乳铁蛋白及其生理功能

乳铁蛋白是一种天然糖蛋白,主要存在于哺乳动物各种外分泌物中。因乳铁蛋白在抑菌、抗病毒、免疫调节、促进铁吸收等方面具有独特生理功能,从而对乳铁蛋白开发和应用具有广阔前景。     

乳铁蛋白的国内外研究动态及趋势

乳铁蛋白是一种铁结合性糖蛋白,具有多种生物学功能,近年来成为国内外研究的热点。本文综述了乳铁蛋白的近期研究热点:活性乳铁蛋白的开发应用,高效表达人乳铁蛋白的转基因技术进展,工业化生产途径的最新研究以及乳铁蛋白的开发应用前景。     

哺乳动物小肠乳铁蛋白受体及其功能的研究进展

乳铁蛋白是哺乳动物体内具有多种生理功能的铁结合性糖蛋白。乳铁蛋白作用的靶细胞及细胞表面的特异性受体是其发挥多种生物功能的基础。本文主要介绍哺乳动物小肠乳铁蛋白受体的结构、结合特性和生理功能;阐述人和小鼠小肠乳铁蛋白受体的特性,及其促进铁离子吸收和调节机体免疫的功能。     

添加乳铁蛋白对延长巴氏奶贮存时间的影响研究

本文对添加乳铁蛋白延长巴氏奶贮存时间进行了研究。乳铁蛋白是从牛初乳中分离出来的一种功能性成分，具有广谱抗菌、抗病毒感染作用，同时还能促进人体对铁的吸收。因此，将乳铁蛋白添加到巴氏奶中，不仅可以增强其抗菌能力，延长保质期，同时还能够提高产品的营养价值。在不同温度下(恒温37℃、常温23℃、冷藏4℃)，在巴氏奶中添加不同浓度(0．025、0．05、0．1mg／ml)的乳铁蛋白，通过对巴氏奶添加乳铁蛋白和不添加乳铁蛋白在不同温度贮存时微生物的变化的比较，观察其微生物生长变化情况；结果表明，添加乳铁蛋白具有延长巴氏消毒奶保藏期的作用。     

乳铁蛋白的补铁作用

实验研究了在磷酸根存在的中性条件下,乳铁蛋白对铁离子溶解作用的影响。随着乳铁蛋白加入量的增加,上清液中二价铁和三价铁的浓度呈线性增加,表明乳铁蛋白对二价铁和三价铁均具有明显的增溶作用。乳铁蛋白可以使铁的溶解度提高60~70倍,远远超过其分子的含铁量,这样,乳铁蛋白必然能够成为一种治疗缺铁性贫血的功能性食品的重要添加成分。     

乳铁蛋白分离纯化研究进展

乳铁蛋白是一种非血红素转铁蛋白,与血清转铁蛋白、卵转铁蛋白和黑素转铁蛋白共同组成转铁蛋白家族。乳铁蛋白是一种多功能性的糖蛋白,具有很多的活性,被广泛应用于保健食品、配方奶粉、医药等领域中。归纳传统的与新开发的乳铁蛋白的回收方法,比较每种方法在提取回收乳铁蛋白中的优势与不足,对今后开发出更佳具有优势的乳铁蛋白的回收方法提供一些思路。     

重组人乳铁蛋白抗氧化活性研究

目的考察重组人乳铁蛋白自身及其在奶粉中的抗氧化活性。方法通过二苯代苦味肼基(DPPH)自由基抑制率、羟基自由基抑制率、超氧阴离子自由基抑制率、还原能力和抑制大鼠肝脏体外脂质过氧化等试验评价重组人乳铁蛋白和牛乳铁蛋白的体外抗氧化性能。结果重组人乳铁蛋白和牛乳铁蛋白的浓度与DPPH自由基抑制率、抑制羟基自由基能力、抑制超氧阴离子自由基能力和还原能力之间呈明显剂量-效应关系,且差异有统计学意义(P0.05);样本和浓度之间没有交互作用,重组人乳铁蛋白和牛乳铁蛋白在不同浓度下所得值的趋势相同。重组人乳铁蛋白和牛乳铁蛋白在对大鼠肝组织匀浆抗氧化性影响差异有统计学意义(P0.05),不同浓度乳铁蛋白之间差异有统计学意义(P0.05)。结论重组人乳铁蛋白和牛乳铁蛋白具有一定的抗氧化活性,可以添加到保健品或者化妆品中作为天然抗氧化剂。     

