Effects of Polymers on Secondary Nucleation of Ice Crystals

The kinetics of ice crystallization in various polymer solutions were studied by the thermal response method in a batch crystallizer. Polymers suppress the secondary nucleation of ice crystals, depending on the kinds of polymer and concentration. The decrease of the nucleation rate constant in polymer solutions was related to the increase of viscosity. The effects of polymers on the nucleation rate were also observed in solutions containing low molecular weight compounds.     

羧甲基壳聚糖的降解及其抗氧化性能的研究

羧甲基壳聚糖是壳聚糖的一种重要衍生物。本研究采用过氧化氢氧化法对羧甲基壳聚糖进行降解,并考察了降解时间及过氧化氢用量对降解的影响。用粘度法和改进的Schales’方法测定了降解产物的分子量。并用流动注射化学发光分析法检测了降解产物的抗氧化能力--对羟基自由基的清除活性。结果表明:随着过氧化氢在降解体系中的浓度的增大,降解产物的分子量将趋于一固定值;当H2O2在总反应体系中浓度大于1.3mol/L,降解时间大于16h,将得到分子量低至1100左右的羧甲基壳聚糖;经降解得到的羧甲基壳聚糖均具有一定的羟基自由基清除活性,且分子量越小,其抗氧化性能越强。     

壳聚糖抗菌性能的研究

本实验研究了客观因素对壳聚糖抗菌性能的影响,以确定壳聚糖的最佳抗菌条件。以金黄色葡萄球菌为实验菌,接种到含一定量壳聚糖的液体培养基中,通过测定光密度值研究壳聚糖的浓度、溶解度、分子量、培养基pH值对其抗菌活性的影响。抑菌实验结果表明:脱乙酰度、分子量相同的壳聚糖,对金黄色葡萄球菌的抑制能力随浓度的降低而减弱;壳聚糖溶于浓度为2%的醋酸溶液中,培养基pH控制在6.0最有利于发挥壳聚糖的抗菌活性;通过微波辐射法制得的低分子量壳聚糖水溶性很好,但对金黄色葡萄球菌的抑制能力有所下降。     

降解瓜胶与降解黄原胶的协同凝胶化及其流变性研究

首次用降解瓜胶与降解黄原胶在一定条件下共混,形成凝胶体系。考察了总胶浓度、氯化钾浓度、制备温度、放置时间、苯甲酸钠及降解食品多糖的分子量等因素对共混凝胶体系黏度的影响,并对其流变特性进行研究。结果表明,降解瓜胶与降解黄原胶可以形成凝胶体系,该体系具有显著的黏弹性和触变性。     

不同质均分子质量菊糖凝胶的形成条件

将菊糖原料分级后,探究不同处理条件对热溶冷凝法制备不同质均分子质量菊糖凝胶的影响。采用分步分级法用乙醇将菊糖分为9个级分,SephadexG-50凝胶柱层析检测分级效果,采用黏度法测定各级分菊糖的质均分子质量,用热溶冷凝法制备菊糖凝胶,研究分子质量、加热温度和溶液浓度对菊糖凝胶形成的影响。结果表明:分离得到的各级菊糖的质均分子质量较为均一。菊糖的质均分子质量越大越易形成凝胶,小于一定数值则无法形成凝胶。凝胶的形成随处理温度的升高先易后难,温度过低或过高对凝胶形成都有负影响,70℃下形成凝胶所需的溶液浓度最小。随着菊糖溶液浓度升高,形成凝胶的温度范围增大,当浓度为35%时,可形成凝胶的温度范围最大。     

分子量对淀粉玻璃化转变温度的影响

采用相对黏度法及TDA与DSC法测定了淀粉同系物的黏均分子量和玻璃化转变温度,得到分子量对淀粉同系物的玻璃化转变的影响关系:即随着分子量的增加玻璃化转变温度也增加,当分子量增加到一定程度以后玻璃化转变温度增加趋于平缓,并得到实验关联式。根据这种关系我们可在一定的范围内根据实际生产、加工及贮存的需要,用改变淀粉体系的分子量分布的方法来改变其玻璃化转变温度。     

牡蛎功能短肽的制备及ACE抑制活性

以新鲜无壳牡蛎为原料,采用酶水解的方法制备牡蛎短肽,经SephadexG 15分离,并用HPLC测定其相对分子质量分布,通过HPLC法定量马尿酸测定各组分的ACE(血管紧张素转化酶)抑制活性。结果表明,牡蛎水解液中相对分子质量较大和较小部分的ACE抑制活性偏低,只有相对分子质量在一定范围内的短肽,对ACE具有较好的抑制作用,质量浓度为0.4mg/mL的牡蛎功能短肽的ACE抑制率为51.4%.     

