牛奶中酪蛋白和乳糖的分离方法研究

用蛋白质等电沉淀法从牛奶中分离酪蛋白和乳糖。酪蛋白分离的最佳工艺参数为:提取温度40℃,pH值4.8,乙醇用量20 mL/100 mL牛奶;乳糖分离的最佳工艺参数为:pH值4.8,碳酸钙用量2.5 g/100 mL牛奶,结晶时间4 d。温度对乳糖得率的影响不大。     

牛奶中抗生素残留检测的研究现状

牛奶在人们饮食中占有重要地位,但是种种原因使得抗生素残留于牛奶中,严重影响奶品品质及人体安全,乳品中抗生素残留的检测和管理尤为重要。本文主要介绍牛奶中抗生素残留的三种检测方法:微生物检测法、理化检测法和免疫法。而我国在生产管理上常用的筛查检测方法有TTC法和SNAP法,两种方法各有优劣,而基于TTC法的试纸检测法是一种正在研发的有潜力的筛查分析方法。     

耐温性牛奶香精的调配

耐温性牛奶香精是奶类香精中最常用的品种之一,主要用于饼干、蛋糕、糖果等食品加香中。本文通过对牛奶香精配方架构进行调整,来阐述耐温性牛奶香精的调配。     

纳滤技术回收乳制品废水中乳糖的研究

以回收乳制品废水中的乳糖和再生废水为目的,研究了纳滤膜法回收废水中乳糖的工艺,系统地讨论了操作压力、进料流量、浓缩比等因素对回收率和对COD去除率的影响。在本实验条件下,纳滤膜法回收乳制品废水中乳糖的最佳操作压力为1.0 MPa,进料流量为28 L/min。在此最佳操作压力和进料流量下,废水中乳糖的回收率为100%。而纳滤膜处理后乳制品废水的各项水质指标也达到了再生水的水质标准。     

工业生产中菌种的常用保藏方法

介绍了工业生产中常用微生物菌种的保藏方法,即斜面低温保藏法、甘油保藏法、甘油乳糖保藏法、沙土管保藏法并比较了它们的优缺点。     

琼脂糖及其衍生物的简介

琼脂糖(Agarose,亦译琼胶素)是从琼胶(Agar,亦译为琼脂)纯化制得的,主要是由D-半乳糖和3,6-脱水-L-半乳糖相间结合构成的链状中性多糖。其结构见图1。琼胶的另一主要组分是琼胶酯(Agaropectin,亦译果胶),琼胶酯也是由D-半乳糖和3,6-脱水-L-半乳糖构成的,但含有相     

英国将用乳清生产蛋白甜味剂

<正> Cornirg Glass公司英格兰和威尔士牛奶推销公司于82年三月份开始在沃浦东南部的乳酪乳脂制造厂合伙生产富含蛋白质的甜味糖浆。后两家公司都采用了Cornirg公司的生物技术工艺:在多乳硅粒子上发酵乳糖     

固体超强酸催化剂SO42-/高岭土制备乙酰丙酸

利用二次浸渍焙烧法制备固体超强酸催化剂SO42-/高岭土,对其催化水解乳糖制备乙酰丙酸的反应机理作了推理,并通过单变量法考察了催化剂的焙烧温度、乳糖浓度、反应温度、反应时间、催化剂用量等对乙酰丙酸相对收率的影响,采用正交实验来确定最佳工艺条件,研究结果表明:当催化剂的焙烧温度为650℃、乳糖浓度5 g/L、反应温度200℃、反应时间120 min、催化剂用量为乳糖加入量的15%时,乙酰丙酸的相对收率最大,达到79.13%。     