乳铁蛋白和乳铁素的抗菌活性比较

牛乳铁蛋白是从牛乳中提取出来的一种铁结合性糖蛋白，牛乳铁素是从牛乳铁蛋白N-端水解下来的25个氨摹酸残荩。它们具有多种乍物学功能，其中的广谱抗菌性尤为引人注目。本实验以牛初乳中提取的乳铁蛋白及其水解产物乳铁素为研究对象，选取大肠杆菌为实验菌株，进行铁饱和乳铁蛋白和缺铁性乳铁蛋白、乳铁素对大肠杆菌生长抑制的比较研究。研究结果表明：铁饱和乳铁蛋白、缺铁性乳铁蛋白和乳铁索的最小抑菌浓度分别为6mg／ml、3mg／ml和15μg／ml，乳铁素的最小杀菌浓度为30μg／ml。乳铁蛋白水解后，经纯化获得的乳铁素，其抗菌能力较缺铁性乳铁蛋白增加200倍，较铁饱和乳铁蛋白增加400倍。     

三元公司乳品新技术研究最新进展——人乳铁蛋白基因及真菌中表达(连载四)

乳铁蛋白作为一种活性蛋白，在功能营养食品及医药等方面具有广阔的应用前景。但很久以来，如何获得廉价的人乳铁蛋白一直是开发乳铁蛋白遇到的最大难题，而利用基因工程技术生产重组蛋白给乳铁蛋白的开发利用提供了可行性途径，这也是乳铁蛋白研究的发展趋势。随着基因工程技术和遗传学的迅速发展，以及人们对乳铁蛋白基因及其表达调控机制深人了解，重组生产将成为的人乳铁蛋白来源的主要渠道。     

浅谈乳铁蛋白在肉类保鲜中的应用

乳铁蛋白作为一种天然的、具有许多特殊生理功能的糖蛋白,已经引起国际上广泛关注。本文叙述了乳铁蛋白的抗菌机制,包括:乳铁蛋白的结构特性、抗菌作用、抗菌机制等,并对其在肉类保鲜中的应用前景作了展望。     

One-step isolation of lactoferrin using immobilized monoclonal antibodies

Immunoaffinity columns made with monoclonal antibodies to either human or bovine lactoferrins were prepared to isolate human lactoferrin or bovine lactoferrin from milks by a single chromatographic step. Recoveries of human lactoferrin and bovine lactoferrin were 98 and 97%, respectively. The human lactoferrin recovered from defatted human colostrum was 98% pure with 93% iron-binding capacity. Amount of recovered bovine lactoferrin, as well as purity and iron-binding capacity, varied widely depending on the source of bovine milks and pretreatments (particularly pasteurization temperature). The best source to isolate bovine lactoferrin was raw skim milk yielding a protein 97% pure and with a 99% iron-binding capacity. Thus, immunoaffinity chromatography provides an effective one-pass isolation of highly pure human or bovine lactoferrin with reasonable recovery and iron-binding capacity.     

