In May 2025, global food safety systems sounded consecutive alarms: Italian turkey meat shipments intercepted for Salmonella contamination on the 23rd, followed by Iranian pistachios rejected for excessive aflatoxin levels on the 22nd. These incidents represent merely the visible peaks of a massive contamination iceberg threatening global food security. Each year, contaminated food contributes to 600 million illnesses and 420,000 deaths worldwide, with microbial pathogens accounting for 65% of microbial infections a nd 80% of chronic infections. As food supply chains grow increasingly complex, understanding contamination origins and implementing science-based prevention strategies in food production facilities has become an urgent imperative for industry stakeholders and public health officials alike.
Microbial threats: understand the ways of food contamination and take preventive measures
The main reasons why food is contaminated with bacteria, mold and other microorganisms usually involve loopholes in multiple links such as production, processing, storage and transportation.
1. Raw material contamination
Raw materials carry microorganisms: Crops (such as grains, fruits, and vegetables) may be contaminated by soil, sewage, or animal feces during planting, harvesting, or transportation; animal-derived foods (such as meat and dairy products) may carry pathogens such as Salmonella and Escherichia coli.
Incomplete pretreatment: Inadequate cleaning, disinfection, or sterilization (such as insufficient pasteurization temperature) fails to effectively kill microorganisms.
2. Problems in production and processing links
Equipment hygiene does not meet standards: Incomplete cleaning of production equipment (such as pipeline residues and cross-contamination of knives) leads to the growth of microorganisms.
Processing environment pollution: Improper temperature and humidity control in the workshop (high temperature and high humidity promote mold growth), low air cleanliness (such as no high-efficiency filter installed), and poor personnel hygiene management (such as not wearing protective clothing or hand disinfection).
Process defects: insufficient heat treatment time/temperature (such as incomplete sterilization of canned food), uncontrolled fermentation process (such as the growth of bacteria other than probiotics).
3. Improper storage and transportation conditions
Failure of temperature control: Foods that need to be refrigerated (such as dairy products and seafood) exceed the temperature limit during transportation or storage, resulting in the proliferation of psychrophilic bacteria (such as Listeria); dry goods cause mold (such as Aspergillus flavus) due to the humid environment.
Packaging defects: damaged packaging, poor sealing (such as vacuum packaging leakage) or excessive air permeability, resulting in microbial invasion or growth of aerobic bacteria (such as mold).
Excessive storage time: if the shelf life is exceeded or the food is not consumed in time after opening, the preservative becomes ineffective and microorganisms multiply in large numbers.
4. Food characteristics
High water activity (Aw): Foods with high water content (such as cooked food and fresh-cut fruits) are prone to bacterial growth.
Rich in nutrition: Foods with high protein and sugar content (such as meat and pastries) provide sufficient nutrition for microorganisms.
Appropriate pH value: Neutral or weakly acidic foods (such as milk and bread) are more conducive to the growth of bacteria and mold.
5. Inadequate antiseptic measures
Improper use of preservatives: no addition or insufficient addition (such as sodium benzoate and potassium sorbate), or insufficient concentration of natural preservatives (such as salt, sugar, and alcohol).
Defects in sterilization technology: Non-thermal sterilization technologies such as irradiation and ultra-high pressure treatment, do not cover all microorganisms.
6. Cross-contamination
Raw and cooked food mixing: Raw meat and ready-to-eat food share knives and cutting boards, leading to the spread of pathogens.
Improper operation by personnel: Employees handle food without washing their hands after contact with contaminants.
For the two key risk points of production and processing problems and cross-contamination, some preventive measures can be taken:
I. Preventive measures for production and processing problems (focusing on equipment, environment, process, and personnel)
Hygiene management of equipment and utensils:
Establish a strict cleaning and disinfection procedure (SSOP):
Regular cleaning: Thorough cleaning and disinfection must be carried out at the end of each shift, production conversion, and after handling different types of raw materials.
