Extracellular polysaccharides of bacteria are composed of a number of different homo- and heteropolysaccharides that are of prime importance in the attachment of bacteria to surfaces and in the formation of bacterial biofilms. Enzyme catalysed removal of biofilms has been studied very little and only a few reports are available. A distinction can be made between the enzymatic release of microorganisms from biofilms and the bacteriocidal activity of different enzymes (Brisou, 1995). Due to the heterogeneity of the extracellular polysaccharides, an enzyme cocktail comprising several different enzyme activities appears necessary for sufficient removal and killing of bacterial biofilms. Glucose oxidase combined with lactoperoxidase was shown to exert bacteriocidal activity on a mixture of Gram-positive and Gram-negative biofilm bacteria, but did not release the biofilm from the model surfaces (Johansen et al., 1997). In contrast, a multicomponent polysaccharide hydrolysing enzyme preparation (comprising pectinase, arabinase, cellulase, ^-glucanase, and xylanase activities) released bacterial biofilm from steel and polypropylene model surfaces but did not kill the bacteria in the biofilm. The combination of the oxidoreductases and the polysaccharide hydrolysing enzyme preparation, caused both removal and a bacteriocidal effect on the biofilms (Johansen et al., 1997). At present, the identity of the polysaccharide hydrolysing enzymes that are most important for the enzymatic degradation of biofilms is largely unknown.
4.5 Combining antimicrobial enzymes with other preservation techniques
The concept of combining several factors to enhance microbiological safety of foods was advanced by Leistner several years ago (Leistner and Gorris, 1995). The strategy of designing a series of hurdles - or rather to combine several factors to obtain synergistic effects - has also proved fruitful in improving the efficiency of enzymes as antibacterial food preservatives. In this section, particular focus will be directed towards the efforts aimed at improving the antibacterial potency of lysozyme; data on boosting the activity of lactoperoxidase will also be briefly summarised.
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