The Study Of Bacteriacial Effect Of L-Ascorbic Acid Aggaist Escherichia Coli Cells

Sterilization is a necessary measure in the process of drinking water treatment. Now there are many sterilization methods and technologies: common ones such as chlorine, ozone, ultraviolet radiation; new ways such as T1O2 spectrum catalyzing, plasma. Although these methods have good bactericidal effect, but also bring some negative problems. As the condition of water pollution is more and more severe, finding a convenient, effective and inexpensive way has been of great urgency.L-Ascorbic acid is a water-soluble vitamin, playing an important role in various life activities, and in a certain usage, it will not harm humans and animals. From the latter half of the 20th century, the beginning of 30 years, the bactericidal effect of L-ascorbic acid had been reported, but up to now its reaction mechanism is still on studying.In order to study the bactericidal mechanism of L-ascorbic acid and the factors affect bactericidal effect further, Escherichia coli is used as experiment subject, and ESR (electron spin resonance instrument) plus SEM (scanning electron microscope) are applied as supplementary analytical tools to conduct a pilot study. The results are showed as follows:(1) In the presence of transition metal ions, the L-ascorbic acid can be used as a prooxidant to generate·OH with strong oxidizability which can kill cells. The system of L-ascorbic acid plus Cu²⁺ had an excellent bactericidal effect, all cell killing could be reached after 0.5h in weakly acidic condition; the system of L-ascorbic acid plus Fe²⁺ also had a not bad bactericidal effect, survival rate of E.coli reached to 0 after 24h; the system of L-ascorbic acid plus Fe³⁺ had a worse effect, 12.5% of E.coli was still alive after 24h. because of the toxicity of Cr³⁺, either it alone or with L-ascorbic acid together, the survival rate of E.coli decreased to 0 around 0.5h.(2) When ascorbic acid alone, it also has a certain bactericidal effect, but is subject to the pH in reaction system, the concentration of ascorbic acid, oxygen and content of Fe in the bacteria medium, and have such rules: 1. In the range of pH4 to pH7, the higher the pH, the stronger the effect. 2. The higher the concentration of L-ascorbic acid, the stronger the effect. 3. Oxygen is necessary in the process of disinfection. 4. Fe added into bacteria medium can promote the disinfection effect.(3) Based on the reaction mechanism of ascorbic acid plus transition metal ion, it can be inferred that ascorbic acid and Fe contained in cell conduct a Fenton-like reaction, meanwhile producing a small amount of·OH, while low concentration of·OH also has good disinfection effects.