Electrolyzed oxidizing water active against P. expansum.

Penicillium expansum is a microorganism of concern found in apple processing facilities. It causes economic losses that result from the spoilage it causes in apples. It is also a food safety hazard because it leads to the production of the mycotoxin, patulin.

Electrolyzed-oxidizing (EO) water has been shown to be lethal to a variety of bacteria and fungi. But no studies have been done to determine its effect on Penicillium species. The objective of research at Pennsylvania State University was to investigate the effect of EO water on conidia of P. expansum in suspension.

Based upon Russian and Japanese research, EO water is produced by passing dilute salt water (0.01%) through an electrical field and a separation membrane. Two types of water are created--alkaline (11.3 pH and higher) and acidic (2.7 pH and lower). The alkaline water is finding use as a cleaner and degreaser, while the acidic water, containing 30 ppm hypochlorous acid (HOCl), has an extremely powerful bactericidal effect.

The ability of the acidic water to kill harmful bacteria is due to its high chlorine content, a very low pH, which slows most enzymatic activity, and its strong oxidation-reduction potential (ORP). The ORP, when combined with the first two attributes, produces a synergistic effect that kills microorganisms in a short amount of time.

Penn State scientists suspended 107 logs cfu of P. expansum PP497A for up to 5 minutes in acidic EO water that had been diluted with sterile tap water to achieve ORPs of 850 mV, 895 mV, 967 mV and 1133 mV, as well as 10.1 [micro]g per g, 33.5 [micro]g per g, 50 [micro]g per g and 59.6 [micro]g per g of free available chlorine, respectively. The suspensions were filtered through 0.22-[micro]m filters and washed with sterile distilled water. Serial dilutions were spread onto potato dextrose agar (PDA) plates to enumerate viable conidia.

Colony counts revealed significant activity of EO water against P. expansum at ORPs greater than 895 mV. EO water at pH 2.7, 1133 mV ORP, and 59.6 [micro]g per g free chlorine reduced viable conidia by 4 log units within 30 seconds of exposure. At pH 6.02, 895 mV ORP, and 33.5 [micro]g per g of free chlorine, a reduction of 3 log units was achieved.

Although the ORPs in these treatments remained relatively high after an initial drop within 30 seconds, researchers observed a tailing effect on the inactivation kinetics after 30-second treatments. Inactivation was not enhanced by re-suspending previously treated conidia in fresh EO water at pH 2.7, 1133 mV ORP and 59.6 [micro]g per g of free chlorine. Successive treatment with alkaline and then acid EO water did not increase any inactivation.

The scientists found that EO water possesses significant activity against P. expansum. It may be a useful sanitizing agent in apple-processing operations.

Further information. Derrick Okull, Department of Food Science, Pennsylvania State University, 111 Borland Laboratory, University Park, PA 16802; phone: [phone]; email: [e-mail].