对乳清的超滤渗透液进行纳滤脱盐的试验研究

采取超滤膜对乳清进行预处理,研究了不同操作条件下NF270纳滤膜的通量衰减规律以及对乳清中盐和乳糖的分离效果.结果表明:压力由0.4 MPa增加到0.6 MPa时,纳滤膜稳定通量增大,膜通量衰减加重.纳滤膜的盐截留率先下降后上升,乳糖透过率略有增加,增加压力有利于乳糖和盐之间的分离;当压力为0.6 MPa,转速为418.6r/min,在蛋白质的等电点pH值为4.8时,纳滤膜通量小且膜污染最为严重,此时盐截留率最低;pH值为3时所对应的膜通量与料液呈中性时相比,乳清通量增加,且通量衰减幅度小,此时盐截留率为30％,乳糖透过率达80％,因此酸性条件有利于提高通量及乳糖和盐之间的分离效果;提高膜表面的湍动程度时,膜通量增加且膜污染减弱,相应的纳滤膜的盐截留率较小,而对乳糖的透过率影响不明显.     

Sensory evaluations and stability determinations of goat milk containing galactooligosaccharides

The objectives of this study were to evaluate the feasibility of producing goat milk containing galactooligosaccharides (GOS) by β‐galactosidase and to determine the sensory attribute and stability of goat milk containing GOS. The results indicated that the maximum GOS obtained were approximately 13.9% of total sugars at pH 4.5 and temperature 40 °C. The sensory attribute of the obtained GOS was determined using a 5‐point hedonic scale in terms of taste, flavour, appearance and overall acceptability. There were significant increases in taste and overall acceptability of goat milk containing higher GOS concentration when compared to regular goat milk (control). Also, goat milk containing GOS presented a good stability over the acidic conditions. GOS in goat milk were also stable after the high heat treatment and shelf life conditions.     

电化学生物传感器测定牛乳中乳糖含量的条件研究

将牛乳中特征物质乳糖浓度的变化引起的电化学性质用电信号表征出来,探索了电化学生物传感器测定牛乳中乳糖含量的条件,得出实验条件如下:选定突变电压为1.2V,电流测定的最佳条件是:反应温度为45℃,酶固定量为0.4μL,pH值为6.5,线性回归方程为Y=15.153X+1.5131,相关系数R2=0.9925,曲线的相关性很好;方法学考察说明,精密度为1.134%,重复性为2.624%,加标回收率为100.258%,该方法的稳定性、重复性好。     

糖基化反应对乳清蛋白-乳糖复合物乳化性的影响

糖基化反应是改善蛋白质功能特性的一种有效方法.研究了糖基化反应对乳清蛋白-乳糖复合物乳化性的影响.结果表明,糖基化反应能够改善乳清蛋白-乳糖复合物的乳化性和乳化稳定性.     

糖类手性固定相的合成及其色谱应用

制备了葡萄糖、纤维二糖、棉子糖、乳糖的高效液相色谱手性固定相,并在正相条件下对32种手性化合物进行了拆分,结果表明,四种手性固定相分别分开手性药物11,14,17,11种,拆分效果良好。     

Particle crystallization during spray drying in humid air

A new and modified spray drying setup was arranged to produce spray-dried crystalline lactose particles. According to Williams–Landel–Ferry kinetics (WLF), it was suggested that a higher particle temperature and lower glass-transition temperature would increase the crystallization rate of the particles during the spray-drying process while still giving dry powders. The new experimental setup allowed the particle temperature to reach higher values by using an insulated drying chamber and also allowed the particle glass-transition temperature to reach lower values by maintaining a higher gas humidity with the aid of a condenser unit attached to the dryer. Modulated differential scanning calorimetry (MDSC) and moisture-induced sorption analysis were used to verify the crystallinity of the spray-dried lactose powders. These analyses showed a higher degree of crystallinity for the particles than have previously been reported in the literature. X-ray diffraction and Raman spectroscopic analyses were further used to identify different lactose anomers. The results suggest that only α-lactose anomer exists in the products as obtained from the modified spray-drying system. The micrographs from scanning electron microscopic analysis also indicated a very crystalline nature for the particles.     

