复绿海带中叶绿素稳定性研究

研究了光照、温度、pH、金属离子、抗氧化剂、常用食品添加剂及络合剂对复绿海带叶绿素稳定性的影响情况。结果表明:日光、高温、酸、碱、Fe3+和Cu2+对海带叶绿素的稳定性具有显著性破坏作用,蔗糖、食盐和葡萄糖对叶绿素稳定性影响不显著,而抗氧化剂及络合剂对叶绿素的稳定性具有保护作用。     

The Complexing of Concanavalin A and Glucans

The complex between concanavalin A and glucans was again analyzed with respect to the recent results reported by Doyle. A discussion of the complexing behavior of various glucans again illustrates that C-6 and C-4 hydroxyls must be involved in the complexing mechanism. Carboxylate groups are most likely not involved in the complex, because 4.2 M NaCl can not prevent the complex from forming. That is, if carboxylate ions were involved, such concentrated Na ⁺ ions would act as inhibitors to the reaction with more strength than neutral molecules such as D-mannose. Carboxylate groups are most likely chelated to Mn⁺⁺ions and hence are involved in the stabilization of the protein tetramer. Such complexing as well as the folding of the protein could account for change in pK and inactivation of these groups.     

Antibacterial effect of the glucose oxidase-glucose system on food-poisoning organisms

The antibacterial effect of the glucose oxidase-glucose system was studied on food-poisoning organisms including Staphylococcus aureus, Salmonella infantis, Clostridium perfringens, Bacillus cereus, Campylobacter jejuni, Listeria monocytogenes and Yersinia enterocolitica using automated turbidometry. The bacteria were grown in sterile-filtered meat medium which was either raw or heat-denaturated. The results showed a clear growth inhibition with combinations of 0.5-1.0 mg/ml glucose and 0.5-1.0 IU/ml glucose oxidase. The growth inhibition was more effective in the heat-denaturated meat medium. The most resistant pathogens were Campylobacter jejuni and Listeria monocytogenes, however growth inhibition was still evident. The possible application of the glucose oxidase-glucose system in food products inhibiting the growth of pathogens and spoilage organisms is discussed.     

黄鲫蛋白抗菌肽—葡萄糖美拉德反应物的抑菌性实验研究

利用响应面分析法优化黄鲫蛋白抗菌肽-葡萄糖美拉德反应条件,提高产物的抑菌活性。以大肠杆菌为指示菌,在黄鲫蛋白抗菌肽初始反应pH为5.58条件下,进行葡萄糖添加量、加热温度和加热时间三因素三水平Box-Benhnken响应面分析实验,得出黄鲫蛋白抗菌肽-葡萄糖美拉德反应最优条件为葡萄糖添加量0.25%(w/v)、加热温度100℃、加热时间60 min。在最优反应条件下,黄鲫蛋白抗菌肽-葡萄糖美拉德反应物对大肠杆菌的抑菌圈直径为28.9 mm,与理论值28.4 mm接近。     

啤酒中的铁离子

铁离子可促进酵母生长发育;又可引起啤酒混浊、产生金属味,降低啤酒质量.啤酒中的铁离子主要来源于原辅材料、设备管件及酿造用水等.铁离子在酿造过程易发生氧化还原、催化和络合反应,对麦汁糖化、发酵及成品啤酒质量产生影响.控制铁离子含量的方法有:控制原辅料及所用水的铁离子含量;适当提高糖化醪液的pH值;选用优良、强壮的酵母种;选用含铁较少的硅藻土助滤剂;选用耐酸不锈钢容器和管道,并作好防腐措施.(孙悟)     

EFFECT OF ALKALINE-EARTH METAL SALTS ON FLOCCULENCE IN SACCHAROMYCES CEREVISIAE

Flocculation in three strains of Saccharoymces cerevisiae is inhibited by two classes of ionic substances: (1) the alkaline-earth metal ions Sr and Ba, and (2) Ca complexing substances. Sr appears to be competitive with Ca in the flocculence mechanism because the extent of inhibition depends mainly on the ratio of Sr and Ca concentrations. The observations imply that the Ca requirement for flocculation is by a specific, unique process, and not by the commonly presumed charge neutralization or Ca salt-bridging mechanism.     

