Micro-organisms microbial inhibition

FIGURE 61.5 Schematic representation of antimicrobial active-packaging. Micro-organisms hydrolyze starch-based particles, causing release of the antimicrobial lysozyme, resulting in inhibition of microbial growth. (From De Jong, A.R. et al.. Food Addit. Contain., 22(10), 975, 2005.)... 

Three methods may be used for the enumeration membrane filtration, plate count, and most probable number (MPN) method. The advantages of the membrane filter method are its low limit of detection (LOD) of < 1 CFU/g or mL and the efficient separation of the micro-organisms from components of the product, particularly antimicrobial agents. For the pour-plate method, the sample is generally 1 10 dissolved in the diluent, and 1 mL of the dilution is mixed with the agar. This corresponds to a LOD of 10 CFU/g or mL. The LOD is sometimes higher (e.g. 100 CFU/g or mL) if the product needs to be further diluted due to microbial inhibition, or lower in case of products with low microbial acceptance criteria. If the spread plate count technique is used the LOD is a factor of ten higher (>100 CFU/g or mL), because only 0.1 mL of the... 

Temperature Low temperature (below 30°C) or warm machines (above 50°C that are often observed with TMP and also with DIP treated with hot dispersion) will reduce biological activity and make the machines less favourable for microbial growth. The use of non-oxidising biocides can then be reduced and the treatment mainly based on the usage of polymers/surfactants blend to inhibit the growth of micro-organisms or remove the biofilm. 

Micro-organisms may not always enhance corrosion. The same bacterial species may show both corrosive and protective effects. For example, Hernandez et al. [56] reported the corrosive effects of two microbial species, one of which was Pseudomonas sp. By changing certain conditions, the very same micro-organisms were showing protective effects and slowing down corrosion. Those researchers also reported that in the presence of bacteria such as aerobic pseudomonades sp. and facultative anaerobic serratia marcescens in synthetic seawater, corrosion of mild steel is inhibited. The effect seemed to disappear with time in natural seawater. Jack et al. [57] reported monocultures of an aerobic Bacillus sp. that induced greater corrosion than that of an abiotic environment, but the rate of this corrosion decreased to that of a sterile control after 17 days. 

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