C_(6)/C_(6+)糖基碳水化合物选择性转化为糠醛的研究

糠醛是一种广泛应用在食品、医药、农药和化工等领域的重要的精细化工品。通常,半纤维素解聚到五碳糖后进一步脱水可转化为糠醛,而纤维素解聚后生成的六碳糖难于转化为糠醛。基于此,实验研究了葡萄糖(C_(6))选择性转化糠醛的影响因素,提出了可能的反应路径;比较了几种典型的C_(6)/C_(6+)糖基碳水合物转化为糠醛的差异。结果表明葡萄糖在硫酸-环丁砜体系中可转化收率为32.6%的糠醛,且糠醛在硫酸-环丁砜体系中保持6.0 h后的浓度依然较为稳定,损失率仅为4.6%。以果糖、蔗糖与纤维素为原料时,可分别得到收率为32.4%、46.5%和43.5%的糠醛。上述结果说明溶剂的性质及其对糠醛的稳定作用,糖基碳水化合物的碳链长度和结构是影响糠醛选择性生成的重要因素。

Sn-MCM-41与SnO_2/SiO_2催化转化生物质基碳水化合物制乳酸甲酯

以生物质基碳水化合物为原料,以Sn-MCM-41和SnO2/SiO2为催化剂,在亚临界甲醇中制备乳酸甲酯.发现具有高度有序介孔结构的Sn-MCM-41和部分有序介孔结构的SnO2/SiO2-a都有较好的催化活性,在最优反应条件下,乳酸甲酯的收率可达40.3%.采用X射线衍射、N2吸附-脱附、透射电镜、吡啶吸附红外光谱和NH3程序升温脱附等技术对反应前后的催化剂进行了表征.结果表明,乳酸甲酯的收率与反应时间、反应温度以及催化剂的酸量有关.另外,Sn-MCM-41和SnO2/SiO2催化剂循环使用5次后其活性变化不大.结果显示,反应后这两种催化剂的Sn流失量小于0.15%,其结构以及酸性种类也没有明显变化.

脂肪替代物研究进展

脂肪作为三大营养物质之一,提供了人体所需的养分,然而过多摄入脂肪则会导致一些心脑血管疾病的产生,因而,随着人们合理膳食的需求日益增加,低脂,无脂食品的研究近年来受到越来越多的重视,脂肪替代物作为低脂,无脂食品生产过程中重要的添加剂,正是研究者着力研究的对象,脂肪替代物主要分为蛋白基脂肪替代物,脂肪基脂肪替代物和碳水化合物基脂肪替代物这三大类,目前,三大类型的替代物不仅可以做到最大程度降低食品中的脂肪含量,同时还能有效地模拟脂肪的风味和外观并增加一定的功能性,使食品在添加脂肪替代物后,既能符合消费者对脂肪口感的需要,同时又能做到低脂肪膳食。在结合国外文献报道的同时,本文介绍了脂肪替代物的分类以及各类脂肪替代物目前的研究应用情况。

脂肪替代品的现状及展望

概述了脂肪替代品的发展现状、基本类型以及它们各自的特点和应用范围。

糖玻璃化抗坏血酸胶囊制备的挤压工艺研究

采用挤压法制备糖玻璃化抗坏血酸胶囊,考察了挤压腔温度、螺杆转速和喂料速度对挤压过程中电机扭矩(扭矩百分比)、模头压力的影响。分析了挤压产品的还原性抗坏血酸含量、产率和挤压产品玻璃化转变温度等理化指标。结果表明:提高挤压腔温度、增加螺杆转速和降低喂料速度可以减小电机扭矩及模头压力。确定的挤压腔温度、螺杆转速和进料速度分别为中温(85℃-105℃-120℃-105℃)、60r/min和1.1kg/h。该挤压条件下挤压产品中还原性抗坏血酸的载量15.76%～15.86%,产率大于98%。挤压产品的玻璃化转变温度高于40℃。

