酶法降低牛乳蛋白致敏性的研究进展

酶解牛乳是牛乳加工中的常用技术之一,并且作为低致敏牛乳制备的关键技术已成功应用于实际中。本文综述牛乳中主要过敏原及酶解机制,并详细介绍不同种类的单一酶解和复合酶解用于降低牛乳蛋白致敏性的研究,以期为制备和生产低致敏性乳制品提供一定依据和理论基础。     

热处理对乳蛋白消化特性影响的研究进展

乳蛋白为人体提供必需氨基酸,生物利用率高,是优质的蛋白质来源。在乳制品加工过程中,热处理会改变乳蛋白的空间结构及化学修饰,从而对乳蛋白的消化特性产生影响。热处理程度越剧烈,乳蛋白在胃中形成的凝块越松软,且变性乳清蛋白形成的聚集体有利于胃蛋白酶的消化。同时,热处理也改变了胃消化动力学及乳蛋白衍生生物活性肽的释放。热处理诱导的化学修饰如美拉德反应产物被认为降低了整体消化率,但近期研究也指出了其作为益生元的潜在功能。文章梳理了热处理对乳蛋白结构、功能性和营养性的影响,以期为乳制品的热处理工艺优化提供借鉴。     

热处理对鲜牛乳和复原乳蛋白多态性的影响

利用三种模拟生产加热处理,来研究鲜牛乳和复原乳蛋白多态性变化。通过调控pH和加热温度,发现鲜牛乳和复原乳中α-乳白蛋白、β-乳球蛋白、非沉淀酪蛋白和蛋白胶束的粒径大小均变化差异显著。      

热致乳蛋白微米凝胶的特性

乳蛋白在非常规的条件下,通过控制聚合程度,会形成一种特殊结构的蛋白质聚合物,即微米凝胶。研究了这种微凝胶与常规乳蛋白聚合物之间的差异,分析了浊度、Zeta-电位、DSC及流变学性质的变化。     

热处理对牛乳蛋白还原性的影响

借鉴AOAC的蛋白-还原物质（PRS）测定法,对不同受热处理的牛乳以及酪蛋白、乳清的还原性进行了检测研究。通过比较、分析不同热处理牛乳PRS,得到了区分巴氏乳与其它热处理牛乳PRS,同时得出乳清蛋白与酪蛋白之间的热反应性是影响牛乳蛋白还原性的主要原因,为进一步研究乳清蛋白的热变性以及乳清蛋白与酪蛋白之间的热反应奠定了基础。     

GDL诱导乳蛋白酸凝胶特性的研究进展

综述了国内外GDL(葡萄糖酸-δ-内酯,Glucono-δ-lactone)诱导乳蛋白质酸凝胶特性的研究方法,并分析了影响凝胶特性的主要因素。目前,研究乳蛋白酸凝胶特性的方法主要有测定凝胶的流变学特性、凝胶的脱水收缩的能力以及凝胶的质构等。乳蛋白在酸凝胶过程中不仅受到GDL添加量的影响,还受到凝胶温度、预热处理及离子强度的影响。     

超高压对食品凝胶特性影响的研究进展

蛋白质和多糖是食品中两大重要组成成分,凝胶性是它们共有的功能特性之一,超高压技术可改变它们的空间构象并进一步相互作用而形成凝胶。本文对超高压技术的概念、原理、特点进行概述,并将其对蛋白凝胶、多糖凝胶、蛋白-蛋白凝胶、多糖-多糖凝胶、蛋白-多糖凝胶的特性影响进行分析,旨在全面了解超高压技术对食品凝胶特性的影响。在此基础上提出该领域未来可能的研究方向,为扩大其应用范围提供理论依据。      

蛋白质热处理对绿豆蛋白-高酰基结冷胶乳液凝胶性质的影响

本实验将绿豆蛋白在40、55、70、85、100℃的条件下热处理15、30、45、60、120 min,制备绿豆蛋白-高酰基结冷胶乳液凝胶,分析了凝胶的硬度、持水性、色度、溶解度、蛋白质二级结构及凝胶微观结构,以探究绿豆蛋白热变性对其形成乳液凝胶的性质影响.研究表明:随着热处理温度提高,热处理时间延长,凝胶硬度、持水性...     

鸡蛋蛋白质凝胶特性影响因素的研究进展

为了进一步了解不同因素对鸡蛋蛋白质凝胶特性的影响,国内外研究者已经针对性的进行了大量的研究工作.本文综合论述了鸡蛋中蛋白质的组成和凝胶的形成机理,分析了温度、压力、pH、酶、盐、蛋白质浓度、处理时间等因素对鸡蛋蛋白质凝胶特性的影响,其中温度、压力、pH、盐、处理时间几个因素对鸡蛋蛋白质凝胶特性的影响研究已较为全面,但生...     

