Koji Yamazaki,

Ensuring Food Safety

Koji Yamazaki, , Associate Professor

Faculty of Fisheries Sciences/Graduate School of Fisheries Sciences (Department of Marine Bioresources Chemistry, Faculty of Fisheries)

High school : Mie Prefectural Yokkaichi Senior High School

Academic background : Graduate School of Fisheries Sciences, Hokkaido University

Research areas
Food microbiology, food hygiene
Research keywords
Microorganisms, aquatic food, seafood, food poisoning, microbial control, food safety

What are your goals?

Public interest in food safety has grown considerably in recent years as a result of the increasing occurrence of large-scale food poisoning by noroviruses, enterohemorrhagic E. coli 0157 and other microorganisms, food fraud, food contamination and other food-related problems. Some kind of microbial control is required to prevent food poisoning. Heat treatment or food additives (food preservatives or shelf life improvers, etc.) are typical control methods, but because consumers are increasingly showing a preference for foods that contain no additives and have a taste and texture that is as natural as possible, we need to develop new microbial control techniques. In my lab, we are conducting R&D on microbial controls aimed at ensuring that seafood, which is generally distributed at low temperatures, is still absolutely safe to eat when it reaches consumers without affecting quality.


What kind of research are you carrying out?

Photo 1. Isolation and culture of a food poisoning bacterium

From ancient times, people experientially developed and passed on food processing and preservation techniques designed to prevent food spoilage by microorganisms and protect their health. Of particular note are fermentation techniques that leverage microorganisms to process and preserve foods. Such techniques have long been used throughout the world to produce dairy products, pickles and other fermented foods that are much favored by many different peoples. By making active use of the functions of microorganisms, people have created foods that have distinctive flavors and can often be preserved for prolonged periods. It would be no exaggeration to say that fermented foods and the processes used to produce them owe their existence to outstanding bio-preservation techniques. In my lab, we focus on bacteriocins (antimicrobial peptides), a class of bio-preservatives produced by lactic acid bacteria. We are conducting research on how they can be applied to the preservation of food.

We isolate bacteriocin-producing lactic acid bacteria from various food and environmental samples to investigate their antimicrobial activity against test bacteria known to cause food poisoning and spoilage. If we find a microorganism that prevents or inhibits the growth of the test bacteria, the next step is to determine the species by looking at the microorganism’s various properties and gene sequence information. This is known as identification. We then use various types of chromatography to isolate the antimicrobial substance from a culture of the isolated microorganism and purify it so as to investigate its properties in detail. We check it for heat resistance and pH resistance, and investigate the kind of microorganisms it exerts its antimicrobial effects on (this is called the antimicrobial spectrum), and the mechanisms by which it exerts those effects on the target microorganisms. We also use mass spectrometers, amino acid sequencers and other devices to determine the structure of the antimicrobial substance. Finally, we evaluate the antimicrobial substance’s effectiveness with actual food by investigating the conditions required for it to exert its antimicrobial effects on food products.


Photo 2. Using fluorescence microscopy to observe bacteria, and a sample image

Photo 3. Inhibition of growth of Listeria (Listeria monocytogenes) and acidophilic spoilage bacteria (Alicyclobacillus acidoterrestris) by a bacteriocin (NisinA)


Photo 4. FSP1, a bacteriophage that infects the histamine-producing bacterium Morganella morganii, and how it infects a host cell (transmission electron micrographs)

We are also doing research on microbial control methods that use viruses that infect bacteria (called bacteriophages or phages). Phages destroy the bacterial cells that they have infected after multiplying inside them, and so we are looking at ways of applying this capability (known as lysis) to microbial control. Research on the application of lysis to microbial control in foods is still in its infancy, and we are currently in the process of evaluating its potential as a tool for such purposes.


What do you plan to do next?

Today’s consumers prefer foods that have undergone as little heat treatment or processing as possible. It’s extremely difficult to both meet the needs of these consumers and guarantee food safety, but there is still many microorganisms in nature with outstanding capabilities. By uncovering these outstanding capabilities and combining them with other antimicrobial substances and microbial control techniques, I think it should be possible to develop microbial controls tailored to individual foods. However, we also need to tackle issues like the declining effectiveness of antimicrobial activity as a result of interactions with food ingredients, and the risk of emergence of resistant bacteria. We hope to contribute to the supply of safe and tasty food by resolving these issues.