脂肪替代物的分类及在食品中的应用

过多摄取富含脂肪的食品严重危害人体健康,并与肥胖症,高血压、动脉硬化和冠心病密切相关。因此,低脂肪膳食一直为营养学家所倡导,食品逐渐向脱脂、低脂方向发展。消费者对脂肪含量非常敏感,但又无法接受无脂食品的粗糙口感。于是,脂肪替代物便应运而生。脂肪替代物的研究起步较晚,但发展很快,到目前为止,已形成了多种脂肪替代物。优质的脂肪替代物不仅能最大限度的降低食品中的脂肪含量,而且能尽可能的保持甚至改善原有食品的感官品质,制得的产品各项指标都非常接近高脂产品,与传统产品在外观、凤味、口感以及总接受性方面无明显差异。本文主要介绍脂肪替代物的分类和在食品工业中的研究与应用。脂肪替代物因其自身的功能,已愈发引起人们对它的关注,其市场前景相当广阔。

Chemical characterization and composition of dissolved organic matter in Jiaozhou Bay

Biologically utilizable dissolved organic compounds,including dissolved organic carbon (DOC),dissolved carbohydrates (DCHO) and dissolved free amino acids (DFAA) were analyzed in filtered surface seawater samples collected at 19 stations in Jiaozhou Bay,China,on June 3,2007.In these samples,concentrations of DOC,dissolved free carbohydrates (DFCHO),dissolved combined carbohydrates (DCCHO),total dissolved carbohydrates (TDCHO) and total dissolved free amino acids (TDFAA) ranged from 141.7 to 191.1 μmol C/L,1.98 to 18.18 μmol C/L,5.04 to 24.90 μmol C/L,14.52 to 30.36 μmol C/L,and 1.83 to 11.89 μmol C/L,respectively.As a major component of the dissolved carbohydrates,the concentrations of DCCHO were about three times higher than those of DFCHO.Three major constituents of the DFAA were threonine (23.0±5.7 mol%),glutamic acid (16.6±3.2 mol%) and arginine (9.1±3.3 mol%).Based on the composition of DFAA,a molar C:N ratio of 3.60±0.75 in DFAA was derived,indicating longer carbon chains in the amino acids.DCCHO (8.1%) was the most abundant fraction of DOM in most samples,followed by DFCHO (4.8%) and TDFAA (2.7%).These DOM concentrations displayed a decreasing trend from the coast to the central region.Significant correlations were found between the DCCHO and DFCHO concentrations (r=-0.724,n=19,P<0.001) and the DCCHO and TDCHO concentrations (r=0.506,n=19,P=0.027).

Spatiotemporal variation of dissolved carbohydrates and amino acids in Jiaozhou Bay,China

Surface seawater samples were collected from Jiaozhou Bay,China,during six cruises(MarchMay 2010,September-November 2010) to study the distribution of dissolved organic matter including dissolved organic carbon(DOC),total dissolved carbohydrates,namely monosaccharides(MCHO) and polysaccharides(PCHO) and total hydrolysable amino acids.These included dissolved free amino acids(DFAA) and combined amino acids(DCAA).The goal was to investigate possible relationships between these dissolved organic compounds and environmental parameters.During spring,the concentrations of MCHO and PCHO were 9.6(2.8-22.6) and 11.0(2.9-42.5) μmol C/L,respectively.In autumn,MCHO and PCHO were 9.1(2.6-27.0) and 10.8(2.4-25.6) μmol C/L,respectively.The spring concentrations of DFAA and DCAA were 1.7(1.1-4.1) and 7.6(1.1-31.0) μmol C/L,respectively,while in autumn,DFAA and DCAA were 2.3(1.1-8.0) and 3.3(0.6-7.2) μmol C/L,respectively.Among these compounds,the concentrations of PCHO were the highest,accounting for nearly a quarter of the DOC,followed by MCHO,DCAA and DFAA.The concentrations of the organic compounds exhibited a decreasing trend from the coastal to the central regions of the bay.A negative correlation between concentrations of DOC and salinity in each cruise suggested that riverine inputs around the bay have an important impact on the distribution of DOC in the surface water.A significant positive correlation was found between DOC and total bacteria count in spring and autumn,suggesting bacteria play an important role in the marine carbon cycle.

