乳酸链球菌素(Nisin)从乳酸链球菌发酵液中提取的一类多肽化合物，可以抑制大多数革兰氏阳性细菌，并对芽孢杆菌的孢子有强烈的抑制作用。乳酸链球菌素作为新型、高效、无毒、安全的天然食品防腐剂被广泛应用于食品保鲜防腐中，到目前为止，全世界已有五十多个国家和地区批准Nisin作为食品防腐剂。

乳酸链球菌素是由34个氨基酸残基组成，分子量约为3500Da，结构式中含有多个游离氨基，这导致其溶解性、稳定性都与溶液的pH值密切相关。其溶解度随pH值的下降而提高，pH2.5时溶解度为12%，pH值为5.0时下降1.4%，在中性及碱性条件下几乎不溶解。其在酸性条件下较稳定，有资料显示在pH2.0条件下可耐受高温处理(121℃，15min)而无活力损失，而在中性或碱性条件下即发生失活。

乳酸链菌素的用途广泛，所以不同行业采取不同的质量标准，这也导致乳酸链球菌素分离纯化工艺的多样性。

食品级乳链球菌素通常含盐量较高，产品纯度相对较低，采用以下工艺步骤：

The fermentation broth is acidified to inactivate the bacteria and precipitate the proteins. The solid-liquid separation and protein removal are achieved through ceramic membranes. The concentration is increased to enhance the Nisin content. Sodium chloride is added for salting out. The product is obtained through spray drying or after filtration, washing and drying. 

High-purity lysozyme usually has limited requirements for impurities such as analogues, chloride ions, and residual organic solvents. To meet the quality standards, more refined separation methods are often employed. The following process steps are adopted:

The impurities not related to the main product are removed through organic membrane decolorization. The similar impurities are removed by using large-pore adsorption resin or C18 preparative chromatography to improve the purity. Then, the product is concentrated through organic membrane and precipitated with organic solvents to finally obtain a high-purity solid product. 

In the separation and purification process of lysozyme, ceramic membrane separation technology, as one of the core technologies, holds a significant position in the industry of extracting lysozyme from fermentation broth due to its advantages such as high separation accuracy, high temperature resistance, and resistance to acids and alkalis. 

Wuhan Bona uses its independently developed and manufactured ceramic membranes to achieve high-precision and high-throughput filtration of lactic acid streptococcal acidification liquid. Combined with the control of filtration process parameters, it significantly reduces energy consumption and lowers production costs. 

The intermediate process liquid of lactic acid bacterium lysozyme has a relatively low acidity (approximately pH 2-3). By selecting organic membranes with excellent acid resistance, the purpose of low-temperature filtration for impurity removal, concentration, and desalination can be achieved. This replaces the traditional vacuum concentration process and avoids the phenomenon of high-temperature degradation, thus enabling high-quality production of lactic acid bacterium lysozyme. 

For many years, Wuhan Bona has been dedicated to the development of application processes for membrane separation technology. By integrating processes, membranes and equipment, it has accumulated rich experience in product purification and engineering-scale expansion. This has not only solved manufacturing challenges but also improved product quality, and together with customers, it has enhanced the technical level of the industry