They have used tetrazolium salt (MTT) to reduce the time taken to measure the number of viable bacteria in food electrochemically from two days to approximately one hour, irrespective of the bacterial species.
The technique can reportedly verify food safety before shipment from factories and prevent food poisoning – a major breakthrough, they note.
WHO states that food safety, nutrition and food security are inextricably linked, with an estimated 600 million people falling ill and 420,000 dying each year due to contaminated food consumption.
Food safety and hygiene in the food industry is of paramount importance.
Dr. Hiroshi Shiigi, professor and research lead at the Department of Applied Chemistry, Osaka Metropolitan University states, “In this study, we focused on the electrochemical properties of tetrazolium salts and developed a simple method for evaluating viable bacterial counts as an indicator of hygiene control in food and pharmaceutical production sites.”
The researchers flag that the technique can confirm the safety of food products before they leave the factory and prevent food poisoning.
“One of the most important assessment indicators for ensuring that food is free from contamination is the number of viable bacteria. However, conventional measurement methods take up to two days to yield results, and these results are only available after the food has been shipped from the factory—leading to potentially fatal consequences,” explains Dr. Shiigi.
“Therefore, it is imperative to have a testing method that speeds up the process of identifying bacterial contamination before shipment,” he adds.
According to Dr. Shiigi, the team will continue to optimize the measurement conditions and expect to see the “development of a portable sensor” in line with the development of research aimed at practical applications.
Notably, the method does not require complicated operations or expensive equipment.
The scientist flags that MTT, a water-soluble molecule, has excellent cell membrane permeability and changes into insoluble reduced formazan inside the cell.
“The number of viable bacteria can be estimated by focusing on the reduction current of MTT remaining in the suspension,” says Dr. Shiigi.
Further, he notes that the standard MTT assay is used as a colorimetric method but requires sufficient incubation time to obtain absorbance. The team found that MTT has electrochemical activity and by “focusing on its current response, highly sensitive measurement became possible.”
The research team has developed the technique based on opinions obtained from interviews with several food product manufacturers in Japan.
“We believe that the product is highly marketable. The plan is to proceed with development with a focus on device realization in the future,” he concludes.
Their results were published in Analytical Chemistry.
Reference:
Journal: Analytical ChemistryTitle: Evaluation of Bacterial Activity Based on the Electrochemical Properties of Tetrazolium SaltsDOI: 10.1021/acs.analchem.3c01871Author: Hikaru Ikeda, Akira Tokonami, Shigeki Nishii, Xueling Shan, Yojiro Yamamoto, Yasuhiro Sadanaga, Zhidong Chen, and Hiroshi ShiigiPublished: August 10, 2023
Abstract
This study focused on the electrochemical properties of tetrazolium salts to develop a simple method for evaluating viable bacterial counts, which are indicators of hygiene control at food and pharmaceutical manufacturing sites. Given that the oxidized form of 3-(4,5-di-methylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT), which has excellent cell membrane permeability, changes to the insoluble reduced form of formazan inside the cell, the number of viable cells was estimated by focusing on the reduction current of MTT remaining in the suspension. Dissolved oxygen is an important substance for bacterial activity; however, it interferes with the electrochemical response of MTT. We investigated the electrochemical properties of MTT to obtain a potential-selective current response that was not affected by dissolved oxygen. Real-time observation of viable bacteria in suspension revealed that uptake of MTT into bacteria was completed within 10 min, including the lag period. In addition, we observed that the current response depends on viable cell density regardless of the bacterial species present. Our method enables a rapid estimation of the number of viable bacteria, making it possible to confirm the safety of food products before they are shipped from the factory and thereby prevent food poisoning.