Effect of lactoferrin in combination with penicillin on the morphology and the physiology of Staphylococcus aureus isolated from bovine mastitis

The objective of the present study was to evaluate the therapeutic potential of bovine lactoferrin or lactoferricin in combination with penicillin G against Staphylococcus aureus. Minimal inhibitory concentrations of lactoferrin, lactoferricin, penicillin, and combinations of lactoferrin or lactoferricin with penicillin were determined for 15 S. aureus strains including several strains resistant to beta-lactam antibiotics. The fractional inhibitory concentration index indicated a synergistic effect between lactoferrin and penicillin. Combination of lactoferrin with penicillin increased the inhibitory activity of penicillin by two- to fourfold and reduced the growth rate in S. aureus strains tested, whereas the increase in the inhibitory activity of lactoferrin by penicillin was 16- to 64-fold. The addition of iron to the medium containing a combination of penicillin and lactoferrin had no effect on growth inhibition. Electron microscopy revealed that concentration below the minimal inhibitory concentrations of penicillin induced important ultrastructure alterations, which were further enhanced by the presence of lactoferrin. When S. aureus cells were grown in the presence of a combination of penicillin and lactoferrin, changes in the protein profile of the bacteria, including the disappearance of several protein bands due to the presence of lactoferrin, were observed. These data suggest that bovine lactoferrin or lactoferricin in combination with beta-lactam antibiotics can increase the antibacterial activity of these antibiotics against S. aureus resistant to antibiotics.     

A probe for capture and Fe3+-induced conformational change of lactoferrin selected from phage displayed peptide libraries

Linear pentadecamer and cyclic hexamer peptide phage libraries were used to isolate phage clones with binding affinity toward lactoferrins purified from human and bovine milk. Phage clones with high specificity toward lactoferrin were selected with different binding strengths depending on the sequence of the peptide displayed by the phage. Phages coated to a microtiterplate were able to capture lactoferrin from crude milk samples without prior treatment. One of the selected sequences, EGKQRR, failed to bind to lactoferrin. In contrast, a branched tree-peptide bearing 4 EGKQRR sequences did bind to lactoferrin (Kd approximately 29 microM) and was also capable of inhibiting the binding of the phage to lactoferrin (IC(50) approximately 17 microM), indicating that avidity was important. Unexpectedly, the affinity of the phage for lactoferrin was influenced by the amount of bound Fe(3+), with a much lower affinity when lactoferrin was saturated with Fe(3+) as compared with the iron-depleted or partially saturated (natural) lactoferrin. As the phage does not bind to the Fe(3+)-binding site, the difference in binding affinity is due to differences in conformation of lactoferrin induced by Fe(3+). These results demonstrate that avidity or multipoint attachment and Fe(3+)-induced conformational changes play an important role in the binding of the selected phage to lactoferrin. Thus, we could demonstrate that, by the use of selected phage clones, we are able not only to detect lactoferrin, but also to capture lactoferrin from crude milk samples. Furthermore, the extent of phage binding provides additional information about the iron content and the concomitant conformation of lactoferrin.     

Lactoferrin concentration during involution of the bovine mammary gland.

Electroimmunodiffusion assay was used to quantitate changes in lactoferrin concentration in mammary secretions during involution of the bovine mammary gland. Concentration of lactoferrin began to increase 2 to 4 days after cessation of regular milking and continued to increase linearly at a rate of 1.15 mg/ml per day as a result of increased net synthesis of lactoferrin during the first 14 to 21 days of involution. Maximum lactoferrin concentration (approximately 20 mg/ml) was attained after 3 to 4 wk of involution. These changes represent a 100-fold increase in lactoferrin concentration over that in normal milk. Maximum lactoferrin concentration was variable between cows. In some cows, the concentration of lactoferrin plateaued at less than 10 mg/ml after 10 days of involution. In others, much higher lactoferrin concentrations of 75 to 100 mg/ml were measured. Lactoferrin concentration decreased markedly prior to parturition and onset of lactation. The increase in lactoferrin concentration during mammary gland involution appeared to be related closely to the process of involution.     

Kinetic Parameters for Denaturation of Bovine Milk Lactoferrin

Kinetic parameters for heat-induced denaturation of lactoferrin under different conditions were determined over a temperature range 72–85°C. Denaturation of lactoferrin could be described by first-order reaction kinetics. Lactoferrin is denatured more rapidly in its apo form than in the iron-saturated form. Both apolactoferrin and iron-saturated lactoferrin are more heat-sensitive when treated in milk than in phosphate buffer. Values of change in enthalpy of activation of lactoferrin denaturation are high which indicates that a large number of bonds are broken. The association of lactoferrin with β-lactoglobulin does not significantly influence the change in enthalpy of activation of lactoferrin denaturation.     

