Application of metal detectors in food processing

Abstract: During the harvesting of raw materials and subsequent processing of food, foreign objects may be mixed into them due to improper methods or some unavoidable factors. These substances can cause harm to consumers' bodies and even endanger their lives, which are usually referred to as physical hazards. At present, in developed countries such as Japan and the United Kingdom, complaints from food manufacturers have been reported.

During the harvesting of raw materials and subsequent processing of food, foreign objects may be mixed into them due to improper methods or some unavoidable factors. These substances can cause harm to consumers' bodies and even endanger their lives, which are usually referred to as physical hazards. At present, in developed countries such as Japan and the United Kingdom, among the complaints of food manufacturers, as many as 70%-80% of the complaints caused by the incorporation of foreign matter are reported. Therefore, how to eliminate the foreign matter mixed into the raw materials, prevent the foreign matter from being mixed in the production and packaging process, and find and remove the foreign matter that has been mixed has become an important research topic.

The main methods for detecting foreign objects in food are x-ray detection, metal detection, visual inspection, electronic scanning and other methods, but so far, there is no detection method that can completely detect or eliminate all foreign objects that may be mixed in. Metal detection is one of the most common methods. Among them, a metal detector is a metal detection device on food packaging and material transmission lines. It can effectively identify metal substances mixed in food and materials, and remove the metal substances in an appropriate manner. Get rid of. Since the transmission line is unidirectional, food and materials only pass through the metal detector once, which requires it not only to have high detection sensitivity, but also to have a reliable detection effect.

1. The purpose and precautions of using metal detectors

The use of metal detectors is ultimately to improve product quality, maintain corporate image and protect consumer interests. The purpose and precautions for use in different stages of food processing are as follows:

1. Raw material storage stage

The use of metal detectors in the raw material storage stage can detect the metals mixed in the raw materials, and prevent the metal foreign bodies mixed in the raw materials from damaging the production equipment, and will not affect the subsequent processes. The production line must be designed to allow powdered or granular raw materials to flow through; when detecting liquid substances, a pipeline-type metal detector must be selected and passed through a pressurized pipeline. The smaller the diameter, the better;

The lower the raw material temperature during testing, the better, and the better is complete freezing.

2. production process

·The use of metal detectors in the production process can detect metal foreign objects mixed in the process: screws and nuts on the production equipment, tool fragments, metal dust, rust, metal tool fragments, staples, workers Accessories and sewing needles. It can avoid the effects of packaging materials from affecting the detection results, and increase the effective utilization rate of packaging materials, especially when aluminum packaging or oxygen scavengers are used, the detection should be carried out at this stage as much as possible. The production line is best designed to allow the object to be inspected to pass longitudinally.

3. Single package

The detection is carried out after the individual packaging, and higher sensitivity can be obtained. It should be noted that the detection of aluminum-plated packaging products requires the use of metal detectors dedicated to aluminum packaging, and the detection of aluminum foil packaging products requires the use of metal detectors dedicated to aluminum foil packaging.

4. Multiple packaging and shipping

A final metal inspection before shipment can find nuts or screws that may be mixed after the monomer production line.

In short, in order to prevent metal contamination from being transported to the next production stage, the following must be considered when using metal detectors:

a. Choose a metal detector suitable for the production line and improve the environmental conditions for installing the metal detector.

b. Evaluate the best entry point in the composition of the production line to obtain high sensitivity of the metal. The initial inspection is best carried out at the raw material stage.

c. The smaller the object to be inspected, the better.

d. The metal detector needs to be optimally set before use.

e. Operate and maintain the metal detector correctly.

2. How to develop a HACCP plan for metal detection key control points

At present, metal detectors have been widely used in the production of different foods such as quick-frozen food, aquatic products, meat, vegetables, etc., and metal detection is usually included in the HACCP schedule as a key control point to control. Recently, however, it has also been discovered that some companies have deviations in their understanding in the process of formulating HACCP plans for metal detection key control points. For example, the concepts of “monitoring” and “verification” are confused. The following is an example of the broiler processing process.

The processing technology of broiler chickens is in order: raw chicken receiving, hanging chicken, slaughter, bleeding, scalding, dehairing, scouring, post-mortem inspection, washing, pre-cooling, dividing, packaging, metal detection, and freezing. Through the hazard analysis worksheet, six key control points can be determined as raw material chicken receiving, evisceration, post-mortem inspection, washing, pre-cooling, and metal detection. During the audit process, it was discovered that the HACCP plan of some of the metal detection critical control points of some enterprises was formulated as shown in the table:

HACCP schedule

Critical control points Description of significant hazards Critical limits for each preventive measure Monitoring Corrective actions Recording Verification

What, how, frequency, who monitors

metal detecting

CCP Metal fragments FeФ>1.5mm shall not be detected

SusФ>2.5mm shall not detect metal fragments in each package of chicken. Use a metal detector to test the metal detector with a standard block every hour. If the metal detector does not operate normally, stop production and re-adjust to normal.

Re-pass the products passed after the instrument was normal last time through the metal detector. Metal detection records and correction records. Re-check records every day

In the table, the "frequency of monitoring" is to test the metal detector with a standard block every hour, that is, take the product and put it on the conveyor belt. If it can pass, put the FeΦ1.5mm under the detector. If it fails, it is judged that the metal detector is normal; If it can pass, it is judged as abnormal. SUSΦ2.5mm is tested in the same way. "Verification" is to review the records every day. This method of planning is actually mixing the concepts of "monitoring" and "verification".

The definition of monitoring is the implementation of a planned continuous observation and measurement to assess whether a CCP is under control, and to make accurate records for future verification. Monitoring can be continuous or discontinuous.

Verification refers to the methods, procedures or testing and audit methods used to determine whether the HACCP system is operating according to the HACCP plan or whether the plan needs to be modified and reconfirmed, in addition to monitoring methods. The calibration of the equipment and the review of the calibration records are two items in the CCP verification. Therefore, for the above-mentioned HACCP schedule, the monitoring frequency should be continuous monitoring of each package of chicken. The content of the verification is to test the metal detector with standard blocks every hour, and to recheck and monitor the calibration records of the metal detector every day.

Only by accurately understanding the concept of monitoring and verification according to the above-mentioned methods, can we formulate a correct HACCP plan, make the key control points of metal detection truly controlled, and ultimately achieve the purpose of ensuring product quality.

Third, the development direction of metal detectors

At present, metal detectors are the most widely used equipment for detecting foreign objects in food. Its advantages are easy to operate, economical and reliable, and widely applicable. Of course, it can only be used for the detection of metal foreign bodies. The disadvantage of the metal detector is that it is not sensitive enough and is greatly affected by the environment. Since the transmission line is unidirectional, food and materials only pass through the metal detector once, which requires an ideal metal detector not only to have high detection sensitivity, but also to have strong anti-interference ability. Compared with metal detection systems,  can detect foreign objects in a wider range. In addition to metals, they can also detect whether food contains glass, rocks, bones and other substances. It is worth mentioning that foods with high moisture or salt content, as well as some products that can reduce the sensitivity of metal detectors, can also be put into the X-ray inspection system for inspection. use the density comparison of foreign objects and food to detect. The disadvantage is that it is expensive, which discourages many manufacturers.

In order to meet the needs of the market, relevant manufacturers are actively researching and developing new types of metal detectors with higher cost performance. It is believed that in the near future, there will be a metal detector that has higher sensitivity, can detect any object, can work in harsh environments for a long time, and is more convenient to operate.