牛乳蛋白生物脱敏技术研究进展

牛乳及乳制品具有重要的营养价值,但是牛乳过敏会导致患者出现呼吸道问题,严重者甚至会休克或死亡,因此低致敏乳制品的研发具有重要意义。目前常见的牛乳脱敏技术被分为物理法、化学法和生物法,其中生物法更具有前景。简述了牛乳的主要过敏蛋白,阐述了生物酶法、发酵作用和转基因技术这3种生物脱敏技术。其中生物酶法仍然是目前最具有前景的生物降敏方法,水解酶将蛋白质降解为小分子多肽,但在降敏的同时会产生苦味物质,因此,近年来交联酶在该领域的作用逐渐被重视。发酵作用可以降低牛乳致敏性,但其降低程度有限,需与其他处理联合使用。转基因技术可以通过对线性表位氨基酸进行突变,以降低牛乳致敏性。另外,介绍了目前常见的几种牛乳致敏性检测方法,以期望为未来低致敏乳制品的研究提供理论依据。     

Short communication: Effects of nanofiltration and evaporation on the gel properties of milk protein concentrates with different preheat treatments

This study aimed to evaluate the effects of different concentration methods (nanofiltration and evaporation) and heat treatments on the gel properties of milk protein concentrate (MPC). The MPC gels were produced using glucono-δ-lactone (GDL) as an acidifier with different preheat treatments (30 min at 80°C and 5 min at 92°C). We then evaluated the effect of preheat treatments on MPC gel properties, including storage modulus (G′), loss tangent (tan δ), firmness, whey separation, and microstructure. The results indicated that without preheating, evaporation (EP)-MPC had higher G′ and firmness, and lower tan δ and whey separation than nanofiltration (NF)-MPC. These results suggest that EP-MPC produced a better acid-induced gel than NF-MPC when no preheat treatments were performed. After preheating, however, except for a very small difference in the final G′ (EP-MPC was higher), the 2 MPC did not differ significantly in firmness, final tan δ, or whey separation. Additionally, compared with the gel of unheated MPC, both preheat-treated gels (NF-MPC and EP-MPC) achieved increased G′ and firmness and decreased tan δ and whey separation. The preheat-treated MPC also displayed a more flexible-stranded network. These findings demonstrate that, given a suitable heating treatment, NF-MPC compares favorably with EP-MPC in achieving desired gel properties.     

Effects of milk heat treatment and solvent composition on physicochemical and selected functional characteristics of milk protein concentrate

Milk protein concentrate (MPC) powders (～81% protein) were made from skim milk that was heat treated at 72°C for 15 s (LHMPC) or 85°C for 30 s (MHMPC). The MPC powder was manufactured by ultrafiltration and diafiltration of skim milk at 50°C followed by spray drying. The MPC dispersions (4.02% true protein) were prepared by reconstituting the LHMPC and MHMPC powders in distilled water (LHMPC_w and MHMPC_w, respectively) or milk permeate (LHMPC_p and MHMPC_p, respectively). Increasing milk heat treatment increased the level of whey protein denaturation (from ～5 to 47% of total whey protein) and reduced the concentrations of serum protein, serum calcium, and ionic calcium. These changes were paralleled by impaired rennet-induced coagulability of the MHMPC_w and MHMPC_p dispersions and a reduction in the pH of maximum heat stability of MHMPC_p from pH 6.9 to 6.8. For both the LHMPC and MHMPC dispersions, the use of permeate instead of water enhanced ethanol stability at pH 6.6 to 7.0, impaired rennet gelation, and changed the heat coagulation time and pH profile from type A to type B. Increasing the severity of milk heat treatment during MPC manufacture and the use of permeate instead of water led to significant reductions in the viscosity of stirred yogurt prepared by starter-induced acidification of the MPC dispersions. The current study clearly highlights how the functionality of protein dispersions prepared by reconstitution of high-protein MPC powders may be modulated by the heat treatment of the skim milk during manufacture of the MPC and the composition of the solvent used for reconstitution.     

