一种高温乳糖酶的酶学性质及对牛乳中乳糖的水解

对重组大肠杆菌产生的β-半乳糖苷酶学性质的研究表明，该酶最适反应温度为55℃，最适PH值为7．0，在50℃时具有良好的热稳定性，K^ ,Mg^2 ,Mn^2 等对酶有一定的激活作用，而重金属盐如Pb^2 ,Sn^2 ,Zn^2 ,Cu^2 等对酶活有一定抑制作用，对乳糖分解试验研究表明，该酶水解乳糖的能力较强，牛奶中添加2NLU／mL时，55℃保温水解2h可达到55％以上的水解率。     

Thickening of molten white chocolates during storage

When white chocolates are kept molten in storage tanks, problems can arise due to uncontrolled thickening and solidifying of the chocolate mass. The thickening of molten white chocolate was simulated on a laboratory scale using a rotational rheometer under static conditions, interrupted by short shear periods to measure the increasing viscosity. Several chocolates having different dairy components and fat contents were investigated for their tendency to thicken. In addition, sorption isotherms for white chocolates were obtained using dynamic vapour sorption at different temperatures. The sorption isotherms showed the presence of amorphous lactose in all the chocolates that were manufactured from milk powders. Moisture that is released during the crystallization of amorphous lactose causes stickiness and agglomeration of the neighbouring particles and starts the thickening process. This process is highly temperature-dependent. On elevating the temperature the lactose crystallization occurs at lower relative humidities. In order to reduce the tendency of white chocolate to thicken, a high free-fat level should be maintained, based on a high total fat content and on the use of high free-fat milk powders, preferably roller-dried whole milk powders or the combination of skimmed milk powder and anhydrous milk fat.     

乳糖替代凝乳酶制作大豆干酪技术初探

对加酶发酵制作干酪的传统方法进行了改进,用添加乳糖的方法来代替添加酶进行发酵.试验综合考察了影响混合豆乳(豆乳和牛乳)干酪凝乳的几个因素,即豆乳添加量、发酵剂添加量、乳糖添加量和乳酸钙添加量,并确定混合豆乳干酪的最佳凝乳工艺参数.试验结果表明,最佳工艺参数为:80%豆乳 3%发酵剂 3%乳糖 0.1%乳酸钙.     

Numerical modelling and characterization of nanofiltration membranes for the separation of carbohydrate mixtures

The results of an experimental and computational investigation of the selective separation of carbohydrates on nano‐membranes in cross‐flow filtration are reported. Two commercial membranes (NF270‐400 and TFC‐SR3) were characterised in terms of permeability and rejection of carbohydrate solutions. It is shown that the membranes can be used to recover glucose and galactose from their mixtures with lactose. The permeate flux is shown to depend on sugar concentration, with permeate flux decreasing as the concentration increases. Quantitative evaluation using numerical analysis of the above flow and separation process showed that the performance of nano‐membranes can be captured and reproduced with sufficient accuracy, thereby reducing the number of experiments require to evaluate the suitability of membranes in different applications. A Fickian approach is adopted to model the separation, and is shown to be effective.     

Assessment of adhesion and autoadhesion forces between particles and surfaces. Part II. The investigation of adhesion phenomena of Salmeterol Xinafoate and lactose monohydrate particles in particle-on-particle and particle-on-surface contact

The centrifuge technique has been used to compare particle-on-particle and particle-on-surface adhesion with Salmeterol Xinafoate particles on single lactose particles or compacted lactose surfaces. The results from particle-on-particle and particle-on-surface adhesion measurements are not equivalent in terms of median adhesion force. The assessment of adhesion using either particle-on-particle or particle-on-surface systems depends on the process on which information is required: e.g. mixing problems are better investigated by applying the particle-on-particle technique, whereas surface transport problems such as powder compaction or flow can be more appropriately studied using particle-on-surface measurements. Taking autoadhesion measurements from the previous study into account, adhesion and autoadhesion forces were found to allow the prediction and choice of mixture components for powder blends. The results suggest that the homogeneity of such a powder blend depends both on thermodynamic properties and on the adhesion and autoadhesion properties of the single components.     