Evaluation of Three Sunflower （Helianthus annuus L.） Hybrids for Salt Tolerance in Vitro

This study aimed to induce callus from three sunflower （Helianthus annulus L.） hybrids, namely Anna, Alhaja and Kuds, and to evaluate their callus for salt stress tolerance. Cotyledons and hypocotyl were taken from seedling of these hybrids and cultured on MS media contained 2,4-D （0,0, 0.5, 1.0, 1.5 and 2.0 mg/L） and kinetin （0.0, 0.5, and 1.0 mg/L）. The cultures incubated at 25 ＋ I^C under light condition （1,000 Lux） for 16 h/day. After 6 weeks observations were taken on the response of cotyledons and hypocotyl to callus induction. The induced callus were cultured on the same MS media that contained appropriate concentrations of 2,4-D and kinetin for callus induction as well as contained various concentration of sodium chloride NaCI （0.0, 0.05, 0.1, 0.15 and 0.2%）. After six weeks callus fresh and dry weights, proline and total carbohydrates concentrations were measured. The results showed significant differences among the hybrids, explants, 2,4-D and kinetin concentration and significant interaction between them in their percentage response for callus induction. The results also revealed that fresh and dry weights were significantly reduced with increased NaCI concentration in the medium, hybrids showed significant differences in their response to salt stress. Proline and total carbohydrate concentration increased in callus as NaCI increased in the media. Significant interaction was showed between hybrids and NaCI concentration in these parameters.

Protein differential expression in the elongating cotton (Gossypium hirsutum L.) fiber under nitrogen stress

Nitrogen (N) is an essential macronutrient and an important factor limiting agricultural productivity. N deficient or excess conditions often occur during the cotton growth season and incorrect N application may affect cotton fiber yield and quality. Here, the influence of N stress on the cotton fiber proteome was investigated by two-dimensional gel electrophoresis and mass spectrometry. The results indicated that N application rate affects nitrogen accumulation in fiber cells and fiber length. The proteins differentially expressed during N stress were mainly related to plant carbohydrate metabolism, cell wall component synthesis and transportation, protein/amino acid metabolism, antioxidation and hormone metabolism. The most abundant proteins were C metabolism-related. Ten days post anthesis is a critical time for fiber cells to perceive environmental stress and most proteins were suppressed in both N deficient and N excess conditions at this sampling stage. However, several N metabolism proteins were increased to enhance N stress tolerance. Excess N may suppress carbohydrate/energy metabolism in early fiber development much like N deficiency. These results have identified some interesting proteins that can be further analyzed to elucidate the molecular mechanisms of N tolerance.

Synthesis of N(OMe)-linked TF antigen analogue

Tumor-associated carbohydrate antigens （TACAs）, important molecular markers on tumor cells, are major targets for the development of anti-cancer vaccines. However, due to the immunotolerance and weak immunogenicity, native TACAs cannot induce powerful immune response. The use of modified TACAs such as N-glycosides could be an alternative strategy to overcome this problem. Herein, the synthesis of N（OMe）-linked analogue of tumor-associated disaccharide antigen Thomsen-Friedenreich （TF） by the glycosylation reaction is described.

Recent advances in synthetic carbohydrate-based human immunodeficiency virus vaccines

An effective vaccine for human immunodeficiency virus(HIV) is urgently needed to prevent HIV infection and progression to acquired immune deficiency syndrome(AIDS). As glycosylation of viral proteins becomes better understood, carbohydrate-based antiviral vaccines against special viruses have attracted much attention. Significant efforts in carbohydrate synthesis and immunogenicity research have resulted in the development of multiple carbohydrate-based HIV vaccines. This review summarizes recent advances in synthetic carbohydrate-based vaccines design strategies and the applications of these vaccines in the prevention of HIV.

Catalytic transformations of cellulose and its derived carbohydrates into 5-hydroxymethylfurfural, levulinic acid, and lactic acid

The catalytic transformation of cellulose into key building-block or platform chemicals such as 5-hydoxymethylfurfural(HMF),levulinic acid,and lactic acid under mild conditions,has attracted much attention in recent years,as these conversions can be operated without consumption of hydrogen or oxygen and thus are more economical compared to the hydrogenolysis or oxidation of cellulose.This review article highlights recent advances in the development of novel catalysts or catalytic processes for the conversion of cellulose and its derived carbohydrates into HMF,levulinic acid,and lactic acid or their esters under inert atmosphere.We also analyze efficient catalytic systems for HMF production,in particular Lewis acids combined with ionic liquid or biphasic systems.For the formations of levulinic and lactic acids or their esters,we focus on the reactions in aqueous and alcohol media catalyzed by multifunctional catalysts that combine the functions of hydrolysis,isomerization,and dehydration-rehydration or retro-aldol reactions.The reaction mechanism for each process will also be discussed to gain insights into the activation of C–O and C–C bonds in the absence of hydrogen or oxygen.