在食物模型系统中，壳聚糖和壳寡糖抑制金黄色葡萄球菌及大肠杆菌的效果

Fernandes, J. C., F. K. Tavaria, et al. (2008). "Antimicrobial effects of chitosans and chitooligosaccharides, upon Staphylococcus aureus and Escherichia coli, in food model systems." Food Microbiology

译者：乔莹
背景介绍：

Antimicrobial effects of chitosans and chitooligosaccharides, upon Staphylococcus aureus and Escherichia coli, in food model systems,是葡萄牙Católica Portuguesa大学，主要研究了之前较有争议的壳聚糖分子量与其抑菌活性之间的关系。

近些年，壳聚/寡糖作为食品添加剂在日本、韩国等地广为流行，有多项专利，并已应用到日常食品中。一些文章主要以体外的抑菌试验来判断壳聚糖的抑菌效果，而此文将壳聚/寡糖添加到食物系统中，对不同种微生物的接种量及不同分子量的壳聚/寡糖浓度进行抑菌试验,并探讨糖添加后对食物组分有何影响。

文章分别选取金黄色葡萄球菌（S. aureus）--一种革兰氏阳性菌，大肠杆菌（E. coli）--一种革兰氏阴性菌作为抑制的对象。选取的三种不同分子量壳聚糖分别为628，591，107kDa，2种壳寡糖分子量分别<5 kDa和<3 kDa，脱乙酰度均为80-85%，运用常见的抑菌试验及将其添加到牛奶与苹果汁中进行抑菌测试。抑菌试验发现抑菌的活性依赖于细菌接种量、壳聚/寡糖分子量及浓度。当接种量在每毫升103左右的细菌，4小时内，5种糖组分在不同浓度下（0.5%，0.25%及0.1%）均显示出抑菌活性；在更高的接种量，只有0.1%的浓度显示出抑菌活性。当接种量在每毫升105或107左右的细菌，即不依赖于接菌量的情况下，0.25%的2种壳寡糖表现出选择性抑制效果-可显著抑制E. coli，但并不抑制S. aureus。这点并不同于中高分子量的壳聚糖，在0.5%的浓度下均显示出较强的抑菌活性。当在液体食品系统中，中高剂量的壳聚糖仍可保持其抑菌活性，但在牛奶中抑菌活性较弱些。然而壳寡糖在牛奶中4-8小时即丧失其抑菌的效果。将壳聚糖添加到苹果汁中会降低口感，像是涩味，并且这种涩味随分子量增加而增大。

The objective of this study was to elucidate the controversial relationship between the molecular weight (MW) of chitosans and their antibacterial activity (upon different inoculum levels, at several concentrations). The influence of food components on the activity was also ascertained, as well as acceptance by a sensory panel. All the compounds tested exhibited antibacterial activity against Staphylococcus aureus and Escherichia coli. This activity was shown to be closely dependent on the inoculum level, MW and concentration used. Within 4 h at 103 cells/ml, all five compounds, at every concentration (0.5%, 0.25% and 0.1%, w/v), proved to be bactericidal; for higher inocula, 0.1% (w/v) was only bacteriostatic; at 107 or 105 cells/ml, and independently of the inoculum level, 0.25% (w/v) of any chitooligosaccharide (COS) mixture was sufficient to reduce the E. coli initial population by at least 3 log cycles; COS never exhibited bactericidal action over S. aureus, unlike high and medium MW chitosans—which, at 0.5% (w/v), presented a bactericidal effect even against 107 cells/mL. When incorporated in liquid food matrices, medium and high MW chitosans maintained their activity, for both matrices and bacteria, although a slower activity was noticeable in milk; however, COS lost their activity upon both bacteria in milk after 4–8 h. Furthermore, addition of chitosans to apple juice led to several unpleasant off-flavors, such as astringency and after taste—which increased in magnitude with MW.