乳糖诱导重组人睫状神经营养因子在大肠杆菌中的可溶性表达

目的利用乳糖替代IPTG,诱导重组人睫状神经营养因子(Recombinanthumanciliaryneurotrophicfactor,rhC-NTF)在原核工程菌BL-TCS中可溶性表达,并选择最适的诱导表达条件。方法在不同的温度下,利用不同浓度的乳糖及0·5mmol/L的IPTG,诱导含有人CNTF基因的工程菌9h,比较菌体生长、乳糖消耗以及目标蛋白的表达规律。结果乳糖组的菌体A600值均高于IPTG组。乳糖诱导产生的rhCNTF主要以可溶形式表达,各浓度乳糖的诱导效果均能接近或超过IPTG的效果。以2%乳糖在25℃下诱导6h,可以达到比较好的诱导效果。结论乳糖可取代IPTG诱导人CNTF基因表达,并获得良好效果。     

乳果糖的应用及生产技术研究进展

乳果糖是一种功能性低聚糖,具有易于被人体吸收、促进对矿物质的吸附、影响骨骼、降低血液中谷氨酸、降低胆固醇等生理功能,有广阔的应用前景。目前,商业化上主要采用化学异构法生产乳果糖。但由于化学异构法存在碱性催化剂的分离、反应副产物多、高能耗等问题,近年来一些学者开展了酶法转化乳糖合成乳果糖的研究。文章综述了乳果糖的基本性质及生产技术研究进展。     

Hydrolysis of milk lactose in a packed bed reactor system using immobilized yeast cells

BACKGROUND: Hydrolysis of lactose with β‐D‐galactosidase is one of the most promising biotechnological applications in the food industry because of its use in the production of low lactose milk products and whey hydrolysis. To overcome the problem of enzyme extraction from cells due to the intracellular nature of β‐D‐galactosidase and the poor permeability of the cell membrane to lactose, permeabilization of yeast cells was investigated. Permeabilized whole cells have been claimed to have an advantage over more pure enzyme preparations. In view of the advantages of immobilized cell systems over free cell systems, permeabilized cells were immobilized by an entrapment method in calcium alginate gel. A packed bed reactor together with this immobilized cell system has been used for hydrolysis of milk lactose in a continuous system. RESULTS: Different process parameters (temperature, substrate feed rate, biomass load and time‐course) were optimized to maximize lactose hydrolysis. The immobilized yeast cells (300 mg dry wt) resulted in 87.2% hydrolysis of milk lactose at 30 °C and flow rate 7 mL h^?1 in a packed bed reactor system. CONCLUSION: This convenient and relatively inexpensive method of immobilization, resulting in high hydrolysis potential in a continuous system, indicates that permeabilized yeast cells have the potential for the production of low lactose milk and milk products. Copyright © 2010 Society of Chemical Industry     

Lactose tolerance and milk consumption: myths and realities

The disaccharide lactose, the principal carbohydrate of animal milks, requires the enzyme lactase to split it to glucose and galactose. Undigested lactose passes to the colon where fermentation produces hydrogen and short-chain fatty acids that can cause abdominal distention, pain and sometimes diarrhea. Persistence of intestinal lactase after early childhood, is inherited as a highly-penetrant autosomal dominant genetic characteristic. On the basis of a review of over 560 references, all available data on the primary loss of intestinal lactase in Latin American populations are presented in tabular form. Prevalence of lactose non-digesters in Latin American populations ranges from 45% to 100%. However, this is not a reliable predictor of the acceptability of milk and milk products containing lactose. Milk is being used successfully for the supplementary feeding of children worldwide, and most lactose non-digesters can tolerate at least 240 ml of milk or the lactose equivalent in other products. Lactose maldigestion does not interfere with the absorption of the protein and essential micronutrients in milk. Information is provided on the lactose content of milk and milk products, on the usual milk consumption of Latin American populations, and on worldwide experimental and field observations of milk acceptability. Both adaptation to continued use of milk and milk products and relationships of milk use to various disease states in which intestinal lactase activity may be reduced are discussed. Some types of yoghurts are better tolerated because of the lactase activity of the bacteria used in their fermentation. For unusually intolerant individuals commercial enzyme preparations are available for addition to milk products but for most persons the additional cost is unnecessary.     

