Lactoferrin is an iron-binding glycoprotein with a molecular weight of 80 kDa, belonging to the transferrin family. Lactoferrin is highly abundant in colostrum and milk, and较低 in mucosal secretions such as tears, saliva, semen, nasal and bronchial secretions, bile, and gastrointestinal fluid. In addition, lactoferrin is also a component of neutrophils. In 1939, Sorensen et al. obtained a red protein when separating whey proteins; Polis et al. also obtained a partially purified red protein when isolating Lp. However, it was not until 1959 that Groves obtained pure red substance by chromatography and confirmed that this red substance was an iron-binding glycoprotein, naming it lactoferrin.
Lactoferrin was discovered by scientist Johanson Bengt in human milk in 1960. Subsequently, scientists such as Baggin found this protein in body fluids and various cells of some organisms and began extensive research. Studies have shown that lactoferrin (LF) is a natural protein in animal colostrum, a multifunctional protein with broad-spectrum antibacterial effects, capable of regulating iron balance in the body and modulating immunity.
Lactoferrin has a very high affinity for iron ions, 250 to 300 times that of transferrin. Based on differences in iron binding, lactoferrin can be divided into three types: iron-depleted, half-iron-saturated, and iron-saturated. Different types of lactoferrin have different abilities to resist heat denaturation from pasteurization, with the iron-saturated type having the strongest resistance and the iron-depleted type the weakest. Lactoferrin can not only bind Fe3+ and Fe2+ but also Cu2+, Mn2+, and Zn2+.
Regarding the thermal stability of lactoferrin, studies have found that heat treatment at 72°C for 20 seconds or 135°C for 8 seconds hardly affects the iron-binding capacity of lactoferrin, but prolonging the treatment time at either temperature reduces the iron-binding capacity. Heat treatment at 85°C for 10 minutes does not affect the antibacterial activity of lactoferrin. Additionally, studies have shown that under pH 2.0 or pH 3.0 conditions, after treatment at 120°C for 5 minutes, lactoferrin degrades, but the degradation product has higher antibacterial activity than before treatment. This experimental result led to the discovery of the existence of lactoferrin active peptides. Lactoferrin has antibacterial effects on both Gram-positive and Gram-negative bacteria, but its effect on Gram-negative bacteria is stronger. The iron saturation of lactoferrin is negatively correlated with antibacterial activity. Changes in environmental pH affect the inhibitory effect of lactoferrin on Gram-positive bacteria but have little effect on Gram-negative bacteria. The best antibacterial effect is achieved at pH 7.5–8.0. Pasteurization below 70°C does not affect the antibacterial activity of lactoferrin; an increase in HCO3- concentration helps enhance its antibacterial activity.
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