葡萄糖和木糖对热反应鸡肉香精风味影响的研究

用酶解鸡肉-半胱氨酸-还原糖为主要原料,经美拉德反应制备热反应鸡肉味香精时,不同的还原糖:葡萄糖和木糖及其用量对鸡肉香精的风味都有很大的影响,葡萄糖和木糖共用比各自单独添加能产生更好的鸡肉风味。     

Mineral Complexing Properties of Food Carbohydrates

The complexing of minerals by both low and high molecular weight carbohydrates is now well established and can be demonstrated by, for example, depression of conductivity, alteration of specific rotation, redox potential or techniques such as ligand exchange chroma-tography. It is likely that mineral complexes will exist in food systems and, in mixtures of sugars such as glucose syrups, a variety of complexes will be present. Recent interest in the hydrogenated carbohydrates shows that these too complex minerals, sometimes better than their unhydrogenated counterparts. The complexing of Cu²⁺ by hydrogenated glucose syrups, for example, increases as degree of polymerisation decreases and iron salts are also complexed by various simple carbohydrate molecules. Mineral complexing has many consequences for the taste, nutritional value and technological quality of foods. The taste of iron salts is masked for example, by complexing with carbohydrates at high pH, whereas the opposite occurs at low pH. Vitamin C is protected from Cu²⁺ catalyzed oxidation when the cation is complexed with various carbohydrates or their hydrogenated derivatives. Such results have implications for the design, formulation and storage of food.     

Modulation of the postprandial phase by beta-glucan in overweight subjects: effects on glucose and insulin kinetics

Decreasing the postprandial glucose response is potentially of major importance to public health when low-glycemic index or high-fibre content foods are associated with a decreased risk of diabetes. We investigated in overweight subjects the effect of adding beta-glucan (BG) to a polenta (Pol) meal on postprandial metabolism and glucose bioavailability using stable isotopes. In this single-blind, randomized, crossover trial, 12 subjects ate two meals containing Pol with (Pol + BG) or without (Pol) 5 g BG. Concentrations of glucose, insulin, C-peptide, nonesterified fatty acids, triacylglycerol, total and exogenous glucose kinetics were assessed for 6 h postprandially. The kinetics of total and exogenous glucose importantly differed between the meals, but not the quantity of total and exogenous glucose appearing in plasma. Less total and exogenous glucose appeared during the first 120 min after the Pol + BG meal; the phenomenon was then reversed (both p < 0.0001). After 120 min, glucose and insulin responses declined, but remained higher after the Pol + BG meal (p < 0.05) in parallel to the inhibition of lipolysis. The endogenous glucose production (EGP) was significantly more inhibited after the Pol + BG meal. The addition of BG slowed the appearance of glucose in plasma, resulting in longer-lasting insulin secretion which exerted a prolonged inhibition of EGP and lipolysis.     

Role of facilitative glucose uptake in the glucose-inorganic phosphate-mediated retardation and inhibition of development in different strains of mouse embryos

Mouse embryos from different strains develop differently in vitro depending on the composition of the culture medium, and in particular on the presence or absence of glucose and inorganic phosphate. Glucose is both stimulatory and inhibitory in certain conditions. Glucose uptake by cells can be passive, down concentration gradients, or active, through sodium driven pumps, or can occur through facilitative transport. This study investigated the effects of inhibition of facilitative glucose transport on the glucose-inorganic phosphate-mediated blocks in development in three different strains of mouse embryo, CF-1, CD-1 and an F2 hybrid. Development of CF-1 and CD-1 embryos is blocked in medium containing glucose and inorganic phosphate but not in medium containing glucose alone, and F2 embryos are not affected. Inhibition of facilitated glucose transport to the eight-cell-morula stage in CF-1 and CD-1 embryos resulted in development in medium containing both glucose and inorganic phosphate, indicating that the prevention of facilitative glucose uptake can overcome the developmental block. Removal of inhibition before the eight-cell-morula stage resulted in total arrest of CF-1 embryos and minimum development of CD-1 embryos. F2 embryos are not affected by inorganic phosphate and glucose and showed no response to the transporter inhibitor at any stage. These data support the contention that facilitated glucose transport is active in embryos, is phosphate-dependent and that its inhibition can overcome the glucose-inorganic phosphate-mediated developmental blocks in mouse embryos.     

