Tetramethylbenzidine method for monitoring the free available chlorine and microbicidal activity of chlorite based sanitizers under organic matter rich environments
Chlorine is a principal disinfectant for food and environmental sanitation. Monitoring of free available chlorine (FAC) is essential for ensuring the efficacy of food disinfection processes that rely on chlorine. N,N diethyl p phenylenediamine (DPD) is commonly used for FAC monitoring. However, here, we show that upon contact with bovine serum albumin (BSA) or broiler carcasses, chlorite (HClO2) based sanitizers acquire a pink colour, which can interfere with measurement of oxidized DPD absorbance at 513 550 nm. Alternatively, the pink colour did not interfere with 3,3',5,5' tetramethylbenzidine (TMB) based FAC monitoring. The FAC levels of NaClO and weakly acidified chlorous acid water (WACAW) were first adjusted by the TMB method and the killing activity of these sanitizers towards methicillin resistant Staphylococcus aureus (MRSA) and feline calicivirus (FCV) was compared in the presence or absence of 0*5% BSA. At 200 ppm FAC, NaClO lost its bactericidal activity against MRSA after 10 min incubation with 0*5% BSA. Meanwhile, under the same conditions WACAW reduced the number of bacteria to below the detection limit. Similar results were obtained with FCV, indicating that the chlorite based WACAW sanitizer is relatively stable under organic matter rich conditions. Moreover, TMB is suitable for in situ FAC monitoring of chlorite based sanitizers in food and environmental disinfection processes.
Letters in applied microbiology