FOOD SAFETY AND QUALITY ASSURANCE: ALLERGENS AND CONTAMINATION
Diagram
Two kinds of unwanted transfer
Cross-contamination
Microbes move from one food, tool or surface to another: raw meat juices on a board, dirty water from a cracked pipe.
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Cross-contact
Allergen proteins move from one food, tool or surface to another: a spoon from a peanut sauce into a plain sauce.
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The difference
Cross-contamination moves germs; cross-contact moves allergens. Both are stopped by order and cleaning, but the controls differ in detail.
Figure 1: Cross-contamination transfers microbes; cross-contact transfers allergen proteins. Drawn in our own style from the FTN Food Safety and Security notes, Unit 3, and the FTN Quality Control and Assurance notes, Unit 4.
Introduction
Cross-contamination and cross-contact are the two kinds of unwanted transfer between foods, and both happen when something moves from one food, tool or surface to another. The difference is what moves: cross-contamination moves microbes, and cross-contact moves allergen proteins. A cutting board that carried raw chicken and then a salad is cross-contamination, while a spoon used in a peanut sauce and then in a plain sauce is cross-contact. The controls look alike, order and cleaning, but the details differ, and the harm differs too.
The FTN Food Safety and Security notes, Unit 3, call cross-contact the main failure for allergens, and the FTN Quality Control and Assurance notes, Unit 4, describe contamination and its routes. This article follows those two units, with Marriott, Schilling and Gravani, Principles of Food Sanitation.
Quick comparison
Table 1: Cross-contamination compared with cross-contact
| Aspect | Cross-contamination | Cross-contact |
|---|---|---|
| What moves | Microbes: bacteria, yeasts, moulds, viruses and parasites, and the toxins some of them make | Allergen proteins: peanut, milk, egg, gluten and other allergens |
| From where | Raw food, soil, water, air, people, animals and equipment | A food that holds the allergen, and the tools, trays and hands that touched it |
| Example | Raw meat juices on a cutting board, then a salad on the same board; dirty water from a cracked pipe into open food | A spoon used in a peanut sauce and then in a plain sauce; nut cakes in the morning and plain cakes in the afternoon on the same trays |
| Harm | Food poisoning and spoilage, from the germs that grow | An allergic reaction, which needs only tiny amounts to cause serious harm |
| Amount needed | Enough cells to grow and cause illness, which depends on the germ and the food | Tiny amounts: allergens need very little to cause serious harm |
| Killed by cooking | Cooking kills most vegetative cells, but not spores, and not toxins already made | No: cooking does not destroy allergen proteins, so a cooked food can still carry the allergen |
| Control | Separate raw from ready-to-eat food, clean and sanitise equipment, test water, and follow hygiene rules | Make allergen-free foods first, use separate tools where possible, wash hands and surfaces between jobs, and store allergen ingredients in sealed, marked containers below other foods |
| Cleaning | Cleaning and sanitising remove the microbes | Cleaning must remove every trace of the allergen protein, because a trace is enough |
| Labelling | Not a labelling matter: the germs are not on the label | A labelling matter: allergens must be named clearly on the label |
| Main failure | A route left open: a worker with unwashed hands, a cracked pipe, a store that is warm and damp | Cross contact is the main failure for allergens, and it happens in order, tools and storage |
Scientific explanation
Definition
Cross-contamination is the transfer of microbes from one food, tool or surface to another, so that a food that was clean becomes contaminated: biological contamination comes from soil, water, air, people, animals and equipment, and a worker with unwashed hands, a cracked pipe that lets in dirty water, and a store that is warm and damp are each a route. Cross-contact is the transfer of an allergen from one food, tool or surface to another food: a spoon used in a peanut sauce and then in a plain sauce carries the allergen across.
