Foods Susceptible to Contamination by Aspergillus niger

December 21, 2025 •

4 min read

According to the National Institutes of Health (NIH), black Aspergillus species, including Aspergillus niger, frequently cause post-harvest decay in a variety of agricultural products. These fungi are ubiquitous in the environment, and while some strains are safely used in industrial food production, others can contaminate food, posing a risk to both food quality and human health.

Quick Summary

This article explores the common foods and agricultural products that are susceptible to contamination by Aspergillus niger, detailing the environments in which it thrives, the potential health implications of exposure, and how to identify and prevent its growth.

Key Points

Ubiquitous Mold: Aspergillus niger is a common fungus found in soil, compost, and decaying organic matter worldwide.
Food Spoilage: It causes "black mold" on fresh produce like grapes, onions, and apricots, leading to post-harvest decay.
High-Risk Foods: Nuts (especially peanuts), grains, dried fruits, and coffee are frequently contaminated, often during bulk storage.
Industrial Use: Specific, non-toxic strains of A. niger are safely used in the food industry to produce enzymes and citric acid.
Mycotoxin Production: Certain contaminating strains can produce harmful mycotoxins like ochratoxin A, which poses significant health risks.
Health Effects: Mycotoxins can cause kidney damage and other severe health issues, while inhaling spores can trigger allergies and respiratory problems.
Prevention is Key: Proper storage, controlling humidity, and discarding moldy food entirely are the best ways to prevent health risks.
Identification: Black, powdery colonies are the most visible sign of contamination, but mycotoxins can be present even without visible mold.

What is Aspergillus niger?

Aspergillus niger is a species of filamentous fungus, or mould, that is known for its distinct black, powdery appearance. The name Aspergillus comes from the Latin word meaning 'holy water sprinkler,' referencing the fungi's appearance under a microscope. It is found ubiquitously in the environment, particularly in soil and decaying organic matter, making it a common contaminant of crops both in the field and after harvest.

While some strains of Aspergillus niger are leveraged for their beneficial industrial uses—such as the production of citric acid and enzymes for food processing—other strains can produce mycotoxins, which are secondary metabolites that can be toxic to humans and animals.

Industrial Uses vs. Food Contamination

It is crucial to distinguish between the controlled use of Aspergillus niger in industrial food production and its uncontrolled growth as a contaminant. Safe strains, designated as Generally Recognized as Safe (GRAS) by the FDA, are used to produce enzymes like glucoamylase for high-fructose corn syrup and pectinases for wine clarification. However, wild, contaminating strains can produce mycotoxins like ochratoxin A, which poses significant health risks.

Foods Susceptible to Aspergillus niger Contamination

Aspergillus niger is known to cause "black mold" on a wide range of fruits and vegetables, often leading to significant post-harvest losses. The fungus thrives in warm and humid conditions, which can be found both in agricultural fields and during the storage and transportation of food.

Common High-Risk Foods

Fruits and Vegetables: Grapes, apricots, onions, mangoes, pomegranates, and citrus fruits are particularly vulnerable to black mold caused by A. niger. Infection can occur through injuries to the fruit's skin, and the mold can develop during storage.
Dried Nuts and Fruits: The fungus is frequently isolated from dried nuts and fruits, as it can grow in environments with very little water activity. Peanuts are notably susceptible to A. niger and other Aspergillus species.
Grains and Cereals: Studies have shown that Aspergillus niger can contaminate cereals and legumes, especially under damp and wet conditions during bulk storage.
Coffee: Coffee berries and beans can also be infected by Aspergillus species, including A. niger.
Spices: Spices and other sun-dried products are common substrates where A. niger can grow.

How Contamination Occurs

In the Field: Spores from the soil and decaying organic matter can infect crops while they are still growing. This is especially true for crops like onions and peanuts, where the mold can cause black mold or crown rot.
During Harvest and Processing: Wounds on fruits and vegetables created during harvesting or transportation can provide an entry point for mold spores.
In Storage: Favorable storage conditions, such as high temperatures and humidity, can encourage the growth of A. niger on stored products. Poor storage can be a major factor in mycotoxin production.

