Introduction

Microbial contamination is a major food safety risk in food processing facilities. Although food factories are generally subject to different regulatory requirements than pharmaceutical manufacturing plants, they must still operate under strict quality management and food safety systems.

Food production environments are especially vulnerable to microbial contamination because they contain complex raw materials, abundant nutrients, moisture, and processing residues. Ingredients rich in carbohydrates and proteins can support microbial growth, while heat-processing procedures, cooling stages, conveyor systems, pipelines, drains, and difficult-to-clean equipment may create conditions that allow microorganisms to survive and spread.

Among the microorganisms frequently detected in food production environments, spore-forming bacteria are particularly difficult to control. A food processing facility in Shanghai contacted Vantsteri after Bacillus species were detected in finished products. Environmental sampling later identified the same type of microorganism in the production area, and further laboratory analysis confirmed that the contaminating organism was Bacillus cereus.

Vantsteri conducted an on-site investigation and developed a customized vaporized hydrogen peroxide disinfection plan covering production rooms, air-conditioning units, ventilation ducts, environmental surfaces, and difficult-to-access areas.

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Background: Why Spore Contamination Matters in Food Production

Food manufacturing involves raw material handling, processing, cooking, cooling, packaging, storage, and transportation. Microbial contamination can enter the production process at any stage and may spread through raw materials, production equipment, conveyor belts, pipelines, equipment gaps, drains, floor gullies, HVAC systems, personnel, tools, packaging areas, or inadequately cleaned surfaces.

Food ingredients often contain carbohydrates, proteins, fats, minerals, and moisture. These nutrients can support microbial growth if environmental conditions are not properly controlled. Some microorganisms can also form spores that survive unfavorable conditions, including drying, nutrient limitation, heat exposure, and certain chemical treatments.

For this reason, routine cleaning and low-level disinfection may not be sufficient when spore-forming bacteria are present. Effective control requires accurate microbial identification, deep cleaning, appropriate disinfectant selection, complete environmental coverage, and post-treatment verification.

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Case Overview

The customer was a food processing facility located in Shanghai. During routine product testing, Bacillus species were detected in the company’s products. To determine whether the contamination originated from the production environment, Vantsteri engineers conducted environmental sampling in relevant processing and storage areas.

The same type of Bacillus was detected in both the products and the factory environment. Further identification confirmed the microorganism as Bacillus cereus, indicating that environmental contamination had become a potential source of product contamination.

The facility had previously used conventional disinfectants and routine sanitation procedures. However, the selected disinfectants and application methods were not sufficient to control bacterial spores. As a result, contamination persisted in the production environment and eventually affected product quality.

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What Is Bacillus cereus?

Bacillus cereus is a Gram-positive, facultatively aerobic, spore-forming bacterium. It is widely distributed in soil, water, air, animal feed, raw food materials, processing environments, and many types of food products.

The microorganism can easily contaminate foods rich in protein and carbohydrates. Its name is associated with the rough, wax-like appearance of its colonies when grown on certain nutrient media.

Because Bacillus cereus can form spores, it may survive environmental stress and remain present in production facilities even after routine cleaning. Once suitable temperature, moisture, and nutrient conditions return, surviving spores may germinate and multiply.

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Food Safety Risks Associated with Bacillus cereus

Bacillus cereus is a recognized foodborne microorganism. It may contaminate rice and flour-based foods, dairy products, infant formula, meat products, sauces, seasonings, ready-to-eat foods, and other protein- or carbohydrate-rich products.

Foodborne illness associated with Bacillus cereus has been reported internationally for decades. Historical reports include food poisoning incidents linked to contaminated meals, rice products, dairy products, and ready-to-eat foods. Studies have also reported relatively high detection rates of Bacillus cereus in some categories of infant formula and ready-to-eat foods.

For food manufacturers, contamination may result in:

• Product contamination
• Product recalls
• Customer complaints
• Loss of consumer confidence
• Damage to brand reputation
• Export restrictions
• Failure to meet food safety requirements
• Difficulty passing HACCP, BRC, or customer audits
• Increased downtime
• Higher remediation and testing costs

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Why Bacillus Spores Are Difficult to Eliminate

Bacillus species are among the more difficult microorganisms to eliminate during environmental disinfection. Under unfavorable conditions, Bacillus cells can produce highly resistant spores.

These spores are more resistant than ordinary vegetative bacterial cells to drying, heat, ultraviolet exposure, nutrient deprivation, environmental stress, certain chemical disinfectants, and routine cleaning procedures.

Low-level or intermediate-level disinfectants may reduce vegetative bacteria but fail to destroy bacterial spores. If spores survive after cleaning, they may remain on equipment, surfaces, conveyor systems, pipelines, drains, or ventilation components. They can later germinate and cause repeated contamination.

For effective spore control, a high-level disinfection or validated sporicidal treatment method is generally required.

