Stones in lentils or beans may damage a tooth. Years ago, home cooks checked lentils for stones to protect their family from any harm. The number of occurrences of foreign materials in food is now becoming less frequent, and consumers are less used to checking primary foodstuffs for stones, sharp metal pieces or bones, as the food industry continuously improves the safety and quality of their products. 

However, this trend also decreases public acceptance for such occurrences to a level that approaches “zero tolerance.” Any incidence of foreign material harms the consumer, undermines confidence in the brand and generates headlines. The name of the producer and the grocery chain that sold the article are widely reported.

Current Regulations around the World
U.S. Food and Drug Administration (FDA) Regulations on Adulteration Involving Hard or Sharp Foreign Objects 

A physical hazard in food is any extraneous object or foreign matter that may cause illness or injury to the consumer. 

Consumers do not expect hard or sharp components in foods where kernels are normally removed, such as cherries or pitted olives. Hard or sharp pit fragments are unexpected and may cause serious harm if ingested.

FDA considers a product adulterated if it contains a hard or sharp foreign object that measures 7 mm to 25 mm in length, and is ready-to-eat or requires only minimal preparation steps that would not eliminate, invalidate or neutralize the hazard prior to consumption.[1]

Foreign objects smaller than 7 mm rarely cause trauma or serious injury except in special high-risk groups, such as infants, surgery patients and the elderly.[2]

Glass is the most frequently reported foreign material in food to cause illness or injury.

In 1995, the U.S. Department of Agriculture Food Safety and Inspection Service concluded that bone particles less than 1 cm are not a safety hazard; particles 1–2 cm are low risk; and particles greater than 2 cm have the potential to be a safety hazard and may cause injury.[3]

Foreign material other than bone may pose a potential hazard, and each instance should be considered on a case-by-case basis, irrespective of size.

FDA Health Hazard Evaluation Board conclusions in cases of foreign materials (1972–1997) found that 56 percent of objects 1–6 mm in size might pose a limited acute hazard. For objects greater than 6 mm, only 2.9 percent were judged to present no hazard.

Section 402(a)(3) of the Food, Drug and Cosmetic Act prohibits the distribution of foods that may contain repulsive matter, considered as filth, such as insects. Most consumers find the presence of any visible filth contaminant, such as hair in a food product, nauseating.[4]

Canadian Regulations
Canadian regulations support the FDA concept based on the 7 mm to 25 mm size criterion.[5] These limits are not followed by Europe in its regulations on the hygiene of foodstuffs. 

EU Regulations on Physical Hazards in Foods
All food products sold in the EU must comply with regulations on the hygiene of foodstuffs, which demand, above all, that these products must be safe.[6] All potential biological, chemical or physical hazards must be prevented, eliminated or brought down to an acceptable safety level. To achieve such a level of safety, food processors, packagers and distributors should use the Hazard Analysis and Critical Control Points (HACCP) concept, complemented with a quality control system, such as Good Manufacturing Practices (GMPs) or ISO 9000. European regulations introduced the HACCP concept, which obliges food producers to install safety measures to avoid physical hazards and maintain documentation of all events.[7–9]

Hard or sharp foreign objects in foods may cause injury, including lacerations of the mouth, throat, stomach and intestine. Safety concepts, such as HACCP, are being introduced globally. They must cover all stages of the production process, from primary production to retail sales.

Types of Physical Hazards
The type of foreign objects in food affects the technology needed to detect it:

Glass: Sharp glass contamination often occurs during filling processes in glass containers if a container is accidentally broken. Another source, but less frequent, is light bulbs broken during building maintenance.

Metal: Sharp metal objects may include screws and equipment splinters, blades, broken veterinary needles, fragments and clippings of prior processing procedures.

Plastics: Soft and hard plastics may come from packaging material of an intermediary production phase.

Wood: Wood splinters may have their origin at the farm or may come from handling wooden pallets.

Stones: Small stones are common in crops like peas or beans contaminated during harvest.

Classification of Foreign Materials in Food
Every type of food processing has its own specific and potential hazards. Evaluation of the type of product, the intended market for the product and other factors must be considered to determine the risk category of a possible physical hazard.

The Canadian Food Inspection Agency rates the likelihood of occurrence of physical hazards based on the level of control a food processor can exercise to eliminate the risk:[5, 10]

Low risk: If good control measures have been established, but minor infractions occur.

Medium risk: If some control measures were established, but inconsistencies occur.

High risk: If little or no control was established, major and critical infractions occur.

Foreign material may occur naturally in raw materials and food ingredients, such as stones in lentils or bones in fish or meat.

It may be added unintentionally during processing due to poor equipment, as a result of maintenance work or construction in the vicinity of an operating production line. However, it may also be deliberately added to the food during processing or at grocery retail as an act of blackmail, revenge or mental disorder.

Controlling Physical Hazards
It is necessary to implement GMPs, ISO 9000 and ingredient specifications, such as determining that containers are weld-sealed to exclude staples and plastic or twist ties. A vendor’s certification for raw materials must include physical hazard controls. The use of foreign material screening equipment and employee training throughout the whole processing chain is strongly recommended.

An effective physical hazard identification program requires detailed information for every step of the food processing line. To obtain such information, the production processes must be closely observed during all phases of their operation. Procedures to control physical hazards can be determined with such observations, and a Control Point can be included in the HACCP plan.