Working principle
Each kind of contamination has its own route into food. Biological contamination comes from soil, water, air, people, animals and equipment. Chemical contamination comes from the field, from the factory and from the pack: a pesticide applied too close to harvest, a cleaning chemical not rinsed away, a printing ink that migrates through a pack. Physical contamination comes from the raw material itself, such as stones in grain, and from the factory, such as a broken screen or a chipped blade. Knowing the route is the first step to blocking it, because a control that blocks the wrong route wastes effort while the real route stays open. Cross-contact works the same way, but for allergens: a bakery that makes nut cakes in the morning and plain cakes in the afternoon on the same trays can carry traces across, and the control is order and cleaning, making allergen-free foods first, using separate tools where possible, washing hands and surfaces between jobs, and storing allergen ingredients in sealed, marked containers below other foods so they cannot spill onto them.
Apparatus
The books used here name no laboratory apparatus for telling the two apart, so no apparatus list is given.
Measurement procedure
The books used here name no single standard laboratory procedure for telling the two apart. The distinction is made from what is found: microbes are found by the plate count and detection methods of the FTN Food Microbiology notes, Unit 3, while allergen traces are found by the allergen tests a laboratory runs on the food and on swabs of tools and surfaces. The control is layered in both cases: no single layer catches everything, and the layers back each other up.
Factors affecting readings
For cross-contamination, the route decides the risk: raw food next to ready-to-eat food, unwashed hands, dirty water and warm, damp stores are the routes, and each needs its own control. For cross-contact, order and time decide the risk: making the allergen food first and the plain food second on the same tools carries the allergen across, and the amount needed is tiny, so even a trace matters. Storage decides both: allergen ingredients stored above other foods can spill onto them, and raw food stored above ready-to-eat food can drip onto it.
Formulas and calculations
The books used here give no formula for this comparison, so no formula or worked calculation is given.
Industrial applications
- Cross-contamination: keeping raw meat away from ready-to-eat food in storage, on boards and on hands.
- Cross-contamination: testing water and cleaning equipment on a schedule, so dirty water and dirty boards do not carry germs.
- Cross-contamination: designing the plant so clean areas stay separate from dirty ones.
- Cross-contact: making allergen-free foods first, before the allergen foods, on the same line.
- Cross-contact: using separate tools for allergen foods, and washing hands and surfaces between jobs.
- Cross-contact: storing allergen ingredients in sealed, marked containers below other foods, and naming allergens clearly on the label.
Advantages and limitations
- Cross-contamination control, advantage: the routes are known, and layered controls, from intake to the finished product, block them one by one.
- Cross-contamination control, limitation: a single open route, such as a cracked pipe or unwashed hands, is enough to contaminate a batch.
- Cross-contact control, advantage: order and cleaning, separate tools and sealed storage, stop the transfer without new equipment.
- Cross-contact control, limitation: allergens need only tiny amounts to cause serious harm, so cleaning must remove every trace, and cooking does not destroy them.
FAQ
What is the main difference between cross-contamination and cross-contact?
Cross-contamination moves microbes from one food, tool or surface to another, while cross-contact moves allergen proteins.
Can cooking fix cross-contact?
No: cooking does not destroy allergen proteins, so a cooked food can still carry the allergen.
What is the main failure for allergens?
Cross-contact: a spoon from a peanut sauce into a plain sauce, or nut cakes and plain cakes on the same trays.
How is cross-contact controlled?
By order and cleaning: make allergen-free foods first, use separate tools, wash hands and surfaces between jobs, and store allergen ingredients sealed and below other foods.
Why does the amount matter more for allergens than for microbes?
Because allergens need only tiny amounts to cause serious harm, while microbes usually need enough cells to grow and cause illness.
References and further reading
- FTN subject: Food Safety and Security, Unit 3: Chemical and Physical Hazards; FTN subject: Quality Control and Assurance, Unit 4: Contamination, Adulteration and Extraneous Matter: Finding What Should Not Be There.
- Norman G. Marriott, M. Wes Schilling and Robert B. Gravani, Principles of Food Sanitation, 6th ed., Springer (Google Books page read)