壳聚糖对酸性红3B染料的吸附机理研究

以壳聚糖为吸附剂,用可见吸收光谱法研究了壳聚糖对酸性红3B的吸附规律,探讨了吸附剂的形态、壳聚糖的分子量、脱乙酰度对吸附量Qe的影响。结果表明:相同条件下,壳聚糖的形态对吸附有一定的影响,壳聚糖凝胶球的吸附量小于粉末;壳聚糖的分子量和脱乙酰度对吸附的影响是综合的;随酸性红浓度的增大各类壳聚糖的吸附容量均增大,高粘壳聚糖实测值为129.4 mg/g,吸附为Langumuir单分子层吸附机理,吸附速率符合动力学二级方程。     

Effects of β‐glucans on properties of soya bean protein isolate thermal gels

The effects of concentration and molecular weight of oat β‐glucans on properties of soya bean protein isolate (SPI) thermal gels prepared by heating at 90℃for 30 min were investigated. Compared with control (free of β‐glucan) formulations, the presence of β‐glucans (0.5–1.5%, w/v) largely enhanced storage modulus (G′) and texture properties of SPI (12%, w/v) thermal gels measured by dynamic oscillatory rheometry and texture profile analysis, which were developed as increasing β‐glucan concentration and molecular weight. It is possible that β‐glucans could cause the formation of protein aggregates to produce gels through hydrophobic interactions. Mixed gel systems at low ionic strength showed higher G′ resulting from the lower denaturation temperature of SPI, which was beneficial to the formation of gel structure. In addition, although adding a certain amount of β‐glucan into SPI reduced water‐holding capacity of mixed gels, high molecular weight of β‐glucan improved their water‐holding capacity compared to control formulations attributed to the improvement of the structural integrity of the mixed gel network.     

葡聚糖水溶液流变性研究

本实验研究了葡聚糖水溶液的流变性能,选取了五种不同分子量的葡聚糖,分别考查了分子量、溶液浓度、溶液温度等因素对葡聚糖水溶液流变性的影响。结果显示,多数葡聚糖水溶液表现出牛顿流体的特性,而当葡聚糖分子量为531000,溶液浓度为30%时,溶液则表现出假塑性流体的性质,黏度随着剪切速率的提高而降低。当葡聚糖浓度较低时(≤1%),水溶液均表现出一种特殊的流变性,即黏度随着剪切速率增加先降低后升高,本研究对出现这一现象的原因进行了分析。     

Infiltrated Biopolymers Effect on Quality of Dehydrated Carrots

The penetration pattern of biopolymers in plant tissue during processing was studied. Carrot dices were infused with dye-dextran standards of different molecular weights (T10, T40, T70 and T500). Polymers of smaller size were found within the intercellular spaces and the cell walls. Larger polymers were found only in broken cells near the surface of the tissue. Biopolymers of small size were theorized to provide strength to the cell wall of plant tissue and assist in maintaining cellular integrity during dehydration. This was further verified in that the dextrans of molecular weight of 10,000 produced best quality dehydrated carrots with high rehydration ratio, more retention of carotenoids and high water-holding capacity.     

