Microporous Ultrafiltration of Skim Milk

Membranes with porosities of 100 and 200 nm were used to obtain a 4:1 milk volume reduction. Average micelle diameters determined from electron micrographs were 46 nm (permeate) and 52 nm (permeate) for the 100-nm-pore fractions and 46 and 55 nm for the 200-nm-pore fractions. The calculated average micellar volumes of the retentate fractions were about twice those of the corresponding permeate fractions. Casein-whey ratios were 0.7-0.9 in the permeates and 5.0-7.7 in the retentates. Higher α_s2- and lower β-casein contents were found in the permeate micelles than in the retentates.     

Characterization of Milk Proteins in Ultrafiltration Permeate

Pasteurized, unhomogenized whole milk was ultrafiltered with a Dorr-Oliver, Series S, plate and frame pilot unit containing seven commercial S-10 polysulfone membranes with a 10,000 molecular weight cut-off. Permeate was collected and protein was isolated from the permeate. Proteins precipitated from the UF permeate by 12.5% TCA were weighed and then characterized by SDS-PAGE. Only a very small amount of protein (.25 g/l) was present in the permeate and approximately 90% of that protein was α-lactalbumin.     

Comparison of Rat Hepatic Cholesterol Biosynthesis During Skim Milk Versus Whey Permeate Ingestion

Whey permeate is an ultrafiltrate of whey that is devoid of protein but contains lactose, salts, and other soluble low molecular weight compounds. These experiments compared cholesterol concentrations of blood plasma, hepatic lipids, and hepatic cholesterol biosynthesis of rats ingesting skim milk powder versus whey permeate powder. Groups of young male rats weighing 90 to 92 g were fed a casein-based diet into which skim milk powder or whey permeate powder was incorporated isocalorically. No effects of skim milk or whey permeate on plasma cholesterol concentrations were observed at any time during 5-wk of feeding. However, 3-hydroxy-3-methylglutaryl coenzyme A reductase activity was increased by either skim milk or whey permeate feeding. Hepatic cholesterol, triglyceride, and phospholipid concentrations at wk 5 were unchanged. Plasma and hepatic cholesterol responses of rats to whey permeate ingestion are similar to those that occur with skim milk consumption, and plasma and hepatic cholesterol concentrations do not reflect necessarily an increase in hepatic cholesterol biosynthesis.     

Experimental Investigation of the Sweet Whey Concentration by Nanofiltration

The main goal of our work was to examine the possibility of using membrane separation to concentrate sweet whey, which could then be used as the basis of more products (e.g., ice cream, soft drinks containing whey).Whey from cheese making was concentrated by nanofiltration. The operating parameters were determined in permeate recirculation mode, and the concentration experiment was carried out under optimal conditions. The analytical assay of the permeate and concentrate such as total soluble solid content (TSS), protein content, and lactose content was determined using infrared measurements. The retention of lactose was over 95% up to 3.0 volume concentration ratio (VCR) at 20-bar transmembrane pressure. The analysis of the process was based on the resistance in series model and the van’t Hoff law. The model parameters were determined on the basis of lactose content, assuming that lactose is the key component of whey. The values of these parameters are the concentration polarization (β = 1.68) and total resistance (R _TOT = 1.60 × 10¹⁴ m⁻¹). The procedure was also repeated based on TSS, and the value of the total resistance was almost the same (R _TOT = 1.59 × 10¹⁴ m⁻¹). Due to this, the applied models describe appropriately the batch membrane concentration process of whey. The lactose concentration can be used for the calculation instead of TSS, which simplifies the job of estimating the model parameters.     