Potent bactericidal activity of bovine lactoferrin hydrolysate produced by heat treatment at acidic pH.

A hydrolysate of bovine lactoferrin produced by heat treatment under acidic conditions had antibacterial activity at concentrations of 10 micrograms/ml in the culture medium. The optimal degree of hydrolysis for this activity was about 10%. Heat-treated lactoferrin, treated at pH 2.0 and 120 degrees C for 15 min and degree of hydrolysis of about 10%, had no Fe-binding capacity (0%) and less antigenicity (about 10(-6) than untreated lactoferrin. Heat-treated lactoferrin increased in antibacterial activity, and the activity was maintained in an Fe-rich medium. After fractionation of heat-treated lactoferrin by reverse-phase HPLC, several peptide fractions were found that had strong antibacterial activity. It was suggested that lactoferrin latently contains at least one bactericidal domain that is activated upon release by limited acid hydrolysis of the protein. The bactericidal activity of the peptide fragments of lactoferrin was shown to have no relation to Fe chelation, in contrast with the antibacterial mechanism of native lactoferrin.     

乳铁蛋白免疫增强作用评价

根据我国免疫调节功能食品的评价方法,对乳铁蛋白的免疫调节作用进行评价。在实验中,采用Balb/c小鼠建立免疫低下模型,以不同剂量(100μg/mL、1mg/mL、10mg/mL)乳铁蛋白灌胃实验动物,分别进行免疫脏器质量、细胞免疫功能、体液免疫功能、单核- 巨噬细胞功能指标的检测。结果表明,在灌胃剂量为0.1～10mg/mL范围内,结果均为阳性,且以1mg/mL 最为显著。判定乳铁蛋白具有增强免疫力,但与剂量有关。     

牛乳铁蛋白及乳铁素的生产与应用现状

牛奶中的乳铁蛋白和其水解产物乳铁素具有多种生物活性功能。综述了国外的乳铁蛋白和乳铁素生产、分离和纯化的方法,并介绍了乳铁蛋白和乳铁素作为食品保存剂、抗氧化剂、营养强化剂、免疫强化剂、免疫调节剂等应用的现状。展望了我国乳铁蛋白和乳铁素生产的前景。     

Antimicrobial activity of lactoferrin against foodborne pathogenic bacteria incorporated into edible chitosan film

The objectives of this research were to develop and characterize edible chitosan film containing lactoferrin as a natural antimicrobial agent, and to investigate the combination effects of lactoferrin with lysozyme in chitosan film against the growth of Escherichia coli O157:H7 and Listeria monocytogenes. Chitosan films containing lactoferrin, lysozyme, or nisin were fabricated, and the antimicrobial concentrations were 0.5, 1, or 2 mg in a circular disc of chitosan film. Three concentrations of lactoferrin or EDTA (0.28, 0.56, or 1.12 mg per disc) were also incorporated into the chitosan film containing lysozyme to investigate the combination effects of lactoferrin. The water barrier properties of the chitosan films containing lactoferrin were characterized. The antimicrobial activities against E. coli O157:H7 and L. monocytogenes were determined using the agar diffusion assay and cell count assay. The chitosan films containing lactoferrin less than 1 mg per disc did not alter the water vapor permeability of the chitosan film. Although the film containing lysozyme exhibited significant antimicrobial activity, the incorporation of lactoferrin alone into chitosan film did not exhibit significant antimicrobial activity against both E. coli O157:H7 and L. monocytogenes. However, the combination of lactoferrin with lysozyme-containing chitosan film significantly decreased the growth of E. coli O157:H7, exhibiting a comparable effect to that of the combination of EDTA with lysozyme (P < 0.05). Furthermore, the combination of lactoferrin with lysozyme in chitosan film exhibited greater reduction in the growth of L. monocytogenes than did the combination EDTA with lysozyme, resulting in an approximate 3-log reduction.