右旋糖酐酶调控右旋糖酐分子质量条件研究

小分子质量右旋糖酐在医学、化工、食品等领域有广泛的应用,为了得到特定分子质量的右旋糖酐,采用酶解法对大分子质量右旋糖酐的分子质量及分子质量分布进行调控。实验结果表明:在酶解过程,通过控制右旋糖酐酶浓度、底物浓度和反应温度、pH值及时间,可有效调控右旋糖酐的分子质量,且产物均一性较好。较适宜酶解条件:酶浓度为10 U/mL、反应温度为50 ℃、pH值为5.0、底物浓度为30 mg/mL。右旋糖酐酶解前后结构未发生改变,但是其构象从球形链变为柔顺链,右旋糖酐产物分子质量约为5000 u时,在溶液中为较紧凑的球形链构象。酶解法降解右旋糖酐速度快、反应条件温和、能耗低且无污染,在生产特定分子质量的右旋糖酐方面具有良好的应用前景。     

Synthesis and evaluation of molecularly imprinted polymers as sorbents of moniliformin

Moniliformin is a low molecular weight mycotoxin that has worldwide potential to contaminate cereal grains. Although several traditional methods have been developed to detect moniliformin, the lack of anti-moniliformin antibodies has created a need for materials that recognize moniliformin at the molecular level through a binding mechanism. To address this issue, the authors synthesized molecularly imprinted polymers that bind moniliformin. Imprinted and non-imprinted polymers were evaluated by equilibrium binding assays and moniliformin concentrations were measured by LC analysis using ultraviolet light detection. Successful polymers were imprinted with toxin analogues as the templates; non-imprinted polymers exhibited minimal binding in acetonitrile under the assay conditions. Selected imprinted polymers also bound moniliformin in ethanol, methanol and dimethyl formamide. Significant differences in moniliformin binding by the polymers were dependent on polymer composition, and these differences were highly dependent on the template used to imprint the polymer. Polymers were further evaluated as sorbents for molecularly imprinted solid-phase extraction (MISPE), and an imprinted polymer was used for preconcentration and clean-up of a moniliformin spiked corn extract.     

降解黄原胶与降解瓜胶凝胶体系的流变性研究

降解黄原胶与降解瓜胶在一定条件下共混,形成凝胶体系.通过对其流变特性进行研究,表明该体系具有显著的黏弹性和剪切变稀性.考察了总胶浓度、蔗糖、共混比例及降解食品多糖的分子量等因素对共混凝胶体系流变特性的影响.研究了该凝胶体系的本构方程,结果表明,修正Williamous-Oldroyld-4参数模型可确切描述凝胶体系的黏度曲线,计算值与实验值吻合良好.     

Charge effects in the fractionation of natural organics using ultrafiltration

Comparison of two commonly used techniques for molecular weight determination of natural organics, ultrafiltration (UF) fractionation and high-performance size exclusion chromatography (SEC), shows that neither technique gives absolute measures of molecular weight. Investigations of International Humic Substances Society standard humic and fulvic acids as well as natural organic matter concentrated from surface freshwaters show that charge effects and solution conditions are important in both SEC and UF fractionation with various components of the natural organics being affected differently. Membranes with a smaller molecular weight cutoff (MWCO) produce permeates with a lower UV/DOC ratio, suggesting that the more aromatic components of natural organics are removed by the lower molecular weight cutoff membranes. Variation in ionic strength has little effect on the rejection of humic acid fractions but does significantly influence the rejection of low molecular weight acids. pH and organic concentration do not affect DOC rejection significantly over the pH range of 4.5-10 and the DOC concentration range of 15-60 mgL(-1). These results indicate that UF should not be applied for quantitative "size" analysis unless performed under well-defined conditions. If performed under conditions appropriate to water treatment, UF fractionation can give information of direct applicability to treatment such as the MWCO required to achieve significant organics removal.     

大蒜降压肽的制备及超滤分离

为了研究大蒜降压肽的酶解制备与超滤分离工艺,采用响应面法优化制备工艺,酶解后利用超滤技术获得不同分子量范围的组分并进行ACE抑制活性评价。最佳制备工艺为碱性蛋白酶处理、温度50℃、pH11、底物浓度45 g/L、酶底比3%、酶解时间1 h,该条件下ACE抑制率为83.91%±0.13%,半抑制浓度为(157.87±0.44)μg/mL。分子量3 kDa以下部位活性最为显著(P<0.05),优化后的超滤工艺为操作压力0.25 MPa,温度25℃,溶液浓度4%,此时3 kDa超滤膜的膜通量为7.32 L/(m2·h),ACE的半抑制浓度为(63.27±0.25)μg/mL。氨基酸分析结果表明酸性氨基酸、疏水性氨基酸及天冬氨酸、谷氨酸含量较高,分别为35.78、32.86、21.66、14.12 mg/100 mL,分子量分布显示2000~2500 Da部分最为丰富,占比为49.50%。本研究为大蒜蛋白的开发利用提供了新的思路,具有一定的理论水平和实际应用价值。     