It is strongly recommended to be more stringent than the required 7 mm to 25 mm rule of FDA. A customer will be outraged if he finds a 30-mm plastic piece in a jar of pasta sauce or 5-mm hard starch lumps in baby food. Fruit stones, flavor lumps, bone chips, metal fragments, broken injection needles, shotgun pellets, pieces of packaging, stones, glass, pit fragments, insects or other filth materials are serious problems. Such foreign materials represent badly maintained facilities and equipment, improper production procedures and poorly conducted employee training. Any and all are a potentially lethal blow to consumer trust.

Points of Origin and HACCP Corrective Steps
Control methods include raw material inspection and specification, vendor certification and letters of guarantees, metal detectors, X-ray technology, effective pest control at the facility, preventive equipment maintenance and proper sanitation procedures. Also important are proper shipping, receiving and storage practices as well as tamper-proof or tamper-evident packaging.

The food categories, in decreasing order of complaint frequency, are pastries, soft drinks, vegetables, infant foods, fruits, cereals, fish, chocolate and cocoa products.[11]

Of 10,564 cases of foreign object injuries in children included in the Susy Safe Project Registry, 26 percent were due to a food item, resulting in complications and prolonged hospitalization. Bones were the most commonly retrieved food foreign object, while nuts were most frequently associated with complications. The critical group ranging from 2 to 3 years of age requires special food surveillance.[12]

Specific characteristics of foreign bodies associated with increased hazard, such as size, shape, hardness, pliability and elasticity, must be better defined to identify risky foods for children up to 4 years of age. Nuts and seeds are one of the most common food items leading to injuries in children. Control of the hazard level of various foods should be improved, and warning labels on high-risk foods are suggested.[13]

Medical reports on life-threatening incidents of physical hazards in food are plentiful. Several medical reports underline the severity of swallowing food containing sharp objects. Although most pass harmlessly through the gastrointestinal tract and conservative management is generally recommended, 10 to 20 percent require nonoperative interventions and approximately 1 percent require surgery. An estimated 1,500 deaths occur annually from foreign object ingestion in the U.S.[14]

Most upper gastrointestinal foreign objects are related to food ingestion, and meat products are most often found to be the origin of such events.[15]

The removal of sharp foreign objects from the esophagus can be dangerous and challenging. Hyun et al.[16] describe proper apparatus and appropriate techniques that should be employed to avoid life-threatening complications. These authors present a procedure for recovering fish bones from the esophagus.

The types of foreign-object swallowing incidences in children include coins (57%), button batteries (22%), sharp objects (12%), chicken bones (2.3%) and others (6.7%).[17]

Preventing Common Physical Hazards
Care taken to protect the consumer covers bulk food production, portioned packaged foods at grocery stores and fast food. The complete production chain must identify small particles of metal, glass, wood, plastic fragments, stones and other foreign objects, such as moths and beetles, that hurt the consumer or cause a nauseating reaction. Controls should include the following:
Inspection of raw materials and ingredients, looking for field contaminants

Provision of good storage facilities, usage of lamp covers to avoid bulb breakage and maintenance of effective pest control

Development of specifications and controls for all ingredients and components

Effective detection and elimination systems for physical hazards, such as metal detectors or magnets to remove metal particles; use of X-ray and low-power microwave systems to detect nonmetallic materials

Periodic training of employees engaged with shipping, receiving, storing, handling and equipment maintenance that encompasses the entire food production chain, including:

Agricultural Production
These include grains, vegetables, big farms and small organic businesses.

Meat Production
Care should be taken at farms, abattoirs and retail; knives, mincers, meat slicers, vacuum bowl cutters and broken injection needles must be scanned.

Special care is needed for bulk transportation; recovery after road accidents should be observed.

Food Processing Factory
The daily maintenance of transport belts must be assured (Figure 1). Well-sanitized machines that look very good may bear many hazards of foreign bodies in food, like broken parts of defective systems. Audits should concentrate on these problems and daily inspections of peeling machines and vegetable slicers.

Grocery Chains
Personnel should be trained to be attentive to prevent packaging adulteration or criminal attempts of extortion.

Restaurants, hotels and fast food chains should consider introducing GMPs and HACCP.

Technology for Detection of Foreign Particles
Every product presents special technological challenges. Translucent and opaque liquids filled in bottles, colored opaque plastic packages, tin cans or milk cartons respond differently to available detection systems (Figure 2).

Metal detectors: Metal detectors find splinters from machinery, fractions of broken cutters and blades, needles, screws or fragments of clips.

X-ray detectors: These respond to metal, stone, bone, hard plastics and Teflon. Both systems can screen the product after the filling procedure. X-ray detectors may find glass pieces that result when a jar or bottle is crushed during malfunction of the packaging line.

Near-field radar response: Foreign bodies are detected in embedding material by transmitting low-power microwaves through the material, as explained by the Swedish Institute for Food and Biotechnology and the Food Radar System (FRS).[18] The system uses a microwave sensor designed for emulsions and pumpable products. It measures the dielectric properties of the food flow of processing equipment. Foreign materials produce a deviation from the norm, activating a pneumatic rejection unit. The system not only detects denser foreign objects but also is particularly suited to foreign objects such as wood, plastic, bone, extraneous vegetable matter, contaminants such as fruit stones and nut kernels and process faults such as flavor and starch lumps in baby foods.

FRS must be installed within the pipe system, before packaging. Any deviation at the filling station is not covered.

Ample technology exists for detection of foreign material in foodstuffs. To ensure food safety, this technology should be complemented by quality control practices such as HACCP and GMPs, and by ongoing training of personnel. With proper implementation in the production line, illness or injury to consumers can be avoided.

Karl Heinz Wilm is a biochemist at the University Belém do Pará, Brazil. He has 32 years of quality management experience in the German food industry.