Forefront of lactic acid bacteria research

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Introduction to lactic acid bacteria (yogurt and bacteria)

Lactic acid bacteria are so beneficial to humans

There are innumerable bacteria (single-cell microorganisms that are invisible to the eye) existing in nature. They are living anywhere you look, floating in the air, swimming in the sea, even crawling around on our hands and inside our bodies. These bacteria have various unique functions.
While there are myriad different types of bacteria, lactic acid bacteria that are used to make yogurt, etc. have certain functions that are most familiar to and useful for us humans.
Lactic acid bacteria is the collective name used to refer to the family of bacteria that break down glucose, lactose, and other saccharides (carbohydrates) into lactic acid to produce energy that is essential for their growth. Many different types of lactic acid bacteria are known to man, and each strain has its own unique habitat.
The types of lactic acid bacteria living inside humans include a whole range of bifidobacteria and also Lactobacillus acidophilus, which are commonly known as “good bacteria” because they perform functions beneficial to their human hosts.

Lactic acid bacteria used in yogurt-making

The process by which lactic acid bacteria convert saccharides into lactic acid is called “lactic acid fermentation.” While lactic acid bacteria create yogurt and other fermented foods through such fermentation, the type of lactic acid bacteria used varies from one fermented food to another.
The yogurt made through this lactic acid fermentation offers several benefits.
First, the fermentation caused by lactic acid bacteria adds that uniquely delicious flavor to the yogurt.
In addition, lactic acid bacteria serve to improve the yogurt’s storability. As acid is produced during the fermentation, the yogurt becomes acidic, which suppresses the proliferation of undesirable putrefactive (i.e., decaying) bacteria and pathogens. This is why yogurt stays good longer than milk.
Also, lactic acid fermentation makes yogurt more digestible and absorbable by the human body. Even many people who may experience discomfort in the stomach after drinking milk are able to eat yogurt. As lactic acid fermentation offers such benefits, the process has been applied to various types of foods since ancient times. Today, drug companies have even developed and released intestine-regulating medications from lactic acid bacteria.

Lactic acid bacteria provide health benefits even when they are not alive.

When the lactic acid bacteria contained in yogurt, such as Lactobacillus delbrueckii subsp. bulgaricus and Streptococcus thermophilus, are ingested and enter the body, they are exposed to and affected by the gastric acid in the stomach, as well as the bile and other digestive juices in the intestines, etc. As a result, some of them die before reaching the intestines, while others reach there alive.
It is important to note that the lactic acid bacteria consumed as yogurt provide various health benefits, whether they stay alive or die during the digestive process. In other words, live lactic acid bacteria as well as the enzymes and substances of lactic acid bacteria and the various byproducts created during the fermentation process all have beneficial health functions.

The spread of lactic acid bacteria research

While terms such as probiotics, prebiotics,and biogenics have been coined and spread from Europe to Asia and then to the U.S., the concepts they represent have attracted attention in bioscience.
While these terms may be new, what they signify is basically the same as what Mechnikov envisioned more than 100 years ago. In this recent scientific movement, a growing number of lactic acid bacteria and other useful bacteria are now widely used along with yogurt and other foods that contain the bacteria, to maintain and promote good health.
In Europe, which is the birthplace of yogurt, comprehensive research on probiotics is well under way, raising hopes for highly beneficial findings.

Feature (1) Main types of lactic acid bacteria
Lactic acid bacteria can be classified into two main types: rod-shaped bacilli and round-shaped cocci (Lactococcus, Leuconostocaceae, Pediococcus, and Streptococcus), which are further broken down into more detailed subcategories.
Feature (2) Intestinal microbiota
In the intestines, battles are constantly raging between the “good” and “bad” bacteria, with each side trying to expand its territory, and our health is considered to be largely affected by the balance of power between them. The lactic acid bacteria contained in yogurt (L. bulgaricus, S. thermophilus, etc.) are known to help improve such balance.

Putrefactive (i.e., decaying) bacteria

These bacteria inhabit the intestines and break down proteins into ammonia, hydrogen sulfide, amine, indole, phenol, etc. that have either harmful or decaying effects. These substances produce foul odors and are known to be the cause of fecal smell. Research has also found that such substances may be carcinogenic and promote the growth of cancer cells. The types of bacteria that cause diarrhea and intestinal inflammation are all putrefactive bacteria.