Permeate Flux During Ultrafiltration of Whey: Influence of Milk Coagulant Used for Cheese Manufacture

A pilot-scale plate and frame UF system was used to fractionate Cheddar cheese whey and study the effects of different commercial milk coagulants on permeate flux. Coagulants used in this study were calf rennet, Mucor pusillus protease, and Mucor miebei protease. Whey UF performance studies were conducted at a commercial Cheddar cheese plant and at Cornell under controlled conditions. Ultrafiltration was done in a continuous mode and initial concentration factor was set at 2× to simulate the first stage of a multistage whey UF system.Permeate flux decline was rapid in the first 30 min of UF for all wheys studied. More important, the type of milk coagulant used in cheese making had a profound effect on permeate flux during whey UF. No differences in the gross composition of the various wheys were correlated with differences in permeate flux. The highest permeate flux was measured for UF of whey produced during manufacture of Cheddar cheese using coagulant derived from Mucor pusillus. Lowest permeate flux was measured for UF of whey produced during manufacture of Cheddar cheese using calf rennet. Whey from cheese manufactured using Mucor miebei coagulant had flux performance intermediate to Mucor pusillus and calf rennet. The impact of milk coagulants on whey UF process efficiency should be considered by cheese makers.     

超滤法浓缩分离免疫初乳中的抗体

收集经大肠杆菌、沙门氏菌混合疫苗免疫处理的乳牛产后７天之内初乳,经去脂、去酪蛋白后所得免疫初乳乳清,用中空纤维超滤器（分子截留为１００ｋｕ（１００ｋｄ）进行浓缩分离,浓缩４．５～７倍、ＩｇＧ收率在９０％以上。为了制得高纯度ＩｇＧ分离物,可和３５％饱和度的硫胺进行盐析,然后再进行超滤脱盐、浓缩、制得的ＩｇＧ浓缩物纯度达８０％以上,这一工艺适合工业化生产。     

Concentration of Milk and Whey by Membrane Technologies in Alternative Cascade Modes

The aim of the present study was the evaluation of a membrane cascade comprised of ultrafiltration (UF) in series with reverse osmosis (RO) or nanofiltration (NF) in comparison to a single-stage process. It was found that the upstream UF accelerated the NF and the RO, whereby the effect was more distinct for the NF. The maximum volume reduction ratio (VRR) during skim milk and sweet whey concentration could be increased by 78 and 96%, respectively, by substituting a single NF by an UF-NF cascade. The replacement of a single RO by a UF-RO cascade during concentration of skim milk slightly increased the VRR by 3%. However, the energy demand could be reduced by approximately 16%. For the concentration of sweet whey, it was found that it is more advantageous to conduct the RO at a higher transmembrane pressure (TMP) instead of applying an UF-RO cascade.     

Effects of Fermentation and Storage on the Concentration of Orotic Acid and Uric Acid in Skim Milk

Skim milk (SM) and skim milk yogurt (SMY) were produced and analyzed using high performance liquid chromatography (HPLC) for the presence of two organic acids–orotic acid (OA) and uric acid (UA). The concentration of OA in SM and SMY at 0 days was 106.2 and 46.1 ppm, respectively. After fermentation OA concentration was 56% lower (P <0.05) in SMY than in nonfermented SM. UA content of SM and SMY at 0 days was 23.3 and 20.1 ppm, respectively. Unlike OA, the UA contents were not significantly altered after fermentation. No significant differences were detected in the concentrations of OA and UA when values of SM and SMY of 0 days were compared with those after 3 days storage.     

Concentration of Perilla Anthocyanins by Ultrafiltration

Anthocyanins were extracted from perilla leaves using 10% citric acid solution. The pigment in the extract could be concentrated by ultrafiltration (UF) with a membrane of M. W. cutoff 6,000, possibly due to the formation of copigmented complexes. In UF operations, fouling was not severe. Increasing either transmembrane pressure or feed concentration resulted in increased solute retention. Recovery of anthocyanin was over 60% by UF at volume concentration ratio of 4.     