湿热处理对牛奶蛋白复合纤维纱线结构和性能的影响

由于牛奶蛋白复合纤维染整加工中经常伴随着湿热加工,因此,着重研究了湿热处理对牛奶蛋白复合纤维结构和性能的影响.结果表明,湿热处理对牛奶蛋白复合纤维的收缩率、强力、白度及表面形态影响显著,对牛奶蛋白复合纤维结构及结晶形态影响很小.随着湿热处理温度的升高,牛奶蛋白复合纤维织物的顶破强力稳步提高,而白度出现下降;当湿热处理温度大于100℃时,收缩率的增幅明显变大,且手感变硬;特别当湿热处理温度超过130℃时,纤维的表面已经几乎没有平整的地方.因此,牛奶蛋白复合纤维宜采用90、100℃为其最高湿热加工温度.     

Rheological properties of rennet gels containing milk protein concentrates

Different milk protein concentrates (MPC), with protein concentrations of 56, 70, and 90%, were dispersed in water under different treatments (hydration, shear, heat, and overnight storage at 4°C), as well as in a combination of all the treatments in a factorial design. The particle size distribution of the dispersions was then measured to determine the optimal conditions for the dispersion. Heating at 60°C for 30 min with 5 min of shear was chosen as the best condition to dissolve MPC powders. The samples were also characterized for composition, presence of protein aggregates, and ratio of calcium to protein. The total calcium present in MPC increased with increasing concentration of protein; however, the total calcium-to-protein ratio was lower in MPC90 than in MPC56 and MPC70. The level of whey protein denaturation, the presence of κ-casein-whey protein aggregates in the supernatant after centrifugation, and the amount of caseins dissociated from the micelle increased as the protein concentration in the powder increased. The total amount of casein macropeptide released was lower in samples from powders with a higher protein concentration than for MPC56 or the skim milk control. The gelation behavior of reconstituted MPC was tested in systems dispersed in water (5% protein) as well as in systems dispersed in skim milk (6% protein). The gelation time of MPC dispersions was considerably lower and the gel modulus was higher than those of reconstituted skim milk with the same protein concentration. When MPC dispersions were dialyzed against skim milk, a significant decrease in the gelation time and modulus were shown, with a complete loss of gelling functionality in MPC90 dispersed in water. This demonstrated that the ionic equilibrium was key to the functionality of MPC.     

酶解乳蛋白制取乳源肽的研究

用酸性蛋白酶、中性蛋白酶和碱性蛋白酶对牛乳蛋白进行水解，研究了水解工艺，并通过正交试验对工艺进行了优化。结果为：酸性蛋白酶水解牛乳蛋白的最佳工艺条件是：水解温度50℃，时间120min，pH值3．0，加酶量8．0％；中性蛋白酶水解温度50℃，时间90min，pH值7．0，加酶量1．60％；碱性蛋白酶水解温度60℃，时间105min，pH值9．0，加酶量8．0％。中性蛋白酶水解物苦昧最小，最适宜作食品。     

Effect of homogenization and heat treatment on the behavior of protein and fat globules during gastric digestion of milk

The effects of homogenization and heat treatment on the formation and the breakdown of clots during gastric digestion of whole milk were investigated using a human gastric simulator. Homogenization and heat treatment led to formation of coagula with fragmented and crumbled structures compared with the coagulum formed from raw whole milk, but a larger fraction of the protein and more fat globules were incorporated into the coagula induced by action of the milk-clotting enzyme pepsin. The fat globules in the whole milk appeared to be embedded in the clots as they formed. After formation of the clot, the greater numbers of pores in the structures of the clots formed with homogenized milk and heated whole milk led to greater rates of protein hydrolysis by pepsin, which resulted in faster release of fat globules from the clots into the digesta. Coalescence of fat globules occurred both in the digesta and within the protein clots no matter whether they were in homogenized or heated milk samples. The formation of clots with different structures and hence the changes in the rates of protein hydrolysis and the release of milk fat into the digesta in the stomach provide important information for understanding the gastric emptying of milk and the potential to use this knowledge to manipulate the bioavailability of fat and other fat-soluble nutrients in dairy products.     