Effective methods: According to the material of the equipment and the nature of the residue, choose the correct cleaning agent, disinfectant (such as quaternary ammonium salts, peracetic acid, chlorine-containing disinfectants), concentration, temperature, and action time. Follow the principle of “clean first, then disinfect”.
CIP/SIP system: For closed systems such as pipes and tanks, use in-situ cleaning and in-situ sterilization systems to ensure that there are no dead corners.
Removable parts: After disassembly, clean and disinfect separately to ensure that hidden places such as interfaces and gaps are clean.
Cleaning verification: Regularly conduct microbial smear tests (ATP bioluminescence detection, total colony count detection, etc.) and visual inspections to verify the cleaning and disinfection effects.
Equipment design and maintenance:
Hygienic design: Choose equipment with a smooth surface (low Ra value), no dead angle, easy disassembly, and corrosion resistance (such as 316L stainless steel). Avoid threads, blind pipes, and uneven welding.
Preventive maintenance: Regularly check the equipment sealing (to prevent lubricant leakage), tool sharpness (blunt knives increase tissue damage and easily breed bacteria), and conveyor belt condition (to prevent damage and dirt), and repair and replace them in time.
Specialization: Try to make equipment dedicated to different processes and different product lines (especially between raw and cooked, and between allergens and non-allergens).
Control of processing environment:
Air quality management:
Air filtration: Install high-efficiency air filters in key areas (such as cooling areas, inner packaging areas, and ready-to-eat food processing areas) and replace the filter elements regularly. Maintain positive pressure in the workshop (relative to the outside world) to prevent unfiltered air from backflowing.
Ventilation: Ensure sufficient fresh air volume to effectively exhaust moisture and odor.
Temperature and humidity control:
Zoning control: Control temperature and humidity according to the needs of different processes. For example, the raw material processing area can be slightly higher, and the post-cooking cooling area and the inner packaging area must be kept at a low temperature (usually ≤12℃ or even lower).
Monitoring and recording: Install an automatic temperature and humidity monitoring recorder and set the alarm threshold. Calibrate the sensor regularly.
Anti-condensation: Insulate and ventilate well to prevent condensation from dripping from the ceiling and pipes and contaminating the product.
Water/ice management:
Water quality safety: Processing water must meet the standards for drinking water, and microbial and physical and chemical indicators must be tested regularly. Ice in direct contact with food must be made of drinking water.
Prevent water accumulation: The ground is designed with a reasonable slope and unobstructed drainage. Remove ground water and equipment condensation in time.
Pest and rodent control:
IPM integrated management: Seal building gaps, install air curtains, screens, and rat shields. Pest and rodent monitoring and disinfection are carried out regularly by professional companies, and safe and compliant agents are used, and records are kept.
Waste management: Clean up production waste and garbage in a timely manner, use covered trash cans, and store and transport them away from the production area.
Precise control of the production process:
Critical control point monitoring:
Heat treatment: For sterilization/sterilization processes (such as pasteurization, high temperature and high pressure sterilization), strictly control key parameters such as temperature, time, and pressure, and use calibrated instruments to monitor in real time and automatically record. Perform a heat penetration test to confirm that the cold spot reaches the target sterilization value.
Cooling: After cooking, the product should quickly pass through the dangerous temperature zone (60℃ to 4℃), and the cooling medium (water/air) should be kept clean and at a low temperature.
Fermentation: Strictly control the fermentation temperature, time, pH value, initial strain activity, and purity to prevent excessive growth of miscellaneous bacteria.
Process parameter recording: All key process parameters must have traceable automatic or manual records.
Personnel hygiene and operating specifications:
Strict health and hygiene requirements:
Employees must undergo health examinations before and regularly, and those with infectious diseases, purulent wounds, etc. are not allowed to work.