Comparison of Harmful vs. Beneficial Aspergillus in Food


Aspect	Contaminant (Wild Strains)	Industrial Use (GRAS Strains)
Purpose	Spoilage and opportunistic pathogen	Production of enzymes, acids
Environment	Soil, air, decaying matter, improperly stored food	Controlled, industrial fermentation environments
Toxin Production	Can produce mycotoxins like ochratoxin A	Strains selected for safe use, not toxin producers
Visible Signs	Black, powdery mold on food surface	Not present in final product, enzymes extracted
Health Impact	Allergic reactions, mycotoxicosis, infections in immunocompromised	No risk of disease or mycotoxins when used correctly

Health Risks Associated with Contaminated Food

Eating food contaminated with toxigenic strains of Aspergillus niger can lead to several health issues, particularly from mycotoxins like ochratoxin A (OTA). OTA is known to be nephrotoxic, carcinogenic, and immunosuppressive in humans and animals. While ingestion is the primary concern for food contamination, inhaling spores from moldy food can trigger allergic reactions and respiratory problems, especially in sensitive individuals.

Recognizing Contamination

Visual signs of black, sooty mold are the most obvious indicators of Aspergillus niger contamination. However, mycotoxins may be present even without visible mold, particularly in grains and nuts. Given the potential health risks, it is always safest to discard any food showing signs of mold growth, especially soft foods and produce where the mold can penetrate deep below the surface.

Conclusion: Preventing Contamination

Understanding which foods are susceptible to Aspergillus niger contamination is a crucial step in maintaining food safety. The mold thrives in warm, humid conditions and can affect everything from fresh fruits and vegetables to dried nuts and grains. Proper handling, storage, and a keen eye for signs of spoilage are the best preventative measures. Discarding moldy food entirely, rather than attempting to salvage it, is the safest practice, especially for softer items. By implementing good food hygiene and storage practices, consumers can significantly reduce their risk of exposure to harmful mycotoxins produced by this pervasive fungus.

For more detailed information on mycotoxins and food safety, the World Health Organization (WHO) provides extensive resources on safe food practices related to mold and mycotoxin contamination.

Frequently Asked Questions

When contaminating food, Aspergillus niger typically appears as a black, powdery mold, often with a sooty texture. It is most visible on the surface of fruits and vegetables, such as between the scales of onions or on grape skins.

For soft foods, bread, and prepared dishes, it is not safe and you should discard the entire item. Mold can penetrate deeper than is visible on the surface, and mycotoxins can spread throughout the food. For hard foods like hard cheese and firm fruits, cutting away the mold with a one-inch margin is sometimes considered safe, but discarding it is the safest option.

No, not all strains of Aspergillus niger produce toxins. Some strains are considered safe and are used for industrial food production. However, because it is impossible to know if a wild strain is toxigenic without lab testing, it is safest to assume that contaminated food could contain mycotoxins.

The most notable mycotoxin associated with certain strains of Aspergillus niger is ochratoxin A (OTA). OTA can cause serious health problems, including kidney damage, and is considered a potential human carcinogen.

Prevention involves controlling moisture and temperature. You should store food in airtight containers, keep your refrigerator below 40°F (4°C), and use food within its recommended timeframe. Ensuring good air circulation and cleaning storage areas regularly also helps prevent growth.

Yes, inhaling the spores can cause allergic reactions, especially in individuals with asthma or other respiratory conditions. In rare cases, particularly in immunocompromised individuals, it can lead to more serious infections like aspergillosis.

Yes, fermented foods using specific, safe, and controlled strains of Aspergillus niger (often reclassified variants like A. brasiliensis in some cases) are considered safe and distinct from contamination. The fermentation process is carefully managed to prevent toxin production.