Influence of calcium and phosphorus, lactose, and salt-to-moisture ratio on Cheddar cheese quality: manufacture and composition

Eight Cheddar cheeses with 2 levels of calcium (Ca) and phosphorus (P), residual lactose, and salt-to-moisture ratio (S/M) were manufactured. All cheeses were made using a stirred-curd procedure and were replicated 3 times. Treatments with a high level of Ca and P were produced by setting the milk and drawing the whey at a higher pH (6.6 and 6.3, respectively) compared with the treatments with a low level of Ca and P (pH of 6.2 and 5.7, respectively). The lactose content in the cheeses was varied by adding lactose (2.5% by weight of milk) to the milk for high lactose cheeses, and washing the curd for low lactose cheeses. The difference in S/M was obtained by dividing the curds into halves, weighing each half, and salting at 3.5 and 2.25% of the weight of the curd for high and low S/M, respectively. All cheeses were salted at a pH of 5.4. Modifications in cheese-making protocols produced cheeses with desired differences in Ca and P, residual lactose, and S/M. Average Ca and P in the high Ca and P cheeses was 0.68 and 0.48%, respectively, vs. 0.53 and 0.41% for the low Ca and P cheeses. Average lactose content of the high lactose treatments at d 1 was 1.48% compared with 0.30% for the low lactose treatments. The S/M for the high and low S/M cheeses was 6.68 and 4.77%, respectively. Mean moisture, fat, and protein content of the cheeses ranged from 32.07 to 37.57%, 33.32 to 35.93%, and 24.46 to 26.40%, respectively. The moisture content differed among the treatments, whereas fat and protein content on dry basis was similar.     

Modeling of lactose crystallization and color changes in model infant foods

Lactose crystallization and color changes in formulas containing β-lactoglobulin and gelatinized starch were investigated. Model infant formulas were prepared by colyophilization of 3 components (lactose, β-lactoglobulin, and gelatinized starch). A mixture design was used to choose the percentage of each mixture component. These formulas were stored for 3 mo at different relative humidities (RH), ranging from approximately 0 to 94.6%, to study the lactose crystallization and color changes. Crystallization kinetics was studied by gravimetric methods, and lactose state (crystalline vs. amorphous) was verified before and after storage by differential scanning calorimetry. Before storage, lyophilized lactose was amorphous, but during storage it crystallized, depending on the RH. The lactose crystallization RH depended on the quantity of β-lactoglobulin and gelatinized starch, and by increasing these quantities, the crystallization RH increased. For some formulas, the crystallization RH was noted at 3 different RH during storage. The first was noted after 1 d of storage and the second and third were observed later on, showing that crystallization is a time-dependent phenomenon. Nonenzymatic browning was studied in model infant formulas by yellow color changes of samples at 11.3, 43.2, 54.5, and 75.4% RH. In this study, 7 mathematical models were proposed to predict the moisture sorption properties and color changes at different RH, and the models were validated by experimental results.     

Batch kinetics and modelling of ethanolic fermentation of whey

The fermentation of whey by Kluyveromyces marxianus strain MTCC 1288 was studied using varying lactose concentrations at constant temperature and pH. The increase in substrate concentration up to a certain limit was accompanied by an increase in ethanol formation, for example, at a substrate concentration of 10 g L^?1, the production of ethanol was 0.618 g L^?1 whereas at 50 g L^?1 it was 3.98 g L^?1. However, an increase in lactose concentration to 100 g L^?1 led to a drastic decrease in product formation and substrate utilization. The maximum ethanol yield was obtained with an initial lactose concentration of 50 g L^?1. A method of batch kinetics was utilized to formulate a mathematical model using substrate and product inhibition constants. The model successfully simulated the batch kinetics observed at S₀ = 10 and 50 g L^?1 but failed in case of S₀ = 100 g L^?1 because of strong substrate inhibition.     

Role of water in the polymorphic transitions of small carbohydrates

Crystallisation of small carbohydrates (hexoses, alditols, and disaccharides) in solution or from the melt is known to provide different polymorphs mainly due to their affinity with water and their molecular flexibility. Food and pharmaceutical applications sometimes require the use of a specific polymorph especially for its compaction and compression properties.