热处理引起牛乳风味变化的研究进展

热处理是各种乳制品生产过程中不可或缺的工艺步骤,热处理过程中乳体系的风味组成会发生变化。近年来,不同乳制品的风味日益引起国内外学者和消费者的关注。本文介绍了新鲜牛乳中风味物质的基本特性、风味物质的形成途径及乳中异味的来源;探讨了热处理过程中主要风味前体发生的变化;阐述了加热、浓缩、干燥等热处理对乳制品中风味组成的影响及其对储藏过程中风味变化的作用,为乳制品加工中热处理的潜在影响提供理论参考。     

Rheological and structural properties of differently acidified and renneted milk gels

In this study we assessed the rheological and structural properties of differently acidified and renneted milk gels by controlling pH value and renneting extent. Skim milk were exactly renneted to 4 extents (20, 35, 55, and 74%) and then direct acidified to the desired pH (4.8, 5.0, 5.2, 5.5, 5.8, and 6.2), respectively. Rheological properties were assessed by dynamic rheological measurements, structural properties were studied by spontaneous whey separation and confocal laser scanning micrograph, and protein interactions were studied by dissociation test. Results showed that minimally renneted milk samples (20 and 35%) formed weak gels with low storage modulus, and the acidification range within which gels could form was narrow (pH ≤5.2). Highly renneted milk samples formed more gels with high storage modulus. The results of this study revealed that acidification determined the structural properties of highly renneted milk gels. As pH increased from 5.0 to 6.2, highly renneted milk gels had lower loss tangent, decreased spontaneous syneresis, and smaller pores. For both the low and high rennetings, divalent calcium bonds contributed less at low pH than at high pH. In conclusion, renneting increased the pH range suitable for gel formation; acidification determined the spontaneous syneresis and microstructure of highly renneted milk gels.     

Solubility of commercial milk protein concentrates and milk protein isolates

High-protein milk protein concentrate (MPC) and milk protein isolate (MPI) powders may have lower solubility than low-protein MPC powders, but information is limited on MPC solubility. Our objectives in this study were to (1) characterize the solubility of commercially available powder types with differing protein contents such as MPC40, MPC80, and MPI obtained from various manufacturers (sources), and (2) determine if such differences could be associated with differences in mineral, protein composition, and conformational changes of the powders. To examine possible predictors of solubility as measured by percent suspension stability (%SS), mineral analysis, Fourier transform infrared (FTIR) spectroscopy, and quantitative protein analysis by HPLC was performed. After accounting for overall differences between powder types, %SS was found to be strongly associated with the calcium, magnesium, phosphorus, and sodium content of the powders. The FTIR score plots were in agreement with %SS results. A principal component analysis of FTIR spectra clustered the highly soluble MPC40 separately from the rest of samples. Furthermore, 2 highly soluble MPI samples were clustered separately from the rest of the MPC80 and MPI samples. We found that the 900 to 1,200 cm⁻¹ region exhibited the highest discriminating power, with dominant bands at 1,173 and 968 cm⁻¹, associated with phosphate vibrations. The 2 highly soluble MPI powders were observed to have lower κ-casein and α-_S1-casein contents and slightly higher whey protein contents than the other powders. The differences in the solubility of MPC and MPI were associated with a difference in mineral composition, which may be attributed to differences in processing conditions. Additional studies on the role of minerals composition on MPC80 solubility are warranted. Such a study would provide a greater understanding of factors associated with differences in solubility and can provide insight on methods to improve solubility of high-protein milk protein concentrates.     

Efficacy of a novel whey protein gel complex to increase the unsaturated fatty acid composition of bovine milk fat

A novel whey protein emulsion gel (WPEG) complex was developed to protect dietary unsaturated fatty acids from rumen biohydrogenation with the goal of modifying the fatty acid composition of milk fat. Three experiments were conducted with WPEG complexes made from either whey protein concentrate containing 80% crude protein, whey protein isolate, or whey protein concentrate high-gel capacity. Each experiment lasted 3 wk. All cows received a basal total mixed ration (TMR). During wk 1 and 3, all cows received only the TMR. During wk 2, 3 control cows received 330 g/d of soybean oil added to the TMR, and the other 3 cows received 330 g/d of soybean oil in one of the WPEG complexes. During wk 2, C18:2 increased from 3.29 to 5.88 g/100 g of fat in Experiment 1, 2.91 to 7.42 g/100 g of fat in Experiment 2, and 3.57 to 6.56 g/100 g of fat in Experiment 3 for WPEG cows. Fatty acid C18:3 increased from 0.51 to 0.84, 0.52 to 1.15, and 0.51 to 0.97 g/100 g of fat for Experiments 1, 2, and 3, respectively, for WPEG cows. Higher proportions of C18:1 trans-9 in milk fat of control cows compared with WPEG cows were seen in all experiments. The proportion of C18:1 trans-11 was also higher in control cows in Experiments 1 and 2, but not in Experiment 3. The WPEG complexes successfully protected unsaturated fatty acids from rumen biohydrogenation and resulted in an increase in the unsaturated fatty acid composition of milk fat produced by Holstein cows without increasing the trans 18-carbon monoenes.