Respiratory inhibitors affect incorporation of glucose into Saccharomyces cerevisiae cells,but not the activity of glucose transport

Incubation of starved galactose-grown S. cerevisiae cells with cyanide reduced glucose uptake as measured over a 5-s period. The V_max for glucose uptake was decreased by over a factor of two but the apparent affinity for glucose doubled. When measured in the sub-second time scale, however, there was no significant inhibition of glucose uptake, by cyanide, up to 200-ms, clearly demonstrating that, in cyanide treated cells, glucose uptake was not linear for the first 5-s. After a 200-ms exposure of untreated cells to radio-labelled glucose, less than 10% of the intracellular label resided in soluble uncharged compounds. In cyanide-treated cells up to 43% of the labelled compounds were uncharged, with a concurrent reduction of intracellular label residing in anionic compounds. The results suggest that, in the presence of 10 mM cyanide when respiration is inhibited, a reduction in the cellular ATP concentration causes a reduction in hexose-kinase activity which results in an accumulation of internal free glucose, which in turn causes a reduction in net glucose transport.     

Calcium chloride complex formation of glucose syrups and their fractions

Glucose syrups react with calcium salts in aqueous solution to form complexes. As a consequence, the specific rotation, viscosity, electrical conductivity and osmotic pressure of the syrups differ from those of untreated glucose syrups. Complex formation depends on calcium ion concentration, and interaction of the glucose syrup with the calcium salt affects, in turn, the activity of the calcium ions.     

葡萄糖/L-半胱氨酸美拉德反应动力学的研究

以葡萄糖和L-半胱氨酸为反应体系,研究了反应温度对体系底物浓度变化、褐色物质生成以及pH变化的影响,并进行了动力学分析。结果表明,反应温度是影响美拉德反应的重要因素,反应底物浓度、褐色物质含量以及pH的变化速率均随着反应温度的升高而增大。在不同的反应温度条件下。反应底物葡萄糖和半胱氨酸的浓度变化符合一级动力学,褐色物质的生成和pH的变化符合零级动力学。同时研究发现,颜色物质和酸性物质的生成主要发生在关拉德反应的高级阶段,所需活化能较高,分别为164．77kJ/mol和149．17kJ／mol。     

基于长短期记忆神经网络的反应液葡萄糖含量预测

目的 建立皮尔逊相关系数(Pearsoncorrelationcoefficient,PCC)和长短期记忆(longshortterm memory,LSTM)神经网络的反应液葡萄糖含量预测模型用以实时预测葡萄糖酸锌生产过程中反应液葡萄糖含量。方法 通过葡萄糖酸锌制备实验,结合PCC理论确定对反应液葡萄糖含量有较大影响的因素,对这些因素进行数据采集并将其作为神经网络的输入变量,采集反应液葡萄糖含量数据并进行处理,将其作为神经网络的输出变量,进而建立反向传播神经网络(backpropagation neural network, BP)和LSTM神经网络的反应液葡萄糖含量预测模型。结果 通过100次模型迭代训练,对照BP反应液葡萄糖含量预测模型可以看出LSTM反应液葡萄糖含量预测模型在测试集的误差约为0.45%,误差较小,准确度较高。结论 基于LSTM反应液葡萄糖含量预测模型显著提高了预测精度,相比现有检测方法更加智能高效,能够有效辅助生产进行。     

新型金属络合剂：涤／棉混纺织物一浴一步法染色助剂

述评了涤/棉混纺织物一治一步法染色时,解决铜离子对分散染料破坏作用的最有效的方法是采用铜离子络合剂;介绍了铜离子络合剂的种类、应用工艺、性能;推荐了自行合成的新型铜络合剂CI—1.     