Prediction of Permeate Flux During Ultrafiltration of Polysaccharide in a Stirred Batch Cell

Ultrafiltration of polysaccharide macromolecule has been carried out in a stirred batch cell using a fully retentive membrane over a wide range of operating conditions. An unsteady state mass transfer model in conjunction with resistance-in-series model is developed using film theory. The proposed model is used to predict the transient permeate flux decline behavior in gel controlled ultrafiltration. This model is also able to quantify the variation of bulk volume as well as the bulk concentration of solute with time. The variation of viscosity as a function of solute concentration is included in the model. A model parameter is used in this model and is evaluated by optimizing the experimental flux profiles with calculated flux profiles. The model predictions are successfully compared with the experimental data. A parametric study has been performed to observe the effect of different process parameters on the filtration performance in terms of transient permeate flux decline behavior. The proposed model in general will provide a better understanding of gel controlled ultrafiltration.     

Rheological Properties of Chymosin-Induced Skim Milk Gels as Affected by Milk Storage Time and Temperature

Fundamental dynamic rheological tests were used to measure the rigidity (|G*|) and viscoelasticity (tan δ) of gels made from skim milk samples that were (1) never cooled, (2) stored at 4°C, or 3) stored at 4°C and then rewarmed to 25°C. Milk cooled and held at 4°C prior to gel formation produced gels with lower |G*| and higher tan(δ) than fresh milk gels. Chilled milk samples that were rewarmed to 25°C for 16h prior to gel formation produced gels with rheological properties similar to fresh milk gels. The solubilization of β-casein during cold storage was hypothesized to be the cause of observed differences in gel rheology.     

Sodium Caseinate from Skim Milk Powder by Extrusion Processing: Physicochemical and Functional Properties

Sodium caseinate produced on a pilot-plant-scale directly from skim milk powder (SMP) with two-step extrusion process was compared to a commercial product and a sodium caseinate prepared from commercial acid casein by extrusion-processing. The products were compared in terms of physicochemical properties and functional properties, as well as microbiological quality. Although differences existed between the caseinates, overall, those produced from SMP by extrusion appeared comparable to commercial caseinate. Results indicate that a good-quality sodium caseinate with the requisite properties normally associated with commercial sodium caseinate could be produced directly from SMP by extrusion-processing.     

全脂乳与脱脂乳挥发性风味成分对比分析

HS-SPME结合GC/MS对比分析全脂乳(WM)和脱脂乳(SM)的挥发性风味成分。结果表明,50/30μm CAR/PDMS/DVB萃取纤维萃取得到的全脂乳、脱脂乳的挥发性风味物质的种类与65μm PDMS/DVB相当,即:全脂乳11种,脱脂乳8种,只是在萃取含量上有差异。因此,相对于65μm PDMS/DVB而言,50/30μm CAR/PDMS/DVB较适合乳风味挥发性物质的萃取。HS-SPME结合GC-O对比分析全脂乳和脱脂乳的呈香组分结果显示,脱脂乳中未发现香气强度较高的呈香成分。而在全脂乳中辛酸(清香)、癸酸(油脂味)香气强度较高。这些结果能为全脂乳和脱脂乳的风味物质组成提供有用信息。     

超滤法测定表面活性剂临界胶束浓度

对超滤法测定表面活性剂的临界胶束浓度(CMC)的单点式超滤法、超滤曲线法、双点式超滤法进行了研究,比较了理想与真实超滤曲线,对超滤膜用于超滤法测定CMC的适用性及容积效应进行了考察.初步探讨了用双点式超滤法代替作超滤曲线法测定CMC的可行性和准确性,并与单点式超滤法进行了比较.试验结果表明,用双点式超滤法测定CMC具有准确性较高、操作简便、节省时间和节约样品用量等优点.用双点法测得的SDS和SLAS的CMC分别为6.70mmol/L和1.40mmol/L;与超滤曲线法得到的CMC相比,偏差分别为2.9%和3.4%.     