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Main Causes of Contamination Identified During the Investigation

During the on-site assessment, Vantsteri engineers identified several factors that may have contributed to the persistent contamination.

Inappropriate Disinfectant Selection

The disinfectant previously used by the facility was not sufficiently effective against bacterial spores. A product that performs well against vegetative bacteria may not necessarily provide reliable sporicidal activity.

Incorrect Application Method

Disinfection effectiveness depends not only on the selected chemical but also on concentration, contact time, temperature, humidity, application method, surface coverage, organic contamination, and accessibility of the target area.

Incorrect application can significantly reduce the effectiveness of treatment, even when the disinfectant itself is suitable.

Difficult-to-Clean Equipment Areas

Food production equipment often contains gaps, joints, valves, pipelines, conveyor components, motors, guards, and internal cavities. These areas may be difficult to reach through manual wiping or conventional spraying.

Biofilm and Organic Residues

Food residues, fats, proteins, and carbohydrates may accumulate on equipment and environmental surfaces. These residues can reduce disinfectant effectiveness and may support the formation of biofilms.

Microorganisms embedded in biofilms are often more difficult to remove than free microorganisms on exposed surfaces.

HVAC and Air-Duct Contamination

Air-conditioning units and ventilation ducts may become reservoirs or transmission pathways for microbial contamination. If these systems are not included in the sanitation plan, microorganisms may be redistributed into production areas through airflow.

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Disinfection Strategy

Based on the characteristics of the facility and the identified microorganism, Vantsteri developed a customized treatment strategy focused on five areas:

1. Removing organic residues and biofilms
2. Applying a high-level sporicidal treatment
3. Treating rooms and difficult-to-access spaces
4. Including HVAC units and air ducts
5. Verifying the treatment through environmental monitoring

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1. Preliminary Cleaning and Environmental Preparation

Effective disinfection begins with appropriate cleaning because organic matter can shield microorganisms and reduce disinfectant activity.

Before vaporized hydrogen peroxide treatment, the facility carried out deep cleaning in key areas, including production equipment, conveyor belts, equipment gaps, contact surfaces, floors, walls, drains, pipelines, air-conditioning components, and areas with visible product residues.

Removing organic matter and biofilm improved contact between the disinfecting agent and contaminated surfaces.

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2. Selection of Hydrogen Peroxide as the Disinfecting Agent

After evaluating the factory environment and the resistance of Bacillus spores, Vantsteri selected hydrogen peroxide as the main disinfection agent.

Under appropriate application conditions, hydrogen peroxide can provide high-level disinfection and sporicidal activity. After treatment, it decomposes primarily into water and oxygen, making it suitable for food production environments where chemical residue is a major concern.

The treatment was designed to minimize residue risks while achieving broad environmental coverage.

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3. Vaporized Hydrogen Peroxide Distribution

Vantsteri used vaporized hydrogen peroxide equipment to distribute the disinfecting agent throughout the affected spaces.

A total of 15 portable VHP units were deployed during the project. One unit was placed in each designated room, additional units were installed inside relevant air-handling units, and units were also positioned in ventilation ducts.

This arrangement allowed vaporized hydrogen peroxide to reach production rooms, processing areas, HVAC components, and difficult-to-access environmental spaces that could not be adequately treated through manual wiping or conventional spraying.

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4. HVAC and Ventilation-Duct Treatment

HVAC systems can distribute airborne microorganisms throughout food production areas. For this reason, the treatment was not limited to exposed rooms and surfaces.

VHP equipment was positioned inside air-conditioning units and ventilation ducts, and the HVAC circulation process was used to distribute vaporized hydrogen peroxide throughout the intended treatment spaces.

This approach helped address contamination risks associated with air-handling units, ventilation ducts, return-air pathways, internal system surfaces, airborne contamination, and difficult-to-access components.

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Treatment Process

The active vaporized hydrogen peroxide disinfection stage lasted approximately four hours. After the initial treatment period, the air-conditioning system was operated in circulation mode for approximately two additional hours.

This helped distribute vaporized hydrogen peroxide throughout the treatment area, including the production rooms, HVAC system, and ventilation ducts.

The complete treatment process included:

• Site inspection
• Environmental sampling
• Microbial identification
• Cleaning preparation
• Equipment deployment
• VHP generation
• HVAC circulation
• Exposure period
• Aeration
• Environmental monitoring
• Post-treatment verification

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Treatment Results

After the decontamination process was completed, both parties conducted environmental sampling and microbial testing. Monitoring was performed for seven consecutive days and included settle plates, active airborne microbial sampling, surface microbial sampling, and sampling in key production areas and near equipment and ventilation components.

No Bacillus was detected in the monitored environmental samples during the seven-day observation period.

The results indicated that the customized VHP treatment effectively addressed the environmental contamination identified during the investigation. The project also demonstrated the importance of treating not only visible production surfaces but also HVAC systems, ventilation ducts, equipment gaps, and other difficult-to-access areas.