Substitution of sodium chloride by Morton Lite Salt or Mineral Salt in mayonnaise

The effect of substituting Morton Lite Salt or Mineral Salt for sodium chloride in neutral emulsion and in mayonnaise was evaluated by using 1.00% sodium chloride, 1.25% Morton Lite Salt and 1.40% Mineral Salt of the emulsion weight. None, 1.00%, 2.00% and 3.00% of lactose were used to mask the bitter taste associated with potassium chloride. A triangle test using twelve to fifteen panelists was used. Results indicated that both Morton Lite Salt and Mineral Salt had a significant different taste (P ≤ 0.01) as compared with sodium chloride when they were used with none and 1.00% of lactose. Samples which had 2.00% or 3.00% lactose showed no significant taste difference between Morton Lite Salt or Mineral Salt and sodium chloride. It was concluded that a bitter masking agent such as lactose is needed when Morton Lite Salt or Mineral Salt is used to substitute sodium chloride in mayonnaise.     

铁离子检测用自组装膜的光谱特性分析

以聚二烯丙基二甲基氯化铵（PDDA）和聚4-苯乙烯基磺酸钠（PSS）为前驱体,以1-亚硝基-2-萘酚-3,6-二磺酸二钠一水合物为铁离子指示剂,根据静电自组装原理,设计制备了对铁离子具有光学敏感性的自组装膜。采用紫外可见分光光度计考察了敏感膜的自组装制备过程,分析了不同指示剂含量的敏感膜与铁离子作用前后的光谱变化规律,并通过扫描探针显微镜对其微观形貌进行了观察,通过敏感膜与铁离子作用前后的特征峰分析,初步确定了敏感膜吸光度变化量与铁离子浓度间的对应关系。     

β-Galactosidase activity of commercial lactase samples in raw and pasteurized milk at refrigerated temperatures

Many consumers are unable to enjoy the benefits of milk due to lactose intolerance. Lactose-free milk is available but at about 2 times the cost of regular milk or greater, it may be difficult for consumers to afford. The high cost of lactose-free milk is due in part to the added cost of the lactose hydrolysis process. Hydrolysis at refrigerated temperatures, possibly in the bulk tank or package, could increase the flexibility of the process and potentially reduce the cost. A rapid β-galactosidase assay was used to determine the relative activity of commercially available lactase samples at different temperatures. Four enzymes exhibited low-temperature activity and were added to refrigerated raw and pasteurized milk at various concentrations and allowed to react for various lengths of time. The degree of lactose hydrolysis by each of the enzymes as a function of time and enzyme concentration was determined by HPLC. The 2 most active enzymes, as determined by the β-galactosidase assay, hydrolyzed over 98% of the lactose in 24 h at 2°C using the supplier's recommended dosage. The other 2 enzymes hydrolyzed over 95% of the lactose in 24 h at twice the supplier's recommended dosage at 2°C. Results were consistent in all milk types tested. The results show that it is feasible to hydrolyze lactose during refrigerated storage of milk using currently available enzymes.     

生物转化乳糖酸的研究

乳糖酸(Lactobionicacid)是乳糖氧化的产物,具有多种生理功能。目前,欧美等发达国家乳糖酸的生产是通过化学合成法,生产成本高,且有大量副产物生成。研究采用具有葡萄糖氧化酶的菌株BurkholderiacepaciaNo.24细胞培养物进行生物转化生产乳糖酸,55g湿重/1000mL细胞可将浓度为193mmol/L的乳糖转化成188mmol/L的乳糖酸,转化率可达99.8%,且转化液经薄层色谱层析和高效液相色谱检测证明在转化过程中没有副产物生成;同时,该菌株还具有广泛的底物专一性,能将葡萄糖、麦芽糖等糖类转化成相应的糖酸。     

Viscosity of Molten Milk Chocolate with Lactose from Spray-Dried Whole-Milk Powders

Dry whole-milk powders containing 0, 30, 50 and 70% nominal lactose prepared by spray-drying alone, or followed by post-drying crystallization, were incorporated into milk chocolate to give 0–50% substitution of lactose for sucrose. Increasing the concentration of amorphous lactose from spray-dried powders in the chocolates decreased viscosity, increased particle size of refined chocolate mass, and lowered the concentration of surface-active agents at which a minimum in Casson yield value was observed. Increasing the concentration of crystalline lactose from milk powders in the chocolates increased viscosity, decreased particle size, and increased the concentration of surface-active agents at which a minimum in Casson yield value was observed. Conditions which affect lactose crystallinity in milk powders, such as improper storage and handling prior to use in chocolate production, could be responsible for variations in chocolate viscosity noted sometimes by processors.