Control of Microbial Contamination by Electrolyzed Water in Tofu Manufacturing

For further information, see Eizo Tatsumi, JIRCAS Newsletter, 32, 5 (2002), 2003-12-01

Heat-Resistant Bacteria on Tofu

Tofu is a popular processed food in Asia, and recently, it has become popular worldwide as a health food containing high contents of essential amino acids and isoflavone. Since the consumption of tofu is gradually increasing, it becomes very important to maintain hygienic conditions during its manufacture. Especially, the control of heat-resistant spore-forming bacteria, which are predominant on the surface of soybean, is an essential part of tofu manufacturing. This report describes the potential of electrolyzed water to control microbial contamination in tofu manufacturing.

Electrolyzed Water Destroys Microbes

Electrolyzed water can be produced by electrolyzing sodium chloride solution or dilute hydrochloric acid. Nowadays, acidic electrolyzed water is used to sanitize food-processing equipment and fresh-cut vegetables in food industries. Microbial contamination could be effectively eliminated by using acidic electrolyzed water.

Electrolyzed Water Effective but Unstable, Should Be Prepared Just before Use

In this study, soybean was soaked in three types of electrolyzed water: acidic electrolyzed water at pH 2.1, 1185 mV oxidation-reduction potential (ORP) and 100 ppm chloride; alkaline electrolyzed water at pH 11.7, -120 mV ORP; and a mixture (weak acidic electrolyzed water) of both waters at pH 6.5, 891 mV ORP, and 50 ppm chloride. Microbial population of the water became negligible after only 30 minutes of treatment in acidic electrolyzed water and 1 hour in the mixture, while physico-chemical characteristics of tofu and milk made from soybean thus treated were not changed at all. Electrolyzed water is, however, very unstable and should be prepared only at the time of use. Moreover, acidic and weak acidic electrolyzed water are easily inactivated when polluted by organic matter; therefore, it is necessary to always protect them from pollution and to first wash the manufacturing lines with electrolyzed water before use. In order to apply electrolyzed water in the processing of other foods, similar analyses of efficiency, stability, and reactivity (safety) of electrolyzed water in the presence of other organic materials are needed.

Download the PDF. of this document, 21,335 bytes (20.8 KB).