Before entering the workshop, you must: change into special clean work clothes (including hats, masks, hair nets, shoe covers when necessary), wash your hands thoroughly, and disinfect (use hand sanitizer, brushes, disinfectant, hand dryers, or disposable paper towels). Wash your hands and disinfect them again after defecation and contact with pollutants.
It is forbidden to eat, smoke, spit, wear jewelry and watches, put on makeup, and touch non-working surfaces (face, hair, mobile phones, etc.) in the workshop.
Continuous training:
Regular training on food safety, hygiene standards, and standard operating procedures for new and existing employees, emphasizing the risks of microbial contamination and prevention and control measures, and ensuring understanding and implementation through assessment.
Standardized operation supervision:
Managers should strengthen on-site inspections and promptly correct irregular hygiene behaviors (such as improper use of gloves, irregular wearing of masks, and random intercourse, etc.).
2. Prevention measures for cross-contamination (the core is “isolation” and “blocking”)
Physical isolation:
Spatial layout separation:
Strictly divide clean areas (such as inner packaging and ready-to-eat food processing areas) and non-clean areas (such as raw material receiving, thawing, and raw meat processing areas). There should be physical partitions (such as walls and doors) between areas.
Clearly distinguish between raw and cooked areas (or ready-to-eat areas). People, logistics, air flow, and water flow (drainage) should all flow in one direction from clean areas to non-clean areas, and backflow should be absolutely avoided.
Buffer rooms should be set up in areas with high cleanliness requirements (such as aseptic filling rooms).
Time isolation:
When processing different products (especially raw and cooked, containing allergens and non-allergens) in the same area or on the same production line, sufficient cleaning and disinfection intervals must be arranged in the production plan.
Follow the production sequence of “clean to dirty” and “ready-to-eat to non-ready-to-eat”.
Specialization and identification of tools and equipment:
Separate raw and cooked, meat and vegetables, and allergens: Equip special knives, cutting boards, containers, turnover boxes, equipment (such as meat grinders, slicers), etc. with clear color or shape for processing different types of raw materials or products (especially fresh raw materials and ready-to-eat products).
Clear labeling: All special tools and equipment must be clearly marked with their purpose (such as “cooked food only”, “vegetables only”, “contains peanuts”) to avoid misuse.
Storage separation: Tools for different purposes are stored separately to avoid contact contamination.
Personnel flow and behavior control:
Limited activity area: Employees can only move in designated areas, and are prohibited from randomly moving between areas of different cleanliness levels (especially from raw areas to cooked areas). If you need to enter a high-cleanliness area, you must implement a more stringent changing and hand washing and disinfection procedure.
Changing procedures: When entering different areas (especially from non-clean areas to clean areas), you must change into the corresponding clean work clothes and wash your hands and disinfect in the designated changing room.
Personal belongings are prohibited: Personal belongings are strictly prohibited from being brought into the production and processing area.
Material flow control:
Specialized channels and entrances: Raw materials (especially fresh raw materials), finished products, waste, and packaging materials should have independent entrances and exits and channels to avoid crossover.
Closed transportation: When raw materials, semi-finished products, and finished products are transported in the workshop, clean, covered special containers or closed conveying devices should be used.
Prevent backflow: Conveyor belts, elevators, etc. should be designed to prevent products, debris, and water droplets from flowing back to the upstream clean area.
Timeliness of cleaning and disinfection:
After any operation that may cause cross-contamination (such as handling raw meat, handling materials containing allergens, equipment maintenance, and spills on the ground), the affected areas, equipment, tools, and personnel must be cleaned and disinfected immediately.
The effective implementation of all these measures is inseparable from the support of a sound food safety management system (such as HACCP, ISO 22000), including clear responsible persons, standardized operating procedures, effective monitoring, detailed records, and continuous internal audits and verifications (such as environmental microbial monitoring, product testing). Employees’ understanding, recognition, and strict implementation are the key to the success of preventive measures.