The potential value of cultured dairy products for child nutrition

The author suggests that under certain conditions cultured milk, rather than fluid milk, can be used for infant and child nutrition as well as for school milk programs. Some of the major problems with fluid milk, fresh or reconstituted, are discussed. A review of the literature indicates that the assumption of lactose intolerance among many populations is exaggerated. Inappropriate handling of pasteurized milk very often is responsible for a high bacterial count and organoleptic defects. Such quality defects are more pronounced in countries with a warm climate. The use of polluted water in the reconstitution of milk powder, is probably more often responsible for diarrhea than lactose intolerance. For these reasons it is suggested that under appropriate conditions a cultured milk product such as yogurt or quark, be used for infant and child nutrition. The advantages are: 1) the low pH caused by the high lactic acid content detrimentally affects food spoilage and pathogenic organisms in milk; 2) longer shelf life of the fermented product at ambient temperature; and 3) fermented milk products contain the enzyme lactase which facilitates digestion of residual lactose even after ingestion.     

Reduction of the Lactose Content of Skim Milk by Continuous Countercurrent Cascade Ultrafiltration

Abstract

Lactose was continuously removed from skim milk using two ultrafilters in series, with intermediate recycle. Reduced recycle flow rates at constant lactose stream (permeate product) flow rate resulted in slightly better removal of lactose from the milk feed, although this mode of operation increased the protein loss from the final milk retentate product. Increased permeate flow rate at constant recycle rate removed more lactose from the feed but also resulted in more loss of protein. However, at its maximum, the loss of protein reprented only about 6% of the nutritional value of the milk. Under the experimental conditions studied, 58% of the lactose in the original skim milk could be continuously removed for the best combination of recycle and permeate flow rates. The experimental values of flow rates and compositions were reasonably well predicted by a mathematical model of the process.     

Glass transition and the flowability and caking of powders containing amorphous lactose

Many powders contain amorphous components, such as amorphous lactose in milk powders, which when given sufficient conditions of temperature and water content, will mobilise as a high viscosity flow making the particles sticky. This can lead to increased cohesiveness, powder caking and increased adhesion to surfaces. The transition from the glassy state is established by increasing the powder temperature to above its glass transition temperature which can be measured using differential scanning calorimetry. Exposing milk powder to over 10-20 °C above the lactose glass transition makes the powder more sticky, rendering it a lot more cohesive and also increases its adhesion to a stainless steel surface. This glass transition induced stickiness is time-dependent. Over time, crystallisation can take place converting the amorphous lactose into crystalline lactose. Furthermore, the caking behaviour of powders depends on the amount of component present in the amorphous state. Finally, this work presents an approach for applying the measured relationship between the glass transition and water content for predicting caking problems with powders containing amorphous components.     

The chemical composition and nitrogen distribution of chinese yak (maiwa) milk

The paper surveyed the chemical composition and nitrogen distribution of Maiwa yak milk, and compared the results with reference composition of cow milk. Compared to cow milk, yak milk was richer in protein (especially whey protein), essential amino acids, fat, lactose and minerals (except phosphorus). The contents of some nutrients (total protein, lactose, essential amino acids and casein) were higher in the warm season than in the cold season. Higher ratios of total essential amino acids/total amino acids (TEAA/TAA) and total essential amino acids/total non essential amino acids (TEAA/TNEAA) were found in the yak milk from the warm season. However its annual average ratio of EAA/TAA and that of EAA/NEAA were similar to those of cow milk. Yak milk was rich in calcium and iron (p < 0.05), and thus may serve as a nutritional ingredient with a potential application in industrial processing.     

Effects of fat,casein and lactose on high-pressure destruction of Escherichia coli K12 (ATCC-29055) in milk