Thermodynamic evaluation on H2 production in glucose fermentation

The normal maximum H2 yield in mesophilic biohydrogen (bioH2) fermentation is approximately 2 mol of H2/(mol of glucose). Thermodynamics could be the most fundamental control for bioH2 formation, since proton reduction is strongly energy consuming (+79.4 kJ/(mol of H2)). However, most of the electron equivalents in glucose do not accumulate in H2 but in a range of organic acids and alcohols. Thus, evaluating the hypothesis of thermodynamic control requiresthe full stoichiometry of the fermentation. We carried out batch bioH2 reactions with a range of pH values that yielded H2 yields from 0 to approximately 2 mol of H2/(mol of glucose). We constructed complete electron equivalent(e(-) equiv) balances for high or low H2 yield by measuring all e(-) sinks. The highest H2 yield occurred with pH approximately 4 and was coincident with major butyrate accumulation; ethanol or lactate correlated to reduced H2 yields at pH 7 and 10, respectively. Although the Gibb's free energies for all overall reactions were similar (-10.6 to -11.2 kJ/(e(-) equiv)), thermodynamics controlled the H2-producing reaction coupled to ferredoxin; this reaction was favorable at acidic pH but thermodynamically blocked at pH 10. Also, butyrate formation was the most thermodynamically favorable reaction that produced ATP after glycolysis.     

基于纳米酶技术检测柑桔果实中葡萄糖

目的建立纳米酶检测体系快速检测葡萄糖含量的技术。方法采用甲烷氧化细菌的发酵代谢产物甲烷氧化菌素(methanobactin,MB)与Cu²⁺、纳米金(AuNPs)、葡萄糖氧化酶(glucose oxidase,Gox)进行配位结合形成具有过氧化物酶和葡萄糖氧化酶性质的纳米酶检测体系,并对柑桔果实中葡萄糖含量进行测定。结果Gox浓度0.81 U/mL、MB-Cu@AuNPs模拟酶浓度2×10^-5mol/L、对苯二酚浓度5×10^-4mol/L、反应温度60℃、pH 8为最佳检测条件;反应时间5 min,葡萄糖浓度线性范围为1×10^-3-5×10^-2mol/L。结论纳米酶检测体系对柑桔果实中葡萄糖含量的测定具有良好的稳定性,相比较常规快速血糖仪检测速度更快。     

固定化葡萄糖异构酶活化条件对其酶活的影响

固定化葡萄糖异构酶在使用前需先进行活化,从而使酶发挥其最佳催化功效。本文从糖液浓度、温度、pH、活化时间和金属离子五个方面研究了活化条件对GENSWEETTMIGI-SA固定化葡萄糖异构酶酶活的影响。该酶的最适活化条件为:葡萄糖液浓度60%、温度55℃、pH7.5、时间4h。经此条件活化之后,其酶活达815U/g,与常规活化条件相比,酶活提高了40%以上。固定化葡萄糖异构酶活化时不宜加入Mg2+、Co2+、Mn2+和Zn2+。     

Conversion of glucose in lactase-hydrolyzed whey permeate to fructose with immobilized glucose isomerase

The maximum conversion of glucose to fructose in lactase-hydrolyzed whey permeate by glucose isomerase was approximately 52% at .1 g enzyme/ml substrate after 7 h incubation at 60 degrees C. Removal of minerals from the substrate was essential for enzyme activity. The dependence of the enzyme on Mg++ and Co++ for activity in the presence of high ash concentration was demonstrated. Optimum Mg++ and Co++ additions were 250 and 100 ppm, respectively. The isomerization reaction was enhanced more when both 100 ppm Mg++ and 50 ppm Co++ were added. Hydrolyzed isomerized lactose whey syrup with sweetness equivalent to sucrose was successfully produced through enzymatic isomerization of glucose in lactase-hydrolyzed whey permeate after supplementation with pure glucose. Fructose in hydrolyzed isomerized lactose whey syrup was effectively separated from other sugars by Dowex 1X8-200 anion exchange resin in the bisulfite form.