Fernandes João C, Tavaria Freni K, Soares José C, Ramos Oscar S, João Monteiro M, Pintado Manuela E, Xavier Malcata F
Escola Superior de Biotecnologia, Universidade Católica Portuguesa, Rua Dr. António Bernardino de Almeida, P-4200-072 Porto, Portugal.
Food Microbiol. 2008 Oct;25(7):922-8. doi: 10.1016/j.fm.2008.05.003. Epub 2008 May 23.
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 4h at 10(3) 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 10(7) or 10(5) 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 10(7) 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 4-8h. 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.
本研究的目的是阐明壳聚糖的分子量（MW）与其抗菌活性之间存在争议的关系（在不同接种水平、几种浓度下）。还确定了食品成分对活性的影响以及感官小组的接受程度。所有测试的化合物均对金黄色葡萄球菌和大肠杆菌表现出抗菌活性。结果表明，这种活性密切依赖于接种水平、分子量和所用浓度。在10³ 个细胞/mL的情况下，4小时内，所有五种化合物在每种浓度（0.5%、0.25%和0.1%，w/v）下均被证明具有杀菌作用；对于更高的接种量，0.1%（w/v）仅具有抑菌作用；在10⁷ 或10⁵ 个细胞/mL时，且与接种水平无关，任何壳寡糖（COS）混合物的0.25%（w/v）足以使大肠杆菌初始菌量减少至少3个对数周期；与高分子量和中分子量壳聚糖不同，COS对金黄色葡萄球菌从未表现出杀菌作用，高分子量和中分子量壳聚糖在0.5%（w/v）时甚至对10⁷ 个细胞/mL也有杀菌作用。当添加到液态食品基质中时，中分子量和高分子量壳聚糖对两种基质和细菌都保持其活性，尽管在牛奶中活性明显较慢；然而，4 - 8小时后，COS在牛奶中对两种细菌都失去了活性。此外，向苹果汁中添加壳聚糖会导致几种不愉快的异味，如涩味和余味，且异味程度随分子量增加而增大。