High-pressure (HP) destruction of Escherichia coli K12 suspended in commercial pasteurized milk (0, 3.25 and 5% fat), peptone water (0.1%), and phosphate buffer (0.2 mol/l Na₂HPO₄ and 0.2 mol/l NaH₂PO₄) supplemented with different amounts of casein or lactose (1–4%) was investigated. HP treatment resulted in the highest level of E. coli destruction in the buffer (possibly because it contained no nutrients), followed by those in peptone water and least in milk. Therefore, milk and peptone provided some baro-protection to the destruction of E. coli during the HP treatment. Fat content in milk between 0, 3.25 and 5% had no significant (P > 0.05) influence on the HP destruction of E. coli. The supplement of either casein or lactose to milk did not influence the level of HP destruction of E. coli. However, the baro-protection became significant during HP treatment when casein or lactose was added the buffer. The buffer solution supplemented with 1–4% casein showed a baro-protective effect equivalent to that in milk. Lactose supplement to buffer also caused baro-protection, though the effect was relatively less pronounced. However, no significant difference in the baro-protection effect was observed among the buffer samples supplemented with different levels (1, 2 and 4%) of lactose or casein. Therefore the major contributors for baro-protection of E. coli in milk during HP treatment appear to be casein and lactose, rather than the fat content.     

Optimization of Whole Milk Powder Processing Variables with Neural Networks and Genetic Algorithms

Spray-dried whole milk powder, one potential ingredient of milk chocolate, was exposed to high shear and elevated temperatures to increase the free fat content and to crystallize the lactose using a twin-screw continuous mixer/processor. Optimal process conditions were determined using neural networks and genetic algorithm optimization. Response surfaces methodology was used to design the experiments to collect data for the neural network modelling. A general regression neural network model was developed to predict the responses of lactose crystallinity and free fat content from the processor screw speed, process temperature, milk powder feed rate and lecithin addition rate. A genetic algorithm was used to search for a combination of the process variables for maximum free fat content and maximum crystallinity. The combinations of the process variables during genetic algorithm optimization were evaluated using the neural network model. The common optimum process conditions to maximize the free fat content and lactose crystallinity were determined to be 20 kg h⁻¹ feed rate, 284 rpm screw speed, 71.1°C process temperature and 0.01 kg h⁻¹ lecithin addition rate.     

Crystallization and Drying of Milk Powder in a Multiple-Stage Fluidized Bed Dryer

The rationale of this study has been to use fluidized beds to crystallize amorphous spray-dried skim milk powders with multiple stages of processing at different temperatures and humidities with the aim of rapidly making mostly crystalline powders. This paper discusses the performance of a multiple-stage fluidized bed dryer, and a combination of crystallization of lactose in spray drying at high humidity (lactose nuclei formation) and subsequent fluidized bed drying. Two different combinations of spray dryer and multi-stage fluidized-bed dryer have been suggested to crystallize lactose in skim milk powder. The results show significant improvements in the crystallinity of the powders. Moisture sorption test and X-ray diffraction analysis were used to assess the crystallinity of the powders. The processed powders that were crystallized in a humid-loop spray drying combined with a two-stage fluidized-bed dryer/crystallizer showed 92% improvement in lower amorphicity by processing at different stages of 70°C, 50% RH and 80°C, 50% RH for 15 minutes. The conventionally spray-dried powders that were crystallized in a three-stage fluidized-bed dryer/crystallizer showed 87% improvement in lower amorphicity (less moisture sorption) by processing at different stages of 60°C, 50% RH; 70°C, 40% RH; and 80°C, 40% RH for 20 minutes. The multiple-stage fluidized bed system showed distinctive potential to crystallize lactose significantly in skim milk powder using an industrial-feasible process.     

Antisolvent vapour precipitation of droplets with multi-components: Non-soluble encapsulation and simultaneous precipitation of soluble materials

A new antisolvent vapour precipitation technique was developed which enables the production of a large amount of micro spheres from a single droplet. This work explores the potential of this technique for encapsulation of oil and in precipitating multi-component solutes from a droplet. Experiments were undertaken on the single droplet drying rig in Monash University, modified to incorporate antisolvent vapour. Using ethanol vapour, lactose micro particles with spiky surfaces were formed. Oil-infused lactose micro particles were also observed delineated by the smooth surfaces analogous to that of full cream milk. Precipitation of multi-component solutes resulted in partial segregation of the protein and lactose. Precipitated particles with different proportions of protein and lactose exhibited contrasting particles. Particles with higher protein content resulted in smaller particle sizes.