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Evaluation of Hydrogen Peroxide Exposure on Fresh Fruit

To evaluate whether high-concentration hydrogen peroxide treatment might affect exposed food products, additional experiments were conducted using apples, bananas, and cantaloupes.

Unpackaged fruit was placed inside a refrigerated container and exposed to high-concentration hydrogen peroxide treatment. More than 20 experimental trials were conducted.

No visible adverse effect was observed on the external appearance of the exposed fruit during the evaluation, and no obvious abnormality in taste was identified during the sensory assessment.

These results were specific to the tested fruit, treatment conditions, exposure parameters, and experimental environment. Actual food compatibility should still be evaluated according to the characteristics of each product and production process.

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Why Conventional Disinfection Had Failed

The previous disinfection process failed mainly because the selected method was not suitable for bacterial spores.

Common reasons for unsuccessful spore control include:

• Using a disinfectant without reliable sporicidal activity
• Insufficient disinfectant concentration
• Inadequate contact time
• Failure to remove organic residues
• Incomplete surface coverage
• Failure to treat HVAC systems
• Failure to treat ventilation ducts
• Poor access to equipment gaps and internal components
• Lack of environmental verification
• Recontamination after treatment

Repeatedly applying an unsuitable disinfectant does not necessarily improve the result. Effective remediation requires an integrated approach based on microbial identification, environmental assessment, deep cleaning, appropriate disinfectant selection, complete coverage, and verification.

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How Food Factories Can Reduce Bacillus Contamination Risks

Food manufacturers can reduce Bacillus contamination risks by strengthening environmental monitoring and sanitation management.

Control Raw Material Contamination

Raw materials should be inspected and monitored according to their microbial risk. Suppliers should be evaluated regularly, especially for ingredients with a known risk of Bacillus contamination.

Improve Equipment Cleaning

Equipment should be designed, inspected, and cleaned to prevent product residues from accumulating in gaps, joints, pipelines, and conveyor components.

Manage Biofilm Risks

Cleaning procedures should be capable of removing organic residues and biofilms before disinfection.

Select Appropriate Disinfectants

Disinfectants should be selected according to the target microorganism. When bacterial spores are present, a validated sporicidal treatment may be required.

Include HVAC Systems

Air-conditioning units, return-air pathways, filters, and ventilation ducts should be included in the environmental sanitation program.

Strengthen Environmental Monitoring

Monitoring should include airborne microorganisms, settle plates, surface microorganisms, equipment contact surfaces, drains, HVAC components, and high-risk production areas.

Verify Treatment Effectiveness

Environmental sampling should be conducted after treatment to confirm whether the contamination-control target has been achieved.

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Key Takeaways

• Food production environments are vulnerable to microbial contamination because raw materials often contain abundant nutrients.
• Bacillus cereus is a spore-forming bacterium commonly found in soil, water, air, raw materials, and food products.
• Bacillus spores are more resistant than vegetative bacteria and may survive routine sanitation procedures.
• Low-level disinfection may not provide effective control when bacterial spores are present.
• Environmental contamination can spread to products through equipment, conveyor systems, personnel, air, drains, and HVAC systems.
• Deep cleaning is necessary before disinfection because organic residues and biofilms can reduce treatment effectiveness.
• Hydrogen peroxide can provide high-level disinfection while decomposing into water and oxygen after treatment.
• VHP treatment can reach rooms, HVAC units, ventilation ducts, and difficult-to-access environmental areas.
• Post-treatment environmental monitoring is essential for verifying decontamination effectiveness.
• A customized contamination-control plan is more effective than repeatedly applying an unsuitable disinfectant.

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Conclusion

Bacillus contamination in a food processing facility is not simply a surface-cleaning problem. Spore-forming bacteria may survive inside equipment gaps, conveyor systems, pipelines, drains, air-conditioning units, ventilation ducts, and other difficult-to-access areas.

In this case, the same Bacillus cereus detected in the customer’s products was also identified in the production environment. The investigation showed that the existing disinfection method was not suitable for controlling bacterial spores.

Vantsteri developed a customized treatment plan combining deep cleaning, vaporized hydrogen peroxide disinfection, HVAC treatment, ventilation-duct treatment, and environmental verification. Fifteen portable VHP units were deployed throughout the facility. The active disinfection stage lasted approximately four hours, followed by two hours of HVAC circulation.

Post-treatment environmental monitoring was conducted for seven consecutive days, covering airborne microorganisms, settle plates, and surface samples. No Bacillus was detected in the monitored samples during this period.

The case demonstrates that effective control of Bacillus cereus requires a systematic strategy based on accurate microbial identification, environmental source tracing, removal of organic residues and biofilms, selection of a sporicidal treatment, complete environmental coverage, HVAC and ventilation-system treatment, and post-treatment microbial verification.

For food factories, effective spore contamination control can help protect product quality, support food safety compliance, reduce recall risks, and prevent recurring environmental contamination.