Effect of storage conditions on shelf stability of undiluted neutral electrolysed water
Block, Z and Eyles, A and Corkrey, R and Stanley, R and Ross, T and Kocharunchitt, C, Effect of storage conditions on shelf stability of undiluted neutral electrolysed water, Journal of Food Protection ISSN 0362-028X (In Press) [Refereed Article]
Neutral electrolysed water (NEW) is an oxidising sanitiser that can be made locally on-site but is often stored in ready-to-use format in order to accumulate the large volumes required for periodic or seasonal use. The shelf stability of NEW sanitiser was therefore assessed under various storage conditions to guide the development of protocols for its industrial application. To that end, fresh NEW with an available chlorine concentration (ACC) of 480 mg/L, pH 6.96 and oxidation reduction potential (ORP) of 916 mV was stored under different conditions. These were open or sealed polypropylene bottles, three different surface area-to-volume (SA:V) ratios (0.9, 1.7 and 8.7) and two temperatures (4, and 25 °C). NEW stored at 4 °C was significantly more stable than NEW stored at 25 °C, where ACC and pH decreased by 137 mg/L and 0.7, respectively, while ORP increased by 23 mV after 101 days of storage. At 25 °C, ACC decreased to <0.01 mg/L after 52 days in bottles with a SA:V ratio of 8.7 with a similar decrease after 101 days in bottles with a SA:V ratio of 1.7. However, pH decreased by up to 3.7 pH units but ORP increased by up to 208 mV. Antimicrobial efficacy of ‘aged’ electrolysed oxidising (EO) water with different ACC and ORP, but the same pH (i.e., 3.4 ± 0.2) was evaluated against Escherichia coli and Listeria innocua to determine any differences in residual antimicrobial activity. EO water with an ACC of ≥7 mg/L and ORP of 1,094 mV caused at least a 4.7-log reduction, whereas EO water with non-detectable ACC and considerably high ORP (716 mV) had little antimicrobial effect ( <1-log reduction). Results from this study indicate that the efficacy of NEW as a sanitiser for large scale applications like horticulture can be maintained for at least 3 months when stored in closed containers with low SA:V ratio at low temperatures.