Bringing comfort to the masses: A novel evaluation of comfort agent solution properties

Ocular comfort agents are molecules that relieve ocular discomfort by augmenting characteristics of the tear film to stabilize and retain tear volume and lubricate the ocular surface. While a number of clinical comparisons between ocular comfort agent solutions are available, very little work has been done correlating the properties of specific comfort agents (species, molecular weight, and water retention) and solution properties (concentration, viscosity, zero shear viscosity, and surface tension) to the performance and effectiveness of comfort agent solutions. In this work, comfort-promoting properties related strongly to comfort agent concentration and molecular weight, the first objective demonstration of this relationship across diverse comfort agent species and molecular weights. The comfort agents with the greatest comfort property contributions (independent of specific molecular weight and concentration considerations) were hyaluronic acid (HA), hydroxypropyl methylcellulose (HPMC), and carboxymethylcellulose (CMC), respectively. The observed, empirical relationships between comfort property contribution and comfort agent species, solution properties, comfort agent molecular weight, and solution concentration was used to develop novel comfort agent index values. The comfort agent index values provided much insight and understanding into the results of experimental studies and/or clinical trials and offer potential resolution to numerous conflicting reports within the literature by accounting for the difference in comfort agent performance due to molecular weight and concentration of comfort agents. The index values provide the first objective, experimental validation and explanation of numerous general trends suggested by clinical data.     

多分散性树状大分子的合成和性质

以亚酒石酸为单体,采用缩合聚合方法合成了低分子聚合物,测定了低聚物的分子量,并用5%的低聚物水溶液对染料罗丹红Ⅲ的正己烷溶液进行萃取,用紫外分光光度法测定了萃取液的染料质量浓度。结果表明,合成的低聚物分子量达到较高数值时,低聚物就会产生对染料罗丹红Ⅲ的包合作用,表明低聚物中有树枝状大分子结构,树枝状大分子的内部空腔是疏水性的,可以容纳疏水性的染料分子。研究了低聚物的合成条件,结果表明,单体含量10%～20%、温度100℃、聚合时间140～160min,合成的低聚物对染料罗丹红Ⅲ的正己烷溶液有较高的萃取浓度。     

Effect of cellulose ethers on the microstructure of fried wheat flour-based batters

The effect of type, molecular weight, and concentration of cellulose ethers on the microstructure of fried batter-coated potatoes in two batter systems: controlled viscosity batters (CVB) at 1200 cP and controlled initial moisture content batters (CIMB) at 134 g/100 g flour, were studied by coating cylindrical potatoes (10 mm diameter and 50 mm long) with treatment batters and fried at 160 °C for 3 min. The coatings were separated and their structures were viewed by scanning electron microscopy technique. The micrographs of fried batters showed that different types of cellulose ethers with the same molecular weight and concentration did not affect the microstructures of batters. The viscosity and water content of batters as well as the molecular weight and concentration of cellulose ethers altered the microstructure of fried batters. For CVB, the structure of fried batter containing methylcellulose of higher molecular weight and concentration with simultaneous higher moisture content showed greater hole-size which allowed higher amount of oil penetration through the batter into the food substrate. In contrast, the structure of CIMB with a higher molecular weight and concentration of methylcellulose was relatively more continuous; therefore, it might help in preventing oil penetration into the food substrate.     

酿酒酵母在高渗条件下分泌蛋白的研究

以酿酒酵母2144为研究对象,利用不同葡萄糖浓度的YNB(全氨基酸)培养基,通过SephadexG-25和Sephadex G-75分离酵母胞外分泌蛋白,最后采用SDS-PAGE进行分析.结果表明,高糖浓度下16 h分泌蛋白出现了高分子量蛋白,经SDS-PAGE测定分子量为53 KDa与酵母蛋白酶A酶原分子量一致,分泌的低分子量蛋白与正常对照组差异性很大.