Does soy sauce have kojic acid?

April 23, 2026

Table of Content

Yes — soy sauce can contain kojic acid, but it is not intentionally added; it is a natural by-product of fermentation. Moreover, the kojic acid in soy sauce exists in trace amounts, and its impact on the human body is extremely limited under normal dietary conditions, posing no health risks to most people.

🧪 Scientific explanation

1. Source of kojic acid

Kojic acid is a natural organic compound closely related to soy sauce fermentation, and its main source is the metabolic activity of specific fungi.

1.1 What is kojic acid

Kojic acid is a natural organic compound produced by the metabolic activity of certain fungi, among which Aspergillus oryzae (commonly known as koji mold) is the most common and typical producer. It was first isolated and identified from the fermentation product of koji mold in 1907

1.2 Relationship between koji mold and soy sauce fermentation

Notably, Aspergillus oryzae is the core strain used in the traditional fermentation of soy sauce. In the production process of soy sauce, soybeans, wheat and other raw materials are inoculated with Aspergillus oryzae, which decomposes the proteins, starches and other nutrients in the raw materials, producing amino acids, peptides, flavor substances and other components that determine the taste and nutrition of soy sauce — and kojic acid is one of the secondary metabolites generated in this process.

2. Evidence in soy sauce

A large number of authoritative studies have confirmed the existence of kojic acid in soy sauce, and its content is affected by many factors.

2.1 Existence of kojic acid in soy sauce

A large number of food science studies and authoritative food ingredient references have confirmed thatsoy sauce contains kojic acid and its derivatives (such as kojic acid esters).

2.2 Factors affecting the content of kojic acid in soy sauce

The content of kojic acid in different types of soy sauce varies, which is mainly affected by factors such as raw material ratio, fermentation temperature, fermentation time and strain type.

2.3 Role of kojic acid in soy sauce

Although kojic acid is present in trace amounts in soy sauce, it plays a certain role in the quality of soy sauce

2.3.1 Preservation

Kojic acid has a weak antibacterial effect, which can inhibit the growth of some harmful microorganisms in soy sauce, extend the shelf life of soy sauce, and prevent spoilage such as mold growth.

2.3.2 Flavor stability

Kojic acid can interact with other flavor substances in soy sauce to reduce the oxidation of flavor components, helping to maintain the unique umami and aroma of soy sauce and avoid flavor deterioration during storage.

2.4 Difference in kojic acid content between different types of soy sauce

The content of kojic acid in traditional fermented soy sauce is usually slightly higher than that in formulated soy sauce (made by blending soy sauce, seasonings, etc.), because the fermentation process of formulated soy sauce is shorter and the amount of kojic acid produced by yeast metabolism is less; The content of kojic acid in high salt dilute fermented soy sauce (with longer fermentation period and richer flavor) may be slightly higher than that in low salt solid-state fermented soy sauce.

3. Mechanism of kojic acid formation in soy sauce

The formation of kojic acid in soy sauce is a natural metabolic process of Aspergillus oryzae during the fermentation of raw materials, and its specific mechanism can be divided into three key steps

3.1 Decomposition of raw material carbohydrates

First, Aspergillus oryzae secretes a variety of hydrolases (such as amylase, glucosidase) after inoculating the raw materials (soybeans, wheat), which decompose the starch in the raw materials into simple carbohydrates (such as glucose, maltose).

3.2 Conversion of secondary metabolites

Then, Aspergillus oryzae absorbs these simple carbohydrates for energy metabolism. During this process, due to the regulation of metabolic pathways, part of the carbohydrates will not be completely decomposed into energy, but will be converted into secondary metabolites through the “pentose phosphate pathway” — and kojic acid is one of the important products of this pathway.

3.3 Retention in soy sauce products

Finally, the generated kojic acid is released into the fermentation system (soy sauce mash) along with other metabolic products, and remains in the final soy sauce product after filtration, sterilization and other subsequent processing steps.

3.4 Factors affecting kojic acid yield

The production of kojic acid is closely related to the growth environment of Aspergillus oryzae. When the fermentation temperature is between 25-30℃, the humidity is 70-80%, and the oxygen supply is sufficient, the metabolic activity of Aspergillus oryzae is the most vigorous, and the yield of kojic acid is relatively higher; if the fermentation conditions are not suitable (such as too high or too low temperature), the production of kojic acid will be significantly reduced.

⚠️ Important Conclusion

1. Kojic acid in soy sauce is naturally occurring

It is not added artificially by manufacturers to achieve a certain effect (such as enhancing flavor or preservation), but is a by-product of the natural fermentation of soy sauce. This is fundamentally different from food additives such as preservatives and flavor enhancers.

2. Kojic acid in soy sauce exists in small and variable amounts

The content of kojic acid in soy sauce is generally at the microgram level per 100 grams (usually 1-10 μg/g), and the maximum content in individual high-quality traditional fermented soy sauce will not exceed 50 μg/g. This content is far lower than the safety limit specified by international and domestic food safety standards.

3. Kojic acid is not listed as an additive in most soy sauce products

According to the national food labeling regulations, only artificially added ingredients need to be listed in the ingredient list. Since kojic acid is a natural by-product, it does not need to be separately marked in the ingredient list of soy sauce. This does not mean that soy sauce does not contain kojic acid, but that it is not an “added ingredient”.

4. Difference between kojic acid in soy sauce and industrial kojic acid

Industrial kojic acid is produced by large-scale fermentation of fungi, with high purity and high content, and is widely used in cosmetics, food processing (as a preservative in small amounts) and other fields; while the kojic acid in soy sauce is low-purity, trace and naturally existing, and its use scenario and content are very different from industrial kojic acid.

🩺 Impact of kojic acid in soy sauce on the human body

1. Safety under normal dietary conditions

For most people, eating soy sauce containing trace amounts of kojic acid is completely safe.

2. Potential risks of kojic acid in soy sauce

Although kojic acid in soy sauce is safe under normal circumstances, potential risks may exist in the following special situations:

Risk of excessive intake

Risk of allergic reactions

Risk of contamination

Key reminder

When buying soy sauce, focus on choosing products from regular manufacturers with complete labels and qualified testing; when eating, control the amount appropriately (it is recommended to consume 5-10 grams per day), which can not only enjoy the flavor of soy sauce, but also avoid potential risks caused by excessive intake of salt and other components.