脱脂乳粉非酶褐变影响因素的实验研究

在食品、饮料、营养品、医药等行业广泛涉及非晶态粉体产品,这些粉体产品的非酶褐变,会严重影响产品质量。本文对脱脂乳粉的非酶褐变特性进行了实验研究;考查了水分活度、贮藏温度、储藏时间和玻璃化转变温度等参数对脱脂乳粉非酶褐变的影响。结果表明:随着水分活度、贮藏温度、贮藏时间以及贮藏温度T与脱脂乳粉的玻璃化转变温度Tg间的差值(T-Tg)的增加,脱脂乳粉非酶褐变指数显著增大;脱脂乳粉应在较低水分活度(例如0.3以下)和较低温度(例如40℃以下)下贮藏,以延长其货架寿命。     

Passion Fruit Juice Concentration by Ultrafiltration and Evaporation

Passion fruit juice was pretreated with pectinase, centrifugation, and pasteurization. The resulting juice was processed by Ultrafiltration (UF) to 20°Brix. The UF permeate was concentrated by evaporation to 70°Brix and combined with the UF retentate to form the final concentrated product at 40°Brix. The pretreatments caused approximately 20% flavor losses, but accomplished more than 50% flux increases. The UF recovered many important flavor constituents, and improved the rate of evaporation. The final concentrated product contained more than 30% of juice flavor. Results of sensory evaluation indicated that flavor of the reconstituted juice was inferior to fresh juice, but the two juices were not significantly different in overall acceptance.     

复合发酵剂发酵脱脂乳与豆乳的工艺优化

该研究以脱脂乳和豆乳为原料,马克斯克鲁维酵母、嗜热链球菌和保加利亚乳酸杆菌作为发酵剂,以滴定酸度和感官评分作为指标,通过单因素试验及响应面试验,优化脱脂乳豆乳体积比、白砂糖添加量、发酵剂接种量及发酵温度,并对优化后的复配发酵乳在贮藏期间的质构、持水力、滴定酸度、感官评分和活菌数进行测定。结果表明,最佳发酵条件为脱脂乳与豆乳体积比82 ∶18、白砂糖添加量7.25%、发酵剂接种量3.92%,在42 ℃发酵4.5 h,所得复配发酵乳的感官评分最高,为94.85;在该优化条件下制备的发酵乳后熟12 h,硬度为99.39 g,滴定酸度为97.52°T,活菌数为2.7×109 CFU/mL,发酵乳颜色呈乳黄色、组织状态均匀、酸甜适口、口感柔和润滑、具有复配发酵乳独特的豆香味和浓郁的奶香味,在14 d 贮藏期内具有良好的风味、质构及感官接受度。     

Comparison of Electrochemical and Chemical Acidification of Skim Milk

The purpose of this study was to compare chemical and electrochemical acidification, in order to identify differences between the two acidification procedures. The results reveal differences in the acidification profiles obtained with the two methods. Whereas chemical acidification showed a salting‐in effect from addition of salts, bipolar‐membrane electroacidification (BMEA) removes salts through electrochemical demineralization, favoring protein precipitation. Hence, at pH 4.6, all the caseins were precipitated by BMEA, while some were not yet precipitated by chemical acidification. Nevertheless, the chemical composition and the casein fraction composition of the isolates were the same for both chemical and electrochemical acidification.     

Sodium Caseinate and Skim Milk Gels Formed by Incubation with Microbial Transglutaminase

Several suspensions and emulsions containing commercial sodium caseinate or skim milk were gelatinized by Ca²⁺-independent microbial transglutaminase treatment. The characteristics of the gels were largely affected by the enzyme concentrations employed. For caseinate gels generally the higher enzyme concentration gave steep decreases in breaking strength, strain and cohesiveness of the gels. The creep tests on emulsified gels prepared to two different enzyme concentrations showed that the gel made with a higher enzyme concentration was the more viscoelastic. For skim milk gels, the enzyme treatment in higher concentration caused substantial increase of the breaking and hardness while the strain and cohesiveness had little or no changes.