The time when this term suddenly gained significance was in 1969 in the U.K. The popularization of probiotics was triggered by a report published around that time, in an attempt to discourage the addition of antibiotics to the fodder of farm animals to enhance their productivity.
Research at the time had already started to show that each farm animal had its unique intestinal microbiota, and that it was important to keep their microbiota in a normal condition to stop them catching infectious diseases and to improve their productivity.
While scientists gradually realized that the concept of probiotics was the opposite of what antibiotics aimed to achieve, British microbiologist Dr. Fuller came up with the current definition of the term in 1989, specifying that probiotics were “a live microbial feed supplement which beneficially affects the host animal by improving its intestinal microbial balance,” while stressing that the live microorganisms were far more important than the substances.
Probiotics are also considered to be live organisms that perform useful functions in the intestines, and so any food products and live bacterial drugs containing probiotics also fit the definition.
The definition of the term has been modified several times over the years, because of the recognition that probiotics are as important to humans as they are to livestock.
Even more recently, the term has been often defined to include all live microorganisms that perform positive functions on any organisms.
The intestines are not the only parts of the body that are inhabited by bacteria.
As bacteria can be found in various other parts including the skin, oral cavity, respiratory organs, etc., any deterioration in their balance is known to cause various infectious diseases.
While research is yet to identify bacteria that could effectively prevent such diseases, there are high expectations that probiotics will serve such purpose in the future.


This term was coined with inspiration by oligosaccharides that were first developed in Japan. The term was defined in 1995 to mean “a nondigestible food ingredient that beneficially affects the host by selectively stimulating the growth and/or activity of one or a limited number of bacteria in the colon, and thus improves host health.”
The term was initially derived from the substance that promotes the proliferation of bifidobacteria, a type of “good bacteria” in the intestines, which was incorrectly thought of at first as a special trace substance that would only promote the growth of bifidobacteria. However, as subsequent research discovered that it was actually the saccharides that promoted the growth of not only bifidobacteria but also lactic acid bacteria in the intestine, by arriving there still undigested by human digestive enzymes and becoming food for lactic acid bacteria. Based on this finding, several indigestible oligosaccharides such as galacto-oligosaccharides and fructo-oligosaccharides have been developed and released, while dietary fiber is also known to have the same function.


Biogenics are the efficacious substances produced by the function of lactic acid bacteria, which are known to directly improve the host’s immune strength and promote spontaneous healing, without the intestinal microbiota serving as an intermediary. Biogenics were first suggested by Dr. Tomotari Mitsuoka as a crucial research topic in 1988, and have become one of the most popular subjects in this particular research field.
The concept is narrowly defined as food ingredients that beneficially affect the host by lowering blood pressure, stimulating immunity, reducing cholesterols, regulating the intestines, mitigating tumorigenesis, and performing other biological regulatory and protective functions, disease prevention, aging control, etc. Its broader definition also includes other dietary ingredients such as bioactive peptides, plant polyphenol, carotenoid, DHA, and vitamins.

Mechnikov's concept

Considering the definitions of both probiotics and prebiotics, they are virtually identical to what Mechnikov envisioned more than 100 years ago. Mechnikov took notice of Bulgarian yogurt and L. bulgaricus as effective probiotics, stating that certain amounts of lactose and sucrose were needed for lactic acid bacteria to proliferate and prove beneficial.

Dr. Mechnikov responsible for spreading yogurt globally

Comprehensive research on probiotics

Mechnikov’s views on the effects of lactic acid bacteria on immunity and aging mitigation have garnered much attention again in European research of late, and the latest methods in biotechnology and molecular biology are being used to re-examine such matters. Major comprehensive research has been conducted on this topic in the EU.
Projects such as STARLAB and PROBDEMO, which were organized by teams of researchers and probiotics companies from various countries, have been concluded, and the next rounds of projects are already being planned. The research topics are comprehensive and include genetic analysis of various lactic acid bacteria that are used as probiotics as well as their safety and efficacy, and the projects are expected to produce great results. Meanwhile in Japan, researchers are leading global efforts in both basic and applied research, and are hosting a number of international symposiums.