Applicability of surfaces containing silver in domestic refrigerators

Hygiene is an area of great concern in private households. Especially refrigerator interior surfaces are contaminated with food residues or microorganisms. Refrigerator manufacturers are attempting to improve the hygienic conditions by including antimicrobial refrigerator plastic surfaces. However, although refrigerator surfaces are already frequently compounded using, e.g. silver additives, it is still unclear whether these surfaces have the ability to decrease contamination under the special application conditions found within refrigerators. Thus, the aim of this study was to evaluate the ability of surfaces containing silver to decrease bacterial count in domestic refrigerators considering realistic conditions in domestic refrigerators. Laboratory investigations have been conducted concerning the rate of antimicrobial activity of different materials containing silver as regards their functioning to reduce surface contamination as related to test organisms and environmental conditions (e.g. temperature, food residues). The reduction rate on the tested plastic materials containing silver varied between log₁₀ 0.1-7.4 cfu/ml compared with the reference sheets. Thereby the rate is influenced by the plastic type, the microorganism and temperature. Further on the investigations made evident that the inhibitory effect of silver compounds is greatly reduced by the presence of protein residues. Consequently, investigations concerning the hygienic status within domestic refrigerators have been conducted and the cleaning behaviour by refrigerator users has been assessed. It became evident that, in particular, glass surfaces are often contaminated with protein residues. Furthermore, the cleaning frequency is very low as only 16% of refrigerator users clean their refrigerators monthly or more frequently. Thus, under these conditions found in practice, no additional benefit as to hygiene status can be expected by adding silver to refrigerator glass surfaces. Therefore, a careful choice of silver applications in domestic refrigerators is necessary considering the special conditions in private households. In addition, the factor of sustainability needs to be considered with regard to the unnecessary entry of silver ions into sewage.