大,亚甲基蓝去除率亦增大,且当醚化剂与淀粉质量比为3.5∶5时,亚甲基蓝去除率达91.56%.